Can water based polyurethane be used to prevent knots in pine wood from bleeding through white paint

paintpinepolyurethaneprimer

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 0.5×4 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!

Best Answer

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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