Am I asking for adhesion problems

[Larry Fox]

I am currently working on a cabinet project that has quite a number of plywood parts in it. I am applying an opaque finish - specifically Target Coatings EMTECH EM6600 Deep Black Water Based Spray Lacquer (don't ask - it's what she wants so...). Problem is that I ran out of unfinished ply but have a boatload of pre-finished ply. My plan was to scuf sand the pre-finished ply with 180 or 220, lay down a couple of coats of dewaxed shellac and apply the topcoats as normal but I am wondering if I am setting myself up for adhesion problems down the road. I am recalling the old saying "shellac sticks to anything and anything sticks to shellac" and think I should be ok but thought I would poll the group.

The easy answer is to go and get some more unfinished ply but I am trying to thin down my pile of pre-finished so going this route accomplishes the goal of reducing the pile and saves me a trip.

Thoughts?

[Jim Tobias]

Larry,
While I can't say that I have done exactly what you are doing because I don't know exactly what the finish is on the pre finished ply, I feel very confident that you can spray the Target 6600 after a barrier coat of dewaxed shellac.
Before they came out with the pre mixed colors of Target water based lacquer, I have added black Mixol to Target 6000 water based lacquer and used it after shellac was used as a sealer with no issues.
I'm not speaking for him but, if you contact Jeff Weiss at Target, I think he MIGHT tell you that if the pre finished ply is fully cured and you scratch sand it you might be safe but then he would say just to be safe, spray a barrier coat of shellac.

Jim

[Larry Fox]

Thanks Jim - I appreciate the reply. Apologies as I was not clear in my post, I have sprayed gallons and gallons of their EM6XXX product line over shellac and never had an issue. I was more concerned about the shellac to pre-finished ply bond than the EM - shellac bond. The finish on the pre-finished ply is likely either a baked on finish or conversion varnish of some type. I have sanded it before and it sands well so I think I should be ok. I was just not looking forward to sanding the finish completely off that much surface area.

Thanks again for the time to reply

[Jim Tobias]

Gotcha! I understand better what you are asking. I have used the Target lacquer directly over Danish Oil, etc but only after a long cure time. Typically wipe it down with 50/50 water/naptha and then spray Target. If time is an issue, I use dewaxed shellac as barrier coat.
Does that make sense?
Jim

[Larry Fox]

It does - thanks again for the time Jim. I think I will be ok scuffing it and shooting the shellac. Once I have that I think I am off to the races with the EM6XX topcoats.

[Rick Mosher]

Only way to be sure is to make a sample and then do an adhesion test. I do a low tech version with a razor blade but if you want to go all scientific you can buy the test kit from Gardco for $200 to $300.

[Larry Fox]

Testing beforehand - now Rick that's just crazy talk. Appreciate the info and I will give it a try. I agree that testing it is really the only way to be sure.