Moisture cracks in basement floor

[Mike Lamb]

This is the basement in a 50-year-old house. Old paneling. Old floor tiles. There were several small spots where fissures erupted in the floor. I don't think this is a chronic problem. My theory is a failed sump pump may have caused excess water pressure beneath the slab. Does this make sense?

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[kurt]

Could just be shrinkage. Most floor slabs go in too wet; easier to screed around, but they crack.

If there's no heave, I doubt it's under floor pressure.

[John Kogel]

I don't think those are the original tiles. They are thin and curling at the edges.

I think a bit of moisture is working up through the concrete causing that white efflorescence and loosening the tile glue. Past flooding is also possible.

[mjr6550]

The tiles act like a moisture barrier so moisture wicking through the concrete gets trapped. I agree with Kurt regarding shrinkage cracking if there are no signs of heaving.

[Tom Raymond]

Yes on all counts. Shrinkage, newer tile acting as moisture barrier, and, that old black mastic is probably hot.

[Jim Katen]

Pressure isn't necessary. Just damp soil beneath the slab. The moisture wicks up through the porous concrete and evaporates through the tile seams, leaving the efflorescence behind.

Probably half of the vinyl-tiled basement floors in Portland have spots that look like that.

If it were actual liquid water being driven in there under pressure, the water would wash away the efflorescence.

Either do something to make the soil under the slab dryer or replace the non-permeable tiles with something that can allow the moisture to move through the concrete and into the air unimpeded.

[kurt]

Or just forget about it and replace loose tiles. Anyone that got worked up about something that minimal needs to unclench their anal pore.

I've got a couple of those in my 100 year old basement floor. The VC tiles got a couple bubbles after 20+ years. Took them up, mashed the floor flat, put the tile back down. Maybe someone will care, but it isn't me.