Latex paint = waterproof?
February 8, 2011 11:43 PM   Subscribe

Interior latex paint: Is this waterproof?

I have a windowsill next to my shower that gets consistently wet and the paint had started to peel like crazy, so I went to the hardware store, asked for some waterproof paint, stripped the sill and painted 3 coats of paint. I'm now looking at the can of paint and it just seems like basic interior semi-gloss latex paint. Do I have to go buy different paint and start all over? If I do need to do something in addition to what I've done, what would you recommend? I'd much rather not strip off this paint job if I don't have to.
posted by sdis to Home & Garden (9 answers total)
The problem is probably not the paint, but that the windowsill is already wet when the paint is applied. I'm assuming a wooden windowsill. Sorry to say that if this is the case, anything that you paint over it will bubble and peel eventually.

More info is needed. How old is the windowsill? Is it wood? How careful are you to make sure that the windowsill is treated properly before you paint it? Any wood in a bathroom should be treated and cleaned before it is painted. You might even need to replace the sill with something more appropriate. Such as coated aluminum. But since I haven't seen the window in question, I'm just guessing.
posted by Splunge at 12:23 AM on February 9, 2011

Response by poster: It's wood, and I basically just stripped off whatever I could with a metal scraper, and then sanded the whole thing down somewhat to roughen whatever paint wouldn't come off and clean up the exposed wood, and then wiped down the board with paper towels until no more dust would come off. Some of the wood was probably not bone-dry. Given that I'm only staying in this apartment for another year or two (and that I doubt I even have permission to take the wood board out), I'm OK with a solution that only lasts 8 months before I'd have to do it again (but painting every month would get tiresome quick). So I guess I have two questions with potentially different answers: how do I best keep this looking relatively nice for a good chunk of time, and how should I really take care of this once I own a home? What do you mean by "treated"?
posted by sdis at 12:52 AM on February 9, 2011

The best solution might be to buy an inexpensive, clear shower curtain that you can hang over the window.

Otherwise varnish or some other kind of exterior deck paint or other 'weather-resistant' paint. But for 8+months? Clear shower-curtain as curtain-curtain.
posted by From Bklyn at 2:01 AM on February 9, 2011

As splunge says. Even if you seal the piece with some super-high-tech-watertight seal, the humidity beyond would want to come out eventually, and the paint would detach. To avoid bubbling, the wood should be dried out entirely, which takes many months of no exposure to humidity.
Then one would get rid of all the old paint with a heat gun, sand the surface, apply some prime-brand base oil, put a layer of primer on top, and, for humidity-exposed surfaces, use outdoor oil-based paint, which is rougher in appearance than indoor finish, but sturdier. Even so, if you keep splashing water directly on top of the windowsill, your average life-length of such a coating would be limited to a few years.

If you're not staying long in your apartment, and don't want to tackle this in an in-depth way, keep patching the paint, should it come off again, it's the only way, and not the worst.
posted by Namlit at 3:01 AM on February 9, 2011

Your existing solution may not be perfect, but I doubt it will go to pieces so quickly as you fear. For now I would do nothing. If it fails again while you're there then perhaps come up with another strategy, but it wouldn't surprise me if it were just fine.

Maybe get in the habit of wiping standing water off the sill as you finish drying yourself off.
posted by jon1270 at 4:53 AM on February 9, 2011 [1 favorite]

Another data point : If the window was ever painted with an oil based paint, you will have a hell of a time getting latex to stick. You would almost have to take it down to bare wood, prime it, then repaint it. If you want to use oil based (Bathroom/Kitchen) paint, you should remove the latex, prime, and repaint. You ARE fighting an uphill battle with a wet area.
posted by lobstah at 4:59 AM on February 9, 2011 [1 favorite]

You did everything right except it sounds like you didn't use an oil based primer before you painted... Oil primers should always be used over bare wood before painting (whether the paint be oil or latex..) The reason is that the oil primer penetrates the surface of the wood, and seals it up below the surface of the wood. A latex primer (or just using a latex paint, for that matter) sits on the surface of the wood. So always use an oil primer first, than apply your paint.

Most professionals these days use a latex paint for their top-coat. You were right to use semi-gloss, and the higher the sheen, the more moisture resistant the paint will be. Everyone that said you should have waited for the sill to dry thoroughly before painting was correct, however it doesn't take months... The wood was likely dried in a kiln to somewhere between 6-8% moisture content before it was installed in your bathroom. So the moisture that lives inside the cells of the wood is mostly gone. The moisture that is there from your shower is between the cells of the wood, and should only take a couple days to dry at most.

There is no such thing as a "waterproof paint". If there was, I'd be out of a job, cause I'd paint a house once and never have to paint it ever again! The best you could do would be to get some marine under-paint, that's used for painting the hulls of boats, but at a minimum of 150 bucks per gallon, you'd be going way overboard!

Next time do everything you did, but let the sill dry for a couple days, then hit it with an oil primer before you paint it!
posted by Glendale at 6:38 AM on February 9, 2011 [2 favorites]

Another thing, since it's near the shower: don't use the sill as a shelf for cosmetic products. Many soap and lotion residues will soften paint.
posted by jon1270 at 8:26 AM on February 9, 2011

This is just a fact of life in small apartments with poorly ventilated bathrooms. Every bathroom I've had in New York City has had at least a little bit of peeling paint around the shower.

The best way to minimize peeling is to make sure you're working on a thoroughly dry surface (as Splunge says - also his advice about making sure any wood is properly treated), and that any previously peeling paint has been stripped away.

Try to keep things as well-ventilated as possible and make sure that your bathroom isn't damp all the time. If water collects in the windowsill, this may mean wiping it down after you shower. Also, keep it clean - mold isn't great for maintaining a good finish on paint, either.

Semigloss paint is best for surfaces that get damp and/or dirty easily, but it's not "waterproof" per se.

Another solution would be to take baths instead of showers if possible. You'll spread less moisture around the room, and things will dry off more quickly.
posted by Sara C. at 12:20 PM on February 9, 2011

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