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shorty46 06-17-2008 12:18 PM

cleaning and painting exterior raw wood
I had a new roof put on my old garage last fall. Some of the wood on the edges of the roof had to be replaced because of rot. I was unable to paint these areas before winter.

How should I clean the surface before painting?

Also, I am painting the exterior of my house, and although most areas needed little scraping, there is one area where the paint has badly lifted and the wood has been exposed for a while. I assume that I should clean this some way also. Anything else I should do to prep raw wood before priming?

slickshift 06-17-2008 08:16 PM

Clean with a nice TSP/Bleach/Water mixture (recipe on the box of TSP)
Feather sand (80/120)

Nestor_Kelebay 06-17-2008 10:57 PM

I'd paint the areas where you found wood rot with a paintable wood preservative first. Allow to dry, and then paint. Or, use copper naphthenate, and wipe it down with mineral spirits to remove any oily residue on the surface before priming with an exterior oil based primer and painting.

Zinc naphthenate simply isn't as effective in killing the wood rot fungus (called "serpula lacrymans") as copper naphthenate, so stick with the green copper naphthenate.

Is this a latex paint you'll be painting over? If so, check the label on any TSP you buy or phone any 1-800 customer service phone number you can find on the packaging to see if it etches latex paints.

Just sand down any grey weathered wood until you hit solid yellow wood, clean off the dust and prime, preferably with an exterior oil based primer, but latex over bare wood is OK too.

shorty46 06-18-2008 10:54 AM

Thanks. I've been using TSP substitute to clean and remove chalking, and the instructions say it is not to be used on bare wood. I'll go get some TSP.

And thanks for the info on sanding down to yellow. I'll need to do that on a couple of spots on the side of the house. I'm guessing that that wasn't done before on those spots, because all of the old the paint, all of it, primer and top coat, is lifting off like a sheet, as if it never adhered at all.

Do you have any recommended brand names/product names for the wood preservative? Last year, I asked at Home Depot (I KNOW, don't ask ANYONE anything at Home Depot about painting), and they didn't know what I was asking about. I think I should use some on my porch steps before I paint, too.

Nestor_Kelebay 06-18-2008 05:14 PM


I use an end cut preservative made by Wolmanite that has 2.35 percent copper naphthenate in it. The reason why I use it is because it's got the highest percent copper naphthenate I could find. If you can find higher than that, buy it. The higher to copper naphthenate content, the more of the effective ingredient is in it.

Also, TSP was used years ago when drying oil type paints were common. The reason why is NOT because TSP is a great cleaner or degreaser. It's because TSP will etch the gloss of drying oil type paints. That is, linseed oil paints. The etched surface will be rougher so that a subsequent top coat of paint will stick better. It's always a politically sensitive issue to say that in a new forum because there's always going to be somebody saying "Hey, it's common knowledge that you use TSP to clean walls before painting them." and they'd be right. It is common to hear people give that advice. But, there's no benefit in using TSP to clean a latex paint like there is in using it to clean an old linseed oil based paint because TSP won't etch the gloss of latex paints. So, if you're cleaning a latex paint in prep for painting, you may as well at least use a good cleaner like Mr. Clean or Fantastic.

People keep asking for TSP to clean paint with and so stores keep selling it, but all you have to do is try cleaning a high gloss latex paint with TSP and you'll find it doesn't dull the gloss like it does with linseed oil based paints, so there's really no purpose in using it other than cleaning linseed oil based paints.

If you're planning on repainting over a glossy latex paint, clean the wall with any good cleaner and one of those 3M Scotchbrite scouring pads they sell in grocery stores for scouring pots. If you go to any place listed under "Machinists Equipment & Supply", you'll be able to buy the same kinds of pads but in a much larger size and in a wider variety of grits. Machinists use them to polish metal after machining. You can put them in a pole sander and use them to clean walls and ceilings.

I my case, I own a small apartment block, so I do a lot of cleaning. I regularily use my garden sprayer to spray cleaner on walls and ceilings and then scrub those walls and ceilings with a Tampico fiber brush. however, if I'm planning on repainting dingy brown walls after a smoker has moved out, I'll use a Scotchbrite "Ultrafine" pad to both scrub the surface layer of paint off (thereby removing the dirt and nicotine) and leave the surface dull for good adhesion of the next coat.

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