Painting Jambs
By Brian Martin

There is as many ways to paint jambs as there guys doing it. Unless it is an out and out show car I say paint the jams and then paint the outside. Many guys will say do it all at once with the panels off. The extra work and chance of damaging your new paint are so great, I say save that for the out and out show cars. If tape off the jambs well, you can barely tell the difference.
These are a few things I have learned that save a lot of work. First off, when you paint the jambs, apply both color and clear. DO NOT let the overspray go out onto the outside! This can cause HUGE problems along with the extra sanding that can be avoided. Unless completely removed, that overspray can ruin you work. The solvents from the paint on the exterior will get under the thin overspray and lift! What you want to do is be sure that the outside is TOTALLY done and READY to be final sanded and painted BEFORE you do the jambs. Now, tape off the outside along the jamb edge with at least 18" paper so you don't get that direct overspray out on the exterior. I tape the paper up to about 1/8" from the edge of the jamb. Then take your tape and "backtape" to the edge. This is when you lay the tape up to the edge on the outside so it is hanging over the edge, then gently fold it back, exposing the jamb but keeping the outside covered right up to the edge. This back taping will make a "softer" edge and be much easier to sand.
Go ahead and paint and clear the jamb, and remove that last tape that is back taped while the clear is still a little wet if you want (not necessary but you could choose to do that) the clear will then flow a little at the edge and leave you will even less of an edge to sand off.
Now when you paint the outside tape off the jambs up to about 1/8" or 3/16" from the edge so the seam won't be seen when the door is closed. Sand the exterior including that little edge left from the jamb paint and do the last little bit of jamb paint up to the new tape line with a gray scuff pad. I even will put that tape a little bit further away (about another 1/16") from the edge and after the scuffing with the gray scuff pad, apply a fine line (the blue plastic tape) tape over that last tape but hanging over the edge onto the new jamb paint that 1/16" bringing the line up to the original desired 1/8" to 3/16" from the edge. This will ensure that your jamb edge doesn't peel.

You could also use "aperture" foam tape that 3M makes. It is a rope made of foam with adhesive on it and is like "back taping" it leaves a "soft" edge.
I can go even more anal for you.
This may not work well in your jambs but if you can open the doors before clearing you could do it. I have found an even better way to all but eliminate that edge.
Tape off the edge as described with the extra line of fine line tape over the last 1/16" of new jamb paint (this works with when painting up to any paint actually, it doesn't need to be new paint you are painting up to). Then add ANOTHER strip of fine line the same way, over the next 1/16" or 3/32" getting up even closer to the jamb edge. Now, after you paint the color on the outside, you remove that last fine line added BEFORE you clear the exterior. Now, you will be burying the edge of the base coat under the clear! You don't have to do this by any means but it adds to that detail that is almost like you removed the doors to paint.

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