Lacquer Adhesion Over Glaze

      A reported problem getting nitrocellulose lacquer to stick over a heavy-bodied glaze leads to a discussion of possible solutions. November 8, 2007

I am doing an entertainment center and I am having a terrible time getting the topcoats of lacquer to bond over the glaze. The lacquer keeps coming off with blue tape when the installers attempt to put it in.

The wood is alder and I sealed it with a tan pigmented Valspar lacquer and then sanded it. I then applied a second coat, let it dry, and put a Mohawk heavy bodied glaze over that, trying to not get too thick with it. I followed the directions on the can (let dry 1 hour, light topcoat, dry 1-6 hours, then apply topcoats) and two days later the installers were lifting the finish right off.

I basically peeled off all of the lacquer, reglazed it, and let it dry for 2 days. (I did not let it super-dry the first time because I once had wrinkling issues when the glaze was completely dry when I topcoated it.) I then sealed in the glaze with shellac and let that dry overnight. Then I topcoated that with lacquer and let it dry overnight. I then went in the next day, put on some blue tape, and peeled that stuff right up. Ouch. Please help...

Forum Responses
(Finishing Forum)
From contributor T:
Are you using pre-cat or CV? We use Valspar CV pigmented a lot with glazes, topcoated with their CV clears. If you are using a pre-cat, skip the shellac and lock in the glaze with a clear vinyl sealer. This should melt into the color coat. Scuff lightly and topcoat with dull 15% sheen. This is what we did when we used MLC Magnamax. Switched to Valspar now.

Do you have a sales tech to ask? I got mine to write down the best system for pigmented, stained, glazed, clear, etc. This became our shop finishing manual.

As always - test piece!

From the original questioner:
I am using regular nitrocellulose lacquer. I am afraid I might be asking for more trouble by using pre-cat over glaze (over regular pigmented lacquer), but at this point I will try anything. Maybe dusting a couple of coats first, but the bottom line is I need something that will stick to the glaze. The glaze itself appears to be sticking fine to the pigmented lacquer after it has fully dried. I already applied the shellac over most of the pieces and I am not sure if pre-cat will bond too well to shellac (which doesn't appear to be bonding all that well to the glaze).

From contributor M:
Glazes can be tricky. Most problems occur because the glaze is not brushed out enough. Many finishers use one brush that loads up and leaves excess oil on the surface. Other finishers like the look of the heavy glaze; they think the color will be darker with lots of glaze left on the pieces. If they brushed out the glaze better, they would find that once they coated the glaze, the color would pop right out.

Misting or fogging on a few passes may help set the glaze, then the flow coats are applied. You may need to allow more time for the coating to cure over the glaze. You may be better off learning to make up your own glazes.

What is the purpose of using the tape? Is the tape on the tan coat, sealer, glaze, clear coat? Try allowing more drying times, and please learn to make up start to finish samples before you begin to work on a project, so you know you have compatibility. (Learn on your samples, not on your projects.)

From contributor J:
Have you tried using the Valspar glaze rather than Mohawk's? I switched to Valspar's glaze from MLC's and could not be happier with it. It seems to have more pigment in it, so I can brush it out more and leave less on the surface and still get the effect that I'm after. That, in turn, means it does not have to dry as long before I can topcoat over it. I use it under Valspar's pre-cats and CV all the time with no vinyl sealer. It has no re-coat windows either. I don't remember if Mohawk glaze does.

From the original questioner:
The tape was being used when the installers were scribing sections as they put them in.

Yes, Mohawk does have a recoat window which I initially followed, only to have these problems. Now I am trying this other angle, which is the shellac barrier, and finding this is about the same.

Any suggestions on what to do from this point forward? Remove shellac and glaze and try different glaze (over NC basecoat and stick with NC till the end), or attempt to use pre-cat over shellac, or remove shellac and use pre-cat, or any other ideas? I'm coming up on a deadline real quick and I don't want to lose this client (a cabinetmaker). They already put off their client due to this first failure and if this fails again, I believe it would be the end of this workstream for me.

From contributor B:
What I'm having a hard time understanding is why the clear topcoat of nitro lacquer won't burn into the pigmented coat of lacquer. As I understand it, you used Mohawk's heavy glaze right on top of the pigment lacquer without a sealer or barrier coat? Then after 1 hour, you put a light coat of clear lacquer, and then 6 hours later, you put the clear lacquer topcoat on? Obviously there's an adhesion problem somewhere. What kind of clear lacquer did you use? Nitro lacquers should burn into each other. Evidently this topcoat did not, thereby causing the problem. Either product (glaze) or time or topcoat or combination is the culprit. I have never had a problem with pre-cats on top of glazes. Of course I use a lot of vinyl sealers with my glazes. You need for that sealer or topcoat to burn through the glaze to the color coat to have good adhesion. Need to know what you used. And you mentioned shellac... when was that used? I've used CV on top of shellacs before and haven't any problems.

From contributor M:
You might want to wait for the window to close, and allow the glaze to dry longer. Then do a misting to set the glaze, and then a flow coat, and then allow to flash. Then it should be ready for more coats if needed.

Be sure you're mixing the glaze as you work, and try brushing out the glaze. The less you leave on it, the better off your finish will be.

Try the Valspar or another brand.

From the original questioner:
I used Valspar nitro cell lacquer over the glaze in that 1-6 hour window. When that failed I peeled off the lacquer, wiped off the glaze with mineral spirits, re-glazed and then let it dry for about 2 days. I then sprayed a coat of the Zinsser/Bullseye shellac over the glaze hoping it would stick, since the attempt to get the lacquer to bite through the glaze into the lacquer undercoat didn't work. I let the shellac dry for 2 days and today I coated that with uncatalyzed vinyl sealer (luster-lac by Valspar) and then topcoated with Valspar pre-cat. I will find out tomorrow if this will work. If it doesn't I'm back to the drawing board.

It appears from scanning this website for hours I am not the only one who has had problems with the Mohawk heavy bodied glaze, so I think that might be the culprit. For whatever reason it does not allow the topcoat to penetrate through it into the undercoat - at least with regular nitro cell lacquer anyway. The CV and pre-cat might be a different story - more potent and consequently able to bite through the glaze into the undercoat? And I made sure I didn't put it on crazy thick for fear this might become an issue...

Overall, though, I have this ill feeling it isn't going to work. If that is the case, I might just end up going to Sherwin Williams and having them make up an undercoat/glaze/sealer/topcoat system that is guaranteed (by them anyway) to work. I think the Mohawk heavy bodied glaze just might be a bad apple. What is the sure-fire system you use?

From contributor Y:
I don't think a pre-cat lacquer will solve your problem, as they do not dissolve into previous coats.

From contributor N:
I've not used the heavy bodied glaze, but have used many gallons of their finisher's glaze without any problems. I use vinyl sealer and post cat lacquer, all Mohawk.

From contributor M:
Contributor Y, that depends on when you recoat it!

From contributor R:
What type of finish are you trying to get that made you use the heavy bodied glaze? There are many other ways to match a sample. If you could give some details on the look you are after, perhaps we could make some other suggestions. (Are you trying to do a striping finish or something else?) I also have had some problems with the heavy bodied glaze - mostly if I leave too much on the surface, like in corners, etc.

From contributor Z:
Vinyl sealer will not let the oils from the glaze affect the finish. It bonds well to the oils in the glaze and allows you to topcoat. All you have to do to the vinyl sealer is lightly scuff it, then apply finish.

From contributor J:
Again, I would recommend going with the Valspar glaze. They also make a vinyl base coat that is actually a primer/surfacer that can be tinted to any color. This stuff takes glaze very well, almost too well.

I never really understood why other finishers intermix products all the time, when it's not necessary. Finish manufacturers go to a lot of trouble to make sure that their products work well with each other, and if you have a problem, both companies will point the finger at each other. I learned over the years that sticking with all one brand of materials whenever possible is the best tactic in the book.

This is a typical glazing schedule:
2 coats of tinted vinyl base coat, sand like a primer surfacer.
If I want a clean glaze look, seal over the vinyl base color with Valtec pre-cat 20 sheen.
If I want the glaze to darken and really bite into the color, I don't seal it first, glaze right on top of the tinted vinyl primer.
Use the VWS0912 series oil glaze.
Brush and rag the glaze and let dry for 2-8 hours depending on how heavy it was applied.
Seal over the glaze with 1 coat of Valtec 20 sheen pre-cat clear.
Let the seal coat dry and scuff with 320 grit.
Dust it off and topcoat with one more coat of Valtec pre-cat 20 sheen.

I've done 20+ jobs with this schedule, or slight variations of it, with no problems or callbacks.

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