Painting: dry time after pressure wash?
geoffhazel
| Posted in Construction Techniques on
I was having a discussion with a friend today and said I was planning to pressure wash one day to knock off the loose paint and start painting the next day (Latex ext. paint). He, in a shocked tone, told me he lets houses dry for two weeks after pressure washing if you get down to bare wood.
I’d like to hear some other opinions on the subject.
Replies
Moisture meter, < 15%. -- Totally depends on the climate/weather.
Painted once in Seattle on a 50 F day in January, never got below 40F at night, paint was not dry even 3 weeks later.
Was in Mesa AZ in '94 when the high was over 125F for 8 days straight. Dry enough to paint in 1/2 hour, but you wouldnt want to then either.
Here in the Midwest, it is essential to wait at least 3-4 good drying days after powerwashing to paint. Generally there will be scraping even after the powerwashing. Do you give a warranty on your exterior work?
Agree with your friend. You want the moisture content down, and you want to be able to sand. Especially if you've gotten to bare wood, because doing that with a pressure washer will likely gouge the dickens out of the siding. If you put latex over it and the wood is not dry, as the siding heats and the moisture tries to exit, it will do so by popping the paint off in nice large bubbles.
"If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man." - Mark Twain
OK, I'm convinced. I think there may be just enough peeling paint that it's nearly a toss-up between press-wash and manual scraping; I'm in a hurry on this job, so I think I might wind up scraping by hand.
Don't put latex on bare wood, or you'll end up repeating the whole process in two years.
When recoating with latex (over latex) it actually helps if the surface is ever so slightly damp, especially in warm, dry weather when the paint would otherwise dry to fast.
But when painting with oil (or priming with alkyd primer) the surface needs to be completely dry.
I never pressure washed for paint prep, and have never seen a good pro do so; unless you are in the desert you will put too much water into the wood.
Here in New England the water would be there until winter; in the boards, under the boards.
Surface has to be dry, stable and clean; all three.
mho pressure washer rarely ever a good tool around wood
better methodology - do your dirty work; scraping, grinding & sanding cleaning areas well
apply good primer and plenty of time to dry then wash down house w/ tsp or bleach & water w/ boatbrush and spray nozzle on hose
in good weather the side you started cleaning on will be ready for paint
Why would you wash AFTER priming?
I think he's assuming that you're only spot priming the areas where bare wood has been exposed. The washing is used to prep the remaining areas.
All the paionters I know gave up using presure washers years ago, because they ruin a job.
Even using light spray, you need a couple weeks, but that time can be well spent doing the rest of the prep woprk, sanding etc.
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yes Javier - as Dan saysa typical painting scenario ( definitely the one the poster was considering ) is to power wash structure then prep and paintoften in the prep work one has made the surface "dirtier" than it was before power washinglike on interior trim the least you can do is follow light sanding w/ tack rag of liquid etch or thinner after using a vacuum to get the majority of dust - giving good clean "tooth" is the least we can do
question: how does it get "dirtier" after pressure washing?
every painting job is unique but what I "saw" was powerwashing ; then scraping, sanding, bondo, spackle etc then painting without a wash cycle to remove who knows how much dust has been created
OK -- thanks. I've seen some horrific power wash attempts, especially on old clapboard. An additional benefit of hand prep is that you are forced to go every square inch, which gets you to notice nail pops, split boards, loose caulk, etc, -- all of which should be remedied before painting.
I guess I'm the only nitwit here. In Michigan and in Chicago I painted houses routinely. And I painted the day after washing and even a day after raining, but not first thing in the morning. Never used an alkyd primer on those situations or it would peel off as the siding dried and the moisture migrated to the surface. Back then the paint can label stated that on hot days one should mist the surface. The purpose was so the moisture would pull the paint into the substrate as apposed to just laying on the surface. I've also been working on the above premise for the past 14 years here in south Florida. Not once have I ever had a call back.
Yeah, when I'm painting with latex/acrylic I like to wash the wall and then paint when it's not quite dry. Seems to work out well.But I'd never do this over bare wood (always prime with alkyd first, when the surface is at least 24 hours dry).
Nitwit?I'd never accuse you of having nits in your wits, but that's a new one to think about;)
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Hey, at one time or another, I think we all catch a "nit" in our "wit." God knows I've had several. Just ask my kids. They usually start with "Daaaaad!"
Very interesting, Sonny, good to know about the moisture/latex painting relationship. It changes my ideas about dry time before painting. However, after I give a home a good thorough washing and spend a couple days on prep, I will still get water drops here and there when painting aluminum/vinyl soffits. Not hard to remedy, but I'd rather avoid it.
Edited 5/18/2005 1:11 pm ET by bbqjason
Are you sure the reason for misting the surface on hot days was to pull the paint into the substrate? Wouldn't you want that to happen on all days? I was under the impression that misting was to keep the water in the paint so that it could setup under "controlled" conditions. The paint formulators didn't want the hot, dry wood to suck the water out of the latex. The misting might have also cooled the surface to some extent. When doing some tile work, at least one thinset mortar manufacturer suggests misting the cement backer board so that it does not suck the water out of the mortar so that the mortar can harden properly.
I'm with Piffin and the painters he knows.
Pressure washers should not be confused with an appropriate paint removal tool for painted wood surfaces just because they can cause paint to come off and fall to the ground.
We all try to build so that moisture cannot access the backside of the siding, because for one reason......it will cause paint to peel/fail. When you pressure wash, you force water behind the existing film of paint and in to the wood. IME (and I've tried this way more than once whilst learning the hard way) you usually end up creating as much peeling paint as you removed with the PWer. Time for the scraper. All the time I spent PWing was a waste of time and energy.
Pressure washers definitely have their place, but painted wood siding is not one of them, IMO.
As for as i know power washing is a working way to prepare the surface before painting. The surface should be as clean as possible because the dirt spoil all your further works. Exterior painting demands professionality and preparation, if you're interested you're welcome to read more about exterior painting https://ikhomepros.com/exterior-painting/ and perform it even by yourself. If you're inexperienced it's easier to take professinal services because mistakes can spoil your job.