How to clean unfinished plywood floor.
August 28, 2010 8:42 PM   Subscribe

How to clean unfinished plywood floor. I want to mop and freshen the bare plywood floor in our unfinished attic. I've already swept and vacuumed it. The floor is not filthy, but there was rodent activity. I'd like to use a solution that sanitizes, if possible. But my priority is not to damage the wood. There is an oily patch left by the former owners. Smells like they spilled a bottle of lotion. I'm inclined to just mop over that patch and not try to remove the spot. We use the attic for our home gym -- it's not a place where we bring company. My bottles of Murphy's Oil Soap and Simple Green say "do not use on unfinished wood". Any recommendations for a cleaning solution?
posted by valannc to Home & Garden (19 answers total)
Nothing "wet" is going to work. Unfinished plywood is not really cleanable this way.

If you're looking to get it pretty clean, you can sand it down somewhat and then vacuum and get the dust of that out pretty good. After that you can try to finish it in some way, but it's probably not worth it.
posted by RustyBrooks at 8:46 PM on August 28, 2010

Really sweeping is about all you do. I wouldn't use water or anything wet on any untreated wood, even plywood, I wanted to keep around. It's just asking for mold, mildew and warping/cupping. I would probably just throw down some cheap carpet or more likely linoleum.
posted by sanka at 8:46 PM on August 28, 2010

Maybe scatter something dry which will absorb the odor, then vacuum that up?
posted by pickypicky at 8:48 PM on August 28, 2010

Dry wood is not exactly a bacteria haven so it's not like you have a whole lot to worry about.

If I were you, I'd go rent one of those random orbit floor sanders from Home Despot or the like, give it a really quick once over with that using the finest sandpaper they have for those things, then vacuum again and give it a quick once over with some kind of penetrating sealant.
posted by Kid Charlemagne at 9:10 PM on August 28, 2010

Sounds like you want to keep the natural finish, maybe make it a feature? In that case best bet may be to cut that section out and replace it, or replace the whole sheet.

Having said that, as I type this I am looking at some ply stiffening on my (under contruction) garage, which has been in the weather for a month or more, during which we have had a lot of rain, and it appears totally unaffected...

If you really want the warm wood effect, and there is no other way of removing the stain, maybe you have little to lose?
posted by GeeEmm at 9:19 PM on August 28, 2010

Washing down plywood with water is not recommended. Done repeatedly it can damage the plywood by making the layers separate.
posted by Chocolate Pickle at 9:42 PM on August 28, 2010

What I'd probably do is go to Home Depot, into the paint section, and then to the 'Bargain Paint.' This is stuff they mix wrong or that somebody doesn't want or whatever. Buy a couple of gallons of interior latex in a light, inoffensive color in any finish except flat. If you can get the 'premium' grade that's paint and primer together, bonus.

Also buy some traction sand and a bucket. Dump paint into bucket, add sand, mix, paint onto floor. If you use a roller on a long handle you can do it in not much more time than it would take to mop really thoroughly.

Nice, clean, high-friction floor surface. With the exception of the oily spot, which you may need to prime over first (or just avoid), the rest of the surface just needs to be broom clean to paint. It will lock in odors and let you use a damp mop (as long as you don't scrub too hard) once it cures.

There are special floor paints that you can buy, but for a light-traffic area that's out of sight, I don't think that I'd bother.
posted by Kadin2048 at 11:01 PM on August 28, 2010 [3 favorites]

Man, Kadin has got it...
posted by dancestoblue at 11:36 PM on August 28, 2010

I'd try scattering a thick layer of baking soda on the grease spot, kind of grind it into the grain of the wood a bit with your hand or a rag, and then leave it for a day or so, then vacuum up. It might absorb some of the oil, and even if it doesn't work, it only costs 99 cents and it won't harm the wood.
posted by pseudostrabismus at 1:04 AM on August 29, 2010 [1 favorite]

Washing down plywood with water is not recommended. Done repeatedly it can damage the plywood by making the layers separate.
posted by Chocolate Pickle at 9:42 PM on August 28

1. Nobody is suggesting it be done repeatedly.

2. Modern ply has waterproof glue (well some at least). Not that I would necessarily assume the ply in question has, but it is not true that all ply will come apart at the first sight of a bucket of water ... ;-)

It may not be the solution most likely to work, but if nothing else does the job I would be looking at a bucket of water with a suitable detergent, and a scrubbing brush, though I would be carefull about how much water I used - ie not flooding the surface).
posted by GeeEmm at 1:31 AM on August 29, 2010 [1 favorite]

If you want to get the dust up and any surface dirt, you can use a barely wet (well rung out) sponge mop on it. Just sweep it towards you, much like a broom. Be sure not to let the water soak into the wood, or it may warp.
posted by The Light Fantastic at 1:34 AM on August 29, 2010

Any water at all will cause surface fibers to swell and stand up, making the floor rougher to the touch. If you need the floor to be smooth enough for walking on in bare feet, you'll end up having to lightly sand the whole floor after mopping. Cleaners like Murphy's and Simple Green will soak in a bit and be impossible to rinse off without using more water than is good for the material.

As long as the moisture is kept to a minimum, i.e. damp mopping rather than flooding with water, you're not risking serious damage. Warping, mold, mildew, delamination, etc. all require prolonged exposure to a lot of water. You are not flirting with any of that.

If you want to sanitize the whole floor, damp mopping with a little bleach water (to be followed with light sanding when dry) is your best bet. For the oily spot, I'd use a little dishsoap and water, scrubbing with a stiff brush. You probably won't be able to remove the visible stain, but you can at least remove enough of the oil to allow a finish to adhere.
posted by jon1270 at 2:22 AM on August 29, 2010

The "rodent activity" skeeves me out a bit, as it brings possible hantavirus infection into the picture. Though the possibility is remote, it's nothing to mess with. Your local Washington Department of Health says that hantavirus does exist in your state, and recommends not sweeping or vacuuming rodent-infested areas, but instead wet-cleaning with a bleach solution -- messy and perhaps damaging, but better than a bout of 30%-mortality hantavirus pulmonary syndrome caused by inhaling virus-laden dust.

For future reference, the CDC gives a "textbook answer" on how to sanitize a rodent-infested attic. It involves first setting and checking traps to make sure that all the rodents are dead/gone, waiting 5 days after the last observed sign of rodent activity (hantavirus inactivates after 2-3 days outside the host under indoor room temperature conditions), ventilating the space, donning rubber gloves, soaking all nesting/droppings/urine with a 10% bleach solution, removing them with paper towels, and then mopping the floor with a 10% bleach solution or other disinfectant.
posted by Dimpy at 2:41 AM on August 29, 2010 [1 favorite]

For the oily patch use neat washing up liquid on a damp sponge, don't try to rinse it off or anything like that, just to break down the grease, let dry fully, then do what kadin says.
posted by koahiatamadl at 3:25 AM on August 29, 2010 [1 favorite]

I'd go for the 10% bleach solution and a damp, not wet, cloth. You aren't really going to damage the floor to the point of it being unsafe or unsightly.
posted by littleflowers at 4:36 AM on August 29, 2010

I would probably want to bleach it down as littleflowers suggests. 10% bleach really only has to be in contact with the surface for a few seconds. The only downside is that it would probably need to be rinsed afterwords so the bleach doesn't continue to work on the wood. If it is standard plywood, it can take being wet just fine, as long as it dries out quickly enough. What it doesn't like is not being dry most of the time. As [someone above] said, most construction grade plywood can handle being exposed to the weather for a certain amount of time without losing structure.

Then I would sand it down with maybe some 100 or 220 grit paper on a hand sander- either just a $8 sanding block with a handle from Menard's, or splurge and spend $39 on a cheap oscillating sander (not a belt sander). Go with the grain. That really shouldn't take all that long, since you are sanding a softwood, and since you aren't looking for a mirror finish. All you are doing is knocking down any high spots. Vacuum it up, give it a once over with a damp cloth, and then paint it. Or lay down a couple layers of water-based polyurethane. That will harden the floor, whose surface wasn't really meant for traffic anyway, and make it more impenetrable to future stains and whatnot.

If you have one, running a dehumidifier for a day or two between the wash and paint is a good idea. I wouldn't go out an buy one just for this though.

"Cover up" paint, like Kilz, is also a good possibility.

The "bargain paint" idea is a great one, especially if you can find floor paint or furniture paint. I'm not sure wall paint would work very well. If it was me, I would thin it down a little and put on extra coats for durability. Wall paint seems a little too "thick" to me- both in consistancy and in the final texture. But being a simple work space, I'm sure whatever you find will be fine, especially if you are content with having to repaint it occasionally.

For the oily area, I would indeed try to scrub it down with some soap (not detergent- good old lye-based soap. I think Murphy's is.) Then dry it as quickly as possible. If it looks good enough at that point, just sand it flat. If it still looks gross, try scrubbing it with some 91% isopropyl alcohol. Scrub it for a while, sop it all up, and then scrub it some more. Between the soap and the alcohol, that should dissolve the stuff that made the stain good enough.

The damp cloth thing is fine for getting up that last bit of dust, if that's all you want to do. Another option is to get a few large sponges. They are easier to wring out than cotton cloths. (Or go to a restaurant supply store and get some of those weird white and pink wiping up cloths- those wring out easily too.)
posted by gjc at 6:51 AM on August 29, 2010

My mother used Coke a Cola on the old wood floors in a farm house my parents bought to fix up to sell. A little and toothbrush, took her a day to remove a lot of old oily stains but it worked. Dad dried then sealed the floors and they still look.
posted by bjgeiger at 7:17 AM on August 29, 2010

Best answer: I have a lot of wood-finishing experience. For the lotion spot, I'd use paint thinner or denatured alcohol and lots of rags. Both chemicals are available in stores that sell finishing products. With either one, don't just scrub and let it dry -- pick up the soiled solution. There wouldn't be major harm if you used water and a degreaser like ammonia just in that area. Just keep the edges of the plywood sections from getting wet with water. If the grain is raised by the moisture, let it dry and sand off the fuzz.

You can also go over the whole floor with thinner or alcohol to remove germs and whatnot. Sanding would be good to improve the floor's appearance and smoothness, but that's a lot of work.

If you do clean the entire floor, you might want to protect it with water-based polyurethane. It has vertually no smell and it dries fast. Several types leave the wood looking very natural and bare, without changing the color or adding sheen. You need to mix it very well, apply it generously with a roller, and give it at least a few coats. which is a much more pleasant operation than using paint or oil-based poly.

Feel free to MeMail me.
posted by wryly at 1:40 PM on August 29, 2010

Response by poster: I really appreciate all this advice. You guys saved me from something stupid... I was all ready to wet mop that floor.

For now, we are making do with a good thorough vacuuming.

Dimpy, I appreciate your alert about hanta-virus. I checked and it's not a problem in our immediate area. The rodent signs we found are very old and in out of the way spots. I wiped those small areas with slightly damp disinfectant rags.
posted by valannc at 2:37 PM on September 7, 2010

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