affects of contraction/swelling of pine floor on face nailing/varnishing

If you think it through, you’ve already answered your question. Nailng through the tongue allows that board to move (expand/contract) away from (or toward) the nailed edge. If you face nail on the groove side, the board will still try to move but can’t. It will either bow or split.

-- Adversity doesn't build character...................it reveals it.

What is underneath the floor? If it is concrete, did you place a vapor barrier? How far apart are tied strips?

Your floor should not move so much, and the varnish should in fact help keep it relatively constant in humidity if you placed a vapor barrier underneath.

-- Just because you’ve always done it that way doesn’t mean it’s not incredibly stupid.

this pine floor is on the second level of house, on 3/4 plywood. I used some vinyl tiles to raise the low spots (a large spot in center of subfloor) and then put down a few layers of resin paper to smooth the whole thing out.

Sawkerf, I understand what you’re saying; I didn’t think about the lateral freedom of movement afforded by the tongue nails.

I also thought about reduced moisture flow once the varnish was on. Pine will allow relatively deep oil absorption, and since the main vector of moisture is from the face (vs. subfloor), I was hoping the wood would be sealed enough to prevent future expansion/contraction, but just don’t have that experience.

fyi, I don’t have to face nail, just wanted the look.

I think my plan will be to wait a bit until the moisture level goes down to a midpoint between summer and winter.

Then, I’ll drill holes just about the same size as the nails, maybe even drill countersink-holes for the heads so they wont have any real bite into the wood, then sand and varnish.

I’m guessing the reduced moisture flow into the wood and room to wiggle around the nails should prevent any damage.

what do you think?