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Question DetailsAsked on 11/22/2016

we have a wet wood smell in a bedroom on the north side of the house. The house is on a slab, in state of SC.

house is on a slab, breezeway next to the room, water sometimes pools in the breezeway. Smell started about a year ago. sometimes it is very bad, other times not very noticeable. The bedroom gets no sun. Windows look fine, ripped up carpet and found white powder., which I understand often means water problems. Any ideas of what is causing the smell and how to get rid of it?

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2 Answers


If smell is mildewy/moldy, likely you have mold/mildew in the carpet and pad, and maybe in the base ofthe walls. If a pungent rotten wood or sometimes rotten vegetable type smell, likely rot in the base of the walls and any wood subflooring that has been staying wet, so may take some digging around to find the source. Smelling the carpet and backing/pad would tell you if that is the source there - nose to base of wall and also sniffing at wall outlets in the area can tell you if the odor source is in the wall(s).

The white powder (assuming not degraded carpet backing or padding material) is generally efflorescence - carbonate minerals like lime that have leached out of the concrete as moisture migrates up through the concrete to the surface and evaporates, leaving the minerals as a white powdery (as least when dry) coating on the concrete surface. Same principle as spotting and streaking on glasses in the dishwasher as they dry, leaving mineral deposits on the glass as the water bearing the minerals dries off.

Since you have water pooling in the breezeway, while a roof or window leak down through the walls is possible, most likely you either have surface water ponding by the house, roof runoff getting onto your slab because it is dropping right next to the slab, or high groundwater issues.

If there is no staining/streaking on the walls inside or out (except maybe right at very contact with concrete slab) likely not roof/window leak. Also, with carpet peeled back and any basebaord at worst location removed, look during heavy rain to see if water is coming down through the wall and out the bottom of the drywall, in which case it would be leaking window/roof. If seeping in under the bottom wall plate (the bottom 2x which rests on the slab) then check outside to see if water is up to the top of the slab. If this is the case, the white residue would tend to have a blob shape from the point of entry to the limit of wetting of the carpet as it spreads out from the entry point.

Look where the white residue is - if general over slab without a distinct shape or pattern, likely high groundwater or general high water around the house when it rains, and the solution is to get the water away from the house - which might be achieveable by some surface grading outside to make sure rainfall/snowmelt water runs away from the house, not towards it. Might also take some berming if sruface runoff is towards the house - but keep dirt level around house at least 4-6 inches below the bottom of the siding - preferably 8-12 inches in termite or intrusive insect country.

If general high groundwater condition, then drainage swales/trenches or french drain may be needed to keep the water table near the house a good few feet minimum below the slab - preferably 5-6 feet because the water wicks up to the slab in the phreatic zone - the area above the water table where the soils is not fully saturated but is damp from the wicking effect of the water surface tension on the soil particles. Just like holding a paper towel vertically with one edge in water will result in the water wicking up into the paper towel a foot or more.

If the problem is rainfall or roof runoff pooling against the house, then the normal solution is surface grading sloping away from the house to a natural drainage route away from the house at least 6 feet from the house, at a slope of preferably around 10% on free-draining soils but minimum of about 2% slope on low permeability soils, and adding gutters with downspouts that direct the roof runoff (your major source of water saround the slab in most cases) well away from the house.

Look around the house during rains - the source may be pretty obvious and easily solved. For surface drainage correction, Landscaping would be the normal Search the List contractor category for significant work, maybe Handyman for limited handwork. If you are in a low area where water runs towards the house, then Landscaping for general yard regrading to control flow, or Excavation if you need substantial earthwork building berms or swales to control surface runoff or provide an exit from your house area.

For french drains or drain pipes, Landscaping if in the yard to control incoming runoff before it gets to the house, or Foundation Waterproofing if you cannot control it away from the house or have high groundwater and need to control it at the edge of the house with a buried french drain to lower the water table locally at the house - like if in an area with generally high water table right up near the surface.

You do not necessarily have to go whole hog right off the bat - especially if you can leave the rug off for awhile to observe wherethe concrete gets wet and when, and whether it is a rainfall event-only thing or chronic due to high water table.

You will note I did not address vapor barrier under the rug - general moisture transmission through the concrete can be controlled with that, but if you are getting significant carbonate buildup on the concrete it is likely getting damp at the surface, not just transmitting water vapor, so putting a vapor barrier down will mean actual water at the interface, which without the vapor barrier going under the wall plates will cause rotting of the wall plates and eventually up into the studs up to a foot to three - so controlling the source is your first step.

Answered 4 years ago by LCD



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