Precat, Cv Or 2kP Over Pre-finished Plywood


From original questioner:

We build our case goods from prefinished plywood, and would like to be able to lay finish on top of the "prefinish" effectively using it as a prime/seal coat. Anyone doing this successfully?

SW ProMar lacquer seems to stick marginally, CV perhaps a little better. I'm most interested in switching to 2k poly, but have no experience with these types, nor can I find any distributor or rep who claims any working knowledge of 2k Poly applied to wood

anyone know what kind of finish"prefinished" import birch is ? I've come across the term UV FINISH a few times, But suspect this is a method and not a type of finish

From contributor Jr

I have used MLC's conversion varnish over UV coated plywood numerous times. I always scuff it up with 320 and a fine scuff pad. Avoid sanding thru the finish. I am currently doing this for a job using the dreaded imported UV birch plywood. I am tinting the first coat of CV then topcoat untinted.

From contributor Mi

I'm also doing it similar to Jr. If I'm painting a prefinished piece I try to just sand that finish off completely then prime and paint. If your wanting to put a clear coat over top of it make sure you scuff it good and by all means don't lay to heavy of a coat. I've had good results with cv and 2k poly doing it like this. I will warn you that if you don't scuff and lay a slightly to heavy of a coat down that when it dries you will be able to take the palm of your hand and wipe that finish back off. No adhesion. Been there and done that on a test piece. Hope that helps.

From contributor Ja

I'm wanting to use prefinished as a cost effective "head start"
from my suppliers, import birch is about $30 unfinished, $35 1 side prefinished and $40 both sides prefinished
There's no way I can prime/seal 4x8 sheets for $5 a side, so I am determined to find a sound system for laying colors and tint/clear coats on top of this,
The MECHANICAL bond I have achieved thus far has been OK, but nothing which I am comfortable sending out the door.
The best yet has been sending the parts through the widebelt (platen down) for a light scrub with 180g hermes antistatic AO belt, after this I lay a wash coat of SW ProMar Lacquer, sponge sand the crunchy and clean, then lay a wet coat of the same, and that's it. Results have been pretty good considering it is just a mechanical bond, but again, I wouldn't want to send this out for delivery with my name on it!

Does anyone know what is used on these sheet-goods and what might achieve a chemical bond with it?

From contributor Mi

I figured out the same thing about three years ago that going to prefinished was a no brainier. I'm a little confused on why you want to lay colors and finishes on prefinished? We only build face frame cabinets. I use prefinished one side ply. The prefinished goes toward the inside and the raw side gets the color and finished. I'm not understanding what the purpose is of trying to add more finish to something that is already finished. Maybe I'm missing something in what you are trying to achieve?

From contributor ni

I have to apply a pigmented solvent CV or pigmented WB on pre-finished ply for one of my customers who insists on putting it in all the boxes be they need finishing by me or not. Much like Mike I made samples until I came up with acceptable adhesion and what worked good for me was a very thorough sanding with either 400 grit...or a thorough 600 grit wet-sand (this worked even better with the WB). Both of these ways worked well but I wouldn't say I am say I'm comfortable enough with either approach to want to make a habit of it.

From contributor Da

A chemical bond? Forget it. A so-so mechanical bond has been my experience. Just don't do a fingernail test. I'm not comfortable with an applied coating adhering nicely to prefinished

From contributor Sc

I wouldn't trust anything sticking to UV finished plywood for very long. The stuff I have been using is resistant to thinner so not much chance of a finish burning into it and bonding,
I am thinking like Mike, I use prefinished plywood so I don't have to finish it, why would you want to finish over the top of it.
Secondly it is really only a good enough quality for casework, to finish it with a solid colour would show all the waves and defects as it is not very flat.

From contributor Ad

The first coat of everything is an adhesive bond. When you switch from primer to topcoat, you have lost any "chemical" bond. You only get a true "chemical" bond if you are recoating a green coat. Once they cure you are back to adhesive.

If you pretend that there is no finish on the sheet and your first coat is the prime coat you will sleep better at nite. We have spray buckets of various finishes, both solvent and wb on top of the UV prefinish. Like the others we sand it well with 240 grit. Trying not to burn thru, which could telegraph.

Do a simple tape test if you are concerned about adhesion.

From contributor Ma

Lowes sells import ply pre primed with white primer, just scuff and spray. I have successfully sprayed pre cat, Cv and 2k poly over it with no issues at all.I don't normally buy materials from big box stores, but that is one product I do buy because my suppliers don't have anything like that.It is reasonably priced also.I recently did a huge walk in closet that all got painted with 2k poly, it saved alot of time and material!