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Question DetailsAsked on 10/24/2017

Can't figure out why floor in front of dishwasher shows damage from underneath just on seams. We see no wet on top

We just had new 100% waterproof vinyl flooring installed in May. It has cork backing. The seams look puffed out with rusty colored crud just in front of dishwasher and sink which are by each other. We took everything out from under sink and pulled dishwasher out and no water anywhere. Flooring is on cement slab. We thought maybe steam from dishwasher drips down into flooring but why don't we see water on floor? Mystery

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2 Answers


Well - several possibilities - I am going to presume the flooring does not go in under the dishwasher.

1) check around outside to see if there is any outside source of water that could be coming in under the wall there, seeping in on top of the slab - blocked gutters or downspout, slope of ground along foundation trapping water there, outside water running to the house foundation, blocked foundation drainage french drain (uncommon with slab-on-grade foundations but sometimes used, especially in low-lying or high groundwater areas) backing up and letting water rise to the ground level around foundation.

2) under dishwasher, put a paper towel strip across under the front edge of the dishwasher (so it covers the floor under the door seal area), then immediately after running a full cycle load check that for water and also unplug it (because there is exposed wiring under there) and then with a stick or such with a rag tied around it wipe all around underneath there to see if it comes out wet. If the paper towel comes out wet you have a door seal leak or one somewhere near there - or condensing steam in the door dripping down under it. If that comes up dry, but the towel wiping comes back damp then you have a leak underneath the dishwasher - probably hose connection or pump or tub penetration seal.

3) also with dishwasher unplugged, run a paper towel or such around the bottom of the drain line from the dishwasher and the water line to it - could be a leak there getting in under the flooring. Usually, after taking toekick plate off dishwasher, you can get in there with a stick and rag without pulling the diskwahser out - just make sure it is unplugged because of the bare wiring underneath the unit.

4) a bit more trouble, especially if it was nailed down - but assuming no water showing under the sink (in the cabinet), take out the "floor" in the cabinet - the bottom flat piece in the cabinet - to inspect the underlying concrete floor for leakage from water or drain lines behind or under the cabinet. Check any water purification unit and any water line to reefer as well.

5) if all those come up negative, check the joint closely - if caulked with silicone (and maybe other materials) sometimes in environment exposed to dampness (including steam) the caulk will turn yellow/orange (looking rusty orange sometimes) and expand out of the joint - common in bathrooms at vinyl flooring seams around toilets.

6) if all those come up negative, then you don't say what previous flooring was, but might be if it was moisture-permeable like ceramic tile or stone, that your vinyl flooring is now trapping moisture coming through the concrete slab, causing moisture issues at the seams. It is real common for a floor to do fine with grouted stone or tile, but have problems from the concrete-transmitted moisture if a carpet, vinyl flooring, linoleum, hardwood, or even mastic-adhered tile is put down.

This sort of flooring should have been installed over a vapor barrier - if it was not, then this mioght be a situation that can only be remedied by either putting in foundation perimeter drainage to lower the water table (might take several feet of lowering - sometimes as much as 8-10 feet in fine grained clayey/silty soils), or removing the flooring and putting in a vapor barrier - though if you are getting free water on the concrete (trial under vapor barrier overnight during highest water table season) that will just cause mold under the vapor barrier and possible wall plate rotting - so not a good solution.

Unfortunately, if this is the problem, generally it is hard to cure completely short of putting in a tile or stone over portland cement mudcoat base floor (which can transmit a fair amount of moisutre and is relatively impervious to the moisture from the concrete). The proper solution (rarely done even though only a hundred or two extra $ at the time) is putting in a graded drainage surface under the slab (so the soil drains to the sides and out from under foundation through the base material) and a full vapor barrier UNDER the foundation and slab.


BTW - if they sold that flooring claiming it was totally waterproof I would have them give your money back for false advertising - cork if very far from waterproof - more like a sponge and makes for a nasty odor when wetted as well. For a "waterproof" kitchen/bath floor you need 100% vinyl flooring - and any backing or padding should be pure plastic as well - usually polyethylene "mini bubble wrap" sheet. But remember - that does not solve the problem if water gets in under it - because you can still get mold issues under the vinyl if water gets in under there - from pipe leakage, appliance or sink overflow, or seepage from outer wall or moisture transmission through the concrete slab.

Answered 3 years ago by LCD


BTW - here are links to a few previous questions about dishwasher area leaks which might be of help if you do find water under the dishwasher. (I also did not mention - with front kick plate off, with some models you can just use a BRIGHT flashlight to look in underneath and asee any wet spots/puddling - depending on how shiny the floor surface under the dishwasher is.

Answered 3 years ago by LCD

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