Rough spots on Birch Ply

[David Huston]

Staining some plywood dividers for my master closet and they have a weird looking rough pattern to them in spots. I sanded up to 220 with random orbital and didn't see any problem areas before I stained. I didn't sand after staining, put on a thinned first coat of poly (probably 20% thinned with mineral spirits) and then these spots really stood out. The picture is taken about 10 minutes after first coat of poly. Have been home today to see if they dried rough. Any thoughts on this problem. Should I just keep building the poly? Should I sand the first coat or build a few more and then sand with 320 or something else? They are just divider for the closet so I am not looking to re-do the whole thing, will live with it if it isn't easily fixed, but like to learn what happened so it doesn't happen again.

Thanks248326

[Howard Acheson]

Are you spraying or brushing the poly? What type of stain did you use and how long have you let it dry? If a Minwax Wood Finish stain, did you thoroughly wipe off the excess after letting it set for 15-20 minutes?

[David Huston]

Brushing the poly on. Minwax stain set for 20 mins and wipes off then dry almost 24 hrs. I am staining some poplar pieces at the same time no problem with them so it seems like it has something to do with the plywood.

[John TenEyck]

Was it rough after you stained? I've seen that happen on birch ply but usually it shows up right away with whatever you apply first. Anyway, if you sand after only one coat of poly you risk cutting through everything and exposing the raw wood underneath. I'd put on at least one more coat before sanding. Then you may have to do another 2 coats, sanding between each, before it's finally smooth.

[Prashun Patel]

That looks like surface contamination to me. That can cause the poly to wrinkle and bubble.

[David Huston]

I have stained and put the first coat of poly on about 8 pieces of the plywood. Wipes down all pieces after sanding so if it is surface contamination I don't know what it could be. I will push forward and put a few more coats of poly on and try to sand it smooth. Good thing its just a closet no one will ever notice the imperfections but me. Just want to know if it is the ply or not. Will find a different source next time if it is the plywood.

What grit would you recommend for sanding the poly?

Thanks

[John TenEyck]

I normally use 320 grit paper on a rubber block, or a Norton 320 grit foam sanding pad.

John