Restoring - General discussions that span across many different groups of years and models > Body, Paint & Sealers

How to repair inside of door on vintage Mustangs?

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Bossbill:
On a flat surface any full surface weight will work to some extent. I'm trying to prevent any shifting of the latex and to spread the filler or glaze out far enough so that there is little or no edge.
This really became an issue with the curved edges at the bottom of the door.
The inward curves were really tough. It's hard to keep the latex in contact with the filler while it dried.
That's where vacuum comes in handy -- to have the pressure differential push the latex into the curve and especially where the weatherstrip is glued.
Plus, the pressure applied to the surface is hard to beat without a vacuum.
12–25 inches of mercury equals 6–12.5 psi on the latex. This pressure is almost impossible to duplicate without "clamping".

http://www.westsystem.com/wp-content/uploads/VacuumBag-7th-Ed.pdf
Section 1.2

I should add that another benefit is one that Jim mentioned. Vacuum will draw out entrapped air. This works well for removing air bubbles from urethane (and other media) poured into a mold -- and from glaze.

After a week of trying I've found this to be very difficult on curved surfaces. After half a dozen tries I have one surface that is tolerable for the bottom of the door. The vacuum system does not work as well as I had hoped as it leaves a wavy surface.
A brayer (roller) is working better.
More updates later.   

67gtasanjose:
Bill, have you had any updates to your technique?

I have repaired a bottom of my driver's door, fortunately, only some small areas to work on that can be seen beyond the weatherstrip.

Bossbill:
I'll find a pic of my finished repair.

I've modified how I do this now as it has taken literally dozens of attempts to find something that works. Be aware that this tends to work best on small areas.

I make a thin latex mold of a good area --  roughly a 4x6 area. Make sure the back is as smooth as possible.
Mix 90% isopropyl alcohol (or Everclear!) with caster oil in a 4:1 ratio and spread on the latex pattern. This is actually the key as it's a mold release and will not allow the bondo to stick to the latex.
Mix up a small amount of finish glaze (finesse bondo).
Spread very thin on the area in question. I use a razor blade or other blade and spread very smoothly. Leave no lines.
Apply the latex. I use tape to keep it from moving around.
I used a rubber roller to roll over the surface of the latex. You do not want to roll hard enough that the latex moves.

Leave the latex on until the glaze kicks. Use a wax and grease remover to remove the castor oil.

An improvement I thought about for very flat areas was to lay the latex flat and to apply some bondo (or other thick adhesive) to the back side. Squish a piece of wood into the bondo. This should turn the latex into a stamp.

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