Last week, the slab was poured for a custom home which is to have stained & scored concrete floors on the interior. A few hours after the pour there was a short but heavy rainfall, which damaged the slab surface enough to make it unacceptable for staining. The slab is also uneven in places. After some discussion with all parties involved, we think the best solution may be to pour a 1-1/2″ to 2″ thick concrete topping over the existing slab and frame on top of that. While this will fix the cosmetic problem of staining the concrete, will it potentially create other problems?? Should we expect any problem with adherence of the topping to the slab? Is there a possibility of any lateral movement/separation between the two? Any suggestions?
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Replies
Adhession is always a concern when trying to bond concrete layers. Another consideration would be trying to evenly finish a 2 inch topping can be a challenge if the intent is to apply a stain finish.
You correctly identified another problem and that differential movement. The first slab is already cured and has done it's initial shrinkage. The greater the area the greater the movement between the two and the more cracks you will have.
Are you sure that you need to add a 2 inch topping?
There are other alternatives to consider. If the uneveness is minor, a skim coat would be easier to apply and it could be done once the house is completely closed in.
Even if the uneveness is more pronounced, you can grind/chip/hammer and patch it first then apply the skim coat.
Before proceeding too far with this project, it would be wise to have an experienced concrete floor finisher look at it. A call to your local Mapei representative would be my first choice and get their input.
Gabe