Finishing Wood Siding
What’s the “gold standard” for painting/staining wood siding?
Martin suggests not doing it at all– leave the wood unfinished to weather naturally [1]. Fair enough. But let’s say that you’re going to paint or stain it. Let’s assume it’s installed over a rainscreen, that we’re not in the desert, and that we’re talking about solid color paint or stain.
Joe Lstiburek says “treat with a penetrating water repellant preservative on all six surfaces, coat with an oil based primer on all six surfaces and top coat with an acrylic latex paint” [2].
No argument on the “prime 6 sides” front – that seems a best practice. But what’s this about treating with a water repellent preservative? I’m unable to find a painter or paint supplier who thinks this is a good idea. Everyone’s afraid that it will either interfere with the primer bonding, or with stain uptake.
So what do you typically spec/recommend/do? Is a preservative treatment overkill? What about a primer beneath solid stain?
(Edited for readability.. reference in first post below)
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[Reference for the above, in case anyone's interested]
Of course, Lstiburek cites his sources: it's recommended by the Forest Service, as of at least 1984 and as recently as 2013 ([3] and [4] respectively.. the former being Lstiburek's reference on the matter and the latter a very readable 4-page guide). I find the same in a 1969 reference book. The 2013 Forest Service paper recommends "water-repellent preservative" + primer + 2 coats of paint, and the same for solid-color stains. Transparent and semi-transparent finishes understandably get different advice.
[1] Holladay "Environmentally Responsible Siding" https://www.greenbuildingadvisor.com/article/environmentally-responsible-siding (quote: "If you intend to install wood siding, I strongly recommend that the siding never be painted. If you paint your siding once, you’re more or less committed to a lifetime of regular repainting. So avoid the original sin.")
[2] Lstiburek "BSI-056: Leiningen versus The Ants Redux" https://www.buildingscience.com/documents/insights/bsi-056-leiningen-versus-the-ants-redux
[3] Feist "Painting and Finishing Wood for Use Outdoors" https://www.fpl.fs.fed.us/documnts/pdf1984/feist84b.pdf
[4] Knaebe "Paint, Stain, Varnish, or Preservative? It's Your Choice" https://www.fpl.fs.fed.us/documnts/finlines/finishline_mknaebe_2013_014.pdf
Karl,
I'd break this down into two questions: What will give you the best coverage and durability on the primary application, and what's the best method knowing you will have to re-coat eventually.
I'll defer to Joe on the first one, but if ease of re-coating down the road is important (and given that the expense and effort involved is substantial I'd say it is) I would forgo the primer and just use two coats of solid colour stain, the first one being applied to all six sides. Unlike the primer and paint, the stain won't blister or peel. You may not get the same time between refinishing, but when you do it's as simple as a light wash and another coat. The stain is also a lot less susceptible to damage from any water that does gets behind it.
Hi Malcolm, your suggestion is a good one-- thank you.
Do you (or anyone else here) use a water-repellent preservative, as seems to be recommended? Any suggestions for what this should be?
Thanks!
For reference (my own, in 20 years?):
- I found the following report very helpful in deciding what to do, jointly authored by reps from the Forest Products Lab and an industry trade group:
https://www.fs.usda.gov/treesearch/pubs/9499
In particular, it features a 2-page surface/coatings compatibility matrix, with estimates for how long various combinations of finishes can be expected to last (e.g., paint on cedar, with/without primer and with/without a water-repellent preservative).
- As for water-repellent preservatives, I found some discussion of choices here:
https://www.finehomebuilding.com/forum/wood-preserve-sealer-before-prime-paint#comment-54697
On my own projects I have gone to unfinished red cedar in board and batten or sawn shingles, with or without painted/stained accents like window and door trim, corner boards, belly boards etc.
I like the look, easy maintenance and cost. Cedar that is exposed to weather will turn silvery, and if it stays dry it will darken.
I'm up against addressing my hemlock siding this summer and have narrowed down my search to pine tar preservative. Have a look at it.
I left my pine/hemlock sided cabin unfinished, and after 18 years the wood shows no signs of any decay and has weathered to a beautiful dark grey/brown that my spouse unfortunately does not like. Hence, the pine tar finish. Also, pine tar is supposed to be unpalatable to carpenter ants. The only downside to the unfinished pine siding that I can see is that a couple years ago I had a few carpenter bees bore some holes in the underside of the roof overhang, and the literature I referenced stated that they prefer unfinished wood.
Interesting, I like the look the pine tar gives.