by 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.