Joe- Thanks for your fast response. I neglected to include some of the background you need – after all, I’m familiar with what I’m doing ;-). I asked the question about the undercutting the hearth a while back, so this is the same project. I’ve attached the layout from that in case it helps. The partial layout I sent earlier is rotated 90 degrees from the whole upstairs layout.

In answer to your question about the direction, I need to run the plank east-west in order to make the transitions between living room / dining room & dining room / kitchen work. So that leaves me looking at doing something with the subfloor, and replacing the particle board looks like the route I might need to go.

Before settling on that, though, I have a couple of questions. Would it be possible to lay plywood on top of the particle board – basically saving having to tear up & then replace the half inch of wood? So I’d be using, say, 7/16, 3/8, & 1/4 layers on top instead of a lot of thinset. And to reduce the chance of the particle board soaking up water & swelling, would it help to seal it with something? The particle board seems to be in good condition, given that it’s 42 years old.

I haven’t discussed the dining room yet, but years back oak parquet was replaced with bamboo, and the installers appear to have made heavy use of thinset (up to 1/4″) to level that floor. I’ve chipped up some of that to clean things up, and the particle board underneath looks to be in good condition. I wonder if it’s because of residual glue or just that they got lucky.

If it would be easier to discuss this on the phone, or if you need photos or other info, I’m glad to do that. I appreciate your insight into the … situation I’m facing.

Chuck