Brushing on a Waterborne Primer

A small-time cabinetmaker looks for a primer he can brush onto the edges of door panels. September 3, 2011

I need to foam brush on a white primer on my panels before gluing up my doors (Iím worried about seasonal movement). I will sand and then apply a sprayed GF Undercoat over the entire assembled door(s). I was told I will not be able to brush it on.

Can I use a basic white wb primer, say Zinsser or equivalent, without issues? Iíve been told no because it may not be compatible. I cannot spray the panels at this time as my shop is not set up for it yet. I will get the booth up by the time everything is built.

Forum Responses
(Finishing Forum)
From contributor Y:
Why not seal the panels with de-waxed shellac? I use flake and DA in a 1lb cut and have never had a problem with either Target or GF. Itís my understanding that neither play nice with Zinsser. Even their sanding sealer can cause crazing of the finish.

From the original questioner:
Well I need a pigmented sealer/primer thatís brush-able, and the de-waxed shellac is most commonly a Zinsser product I believe?

From contributor M:
I would contact general finishes and see what they have to say. They should be able to answer your question, and suggest a proper finish schedule, as well as any steps you need to take if using other products. If this is an exterior door I would stay away from the shellac.

From contributor Z:
I have personally used the Zinsser pigmented primer under GF poly and not had any problems but you will need to test yourself of course. Why are you brushing the edges? Is there a reason you couldn't hit them with a spray gun? I would think that would have to be better and you would not have any brush marks.

From contributor A:
They told me you could. I tried on sample doesn't seem to be a problem. I tried both water based Zinsser and Bin, both seem ok. I was also told you could spray their white poly over pre primed trim you get from lumber yard. I like priming routed panel section with a brush, sand it and then assemble door. Most times primer is very close to top coat color and if shrinkage occurs you will see primer and not bare wood or MDF.

From contributor Y:
Actually, no. What I was referring to was flake shellac that you dissolve in denatured alcohol. I didnít realize you needed pigmented. I thought you were just trying to seal the end grain. The problemís with Zinsser regarding the finish crazing under the topcoat. I have done this since and it works great as a sealer and keeps the grain raise to a minimum once the waterborne hits it.

From the original questioner:
So it sounds like the BIN white primer should work? I called GF and they want me to use their milk paint primer as a brushable primer under the pigmeted poly. Why brush my panels? I'm a moonlighter cabinet guy, I do two, three cabinet jobs a year in limited space so I tear down my spray booth and reassemble when needed. I pre-finish with just de-waxed shellac usually, but the painted kitchens are becoming popular and I have 10 doors/drawers that are five piece and I like pre-finishing the inner panels due to seasonal movement. Then after all is assembled I can blast the whole job at once. I hope that helps? Any pros and cons to the BIN under the GF poly would be great Ė itís going to be one coat just to make sure there's no wood exposed if she shrinks up, and sanded very smooth.

From contributor B:
I've used GF products for many years. I've used pigmented shellac primer under GF's pigmented acrylic before with no problems. I've just used it in a rattle can to prime MDF panels (this would probably work for you with so small of a job). I definitely would recommend that you put their white undercoat on top of the shellac before you topcoat. This will act as a barrier to the barrier coat. Also, don't sand it too fine as you may not get a good mechanical bond. You'll also want knock back the shellac a bit before you put on the undercoat. Lightly sand and hit it with some synthetic steel wool.

From contributor Z:
I guess I don't see any advantage to using anything except their Undercoater as the primer. You can brush that just fine if you are only doing the very edges of the panels. Granted, I might not try to brush the whole door with that particular primer but the edges should not be a problem. The newly reformulated Poly Undercoater is a fantastic product. Much improved over the previous formulation.

From contributor K:
I donít know why you canít brush the GF undercoater on your panels. I have brushed it onto the edges of MDF doors many times with no problems. It probably doesnít flow out very well when brushed but you will be sanding.

From the original questioner:
Thanks all for your tips. I'm going with the GF undercoater.