Like cornfed, I'm also interested in how to properly manage moisture wicking on a slab if anyone knows.
If there’s liquid water under the slab it’s not uncommon to cut a hole(s) and install little permanent pumps to help reduce free water, usually on the side where water is making its way under the foundation footings. For instance a nice green lawn uphill of the house will be notorious for water migration to and under the foundation. However that isn’t always necessary if the moisture is better controlled before it gets to the house.
If there is water under the foundation and slab, there’s probably also considerable moisture on at least one of the foundation walls in the direction of where the water is coming from, usually the uphill side. Some foundations require digging out the dirt well enough to use better moisture proofing on the outside of the basement walls. Some clients paid their teenage boys to dig and were able to get it all dug out for pretty cheap, but they had no clue how dangerous cave ins can be at full basement depth. Another client paid landscapers to dig it their wet foundation wall.
If water is coming through the wall and pooling in the slab, it might not do any good to focus on anything other than foundation walls. Water test kits for foundations are often just poly sheeting you tape to the wall and look for moisture to condense. Might have to open finished Sheetrock in places to inspect and check for moisture. Lots of moisture leaves white residue from minerals so it can be easy to spot.
A retrofitted drainage perforated pipe outside of the foundation sometimes makes sense, such as when there is an entire hillside uphill of the house, or golf course uphill of the house is feeding underground water. These are pretty simple - a dude with a backhoe digs a trench low enough to intercept the water, and fabric and washed stone is placed in the ditch along with the perf pipe. Works great on hillsides where the perf pipe can gravity flow water around to the downhill side.
On a golf course house where gravity flow to get rid of the water wasn’t an option, the perf pipe went to sump pump that raised the water up above ground level so it drained.
If you or neighbors have ditches, ponds or swimming pools nearby that can be a major water source. One client had the auto water valve adjusted too high on the koi pond and water was flowing over the top of the pond liner.
I’ve also seen broken water lines feeding underground water to a foundation. Fixing the cracked line and the foundation dried up.
If you have a lot of rain, downspouts can saturate soil around a foundation. One house had downspouts connected to perf pipe around the footers, so rather than the perf pipe removing water, it was helping downspouts move water to the footers. Other times mold in a crawl space has been limited to areas where downspouts empty out and water just went down the foundation wall and under the footer.
Some places the soil is wet everywhere all the time and the options are ensuring waterproofing on the walls is intact, sump pumps for anything that gets under the slab, and good moisture barrier under the slab so moisture vapor can’t make it into the slab. When we’ve torn out a slab it basically gets fabric, layer of washed rock, concrete sump tank that free water would drain into and will hold the pump, and a layer of foam and maybe a second water barrier if the foam is crap, then the new slab.
Oh, one other source can be surface runoff. One client had water coming into the basement wall, but it wasn’t down low, but at ground level just above the waterproofing. There was a defect in the concrete and a pencil size stream of water would come through during rain storms. That side of the house was re graded so water flowed away from the house and detailing that defect solved the problem.
That’s all I know. Water flows downhill.
