I've got a 110 year old house with a fieldstone foundation and a poured concrete floor. The humidity is too high for my liking (70-80%). I've improved the obvious things like extending the downspouts, improve the swage, installed window well covers, and re-pointed the fieldstone. This has improved the humidity but it is still too high.

I did a "moisture test" on the concrete floor by taping a 3'x3' piece of plastic over the concrete and it was moist underneath. I believe the majority of the humidity is being caused by water vapor through capillary action. I've been researching what to do and the only cost-effective solution for me is to seal the floor with a deep-penetrating sodium silicate based sealer.

I'm looking for advice on these sodium silicate sealers. Does anyone have any experience using them? Are any better than the others? Do they work as well as the manufacturers say they will? After a bit of research I came across these manufacturers and thier products:

RadonSeal
Sani-Tred - Permaflex
Endur-O-Seal - Hydraseal/Hydra-loc
Applied Technologies - Hydra-Block
Bone-Dry Concrete Sealer
V-Seal - 101
Stone Technologies - X-1/X-2
MightySeal

I'm hoping someone can help me weed through this mess. Thanks in advance!

 

Hi XJ, Certainly not a pro on this issue and it plagues my all the time. Here's my concern. Obviously, there is moisture moving through the concrete, so there is more moisture on the other side, probably wet. Right now, the floor feels somewhat dry, because the moisture diffusing through is evaporating as it reaches the surface. All facts supported by your high humidity and your plastic moisture test. So, what will happen if you stop the evaporation by sealing the surface? The moisture level just below the sealer will stabilize at the same moisture level below the concrete, which we suspect is wet. By stopping the evaporation, we bring the moisture closer to the surface and as long as that surface remains perfect, the moisture may stay there. But concrete is always shrinking, cracking and we want to walk on it, so the moisture, now now more wet than before will find a way through.

Another solution is to de-humidify. This reduces not only the moisture in the air, but the moisture at the surface of the concrete. But care must still be taken with anything placed on the floor, or it will result in the same results you saw with the plastic.

The other step, which is unknown as to results, would be sumps, deep enough to capture the moisture/water before it can reach the bottom of the concrete.

It's really tough to correct what should have been done when things were built, maybe you will have to dig those responsible up and explain it to them .

Bud

 

All good points Bud! I've been using a dehumidifier for a couple of years now. The only problem is that it essentially runs 24/7 and can't get below 55% humidity during the summer. The basement is only 600 sq.ft. and I am using an 80pint dehumidifier which I suspect should be adequate for the job.

Since I don't have flooding problems, just excessive moisture....how would a sump pump be installed? I'm very unfamiliar with them. Would it be as simple as cutting a 2x2 section somewhere in the basement and digging 4ft deep and sticking a sump pump in there? Or is it much more complicated than that?

 

Make sure your dehumidifier like cooler temps, some become less efficient. Just run the condensate into a covered bucket to measure the output to confirm it is doing as advertised. I suspect it is removing far less than expected.

As for the sump, the question is how wet the ground is below the slab. If there is water right under the slab, then the sumps will fill and you can pump it out. If there is no gravel below the slab to allow the water to flow to one area, the sump, then multiple sumps may be needed. But the first job is to see how wet it is down there and that can be checked with a small hole. A larger opening and you can see what the soil looks like and really get a look at any water issues. If you don't have a sump, then having one, even in a dry basement is always good, since leaks and such always present a water concern.

Check the dehumidifiers performance and consider checking the soil under the slab.

Bud

 

Thanks again for your help Bud! The dehumidifier is rated for 40 degrees but I agree its not going to be very efficient at lower temps. The temp in the basement even in the winter never gets below 60. I'll have to check the output like you mentioned.

Also, as far as checking the soil right under the slab.... I guess I've done that as well, just not intentially. For some weird reason when the previous owners poured the basement floor (it was dirt once), they left a 6x6 wooden beam goint across the floor and poured the concrete around it leaving the top 1/2" of the beam exposed. It was not structual, I think it was just too big/bulky for them to move or it was part of a partition wall at some point.

Long story short, over the years it had dry rotted. I removed it and left the gap exposed for some time. The soil stayed damp to the touch most of the time and only under severe rain storms (like 5" of rain in 24 hours), would the soil get wet. Only twice did I ever see standing water in the gap. Even then it was only about a half inch of water and it was two inches below the bottom of the slab.

Well, I guess I just talked myself into putting a sump pump on the list....