Have I ruined my plywood subfloors?

March 4, 2013 12:57 AM

I covered my plywood floors in water....it was only once, but when will they be dry again?

I have a contractor who is redoing the rugs in my house. He told me to clean the plywood floors between his pulling out the old rug and putting in the new rug. Like a moron, I agreed. He told me to spray them down with bleach, and cover it with KilZ paint.

Unfortunately, I hadn't read the previous post here on how to clean plywood floors....and figured after you spray something with bleach, you need to rinse it with water (plus there was a lot of carpet glue or something left over).

....so I covered my plywood floors with water, ug. About halfway through I realized it was probably not what I should be doing....but I was unfortunately on a roll.

So now I need to know how long it will take for them to fully dry....I'm unfortunately on a time crunch.... I did soak up all the excess, and it's not very humid here this time of year, but I really need it to be dry within a week....is this a pipe dream?

posted by Lt. Bunny Wigglesworth to home & garden (10 answers total)

...and by rug I mean carpet, sorry.
posted by Lt. Bunny Wigglesworth at 12:58 AM on March 4

They'll be dry easy in a week with low relative humidity. If they don't look mostly dry in 24 hours crank the heat and (if it's not forced air) set up a fan to circulate the air.
posted by Mitheral at 1:07 AM on March 4 [1 favorite]

The danger with wet plywood is that is will warp and delaminate (the layers come apart, mainly due to the sheet being bent). This happens more quickly with thinner plywood; thicker sheets are more stable, because there's less flex in them.

But this takes quite a lot of moisture over a fairly long period. I've left scraps of plywood out in the elements for months and it's amazing how long they survive relatively unharmed. Plywood flooring tends to be firmly anchored down, so there's not much danger of warping. So get it dry as quickly as you can, and you should be fine. Just don't do this every week.
posted by pipeski at 1:54 AM on March 4

I agree with pipeski in that it's very unlikely you did any serious damage. It doesn't sound like they were flooded with water for long enough for water to soak deep into the wood, so when the surface looks dry, that's good enough. I doubt it will take longer than a day or so, and it could be a matter of hours.

That said, plywood doesn't delaminate because it gets bent / warped by water. All sorts of things are constructed by bending plywood around a frame or form, and doing so doesn't cause it to come apart. Plywood that's held flat can nevertheless delaminate if it gets wet enough. Delamination happens because each of the thin layers of wood expands very forcefully across the grain when its fibers are saturated with water, but stays almost exactly the same length. If the wood was still part of a standing tree that was somehow getting wetter and drier, then the tree would get fatter and skinnier but stay the same height. Plywood is constructed with the grain direction of each layer at right angles to the grain direction of adjacent layers. Each layer "wants" to expand and contract across the grain (tree getting fatter and skinnier), but it is restrained from doing so because it's glued to adjacent layers that are stable in that direction (tree staying same height). Thus plywood sheets are dimensionally stable even though they are sandwiches of a material that is not at all dimensionally stable. In normal (dry) circumstances plywood is always a balanced system of opposing tensions. But when plywood gets saturated it's components ReallyReallyReally want to expand a whole lot, and the forces involved become large enough to break the glue, which itself is often weakened by the moisture.
posted by jon1270 at 3:03 AM on March 4

I did soak up all the excess, and it's not very humid here this time of year, but I really need it to be dry within a week....is this a pipe dream?

Did you see about buying or renting a dehumidifier?
posted by dubold at 4:13 AM on March 4

To the plywood experts out there: would it make a difference if his subfloor was interior OSB and not the traditional smooth-faced stuff? I know the exterior stuff usually has a coating to ward off moisture, like when it's used as roof decking and it needs to be able to withstand a few rainstorms during construction.

But what about interior OSB subflooring? I have it in my house and from the parts I can see (like from the basement looking up) it doesn't look coated or anything.
posted by JoeZydeco at 7:01 AM on March 4

Once, due to a problem with our roof (... or lack thereof), we had what I affectionately called "our indoor water feature." Before we installed a complicated system of tarps and tubs, the exposed floor plywood ended up with constant sheet flow and a few standing pools of water at least overnight if not longer. We sopped it up, but it didn't dry out quickly, due to the aforementioned tarps and tubs placed above it. The situation was bad enough that for fear of mold, we tore out the remaining drywall from the basement ceiling below.

But the plywood itself seemed and still seems fine. There's no visible warpage or delamination. Ours isn't playing much of a structural role, because it overlays floor planking, so you might see if it seems noticably more bouncy if you have just the one layer of plywood. But I'm almost certain you're fine.

If you want to speed up the drying process, you could rent a dehumidifier and a few blowers from your local tool rental company. A blower or two would probably be my priority if your funds are limited. Even a $20 box fan from Target would help.
posted by slidell at 8:06 AM on March 4

It will be fine. Sub-floors are often left fully exposed to the elements during construction. Heat and ventilate as much as you can.

@JoeZydeco, I've never seen OSB used as sub-floor, and I would never choose it for horizontal surfaces.
posted by humboldt32 at 9:58 AM on March 4

@humboldt32: Oh it definitely exists. My whole house is 3/4" tongue-in-groove. Googling will show you lots of installations.
posted by JoeZydeco at 11:25 AM on March 4 [1 favorite]

Actually, crud, JoeyZydeco hit the nail on the head - it's OSB.

Unfortunately the heat and electricity were off the last time I was there....but I'll see about getting a box fan and hopefully they will never back on tomorrow....

In the long run I'll probably rip these subfloors out (there's a lot of mold growth) but unfortunately it's not something i can do right now....

Thanks for the help!
posted by Lt. Bunny Wigglesworth at 11:39 PM on March 4