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    Bonding agents for concrete

    Bonding agents for concrete

    New postby phil327 on Tue Jul 09, 2013 1:29 pm

    I have been doing some research on the various methods of bonding new concrete to old concrete. The greater majority of articles suggest a bonding agent that is applied to the existing concrete prior to adding the new concrete. There are lots of different products on the market and they all start with cleaning off the old concrete and then brush, spray or mash the bonding agent in to the old concrete.

    Then, there are the bonding agents that you mix in with the concrete mix. Some of these even suggest brushing on the agent to the old concrete as well.

    Are the mixed in varieties as good as the brushed on types? any studies as to how long each will last?

    Is there a building code that states that a bonding agent must be used? Do the city inspectors look for this?

    I would guess that the mixed in variety will cost significantly less money, taking into account the material costs and labor costs.
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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Sun Jul 14, 2013 10:31 pm

    phil327 wrote:Are the mixed in varieties as good as the brushed on types? any studies as to how long each will last?


    Provided each meets the appropriate standard for the material, both should provide equally good results ... if the proper care is taken in using/applying the bonding agent in accordance with the manufacturer's instructions.

    Is there a building code that states that a bonding agent must be used?


    Yes, most, if not all, codes would refer to ASTM C 926 Standard Specification for Application of Portland Cement-Based Plaster.

    ASTM C 926 states: (bold and underlining are mine)
    - 5. Requirements for Bases to Receive Portland Cement-Based Plaster
    - - 5.1 Metal bases and accessories used to receive plaster shall be installed in conformance with Specification C 1063, except as otherwise specified.
    - - - NOTE 3—All metal, or PVC, or CPVC plastic members should be free of deleterious amounts of rust, oil, or other foreign matter, which could cause bond failure or unsightly discoloration.
    - - 5.2 Surfaces of solid bases to receive plaster, such as masonry, stone, cast-in-place or precast concrete shall be straight and true within 1⁄4 in. in 10 ft (2.1 mm/m) and shall be free of form oil or other elements, which would interfere with bonding. Form ties or other obstructions shall be removed or trimmed back even with the surface of the solid base.
    - - - 5.2.1 Solid surfaces shall have the suction (ability to absorb water) or surface roughness, or both, to provide the bond required for the plaster.
    - - - 5.2.2 Smooth or nonabsorbent solid surfaces, such as cast-in-place or precast concrete, shall be prepared to receive portland cement plaster by one of the following methods:
    - - - - 5.2.2.1 Sandblasting, wire brushing, acid etching, or chipping or a combination thereof,
    - - - - 5.2.2.2 Application of a dash-bond coat applied forcefully against the surface, left untroweled, undisturbed, and moist cured for at least 24 h, or
    - - - - 5.2.2.3 Application of a bonding compound suitable for exterior or interior exposure solid surfaces in accordance with the manufacturer’s written directions.
    - - - 5.2.3 Where bond cannot be obtained over the entire surface to receive plaster by one or more of the methods in 5.2.2, or where total plaster thickness will exceed the total thickness specified in Table 1 for types of solid bases, furred or self-furring metal plaster base shall be installed in accordance with Specification C 1063.

    Do the city inspectors look for this?


    Typically, there is no specified inspection for this, it is up to the contractor to follow all the finer points of the code and the referenced standards. If code inspectors were to inspect all items in the code and the referenced standards - the permitting cost would be prohibitive as the cost would need to be sufficient enough to cover a code inspector to be present at almost all times that workers are present on-site and doing work as most work is, in some manner, covered by the codes and the referenced standards.

    As important as the proper use and application of the bonding agent is, so are all the other aspects of exterior plastering (stucco), including, but not limited to, proper curing of the plaster/stucco. How many times is the stucco properly cured after application? Since the 1970s/80s ... possibly as many times as can be counted on the fingers of one hand (in most places, there may be some areas or strictly enforced jobs where proper curing takes place).

    8. Curing and Time Between Coats
    - 8.1 Provide sufficient moisture in the plaster mix or by moist or fog curing to permit continuous hydration of the cementitious materials. The most effective procedure for curing and time between coats will depend on climatic and job conditions. (See X1.4.2.)
    - 8.2 Sufficient time between coats shall be allowed to permit each coat to cure or develop enough rigidity to resist cracking or other physical damage when the next coat is applied. (See X1.4.2.)

    X1.4.2 Time Between Coats and Curing for Portland Cement-Based Plaster:
    - X1.4.2.1 The timing between coats will vary with climatic conditions and types of plaster base. Temperature and relative humidity extend or reduce the time between consecutive operations. Cold or wet weather lengthens and hot or dry weather shortens the time period. Moderate changes in temperature and relative humidity can be overcome by providing additional heating materials during cold weather and by reducing the absorption of the base by pre-wetting during hot or dry weather.
    - X1.4.2.2 In order to provide more intimate contact and bond between coats and to reduce rapid water loss, the second coat should be applied as soon as the first coat is sufficiently rigid to resist cracking, the pressures of the second coat application, and the leveling process.
    - X1.4.2.3 The amount of water and the timing for curing portland cement plaster will vary with the climatic conditions, the type of base, and use or nonuse of water-retentive admixtures.
    - X1.4.2.4 Some moisture must be retained in or added back to freshly applied portland cement-based plaster. If the relative humidity is relatively high (above 75 %), the frequency for rewetting a surface may be reduced. If it is hot, dry, and windy, the frequency of rewetting must be increased.
    - X1.4.2.5 Consider the physical characteristics of the structure as well as the previously mentioned conditions when selecting the method of curing. The method can be one or a combination of the following:
    - - (1) Moist curing is accomplished by applying a fine fog spray of water as frequently as required, generally twice daily in the morning and evening. Care must be exercised to avoid erosion damage to portland cement-based plaster surfaces. Except for severe drying conditions, the wetting of finish coat should be avoided, that is, the base coat prior to application of the finish coat.
    - - (2) Plastic film, when taped or weighted down around the perimeter of the plastered area, can provide a vapor barrier to retain the moisture between the membrane and plaster. Care must be exercised in placing the film: if too soon, the film may damage surface texture; if too late, the moisture may have already escaped.
    - - (3) Canvas, cloth, or sheet material barriers can be erected to deflect sunlight and wind, both of which will reduce the rate of evaporation. If the humidity is very low, this option alone may not provide adequate protection.
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    Re: Bonding agents for concrete

    New postby phil327 on Mon Jul 15, 2013 1:54 am

    Thank you for the complete answer. I'll have to read through this again to fully understand.

    I think that part of my issue with the mixed in variety is that there is no way to verify what was put in the truck. I have heard of cases where the concrete company will add a gallon, where 5 should have been put in. There are too many places where costs can be eliminated and no one is the wiser.
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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Mon Jul 15, 2013 6:30 am

    Just to clarify, you originally stated "bonding new concrete to old concrete", however, I took the other information as you were referring to exterior plaster, not to actual concrete. The ASTM C 926 standard is for exterior plastering (stucco), not concrete.

    Typically, if you are placing new concrete next to old concrete (such as making a patio slab larger) there is no need for bonding agents. Instead, dowels are typically used to keep the new slab in place and aligned with the old slab.

    If you are 'top coating' an old concrete slab to make it slightly thicker or to align with another surface, that 'top coating' would need to be applied in accordance with it instructions, which may or may not include a bonding agent.

    I just want to clarify that you said "new concrete to old concrete" and that I am referring to 'stucco' - if you are not referring to stucco, then I ask for additional information as to what is being done and what the purpose of the "old concrete to new concrete' is. I want to make sure that I am/have properly understanding what you are asking.
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    Re: Bonding agents for concrete

    New postby phil327 on Mon Jul 15, 2013 10:07 pm

    I was referring to concrete, not stucco. Let me clarify this a little more.

    This is not a patio deck with the concrete on the ground, These are all suspended, up to 7 stories high. The deck is the ceiling for the walkway below.

    There are 4 foot wide walkways, the entrance to each unit is through these walkways. The outside edge had a brick wall. The brick wall was not solid and had a cap on the top. Every 4 feet or so, there were 2 vertical rebars that the bricks were attached to. There were a lot of cracks in the bricks, lots of loose bricks and poorly done repairs over the years. The city came in and told the association they had to remove all the bricks. These will be replaced with an aluminum rail system.

    The balconies, more specifically, the edges are also poured concrete. The same repair work is being done to them as well.

    In almost all places where the vertical rebar was, the underlying concrete slab was damaged. The concrete slab is 4 inches thick and is attached to the vertical walls with rebar. There were also many other areas where the slab was damaged. The company doing the repairs has cut out these bad sections, think notches at least 4 inches deep, or all the way through. I believe that all the cutouts have a piece of rebar exposed. So, there is a mechanical connection as well as a bonded connection.

    There are no feathered edges, no thin set used.

    While I do not think the repaired sections will fall out, I believe, that over time, the area between the new concrete and the old will crack. The reading I have done, ( as well as the engineer's initial specifications ) call for a bonding agent to be applied to the old concrete.

    If you think of concrete as water, portland cement, and sand. Think of the sand the as large stones. If you apply a bonding agent to the old concrete then apply the stone to the bonding agent, it will stick. Now, if you just mix the bonding agent to the new mix, you are assuming that every grain of sand ( or stone ) will be completely covered with a bonding agent. This is not the case, some stones will have cement, some will have only water molecules in contact with the old concrete. The water will not bond the stone to the old concrete.

    OK - I am presenting a worst case with the mixed in bonding agent. I guess the proper way to state this is OK, Better, Best. With OK having no bonding agent and only rebars, Better - having a mixed in bonding agent, Best - applying the bonding agent directly to the old concrete.

    One of concrete roads in NY had repairs done 20 years ago. The patches that had a bonding agent applied to the old concrete are still there. Other patches have come loose and needed additional repairs. New York has freeze and thaw cycles, so any water getting into the crack will eventually force out the new concrete when it freezes.

    I am probably nit picking this to death at this time. However, the restoration project is around a million dollars, a few thousand for bonding agents applied directly to the old concrete seems like a small price to pay for doing it the best way possible.
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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Wed Jul 17, 2013 6:43 pm

    Phil,

    I typed out a long and detailed response yesterday ... but lost it in cyberspace while trying to post it, hopefully I can provide the same information in a condensed form with this post.

    I fully understand your project and question now - concrete restoration to repair spalling concrete damage along the edges of balconies, decks, and walkways.

    I have inspected many balcony/deck/walkway spalling concrete restoration projects, ranging from a single 7 story condo building to multiple 30+ story condo buildings within the same project - all having balcony edge restoration done at the same time (it was a massive undertaking, to say the least).

    Regarding the bonding agent and the two choices: a) surface applied; b) admix which is mixed into the concrete.

    The bonding agent does not hold the new concrete in place, that is the purpose of the steel reinforcement. At most, the bonding agent helps hold the concrete at the joint of the new concrete/old concrete together a bit tighter (and thus helping with water intrusion issues at the joint). There is no need to worry about the 'seal tightness' of the bonding agent if using surface applied bonding agent as there will always be voids in the bonding agent itself, between the bonding agent and the old concrete, and around the steel.

    The mixed-in bonding agent is similar to mixing in the aggregate and concrete, it all mixes together. If you are concerned that the mixed-in bonding agent is may not be fully mixed in and coating the aggregate, then I would be more concerned that the concrete paste (concrete and water) is not sufficiently mixed to fully coat the aggregate and hold the aggregate together into solid concrete.

    The mixed-in bonding agent is the simplest to use and the type susceptible to the least errors in application and use as it is mixed into the concrete mix and becomes part of the concrete. The surface applied bonding agent is more susceptible to application and use errors as it is to be applied to a dusty, dirty, too wet/too dry irregular surface with steel bars projecting out of the surface ... trying to get a proper cleaning of the surface and applying the bonding agent in accordance with its installation instructions is difficult and is seldom done 'exactly' as specified in the instructions (drying/curing/flash exposure time which is sufficient but not overly long such that the bonding agent needs to be re-coated) due to the elements one is working in (from rain to mist to cloudy to hot sun).

    It is far more important that the architect/engineer's drawings and specifications be followed and that the architect/engineer be kept advised of site conditions which vary from those shown in the drawing.

    For example, the drawings may show a 4" thick slab which may only be 3-3/4" thick, or steel size and placement in the original concrete slab which is not as shown in the drawing, or steel in the original slab which does not allow for the intended steel to be installed as intended.

    Contractors take liberties with the architect/engineer's specifications by making undocumented changes to allow them to complete the work given the unexpected conditions encountered during the work - the architect/engineer needs to be advised of all such conditions which do not meet the original drawings so that the architect/engineer can provide a revised method suitable for each such condition. Once the architect/engineer provides the revised method for one condition, the contractor can use that method for all future conditions they encounter (provided the conditions fall within the revised method details, a similar condition covering a larger area may require revisions over what was detailed for the same condition in a smaller area).

    The best thing is to hire an independent inspector/consultant/engineer/etc to inspect the work being done by the contractor. The independent inspection party is working for you and is inspecting the installed repair work in relation to what the approved engineering shows.

    Another thing which is critical is planning and allowing for the guard rail installation at the end of the restoration project - the mounting of the guard rail posts needs to be addressed as does the guard rail post locations, otherwise all the repair work may be for naught as the guard rail installers core/drill through newly replaced steel, cutting the tension element (the steel) into discontinuous pieces instead of the steel being continuous along the edge. This is probably the second most common problem I find, the first most common problem is making changes to adapt to the site conditions without architect/engineer review/approval of those changes.
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    Re: Bonding agents for concrete

    New postby phil327 on Thu Jul 18, 2013 1:52 am

    Jerry Peck - Codeman wrote:Phil,

    I typed out a long and detailed response yesterday ... but lost it in cyberspace while trying to post it, hopefully I can provide the same information in a condensed form with this post.

    I have found in the past that it is sometimes best to type items using WORD, then a copy - paste to the forum. I, too, have typed answers only to have them get lost for one reason or another. There is nothing like spending 15-20 minutes getting your thoughts on the PC only to have it crash in some way. While I use WORD, there are other text editors out there. I make sure I SAVE every few minutes.

    Regarding the bonding agent and the two choices: a) surface applied; b) admix which is mixed into the concrete.

    The bonding agent does not hold the new concrete in place, that is the purpose of the steel reinforcement. At most, the bonding agent helps hold the concrete at the joint of the new concrete/old concrete together a bit tighter (and thus helping with water intrusion issues at the joint). There is no need to worry about the 'seal tightness' of the bonding agent if using surface applied bonding agent as there will always be voids in the bonding agent itself, between the bonding agent and the old concrete, and around the steel.

    All the work here has been poured into forms. I understand that the bonding agent is used to 'bond' the old concrete to the new. The rebars are used to hold the new in place. The wooden forms are used to get a basic shape of the new concrete.



    The mixed-in bonding agent is the simplest to use and the type susceptible to the least errors in application and use as it is mixed into the concrete mix and becomes part of the concrete. The surface applied bonding agent is more susceptible to application and use errors as it is to be applied to a dusty, dirty, too wet/too dry irregular surface with steel bars projecting out of the surface ... trying to get a proper cleaning of the surface and applying the bonding agent in accordance with its installation instructions is difficult and is seldom done 'exactly' as specified in the instructions (drying/curing/flash exposure time which is sufficient but not overly long such that the bonding agent needs to be re-coated) due to the elements one is working in (from rain to mist to cloudy to hot sun).

    You bring up a good point regarding the proper application of the bonding agent to the old concrete. The engineer's specs called for sandblasting the old concrete and sandblasting the rebar to remove the rust. There was also a spec to treat the rebar to prevent future rust. None of this was done. The contractor built vertical forms on the edges of the balconies. These have a scoop on the top to pour in the concrete. I was going to suggest that they open one or two of these boxes to make sure there was no water in the bottoms. It has been raining quite a bit here


    The best thing is to hire an independent inspector/consultant/engineer/etc to inspect the work being done by the contractor. The independent inspection party is working for you and is inspecting the installed repair work in relation to what the approved engineering shows.

    The board president did hire a consultant, but he has not been here since the work started. They are relying on the engineer and the contractor to verify the work is being done properly. We have raised a number of issues with all this and at least they are aware that someone is watching. We are extremely limited as to what we can see or force them to do.

    Another thing which is critical is planning and allowing for the guard rail installation at the end of the restoration project - the mounting of the guard rail posts needs to be addressed as does the guard rail post locations, otherwise all the repair work may be for naught as the guard rail installers core/drill through newly replaced steel, cutting the tension element (the steel) into discontinuous pieces instead of the steel being continuous along the edge. This is probably the second most common problem I find, the first most common problem is making changes to adapt to the site conditions without architect/engineer review/approval of those changes.

    An excellent point. I will have to figure out a way of getting this across to the those involved. Although, I suspect that the company that installs the railings will space the posts based on distance and nothing else. We have emailed the board to make sure that the attachment points are secured with stainless steel.


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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Thu Jul 18, 2013 12:30 pm

    phil327 wrote:You bring up a good point regarding the proper application of the bonding agent to the old concrete. The engineer's specs called for sandblasting the old concrete and sandblasting the rebar to remove the rust. There was also a spec to treat the rebar to prevent future rust. None of this was done. The contractor built vertical forms on the edges of the balconies. These have a scoop on the top to pour in the concrete. I was going to suggest that they open one or two of these boxes to make sure there was no water in the bottoms. It has been raining quite a bit here


    All the restoration work I've seen and inspected has had a form constructed with a bottom to match the original balcony/walkway bottom, vertical forms for the edges, with the top being left entirely open for placing the steel and pouring the concrete into the open area being repaired. Seems to me that the chute would limit their ability to actually seen what they are doing during the concrete placement and severely limit their ability to consolidate/vibrate the concrete to make sure the new concrete is fully against the old concrete, the edges of the forms, and under and around the steel.

    Is the top of the formed area open for finishing the concrete, or is the top covered, creating a complete form with only the chute for placing the concrete through? If fully formed with a top form, I've never seen it done that way before, not saying it cannot be done that way, just that I have never seen it done that way and that there are limitations created by enclosing the top (I am presuming the top is enclosed as you wanted to be able to see the bottom of the form for any water collecting in it - typically, the forms have drain holes in the bottom which would drain out excess puddled rain water.

    The board president did hire a consultant, but he has not been here since the work started. They are relying on the engineer and the contractor to verify the work is being done properly. We have raised a number of issues with all this and at least they are aware that someone is watching. We are extremely limited as to what we can see or force them to do.


    Did the consultant's contract specify on-site inspections, how often, and when, or did it just leave it to the consultant? As a consultant myself, I like to actually "see" with my own eyes what is being done, within the limitations of the contract as the more on-site time there is, the higher the consultant's cost will be. It is a trade-off of time versus money, and money usually wins the first round, but often loses the second round because 'a penny saved' is not always equal to 'a penny earned', sometimes that penny saved equals to dollars lost.

    I will have to figure out a way of getting this across to the those involved. Although, I suspect that the company that installs the railings will space the posts based on distance and nothing else. We have emailed the board to make sure that the attachment points are secured with stainless steel.


    The guard railing installer will install the posts based on their required spacing for the design, the key is that the spacing is accounted for in the placement of the steel at the time the steel is placed. Does not do any good to replace discontinuous steel with continuous steel only to cut the new continuous steel into discontinuous segments. What type of guard rail mounting are they using: core drilled holes into the concrete (the riskiest method for cutting the new steel) or some bracket method which clamps the edge or bolts into the slab? Each method has its drawbacks.
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    Re: Bonding agents for concrete

    New postby phil327 on Thu Jul 18, 2013 6:28 pm

    The vertical walls are 4 inch poured concrete on the balconies. For example, let's say an area 14 inches front to back, and 28 inches top to bottom is removed, leaving a notch in the vertical wall. Take 2 pieces of plywood, 20 inches by 36 inches and attach to the sides of the wall. Keep the front flush with the front of the existing concrete. This will 'seal' the 2 walls. Now, take a third piece of plywood, 8 inches wide by 34 inches tall. Screw this to the front of the wall, but. the top of the plywood should be 2 inches below the top of the notch. This will leave an opening to pour the new concrete in. Then add a few small pieces of plywood to create a 'funnel' at the opening at the top. I could not see if there was any exposed rebars in any of these fixes.

    Get your 5 gallon pail of concrete and start to shovel in the new mix into the opening. While you are doing this, every now and then tap the wood form. You can not see anything inside this box. There could be water at the bottom. ( the boxes have been assembled over the last few weeks and left empty. ) There could even be some critters in there.

    After 2 days, remove the wood forms. From what I can see, they are going over each of these repairs with a thin coating of concrete to fill in any voids and to get the edges flush with the original wall.

    The consultant was hired on a hourly basis, not to oversee the project. Basically to answer any questions.

    I have no idea at this time as to the attachment method of the new railings. I am trying to be selective in my questions to the various parties, picking the ones that would seem to have the greatest impact.
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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Thu Jul 18, 2013 7:12 pm

    Ah, I see ... the spalling repair area has been chipped out back to, and into, the structures walls around the balconies (I was envisioning just around the outer edges of the balconies/walkways.

    Not really many options for pouring those with concrete other than what they are doing, that method is used quite frequently, and any critters in them will simply become cast in concrete ... (bad joke) ... the contractor could take an air hose and spray around the inside of those forms just prior to pouring the concrete to help try to blow out any water (and critters). If the forms are wood, then let the water set a day and it will be gone anyway - it will soak into the wood and the wood will be damp (allowing the concrete to cure better than with dry wood which would suck some of the water out of the concrete).

    Usually, when those 'funnels' are made such that they can be removed shortly after the concrete is poured which allows the excess concrete to be more easily trimmed off while the concrete is still 'green' (not yet 'hard', but good and 'stiff' to hold its shape).
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    Re: Bonding agents for concrete

    New postby phil327 on Fri Jul 19, 2013 1:14 am

    Thank you for your complete answers to this. You made me aware of a few things that I had not thought of.

    In a perfect world, certain methods would be the best. Given the fact that this is not a perfect world, and you have to take into account practical 'construction' methods are the better way to go.

    I will see what I can find out about the railing attachment method they are planning on using.

    thanks again
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    Re: Bonding agents for concrete

    New postby phil327 on Thu Oct 03, 2013 10:53 pm

    phil327 wrote:
    Jerry Peck - Codeman wrote:Phil,


    Another thing which is critical is planning and allowing for the guard rail installation at the end of the restoration project - the mounting of the guard rail posts needs to be addressed as does the guard rail post locations, otherwise all the repair work may be for naught as the guard rail installers core/drill through newly replaced steel, cutting the tension element (the steel) into discontinuous pieces instead of the steel being continuous along the edge. This is probably the second most common problem I find, the first most common problem is making changes to adapt to the site conditions without architect/engineer review/approval of those changes.

    An excellent point. I will have to figure out a way of getting this across to the those involved. Although, I suspect that the company that installs the railings will space the posts based on distance and nothing else. We have emailed the board to make sure that the attachment points are secured with stainless steel.




    Today they started to install the railings. They are cutting a 4 inch circular hole into the walkway edge for the post attachments. All they ones we looked at have cut through the rebar that runs along the outside edge of the walkway. There are even a few cases where the hole had cut through the rebar that extends from the wall to the outside edge, these are a right angles to the rebar that runs along the edge. All the rebar will be segmented into 4-5 foot lengths.
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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Fri Oct 04, 2013 12:10 am

    phil327 wrote:Today they started to install the railings. They are cutting a 4 inch circular hole into the walkway edge for the post attachments. All they ones we looked at have cut through the rebar that runs along the outside edge of the walkway. There are even a few cases where the hole had cut through the rebar that extends from the wall to the outside edge, these are a right angles to the rebar that runs along the edge. All the rebar will be segmented into 4-5 foot lengths.


    "All the rebar will be segmented into 4-5 foot lengths."

    "There are even a few cases where the hole had cut through the rebar that extends from the wall to the outside edge,"

    They did exactly what I expected them to do - all the repairs making the steel "continuous" are now for naught in those areas.

    All the repairs for the rusted out rebar and spalled concrete were also for naught as the guard rail installers just recreated the conditions which caused the problem the first time.

    Someone needs to stop them before the screw up, and ruin, all the work done previously - they are already getting a good start at it based on your descriptions of what has been done.

    Without telling the architect/engineer what the railing installers are doing, send a letter or email to the architect/engineer asking how important is it that the rebar be continuous along the edge, and how important is it for the rebar which is perpendicular to the edge steel to be continuous - that you are curious as you understand that their design addressed making that steel continuous, that the workers doing the restoration work were careful in making sure that steel was made continuous, and that you thank them for all the repair and restoration work. Sugar coat it and spice it all up to it tastes good going down.

    When they respond that the steel being continuous is critical to the integrity of the balcony edges and of holding the guard rails in place, and you now have that in writing, show them the photos (you took photos of the cored out steel, maybe even saved some of the cores, right?) and ask them how the now discontinuous steel should be repaired ... you already have them stating, in writing, that the edge steel needs to be continuous ... and you are now showing them that the railing installers are chopping their work up and making that edge steel discontinuous ... see if they can wiggle out from having to stop the guard rail installers and address the balconies which now have discontinuous edge steel ... they may try to wiggle out of it, or they may actually go after the guard railing installers for repairs ... I am curious as to which happens.

    Keep me posted, please.
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    Re: Bonding agents for concrete

    New postby phil327 on Fri Oct 04, 2013 1:11 pm

    We are sending a letter to the engineer with a request that they respond within 3 business days.
    The three pictures are a sample of the core drilling they have done showing the cut rebar, Also interesting to note is the cracks in the concrete.

    what would be the a proper way to install railings in this environment?

    I found a few ways - core drilling ( the method being used here ) OR surface places OR I have seen edge clamps ( probably the most expensive )

    This one the rebar is only cut part way through.
    Image

    This one -the rebar has been cut all the way through.

    Image

    This one shows the two pieces of rebar that run along the edge being cut. Also cut part way through is the rebar that runs from the wall to the edge, and a few cracks as well....

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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Fri Oct 04, 2013 1:45 pm

    phil327 wrote:what would be the a proper way to install railings in this environment?

    I found a few ways - core drilling ( the method being used here ) OR surface places OR I have seen edge clamps ( probably the most expensive )


    Core drilling with the rebar laid out such that the rebar is not within, or close to, the areas which will be cored drilled by the guard railing installers - this requires coordination between trades and contractors.

    Surface mounts are, in my opinion, the weakest type of mounting as one is relying on the pullout of the anchors and the strength of the anchors themselves, and sometimes the rebar are cut with these mountings too (unless coordinated with the trades and contractors to avoid placing rebar at guard rail mounting locations).

    I have seen the edge clamps and have the same concerns with them as with the surface mounts.

    The best way I have seen is for the contractor to purchase (yes, they are available) circular foam blocks the diameter and depth required for core drilling, install and secure in place the foam pieces in between the steel where the guard railing posts will be installed, then pour the concrete in the forms. When the concrete is sufficiently cured, the foam blocks are removed, leaving holes for the guard railings to be anchored into - no core drilling is required. Yes, this take coordination between the trades and the contractors as the placement of the foam blocks needs to be fairly precise so that no core drilling is necessary.
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    Re: Bonding agents for concrete

    New postby phil327 on Fri Oct 04, 2013 1:52 pm

    The foam blocks would work if all the edge was being removed, Unfortunately, not all the edge was damaged and the repairs on the edge are hit and miss. This is old construction and not all the original rebar is located in exactly the same distance from the edges
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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Sat Oct 05, 2013 6:13 pm

    I recommend using the foam blocks where the repairs are, and locating the rebar at the proposed post locations by using x-ray or some of the new electronic instruments for locating rebar.

    Then adjust the exact post locations to miss the rebar, which will also mean that the guard rail lengths will need to be adjusted to match the revised post locations.
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    Re: Bonding agents for concrete

    New postby phil327 on Sun Oct 06, 2013 2:08 am

    I do not know how much thought went into planning where the posts would be for the railings. They have been manufactured and delivered here with a 'standard' length between the posts. The rebar running along the edge varies in distance from the edge by as much a 2 inches or so. I do not know if the rebar that comes out from the wall is any standard distance apart.

    I am trying to get my head around the logistics of locating each piece of rebar on the walkways, then creating an order for the railing manufacturer to vary the post distance on each segment of railing, then having all this delivered and then having the installers drill out cores at a variable distance, then getting the correct piece of railing segment put in place. certainly not impossible, but most likely beyond the abilities of the companies involved here. There is around 3000 feet of railing to be installed
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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Sun Oct 06, 2013 9:31 am

    This is one way to it with varying spaces between posts:

    Let's presume the original intended post spacing was 8 feet, using a 100 foot or longer tape measure, mark the center of one end post then the centers of the other posts along the tape measure.

    You have eliminated 96% of the area where you need to locate the rebar.

    Check a 4" diameter area around the first end post center and the next post center for rebar, if none is found - good - the posts can be located as marked.

    If rebar is found, check a larger area (lengthwise with the railing) for rebar. When you find a suitable area for the post without rebar mark that for center and go to the next post location.

    The plan is to not keep reducing the spacing between posts but to vary the spacing around the original spacing.

    That means trying for (as an example) 8 feet, 8 feet -2 inches, 8 feet + 4 inches, etc.

    The 8 feet or less spacing uses railings built for the 8 foot spacing and cut to length.

    The longer spacings will need longer railings to cut to fit. The railing company would need to supply some railing sections which were longer.
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    Re: Bonding agents for concrete

    New postby phil327 on Tue Oct 08, 2013 10:27 am

    The catwalk railings have already been manufactured. We do not have all of them on site because some are still in the 'paint' shop. I did ask about cutting through the rebar for the cores. I was told ' That is not a problem because the material used to fill the cores will prevent any rust from forming. I also asked about the railing being segmented - nope - not a problem.

    Is cutting through existing rebar a code violation, or is it just not the best solution ?


    This is a picture of one of the balconies. The edge was removed back to the original pre cast slab. The are only 2 pieces of rebar. Some of the balconies are going to get a railing, which will require cores being drilled out. I think that there are 2 posts, so there will be 2 cores drilled out. I am reasonably sure that these will cut through the rebar. I asked if the center section would be at risk, told once again the it would take over 500 PSI to break the concrete. I would think that with no bonding agent holding the new concrete against the old, the mechanical strength of the rebar compromised - that down the road there is the potential for a problem.

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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Tue Oct 08, 2013 8:25 pm

    phil327 wrote:
    Is cutting through existing rebar a code violation, or is it just not the best solution ?


    Yes and no.

    The construction needs to match the approved documents, if the approved documents show the rebar as being continuous, then that is a code violation. The code violation could be corrected by the engineer submitting revised documents showing that the rebar was allowed to be "discontinuous" (i.e., remove the requirement that the rebar be "continuous").

    If the rebar is not shown on the approved documents as being "continuous", then there is no code violation in that sense.

    However, if the engineering specifies that the rebar is to be "continuous" then revised engineering needs to be provided showing that the rebar is not required to be continuous.

    Having the contractor, or the engineer, "say" that there is no problem is meaningless - the engineer needs to provide a signed and sealed letter stating that, then take that letter to the city and ask if they received a copy of it as the city approved the original engineering and would need to approve the revised engineering.

    Regarding the precast balcony with the added on section with the two rebars shown, those two rebars are what is keeping the added on section in place - bonding agent will not do any good (not much good anyway) of holding the concrete in place.

    IF either of those two rebars is cut and made discontinuous then the strength to hold that added on piece of balcony edge is GREATLY REDUCED ... IF BOTH of those two rebars are cut and made discontinuous ... there is the real danger for that added on portion to fall away from the precast balcony as the steel is the tension strength which keeps the concrete from cracking into chunks and just falling away.

    I hope that none of the rebar in those added on sections is cut, but if they install the railing along that added on edge ... there is the real possibility that both will be cut, and that would not be good.

    You really need to get an engineer out there to look at things for the owners' interests, even if the Board (the actual owners of the structure) do not go along with it, you and as many others as you can get together need to hire an engineer and get their independent opinion from see your photos and seeing the site up close and personal - I am at a great disadvantage as I am limited to your descriptions and photos ... you need an engineer who can get an up close and in person look at those items and then advise you from there. They will be able to see things I cannot and might even downplay some of what I am thinking about it because they have an in person view of it, or they might even tell you to stay off it and make it more urgent than I am considering it to be, they might even get the city involved if they feel it necessary to do so. An 'up close and in person view' will tell you so much more than I can over the internet.
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    Re: Bonding agents for concrete

    New postby phil327 on Sun Dec 08, 2013 10:19 pm

    OK - they removed the edge of the concrete walkway, about 8 inches in. The steel posts ( stanchions ) that were clamped to edge were loosened to allow the concrete to be removed. The steel posts hold the 2x4s and the orange netting, creating the temporary railing system. I am not an engineer, but it seems to me that bailing wire attached to a jackpost and the other end attached to the top of the steel post to hold the temporary railing is - well - not the best practice. The bottom of the stanchion is 'resting' on the newly exposed rebar.

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    Re: Bonding agents for concrete

    New postby Jerry Peck - Codeman on Sun Dec 08, 2013 10:47 pm

    Phil,

    Sounds like you expected them to so something proper? You must be a man of never-ending hope for humankind.

    You could put in a call to the local OSHA office to have an OSHA inspector visit the site by sending them the photo and description and expressing a concern for the workers. Not much else you can do, based on past information.
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