I'm glueing and screwing 1/2" OSB over an existing vinyl floor as additional underlayment. Over the existing plywood, I used OSI SF-450, but it doesn't seem to be approved for vinyl. Any recommendations?

Thanks.

What's UNDER the vinyl floor? If it's particle board, you should have removed it. If it's luan, you're probably ok. And why OSB instead of 1/2" plywood? Let me guess, it was cheaper, right? I don't know about that OSI SF-450 stuff. Is it an adhesive? I'm guessing it is. If you want to glue your underlayment to the vinyl (and I'm not sure you need to IF it's very well attached) one adhesive that IS recommended to glue wood to vinyl is Franklin Advantage ( formally 811 ) Not cheap.