I built a house in the South Carolina area on slab. We are seeing moisture stains on the engineered wood floors show up. The spots are sporatic but many; and not in all rooms. We first thought it might be the pets (urine) but test show otherwise. We have done moisture testing and 3 borings in the house. Also, there are other houses with the same problem in the same subdivison and using the same subs.
The moisture tests show high levels of moisture (18%) and the borings do show the visquine(? spelling) in place. We used 3mil per code.
One thought has been that there could be a spring under the house that showed up after construction but we still wouldn’t be able to explain how the moisture penetrated the visquine & slab.
Another thought was that maybe there are pockets between the visquine & slab and that condensation is building up and making it’s way through the slab.
Has anyone had any experience with this type of problem?
Replies
How old is the house? The slab will continue to give off moisture for quite a while (years). Also, what is the position of the visqueen relative to the concrete--is it directly under?
I'll also second what Dave said. The poly keeps the concrete moisture in place and if the floor was laid quickly after the slab was poured it could be a problem that goes away.
Beer was created so carpenters wouldn't rule the world.
The house is about 3 years old and the visqueen is directly under slab (if I understand your question)
Good puzzle, and everyone has made relevant points. The thinner plastic is prone to damage during prep and pouring of the slab, so water may be coming up thru it. Or, the water used in the concrete itself may be trapped on top of the plastic and still trying to escape.
Just curious where you're located. Here in the Seattle area I've read that an indoor slab will still be giving off significant moisture after 20 years, whereas in San Diego it's only a few years.
David...thanks for your reply.
This forum has been really great. We are located in the North Georgia area. I think the points are good ones. I understand that concrete cures over time but it seems the amount of moisture should be some what constant. Of approx. 200 homes we built in this subdivision only 9 have shown this problem. While I don't know for sure, but could find out, some of the slabs were most likely poured in about the same time by the same sub. What's more is that the homes in question are spread throughout the project.
Only 3 mil? I've always used 6 mil or Tu-Tuf, and even then I worried about the mesh poking holes. I've also seen masons slash vapor retarders, ostensibly to encourage bleed water to drain. I'd be concerned about spot holes in the vb. Also, do you have underslab plumbing?
Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Andy....yes to under slab plumbing. We first thought that could be the problem. I should also mention that the "spots" are seen more in the middle of the house. I agree on the mil thickness...we are going to increase it in the future.
Thanks for the feedback.
As Andy said, the thicker the moisture barrier (retarder) the better and all the little penetrations can let in a lot of moisture.
Also, you're letting in a lot of moisture through the footings and/or stemwall, unless the vapor retarder is wrapped up the sides of the slab. The more mosture along the footing/wall, the more will get transfered to the slab. If everyone has automatic watering right next to the house with little or no water protection along the foundation/footer it could be contributing.
3mil poly is quite thin and easy to tear, so a number of tears during the pour can quickly degrade performance.
You mentioned small areas of moisture showing on the surface (and minerals left due to evaporation?), so I'd guess these are the locations of major rips, tears, poor overlaps.
Are the moisture levels consitant through the slab or is there a pattern, such as higher at the edges of the slab, dropping off toward the center?
Beer was created so carpenters could increase the moisture content near walls and trees.