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Need quick help re primer under exterior stain?

Posted by floete_ri (My Page) on
Mon, Jul 12, 10 at 17:04

We had to have all the paint on our 1930 house taken back to original wood (cedar). We've decided to (solid) stain it. The painter says all you need is two coats of stain, no primer.

At the paint store, however, the shop owner is saying we most definitely do need a primer -- oil based, to go under the water-based stain.

i will say that test areas on the clapboard, with just two coats of stain, aren't exactly great. the finish is dull and i can see through to some of the sanding swirls underneath.

anyway ... what do i do and who is right?

thanks!


Follow-Up Postings:

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RE: Need quick help re primer under exterior stain?

Use an exterior high quality slow drying oil based primer. If you tint the primer towards the finish color, one coat of stain may look just fine on top of the primer. Do not expect primer or paint to fill sanding swirls. Also, do not expect the final look to have much sheen...stain will have a flat finish or a very slight sheen that is barely detectable. I would worry a bit about a painter that claims it is okay to paint directly over raw wood with two coats of acrylic stain.


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RE: Need quick help re primer under exterior stain?

PG is right. Cedar will tannin bleed though the stain so unless your stain color matches the color or is darker than the tannin staining, it will noticeable.


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RE: Need quick help re primer under exterior stain?

could it be there's no uniform truth to the question? i posted the question elsewhere too and got the following:

that's a stain, not a paint. you don't put primer under it, he's right.

typically i might put a coat of turp/spirits/etc to make sure there's no mold/mildew/etc that goes unkilled. but with cedar that shouldn't be much of an issue, since cedar is quite resistant to parasites and fungus on its own.

however, you could do that. walk around the building and inspect for mold/mildew, you know what it looks like (black or grey spots that seemingly originate from nowhere, thus disregarding black spots around nails from nail deterioration). if there is none, you should be fine with his proposed method.

if there is any mold/mildew anywhere, you might point that out and suggest he pre-treat it all with a coat of turp first.

note that this is a STAIN not a paint. it will be a roughly 7 or 8 year maintenance cycle, in that you'll need a new coat every that-many years. but the new coat will be fairly simple to apply, just wash dirt away and go, no other prep needed.

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now i'm just totally confused and big time concerned.


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RE: Need quick help re primer under exterior stain?

No, there is uniform truth. If we are talking about the best way to go about things, you use a primer. The oil based primer will penetrate best, grab hold of the wood best and it will kill tannin bleed. That tannin issue is enough reason to use the primer because the stain by itself will certainly not hold back that bleed, but there are other good reasons to use a primer as well. Sure, a lot of manufacturers claim that you can use their paints/stains as the primer, but this is rarely the best option. Also, mineral spirits and turpentine will not kill mildew.


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