cutting expansion joints in basement

Old 07-12-07, 07:32 PM
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cutting expansion joints in basement

I just poured a 28' x 32 pad in my basement, do I need to cut expansion joints in the floor . I plan on putting tile down later on the concrete floor.

this is a new house in the south

Old 07-13-07, 03:40 AM
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Unless you poured the slab yesterday right before you posted this, it may already be too late. Concrete floors make their own joints by cracking, usually within a day or two of the pour due to drying shrinkage. This will be most noticeable at re-entrant corners (corners that point into the slab, not the 4 outside corners that point outwards). The wetter the slab was poured, the more cracks you'll have.
The joints are mostly for cosmetic purposes. They make the concrete crack in a straight line instead of randomly across the slab. If you're going to cover it with tile anyway, just let it crack and then fill those cracks with thinset before you tile. Make sure you wait at least a month before covering the floor with tile.
People mistakenly call cut joints "expansion joints" when in reality they are contraction joints. The concrete is never going to expand bigger than it was when it was wet. Expansion joints are something different altogether.


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