Hi, I haven’t done a thorough search of all posts, so this subject may have been addressed. Having said that, the searches I have done show nothing.

I have a slab foundation house in northern California (circa 1975). When we moved in there was an atrium in the entry (~15’X22′).

We wanted to use the entry in a more practical way so we dug it out below grade, and had concrete poured to fill it in. The excavation was about 7″ deep, graveled, a moisture barrier, and the final pour. I also requested the concrete company drill into the main house slab, and glue in rebar lengths so the new slab would be attached and wouldn’t ‘float’ from the main slab because we do live in a moist, sandy soil area.

Several years later, we now seem to have moisture visible in low areas of the wall (standard 1/2″ sheetrock). My wife thought at first it was leaking and coming in from the front porch, now we both think it’s wicking up from the floor (where the sheetrock touches the floor). To prove this theory we extensively sealed the front porch, and I also sliced the bottom of the sheetrock up about an inch, so there now is

1/4″ gap between the sheetrock and the 2X4 sill plate around the perimeter of the room.

Unfortunately this seems to have been only partially effective – this winter it seems damp again – and I am desperate for some sage advice!

My wife now wants me to inject low-expanding foam around the perimeter of the room, where there is a gap between the new slab and the original slab. Will this help?

We want eventually to put down hardwood or bamboo flooring but I would REALLY hate it, if our lovely flooring was ultimately damaged by moisture, so I would appreciate any advice on limiting ingress of moisture around the perimiter between the two concrete slabs.

What’s the best way to seal between two slabs?

Thanks for any advice!