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Question DetailsAsked on 4/13/2016

Who would I call to check out my cellar floor. It looks like there is salt on it....I dont have a water problem

but the previous owner painted the floor and now it looks like a mess. I wanted it treated somehow

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Assuming you have not had a leak there that precipitated minerals as it dried, what you have is efflorescence (aka sweaty slab syndrome) - minerals leached from the concrete or soil by water wicking up through it and evaporating at the surface. The surface itself may look basically dry, or more commonly will be darkened in that area because it is damp - though will be cold but likely not damp to the touch. however, if you put a sheet of plastic over it taped down at the sides and let it sit a day or two, I would bet you will have water condensation over the plastic and possibly the surface.

Normally, this means you have water close below the slab or ground surface, but the actual water table is probably a foot or few down - but the wetted or capillary zone above the water table is wetting the soil to the surface and wetting the concrete, which upon evaporating leaves those white deposits, commonly composed of lime and salts. In some cases, the salts are coming out of the concrete itself because it was made with reactive materials - normally pretty minor thickness in that case, nothing like the last image below -

Commonly look like this on soil and on flooring and concrete:

Very tough to stop - generally the solution is to either drop the water table (a significant task in most areas, and has to be a lot deeper than normal underdrains, sonot generally a retrofit solution), or to install a vapor barrier UNDER the slab - obviously not much of a solution for an existing house. Sometimes - but only sometimes - serious pressure washing or acid treatment to remove it, then immediately sealing the surface with an epoxy or polyurea/polyaspartic type floor finish (on the pricey side - $5-10/SF) will seal it in - other times there is enough moisture or acidic material that it eats right through it or blisters it in a fairly short time. Mild cases a good acid cleaning and painting with 2 coats of a garage floor paint will work - an easy DIY job but makes the stripping a bit more esxpensive if it does not and you then try to go with an epoxy or urea type coating later. Plus none of these stop it coming up at the perimeter of the slab.

In minor cases, sometimes placing a vapor barrier over it (sealed to the foundation walls a foot or so above the slab) with a floating floor or carpet over the vapor barrier will control it and put it out of sight, but in rare cases it continues to build and can lift the flooring right up because the salts have a substantial energy of formation - when they form they will press strongly against anything restraining the growth. This is a significant cause of damage in hydraulic structures and roads made with reactive aggregates - especially common in Oklahoma/Texas area.

Many people, especially if happy with a concrete slab floor in a relatively unfinshed basement, just use a mild acid wash (muriatic acid or even high-strength vinegar - ventilate to prevent fume buildup) every few years.

Reducing the humidity in the cellar can also help if you do not have water coming in from outside the foundation walls (precipitation occurring onlhy on slab). If the surface is kept totally moisture free by keeping the air humidity down, the precipitation occurs within the concrete slab and does not show up as much on the surface - though commonly will still appear at joints and around the edges.

You can do some google searching but without throwing a lot of $ at it generally it is not solveable without taking up the slab - or in a location with high headroom, placing a fully edge sealed vapor barrier then another concrete slab over that.

For a contractor - basement waterproofing would be the normal category, though specialty concrete contractor if looking at the sealing route.

Answered 3 years ago by LCD

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