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Old 10-13-2018, 12:08 AM   #11
SAJ
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Join Date: Jul 2010
Location: Auckland, New Zealand
Posts: 513
Default Re: 28 Roadster Door Rust Repair

Here is what I did in my wife’s Tudor which had holes in the door bottom and 2 rust penetrationns in the outside panel very low down. I did not want to repaint the door after burning the paint with welding and I did not want rust to ever occur there again. So I phosphated the existing rust after scraping and vacuuming the recess to remove all loose matter and then pressure washing inside the door. I used an Ospho type product. I cannot remember which brand, but you want a “pure”phosphoric acid one containing a little surfactant to cut through any greasy or oily film, as opposed to one containing phosphoric acid and a water-based coating resin, which leaves a paint type protective film behind. This is because you are going to apply a 2 pack epoxy on top to encapsulate the area forever so that you could fill it with water and it will still not rust the coated part!
You need to buy a 50/50 resin/hardener epoxy with good film forming properties at room temperature. The resin part A's are all similar, but there are many hardener part B types – both in ratios used, temperature and time of cure, strength, temperature resistance etc. A room temperature, 1or 2 hour gel time (working time or pot life) epoxy hardener is what you want. A room temperature “laminating resin” system will be ok. A hardener known as “polyamide” is what I used.
Get the resin from a boat repair supplier. They are known as Ships Chandlers here in New Zealand. Or maybe look up “fibreglass suppliers” to find a source. Get an epoxy rather than a polyester, since epoxies have better adhesion and flexibility for this job.
While you are at the supplier buy some “fumed silica” (Aerosil is a brand name) to thicken the resin and make it anti slump so it will stick to the walls inside the door panel and not just run off into the bottom. You only need a few grams since it is very light and bulky.
Now put a good tape over all the holes under the door to hold the epoxy mix inside the door. Take equal parts of the hardener and resin ( by weight or by eye if you cannot weigh since it is not critical with a polyamide hardener) and before you mix them add quite large volumes of the aerosol powder to each until you like the consistency. They will take an amazing volume and still remain very resin-rich and sticky, compared to thickeners such as talc and chalk, which is why i did not suggest these. You want great waterproofing which fumed silica gives and talc, chalk etc will lessen.
Having both the consistencies right, mix the two components thoroughly and you have an hour or so ( less on hot days) to put a 1/16th or 1/8th coating over the holes and a nice skin on the walls inside the door. For a really badly rusted door bottom you can of course add a layer of fibreglass cloth, but this is deviating from the purists “100 percent real steel” approach. The resin layer I suggested is really only like very thick paint and permissible in even a high points restoration in my view.
After 24 hours remove the masking tape, smooth out any irregularities and coat underneath the door with a similar epoxy mix to keep rust at bay from outside the door. Remember to drill out the drain holes which you will have filled when you treated Inside the door, and if these were drilled through steel and not through resin in a rust hole, you need to coat the sides of the drain holes with epoxy as you coat underneath.
Buy some acetone for clean up as you go, wear some rubber gloves if you are a messy worker and either clean your paint brush in acetone or throw it away after use.
I confess to owning a resin manufacturing business in NZ and maybe making this sound complicated with the detail I have given but it is really very easy and satisfying if you cannot weld steel.
I can put in new steel, but welding is much more invasive of surrounding paint which gets burnt in the weld zone. A resin repair has no effect on surrounding paint, but work cleanly and do not use acetone on your good paint because it will attack lacquers, though not original enamel on fenders.
Remember this epoxy repair is very tough and not like Bondo. If you get it where it should not be -i.e. may be an “icicle” of resin hanging from a hole you missed and did not block with tape – you will need a grinder to get rid of it, not just 180 grit abrasive paper as with Bondo type fillers.
SAJ in NZ

Last edited by SAJ; 10-13-2018 at 01:54 AM.
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