Water based poly over old oil based poly

[Ken Choronzuk]

Hi,
I'm working on a new project. I'm building some new cabinetry next to some existing bookcases that were finished with what I'm guessing is oil based poly (probably Minwax). When I spray apply the General's High Pro Poly to the new work my client has requested that I spray a "fresh coat" to the existing work. The question is will there be any adhesion problems? Do I need to simply scuff the surface or should I spray a barrier of shellac? Any advice would be appreciated.

-Ken

[Joe Chritz]

Without a thorough test it is impossible to say for sure but "generally" water base finishes over oil base is a bad idea and could lead to problems. I would sand for tooth, apply a barrier coat (dewaxed shellac) and then apply the finish. I typically use Target Coatings finishes but use dewaxed shellac almost every time as a seal coat.

Joe

[Jim Becker]

I personally would use a barrier coat as Joe suggests, but if the oil based varnish is fully cured, scuffing and coating with the water borne may work. It's risky, however. Remember, "poly" hates to stick even to itself and it's a little more complicated when a water borne acrylic (with polyurethane resin in it) is added to the mix.

[Jim Balabon]

My kitchen cabinets were sprayed with deft poly in 1986. I contacted minwax to ask if there was a finish to apply over deft
that was not so toxic. They said polyacrylic after deft had been scuffed. Deft was 10yrs old. Applied two coats of wb
polyacrylic satin, with foam brush...cabinets still look good after 15yrs.