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Primer for weathered wood?

Posted by ElisabetK (My Page) on
Tue, Nov 29, 05 at 14:12

Some of the exterior windows on our 60 year old house desparately need painting - in some cases more than half of the paint is flaked off. Most of the rest looks like it will come off easily with duct tape; I tested the method yesterday. (Thanks for the tip, whoever it was who posted that here!) Apparently the previous owners never bothered to prepare surfaces before painting, when they did get around to painting at all.

I don't dare sand the weathered wood before painting, because unfortunately lead paint was used on the window trim. I'll be using Child Guard lead encapsulant paint once I have a sound enough surface.

I'm not sure what the best primer would be in this situation. The ChildGuard label suggests 100% acrylic universal primer for "unpainted wood" but I'm assuming that means new wood, not weathered. The recommendation for chalky dusty surfaces is "chalk resistant primer." I have plenty of Kilz 2 on hand but it recommends sanding the weathering off the wood first - something I absolutely cannot do.

Any suggestions? My goal is too stablize the flaking peeling paint more than to achieve a beautiful smooth finish. Water cleanup is a big, big plus too, but I'll do oil-based if that is the only appropriate product.

Thanks,
Elisabet


Follow-Up Postings:

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RE: Primer for weathered wood?

I'm not sure how weathered your wood is. It depends on how long the wood has been exposed to sun and rain. If the wood appears to be dried out, and is starting to crack and split, then you can paint it with boiled linseed oil, which will soak in and extend the life of the wooden trim. The surface would then have to be allowed to cure for about a year before being primed and painted, with water base paints.

Linseed oil will do nothing to stabilize flaking paint, however. Loose & flaking paint really has to be removed before priming the surface. This will take time and effort, no matter what method you use. Duct tape will work on very loose paint that is ready to fall off. A heat gun can be used to soften old paint, but then it has to be scraped off while it is still warm. Neither of these methods generates very much dust, compared to sanding.


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RE: Primer for weathered wood?

Thanks - I don't think waiting a year for linseed oil to cure would be an option, since the main point is to get the lead paint encapsulated ASAP (we've got a kid, and the paint is flaking off onto areas that get walked on - very bad!) Aesthetic issues are secondary. There's a good chance the window trim will be replaced at some point anyway; it's really not in good shape.

About removing the old paint - don't care if every last bit is removed. Any of it that is stuck to the point of needing a heat gun to remove it might as well stay and be covered with the encapsulant paint, especially given that there is vinyl siding abutting the window trim. I just want to be sure that the primer we put on does stick to the wood, so the encapsulant paint can stick to it. But no way am I going to sand that exposed, weathered to grey wood.

So - would I have a reasonable chance of success with Kilz 2? Do I have to use an oil base primer? Recommendations?


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RE: Primer for weathered wood?

Hmm!

That's a tough one! If the last few coats of paint are latex based (denatured alcohol makes them 'gummy'), then a good latex primer, might seal the lower base coats. I wouldn't mix different paints. Latex over oil is okay; oil over latex isn't; not sure about anything over alcohol based primer (in my experience it eventually peels). BTW, I"m in a two hundred year old house. My son used markers on one wall, the alcohol based primer caused more flaking.

Lead based paint was also used in upscale houses (back in the 40's-60's and earlier and in coal mining/burning areas because it made houses whiter).

Dad


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RE: Primer for weathered wood?

Latex over oil is okay; oil over latex isn't;

This is completly backwords.


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RE: Primer for weathered wood?

I believe dadgardens is correct; if their are less than 5 layers of oil under the new latex.

LATEX PAINTS OVER OIL-BASED

Question
Can you paint over an oil-based paint with latex paint or is it vice versa?

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Answer
The rule of thumb is that, given proper surface preparation, for exterior use you can apply quality latex paints over oil-based, but not the reverse. However, if you have many layers of oil based paint, stick to using oil on oil. For interior use, generally you can use one over the other. Some manufacturers of latex products will recommend a primer when going over oil-based paint.

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Question
Can I paint over oil base exterior paint with a latex paint?

Answer
Yes, you should be able to use a top quality exterior latex paint over oil based paint, if the surface is well prepared. (However, if the old paint consists of a buildup of say 5 or more coats of old oil paint, the safest approach is to continue with oil, because the latex paint can lift the old oil paint if not adhering well.) All dirt, mildew and loose paint should be removed. Sand any glossy areas to eliminate the gloss and get maximum adhesion from the new paint. NOTE: do not sand or otherwise remove any old paint if it may contain lead. Call the EPA at 1-800-424-LEAD for guidance. Some quality exterior latex paint may be applied directly to clean, sound oil-based paint; but check the product directions, as some manufacturers will require a primer, either latex or oil-based.

Here is a link that might be useful: Exterior Paint FAQ


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RE: Primer for weathered wood?

There really is no base coat left to speak of - maybe 10-20% overall. So my concern is to get something to stick to the bare wood, much of which is weathered.

What I'm considering now is to get some wood hardener and apply it to the worst areas - e.g. the sill which has taken the brunt of exposure to the elements. The idea being that that would provide a sounder surface for the primer to bond to. Any downside to going that route?


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RE: Primer for weathered wood?

Minwax manufactures a "wood hardener" that is low viscosity, about the same as water, and therefore penetrates the pores of the wood. It cures quickly, and can be painted over in less than a week after application, unlike linseed oil, that can take several months to cure completely. I have used both products, and they both work.


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RE: Primer for weathered wood?

I have always used an oil based primer. I usually prime every time before I paint (just one of those quirks of mine). I then use a water based paint. I have, on occasion, used an oil based paint. The rule of oil over latex regarding Primers doesn't apply. The make up of primers and paints is different. I have also used shellac based primers with water based paint over. I've been priming and painting this way for a long time and have never had a problem....


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RE: Primer for weathered wood?

The Forest Products Research Society has determined that bare wood exposed to sunlight can lose about half the paint-bonding strength in as little as 3 weeks. Always prime exterior wood immediately. Do use a quality oil primer after gently wire brushing the wood.


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RE: Primer for weathered wood?

ELizabeth,

You have a series of issues:

To get any covering to stick, whatever is under there must be firmly bonded. The top coat is only as strong as the adhesion of any under layer. So if you have loose paint, you should mechanically scrape it off - catching the loose pieces and disposing of them properly. If you don't catch the chips, they can get ground up when stepped on, and become lead paint dust.

The next issue is priming the wood that has already lost its paint and is now weathered. As noted above, weathered wood doesn't hold paint very well, which could lead to failure of your efforts and re-exposure of the lead paint. Weathered wood needs to have a bit of the top layer removed. Sanding is the normal thing here, but you might be able to to it by shaving off the surface, but I can't see how you'll avoid some pulverization of the edges of the persistently painted parts.

It may also need to have some sort of penetrating feeding in order to have decent adhesion. I have used a mixture of linseed oil and turpentine. Never waited more than a short period until it was dry to the touch to proceed with priming.

If you have a dry, prepared, substrate, you can prime it with whatever you like, then continue on with your proprietary paint encapsulation project.

Is there anyway you can have the sash and trim taken off and stripped away from your house? And what about your interior woodwork?

As an alternative (assuming you are in a warm area and it is still possible) is to just wire brush off what's loose (collect the debris), and prime and top coat and resign yourself to doing it as often as necessary to keep it covered? Not efficient, but may be practical for the relatively short window where lead dust is especially hazardous to growing brains.

My husband and I live and work in what is undoubtedly a lead swamp. We always ask for lead tests when we have blood drawn, but it remains normal, after more than two decades of exposure. And I don't do anyting particularly to reduce the risk (though I don't chew on the windowsills).

BTW, I wouldn't choose KILZ as my primary primer for exterior. I'd pick a regular primer (oil or latex as you top coat manufacturer suggests.)

Molly~


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RE: Primer for weathered wood?

Elisabeth,

Read up on this product. I haven't used it yet, but it appears to be very reliable.

Michael

Here is a link that might be useful: Peel Stop


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RE: Primer for weathered wood?

You might also look into a product called Peel Bond. I found it at my local paint store. It seals the wood and builds up a very high film thickness which levels out most of the imperfections.


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RE: Primer for weathered wood?

Also use a respirator - the kind with filter cans on it at least - and not just a paper face mask when working with old lead paint. Otherwise you will regret it as I found out!

I use a shave hook to get old paint off. The shave hook takes it off in big pieces and does it really fast, too. It takes a bit of working with it to get used to it and a bit of practice to sharpen it, but a properly sharpened shave hook just slices the old paint off. You also don't have to buy sand paper or other "throw away" stuff to do the project.

For inside wood, I use Kilz primer. For the outside wood, it was so weathered and rough, it looked like anything would stick just by sheer mechanical bonding, so I just put on the paint. It is still there five years later, so I guess it worked.


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