To Caulk or Not to Caulk

Thoughts on whether, and when in the finishing process, to caulk small cracks in frame-and-panel doors. January 4, 2014

We get orders for shaker cabinet doors frequently. Our basic method of construction is 3/4" maple frame work with a 1/4" thick MDF maple veneered panel. Iím still wondering if to avoid cracking where the panel meets the rail/stile is it better to caulk after priming the door then topcoating? Iím talking strictly pigmented conversion varnish. Our panels fit tight and in this particular job we have even glued some in. Still, in some cases there are little 1/32" gaps. I donít want to just bridge the gap with the CV. So, caulk then top coat, or donít caulk? Should I caulk after top coating?

Forum Responses
(Finishing Forum)
From Contributor G:
If the panels are MDF and glued or nailed in place then the smallest bead of caulk is ok. I do mine after I prime one coat, and if I caulk I always do another prime coat. The hardest thing is to keep the caulk controlled - it gets everywhere.

From Contributor C:
Caulk after primer/sealer. Use the squeeze tubes with the tip cut small.

From the original questioner:
To contributor C: You recommend this method even if finishing with pigmented conversion varnish?

From contributor B:
Contributor Gís right. No matter how careful I am cleaning up, some caulk always gets left behind on the panel. It will telegraph through if you caulk on the second to last coat. So I like to caulk after two SS coats (WB) then two coats of TC. I like to use a popsicle stick or a shim sanded down nice and thin and formed to an angle (two flat edges and angled) to take the majority of the caulk off then wipe. Caulking is a pain but it does look much better.

From Contributor C:
The guys at the architectural wood firm I spent some time at did it a bunch. They said the primer helped them see the cracks. If you have doubt, try it on some scrub panel.

From the original questioner:
Great, but were those guys finishing with pigmented (or just white) conversion varnish? To me, a lot of things change when using conversion varnish because it does not flex like regular paint.

From Contributor G:
That's why I do two coats of primer. If you have some rouge caulk you can deal with it on the primer coat much easier than the finish coat. My views are using conversion varnish - MLC Stealth and Resistant to be exact.

From Contributor C:
Yes, they were using conversion varnish of many colors. I think it was a DAP product they were squeezing. Washcoat primer, scuff, caulk, primer and etc. If you are nervous about the cracking, test it. Play around with the application a little. I recently did a large bookcase with bolection molding and applied carvings - lots of cracks and gaps. In about 300 LF of caulk, I only had three goobers in tight corners that showed up after the second primer coat. The trick is to not apply so much that it forms a lumpy bead on the trailing side of the tip that you have to go back and strike it even. That's where the smears and skins come in.

From Contributor N:
I always caulk, to me it just looks better. It is a lot more work and it can come back to haunt you but thankfully that doesn't happen too often. I agree with all that's been said. Caulking between primer coats is ideal; gives you a smooth sealed surface to work with, but if you're only running one prime coat caulk before priming. I like the squeeze tubes as well. I look for the quick drying stuff like Dap Quick Seal. It's flexible enough to bridge a stable gap but hard enough to keep the CV cracking to a minimum. The longer you let the caulk dry the better. Overnight is great but I have primed over it in as little as two hours without issue.

From the original questioner:
I think one of the other problems that can lend to the CV cracking is the puddling of CV that occurs right in those corners where the rail/stile meet the panel. As hard as I try itís like it always puddles.

From contributor D:
I do finishing for many different cabinet shops and when I get outscored doors such as Conegstoga they back radius stiles and rails so no chalk is needed. When guys build their own doors there are always different size gaps. I have found white Phenoseal is best after first primer coat. I take a square piece of Formica to get it in and make sure all extra is off, corners most important. This is time consuming and I charge about 20% more for guys who build their own doors. Some guys donít glue panels in or use space balls and this can lead to problems.

From contributor F:
I have tried it in the past and never cared for it. As others have said, the caulk gets everywhere and it is hard to make it look perfect and consistent. I realize this is at least partially due to my lack of caulking skills, I have seen others do a better job of it than I can. Personally I prefer something that I can sand smooth which is why I started using 3M spot and glazing putty, the same stuff automotive body guys use over the last coat of Bondo to fill in all the pin holes. It takes a little longer because you can't just squeeze it out of the tube into the joint, you have to use a small putty knife or tool it out with your finger and smooth it with a bit of thinner. It does dry fast, is perfectly sandable and will never gum up if you get into it through the primer the way caulk does.