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I am renovating an old house and, long story short, we have some very knotty solid pine wood planks. They're the economy - or "cottage grade" as menards calls it - tongue-and-groove, beadboard 0.5x4 planks from Menards and they were only a few cents per square foot more expensive than the sheets of imitation stuff (I have a rule, no particle wood or osb in the house!). They will be used to cover the bedroom ceiling.

However, "cottage grade" means that the wood has many large knots, ragged edges and even bark on a few pieces. And I've read how these knots can be a big problem for white paint.

My plan is this:

  1. install them
  2. finish them with water-based polyurethane (water based so the color of the pine does not change/darken, we prefere the 'unfinished' look plus the protection of a urethane)
  3. decide if we like the look or not
  4. paint them white, or another color (light gray?), if we choose.

My hope is that, if we don't like the unfinished look (the water based polyurethane is virtually invisible but will provide the benefits of a urethane such as easier to clean and a little glossy) then it will also act as a sealer coat so we can paint them.

Will the water-based polyurethane be capable of blocking the resins in the knotty pine from bleeding into the paint? If not, can I put something over the polyurethane, and will that be enough? And if so, then what?

Thanks!

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  • the resin in the pine isn't your only issue here. You also need to fill the holes with putty or wood filler. Either way it will take SEVERAL coats of paint to hide the knots completely. You be better off just putting the polyurethane on and leaving it at that.
    – Cody Pace
    Apr 7 '17 at 21:03
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Shellac is usually applied to knots prior to top coating. I've not heard of a absolutely foolproof method of sealing knots so that will stop potential bleeding from occurring. If you do decide to paint, then you have more options for addressing bleed through if it occurs.

I think it's also worth pointing out that if you decide to paint over the finished wood, you will need to prep. That means sanding in preparation for painting. That's difficult work when your surface is overhead on a ceiling. My advice would be to finish a small section and temporarily mounting it on to the ceiling so you can decide whether or not you like the look before you decide on just finishing or painting the wood.

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  • I think you're right. I think we should install a few boards, take a step bake and decide if we like the look or not. If not, then take the unused materials back to Menards and trade them in for something that doesn't have knots.
    – Dan Mantyla
    Apr 10 '17 at 14:19
  • however, still hoping for a yes-or-no answer to the question
    – Dan Mantyla
    Apr 10 '17 at 15:00
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Your knots are going to print through no matter what you do; the knots have a different physical texture than the surrounding wood. Corrcting this would take a painstaking amount of sanding primer and/or fairing (bondo) and sanding, definitely not something you want to do looking up. And at that point leaving it bare wood would be out of the question.

If you don't mind your house being stinky for a day or two, I'm not a fan of water based anything for wood treatment. I would want at the very least something oil based and preferably a 2-part epoxy or urethane. The best source for these is marine brightwork coatings, brightwork being the word for "bare" wood on a boat.

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Needless to say, this stuff is tough as nails.

By the way, "spar" varnish is junk. Well, what's more accurate is that spar varnish is for spars (duh) and other things on a boat which flex a lot. This flexibility comes at the cost of sacrificing away other properties you really do want. Ergo wrong stuff for wood which does not constantly flex. Nonetheless, the marketing teams got hold of it and misuse the term to imply "premium". coughValsparcough

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  • the texture of the knots doesn't concern me, it's the tannins bleeding through the paint that I'm worried about. And I'll keep the info about spar varnish in mind, but so far I like the water based urethane and spar urethane a lot.
    – Dan Mantyla
    Apr 10 '17 at 15:02
  • Yes, the stinky is a deal breaker for a lot of folks. The best source for performance wood coatings is your local chandlery. Epoxy e.g. West System comes to mind as a less-stinky finish coating (if not in direct UV/sunlight), it won't print through that! While water based products are oh-so-convenient, they just can't perform in tough jobs, much as their marketing departments try to put lipstick on that pig. That is why even the draconian California smog districts have exceptions to allow almost any product where needed or desired.
    – Harper - Reinstate Monica
    Apr 10 '17 at 17:59
  • It's not the stink I care about, I just like the way it looks better and that it dries faster. Less stink is a plus though
    – Dan Mantyla
    Apr 11 '17 at 18:38

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