Painted Door Details to Minimize Finish Cracking

A discussion of joint design, glue choices, crack filler, and finish choices in order to reduce cracking and telegraphing of joints. January 28, 2009

I'm working on a painted door design. Im hoping to minimize joint telegraph and cracking issues. The client does not want one piece MDF. I'm thinking five piece mitered door and splined miters using soft maple with a 1/4 inch MDF center flat panel glued into the grooves. The sticking detail is a double round over.

I'll use polyurethane glue to eliminate joint creep on the miters and fill any defects with bondo. Finish will be ML Campbell Clawlock, top coated with stealth tinted to the chosen color. Is this as good as it gets or could my system be improved?

Forum Responses
(Finishing Forum)
From contributor A:
This may read a little critical.

Poor choices:
1. Mitered doors are the most prone to joint cracking. Far more than traditional cope/stick doors.
2. Polyurethane glue(ie Gorilla Glue) is a poor wood glue. Worst choice for your miters.
3. Bondo telegraphs more than most other fillers because it is much harder than wood or plywood.(We use it for big defects but prime it 3 times to bury it)

Good choices:
1. Soft maple is a good choice for high quality painting.

2. Gluing MDF panels into solid frames works well to reduce cracking.
3. Most ML Campbell products are first class. Clawlock is one of them.

Better choices:
1. Typical five piece cope and stick door.
2. Plenty of Titebond 1 style yellow glue.
3. Muralo Pro Grade Spackle is a great product for surface defects before and after primer.

From contributor S:
Is it an interior or exterior door?

From the original questioner:
Interior cabinet doors. I felt the miter might look better when they do crack. By splining the miters, wood movement would be greatly restricted.

From contributor J:
I just did a set and painted then glazed. Cope and stick soft maple frames, full TBII glue coverage in the joints, MDF panels (raised machined areas clawlock or featherfill primed and sanded and primed before assembly). They were assembled and 23ga pinned, thoroughly cured door assembly, widebelt sanded, primed complete, sanded, joints blown and filled with autobody glaze, primed, sanded, tinted magnamax, scuffed, topcoated with satin conversion varnish . They look like plastic. Time will tell on the joints, but Im very confident in the assembled product.