How to: Repairing Damaged Exterior Body Panels

[54PrairieSchooner]

Sent: 4/14/2005

I'm posting this as a potential repair method for the corrugated exterior skin on our Winnies. So far, I have had success, but will need to see how it turns out long term once I paint the area etc.

History: I had a 6 inch gash/dent in the right rear just below the red reflector . The PO had covered the area with a piece of 1/16" thick vinyl and several steel screws..as you know..aluminum and steel create a bimetallic corrosion problem..never use them together unless you isolate one from the other with rubber washers etc.  Anyway, I removed the patch and a thick layer of latex caulk underneath.  I decided to try this method based on a lot of past auto body work experience, noting that repairing aluminum..particularly corrugated aluminum and making it blend with the rest of the rig is seemingly impossible.

Here goes:

- Cut out the damaged area until you have a relatively square, dent-free area; cut out the foam and inner wall panelling  about 2" on each side of the hole. Grind down the edges of the area to a bevel shape. If possible, bend the edges in slightly. (Save the piece of foam for reuse if possible. )

- Using a piece of  thin aluminum or tin, tape the patch to the backside of the hole and mark off the contour lines on the patch..make the angled areas 1/16 to 1/32 inch wider than the surrounding skin as you'll want to place filler material nearby and blend it in as close as possible.

- Once you've marked off the lines, carefully bend (if you have a sheet metal brake, great, I used a 1X3 and another board to make the bends) and shape the metal to the general outline of the skin...ensure the raised portion of the countour (flat section) of your patch is slightly lower than the surrounding skin. Sand the patch with 60 grit paper on the outside to provide a good base for adhesive and filler.

- Using a suitable heavy duty contact cement, JB weld, etc. ( I used an aluminum fortified contact cement for semi truck sheet metal repair available from Do It hardware centers that dries almost to the consistency of solder) place the patch over the backside of the hole and carefully line up the patch countour lines with the rest of the body. Allow to dry overnight. If possible, clamp or brace the area with a piece of board and another board leaned up against the patched area from the outside and inside.

- Once it dries, glue (liquid nails) a 1/4" thick piece of wood along the backside of the patch; if possible, imbed the ends of the board in the surrounding foam. Brace the patched area from the outside to allow the patch to bond with the wood. This is to stabilize the area since all of the foam was removed and prevent it from flexing while you fill the area with filler.

- Once this has dried, clean off as much glue residue as possible from the outside of the patch. Re-sand if necessary and check that all edges of the coach skin are still bent inwards.


Refill the missing foam on the backside of the patch...if you can, reuse what you remove and reattach using Liquid Nails PL series or you can fill it in with Great Stuff expanding foam....layer the foam as you apply it and fill in all the voids...but don't overfill or you may bulge the skin..50% fill while wet is the rule.

- Filler: I use PC-11...a two part long-drying epoxy..it is a marine formula and is available at most hardware stores like Do-It, Ace etc.  Mix up enough of the past to adequately fill the valleys between the existing skin and the angled areas of the patch..top and bottom. Apply a skim coat along the flat portion of the patch and blend all of this in with the body, leaving about 1/16" above the surface of the existing skin for sanding/contouring.

- PC 11 is great stuff and is very durable. I use it to refinish cast iron sinks before resurfacing....It dries to a hard, off white consistency and can be sanded etc. Do not use Bondo as it will not stick to aluminum.  While the skin is wet, use a plastic putty knife to sculpt the angled areas and blend those in with the coach skin...it does not have to be perfect as you will sculpt/sand later..but get it close.


- After about 6 hours, you can return to the patch and, using a straight piece of metal, plastic etc. "form" the PC-11 e.g. you can sculpt it without it coming off on the tool. I use a plastic ruler to press in the angle areas.

- Let it dry for 24 hours and then sand with coarse, medium and fine sandpaper as you would any auto body patch..prime then paint the area.

I wouldn't use this method for areas that a very large (12" or greater)....