Will poly crack if wood bends?

Question

I have a 3/4” wide and 16’ long piece of raw pine that I’m finishing as a countertop for some storage cabinets in the living room. I plan to use water based stain and polycrylic. I’ve been working on it in the garage but will need to move it inside the house to the living room when it’s done. Because the piece is so long, it tends to bend slightly when carrying it.

Anyone have any experience with long lumber? Will the poly crack when I move it? Or can it handle a little movement without cracking?

I’m trying to decide if I need to do the poly in place to avoid that. I don’t want to (for many reasons) but don't want to ruin the hard work of finishing it when I move it.

Answer 1

Film finishes, when new especially, are perfectly capable of flexing within reason. In fact, no finish you apply today will be fully cured by the time you go to install this so no need to worry even if life gets in the way and it's a week or two by the time you get to it.

It's mostly with finishes that have degraded over time that lack of flexibility is an issue. When that happens even the extremely minor expansion and contraction of wood with seasonal changes in humidity is enough to get the finish to begin cracking ('crazing') which just gets worse from then on.

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You can easily confirm the flexibility of any finish you have now or get in the future by applying it to paper. The paper will stiffen significantly as you might expect, but you'll be amazed at how much you can bend and warp the sheet without it cracking — far beyond what any piece of wood can do.

Note that flexibility is partly a function of film thickness. As with glass, a very thin layer is surprisingly flexible when compared to the limited ability of a thick sheet to bend without breaking.