Hi there, about 2 years ago I installed a hardwood floor in 1200sq.ft. of my 5 years old home in fresno ca. last year I noticed several spots turning black and I tore them up and installed a vapor barrier and reinstalled new boards. Now the problem is back. The builder says it's normal moisture coming through the slab and I should not have put down hardwood. It is only happening over cracks in the slab and cold joints no where else. Upon tearing it up again there is liquid moisture on the back of the boards and black mold. It looks to me like there is more going on down there than normal vapor. How much is too much and indicates a problem. Mike

If you see actual condensation on the back side of your barrier then it is too much. Mold and mildew probably aren't going to be covered by your insurance so this will be expensive and difficult. Changing the grade around the home to lower the immediate water table will help. Removing the floor and vapor barrier will get you to a point where you can try to seal the concrete and the cracks. We always test before installing wood on concrete at or below grade. A 12x12 piece of plastic sheeting is taped to the floor on all 4 sides. If droplets form we know we have a problem, like myou are facing now. BTW, the builder is not be truthful and will do what he can to avoid you thinking he has any responsibility here.

Moved from plumbing to construction

If you see actual condensation on the back side of your barrier then it is too much. Mold and mildew probably aren't going to be covered by your insurance so this will be expensive and difficult. Changing the grade around the home to lower the immediate water table will help. Removing the floor and vapor barrier will get you to a point where you can try to seal the concrete and the cracks. We always test before installing wood on concrete at or below grade. A 12x12 piece of plastic sheeting is taped to the floor on all 4 sides. If droplets form we know we have a problem, like myou are facing now. BTW, the builder is not be truthful and will do what he can to avoid you thinking he has any responsibility here.

The wood floor was put in 3 years after the hiuse was built. Was it put in by the builder or another contractor.
It is not the responsibility of the contractor who put in the concrete but rather whoever put down the wood floor.
BTW, this was on Holmes on Homes a little while ago. They determined that it was moisture coming through the slab. He said never put wood over concrete; especially with vapour barrier. Condensation forms on the warm side. Which would be the wood side of the plastic.