Caulking Under Conversion Varnish

Gaps in a piece may become noticeable after a first finish coat. Here's advice on caulking before applying the second coat. March 26, 2013

I'm spraying a couple bookcases and a mantle shelf. They are made of maple and MDF. I primed with MLC Clawlock and now I see some obvious seams between pieces. I didn't build them! Should I caulk these seams and re-coat with Clawlock, or caulk and go right to the finish of Stealth. Any suggestions on an alternative to caulk? I'm just worried about the flexibility of caulk under something like Stealth.

Forum Responses
(Finishing Forum)
From contributor G:
We seem to get joints to open up after the first coat of primer and have always filled with bondo or wood filler. I'm still not sure why the joints do this as they are tight before primer (and most don't open up) but it is just something that we're used to dealing with. I've recommend bondo depending on the joint. Itís easy to work with and dries very quickly.

From contributor L:
The lacquers have little to no bridging capabilities. If there is the slightest space then you will see the gap. When caulking I usually spray a coat of Clawlock and then scuff it. Then I apply the caulk and a second coat of Clawlock to smooth everything out so I get no grain telegraphing. If this is too much you can spot prime the caulk. I've never sprayed stealth directly over caulk - it would probably work. It works on Clawlock and you can use stealth as a self-seal if you'd like to torture yourself with sanding, so it should work. Itís easy enough to do a test. Take two boards and screw them together at a 90 degree angle and then prime and caulk. Then shoot some stealth over it and see what happens. If it sticks you're all set, if not then use primer.

From the original questioner:
In the past I've used Clawlock. I caulked some seams and shot another bit of Clawlock over it. In all those cases my final coat was something like Porter Glyptex, an interior oil finish. I never had any problems with that. I always let the caulk get nice and solid. I guess I'm just concerned about the Stealth cracking. However, if the Clawlock doesn't crack I guess the stealth on top of it won't crack.

From contributor L:
Myself, I've always put Clawlock over it, mainly because I normally shoot two coats of primer to kill any telegraphing. I shoot both coats at 10% thinning.

From contributor M:
Caulk is fine but be sure not to buy a glossy type. I have definitely had peeling issues with glossy caulks. Agreed with the above - prime it, sand it thoroughly, caulk it, cure it longer than you think it might need, spot prime the caulk, gently sand that spot, and topcoat.