Soaked subfloor under kitchen sink

[dlminehart]

A backed up drain and loose sink trap resulted in water getting through the plywood bottom shelf of my kitchen sink cabinet down to the particle board subflooring a 2x4 width below the shelf. The bottom sink shelf turned out to have been opened up before, with a ragged cut taking up about half its area and exposing the subflooring. The hole had been covered up with a couple sheets of plywood, making a new (but leaky) floor to the cabinet.

Anyway, I took out the plywood sheets, propped them by the front of the cabinet with doors open, and directed a box fan into the area for 24 hours. The plywood seems to be drying out a bit, but the particle board subflooring is still pretty soggy.

Any suggestions? Should I remove the rest of the original 1/2" plywood cabinet floor and then, somehow, remove the wet subflooring, replacing it with something dry and probably more waterproof? Should I just get a heater with fan instead of the plain box fan, and give it another day or two to dry? Anyone been through this before?

[newbie2wood]

I would first take care of the problem with the loose sink trap to prevent another reoccurence. It doesn't hurt but there is no need to waterproof the subfloor. Just let it dry to prevent mold from developing. You may want to replace the cabinet floor if it is warp or stained. Using a heater will speed up the drying process but too much heat may warp or crack the wood. Good luck.
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[LJR]

To prevent damage from mold we use the rule of thumb that all materials have to be dried out in the first 72 hours. If that's not possible then the materials that got wet are torn out and replaced. We use air circulation to dry, heat could help, but it's more important to have good air circulation.

I really doubt you're going to get that particle board subfloor dry in 72 hours and water penetration will generally destroy particle board anyway.

I'd suggest take out the bottome of the cabinet completely. Take out as much of the subfloor as you can reach through that opening. Replace the subfloor with similar thickness material, then replace the cabinet bottom with plywood, then I'd put down my waterproof layer. Could even be something as "cheap" as a sheet of plastic.

[cgallery]

I'd be concerned the heater could set a fire. I'd maximize ventilation and keep the fans on it.

-Phil in Milwaukee WI

[dkhoward]

That particle board will probably swell anyway and it will be almost impossible to level the cabinets again. I'm betting that you are going to be forced to do the subfloor and the cabinet bottom to make it look right.

[dlminehart]

Well, I've removed the particle board (entire garbage bag of it!) and dried the plywood subfloor. While I'd initially planned to replace the particle board with some Hardiboard or similar cementatious waterproof material, on reflection I don't see that any use would be served by replacing the particle board covering the subfloor. Instead, I think I should put more effort into waterproofing a new floor for the cabinet itself, including its joints with the cabinet sides and perhaps an inch or so up the cabinet walls. That way, any water that got into the bottom of the cabinet would end up spilling out onto the sheet vinyl kitchen floor.

What do you folks think of this plan?

[dkhoward]

I dunno. Others may overrule me or call me nuts, but I don't like particle board or MDF anywhere there is the possibility of water. In fact, I don't like particle board as subflooring at all. I raised a garage floor in part of my house and originally used 3/4" particle board as subflooring. I never did do well. When we replaced the carpet I redid the whole thing with 3/4 plywood and screws. No squeaks, no movement and no softspots.

Personally, I would never put particle board subflooring in a house and especially not in a bath or kitchen. My two cents. Take it for what it is worth. My wife usually does.

[billwmeyer]

I agree with Dennis. I had the same problem, only the particle board was put on the floor butted up to my cabinets. When the sink trap leaked, it ran under the particle board and the leak wasn't even noticable for several days. Needless to say, it ruined the particle board for about a foot around the sink, and the vinyl flooring. I will never ever use particle board for an underlayment anywhere that moisture will be an issue, and probably not even then. When it gets wet it becomes nasty sawdust.
Bill