Relative Humidity in Concrete Slabs and PH
Relative Humidity in Concrete Slabs and PH
(OP)
Hello All,
I have a project in construction with a slab on grade that is ready to receive carpet and other finish materials. The contractor tested the relative humidy and PH values of the slab, and they were higher than those recommended by the manufacturer. The manufacturer will not honor the warranty if their product is installed on the slabs as-is. Is there any way to somehow reduce the RH and PH values in the slab? This is the first time i've heard of this kind of issue, so any help would be appreciated.
Thanks!
I have a project in construction with a slab on grade that is ready to receive carpet and other finish materials. The contractor tested the relative humidy and PH values of the slab, and they were higher than those recommended by the manufacturer. The manufacturer will not honor the warranty if their product is installed on the slabs as-is. Is there any way to somehow reduce the RH and PH values in the slab? This is the first time i've heard of this kind of issue, so any help would be appreciated.
Thanks!






RE: Relative Humidity in Concrete Slabs and PH
For carpet, neither the pH nor the relative humidity in the slab are significant. Neither will cause much if any issue with carpet.
For barrier floor coverings such as vinyl tile, the moisture and pH are significant factors, primarily because of the latex adhesives that are used. For these, the relative humidity would preferably be below 75%, although up to 85% will work. If you are using the typical calcium chloride dessicant test, the values should be below 3 lbs/1000sf/24hours; although I have had successful installations at up to 7 lbs/1000sf/24hours. As for the pH, the latex adhesives are similar to latex paints and high pH can "burn" these materials resulting in saponification, a type of reversion of the latex materials.
For barrier floor coverings such as ceramic tile that use a cementitious adhesive or mortar bed, moisture and pH are not significant issues.
If the floor covering is a wood material or composite, the moisture issue is significant and should be kept low as in the vinyl tile. The pH is not an issue.
For floor sealers such as calcium or sodium silicate compounds, both moisture and pH sensitivity are possible. These sealers/hardeners are usually applied to hard-troweled concrete and when high moisture is available, there is a tendency to have a white haze or residue develop which is essentially a precipitate of soda ash or hydrated lime. To open the hard troweled surface a bit to prevent such problems, the surface of the floor is etched with an acid wash. I've successfully used muriatic and citric acid for these applications.
An acid wash can be used to reduce the pH where needed for other applications as well. Citric acid is very controllable and not noxious.
RE: Relative Humidity in Concrete Slabs and PH
As to pH, concrete is supposed to be alkaline, and the higher pH the better. Nothing you can do about that, except wait for years for the carbonation process to develop.
RE: Relative Humidity in Concrete Slabs and PH
As for the pH, it is only necessary to reduce the surface pH (usually no more than 1/8" to 1/4" depth). This can effectively and easily be done with a light acid wash using, preferably, citric acid. This reduces the pH to adhesive or coating tolerable levels, and it opens the pore texture of the surface to provide better adhesion and better evaporation of slab moisture. The pH reduction process should be done before the slab drying process.
RE: Relative Humidity in Concrete Slabs and PH
RE: Relative Humidity in Concrete Slabs and PH
Dik
RE: Relative Humidity in Concrete Slabs and PH