Q: How soon can block wall construction begin on the edge of a concrete slab foundation?
A: As is usually the case, there are a lot of factors to consider: How fast is the slab concrete gaining strength (which is related to its mix design and temperature)? How high and heavy will the block walls be? How quickly will they go up? How deep is the footing around the slab perimeter? How is the slab reinforced? A typical safety factor for slab design is 1.7 to 2.0, so if it’s been designed properly, you might reasonably begin loading a slab when it has developed half of its tensile strength. This generally happens within a few days. If you’re not sure of the concrete’s strength, and want to ensure you don’t crack the slab, you should wait five to seven days.