I have a home that has a section of shiplap pine siding on along the bottom (already primed) and a section of T111 above, also primed. The center section is cedar shingles, nearly half of which have been replaced over the last year or so. It’s time to paint, so here’s a few questions for you all:
*How to prep the shingles: is power washing sufficient?
*Some of the shingles have been placed in the last week or two, and were wet- how long to wait before painting?
*Suggestions for primers? For paint?
Replies
Unless there's a decent paint film on the shingles now, I wouldn't powerwash. That would just force water into the wood which will take a long time to dry out.
The new shingles shouldn't be all that wet unless they were laying on the ground outside for a while. A few days without rain should be sufficient.
For cedar shakes/shingles I've used Muralo X200 linseed oil-based primer (http://www.muralo.net/products/exterior_primers_X200.php) with good success. I don't know if the primer needs to be linseed oil-based, but it definitely needs to be oil.
Any good 100% acrylic topcoat will work. Benjamin Moore and Sherwin Williams are 2 good brands that I've used. If cost is not huge factor, consider the Aura or Duration line of paints.
The house is in a mountain environment that gets a fair amount of rain and snow during winters, but is dry and warm 9 months of the year- the damaged shingles I replaced were dry as a bone, and not at all punky underneath. They have probably been there for decades. As dry as it is here, I doubt that the water from powerwashing would last very long...
A roofing company (listed on the Cedar Shake & Shingle Bureau website) based in Portland, OR actually advised against oil-based paints, and recommended a good quality latex from Sherwin-Williams (or similar), after a good priming (he recommended one of the lines of paints you mentioned). He expressed concerns about enviro hazards in use of oil-based paints, and agreed with many comments I've seen here regarding allowing the shingles to breathe, and not seal them in with oil.
What are the +/-'s of using oil vs. latex on exterior cedar shingles?
Latex will allow moisture to migrate trough it. I have seen at least two cases I recall where oil paint on cedar shingles had trapped moisture behind, in the wood, to the point that the paint was what was holding the wood fibres together. Oil does not allow water passage through it, but the nature of shingle siding is such that a lot of wind driven rain can penetrate the surface at all those joints. It soaks into the wood and is then trapped there.That is why I recommend the stain - I failed to say latex
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I only have one experience of painting cedar shingles and NOT using an oil-based primer. It was on my own house. The new shingles that I installed came lightly pre-primed so I just painted them with a latex topcoat. The tannins continued to bleed through despite several coats.
When it was time to paint again, years later, I primed everything with an oil-based primer first (Muralo X200). I'm very happy with how it looks and how it's holding up.
Every other job I've done has had an oil-based primer go on first and I haven't heard of any problems despite oil being less impervious to moisture. On the other hand, I haven't used a water-based stain on cedar shakes/shingles either. Maybe the need for cedar to "breathe" varies based on climate.
The ones where I saw bad results had several coats of oil over the years, one reason probably because oil paint will blister up when water gets behind it.On most exterior wood I believe in backpriming all sides with oil primer.But the pre=-dipped shingles we use from maibec are done with the Cabot's and it works fantastically.I notice too that somebody said the drawback to using a pressure washer is that it gets the wood wet and that then has to dry.
But my main concern with the washer is that the pressure can tear the wood fibres way too easily, shredding or aging the wood
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This is great information- thank you for your efforts. All of the shingles are in place- there is a mixture of old shingles (which were painted a long time ago), and the new replacements (no paint or stain) which are a bit damp still. Dipping/staining individually is not an option. To confirm my understanding:
No powerwashing- but hosing with a cleaner is acceptable. The old shingles are very dry, and don't show any real sign of mold. They're just very dirty/dusty. Best to wash them soon, and let the whole thing dry for a few weeks before painting.
Can the latex-based solid color stain you described (Cabot's) be applied to the old, painted shingles?
Bumping my last question...Can Cabot's solid stain be applied to shingles that are currently painted (after a good pressure washing)?
You can apply a solid stain over a painted surface and will work just fine, but there's really no point to it because you're asking the stain to behave like paint since it won't be able to be absorbed into the wood.
Stain does behave like paint when used this way, but I suspect paint will perform better under these conditions.
When choosing a cleanser find one that has Oxalic acid as an additive. Cleanses better.
Just to be clear, I was recommending an oil-based primer and acrylic topcoat.
I see Piffin is recommending against oil altogether for the breathabilty issue you mentioned. I still think an oil-based primer is a good idea, but Piffin is a very wise man so you'll have to decide for yourself.
The so-called enviro-hazard wouldn't influence my decision. It's not like you'll be regularly adding another layer of oil-based primer that's going to just keep adding more and more VOC's to the atmosphere.
Do not powerwash. You can destroy cedar shingles that way.
If they show a lot of mildew, there are deck and fence wash products at every paint and home center that will spray on with a plain garden sprayer and rinse of with a hose that kill the mildew and algae and remove dead cells on the surface. Sometimes a little scrubbing with a bristle brsuh helps.
Then let dry. The green ones need a month or so anyways.
Then use solid color stain rather than paint. Cabot's is a good choice
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Taunton University of Knowledge FHB Campus at Breaktime.
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