Suggestions on Roof Repair

[landarts]

I was working on my 71 K20 - build thread here getting the back of the cab ready for paint and when I got up toward the top of the roof to address the 2 holes that were in the roof from P.O. that had a C.B. antenna mount I noticed some pitting. As I began to sand the area I could see a few really small pin holes. So I proceeded to push down on a few and they were paper thin and broke through the surface of the metal. I then took my die grinder with a burr bit on the end and drilled through to ready them for repair.

Then I got to thinking about the best way to repair this area so that there will not be an issue down the road in years to come. I thought about just welding up all of the holes, then thought about a complete replacement of the roof. After researching the forum threads on this topic and watching a few videos here is what I have come up with for a solution the repair.

- cut out the area that is outlined in red
- use that piece for a template for new metal
- if there is crown in the metal because of the shape of roof, do a little shaping on planishing hammer if needed
- with the metal cut out treat the metal inner roof and upper inner metal with Ospho 605 metal treatment to convert any existing metal from rust to iron oxide
- after that has done its job then treat all of the metal inside the roof with 3M Cavity Wax Plus 08852 and use the medium applicator wand that sprays the wax in a 360 degree fashion to coat everything for future protection

I have never had to make repairs on top of the roof in all the trucks I have built over the years. Any suggestions would be great and welcomed.

[SkidmoreGarage]

You have far more experience than me with an impressive list of trucks to your name, but if you are asking- I would suggest cutting the red area and inspecting/posting a new picture. Best case, you will be welding in a patch anyway. Worst case, you see a lot more extensive rust/bad repair and you can decide what is next.

It sounds like you are looking for a "forever" repair, and without knowing how far gone the backside is, it's hard to say if what you propose is enough. It strikes me as odd that the rusty spot is "uphill" from the roof seam.

[sick472]

I've done a fair amount of welding up pin holes from inner rust and should say, first, that cutting out the immediate area and replacing with a patch is the best way to go...but, when welding up pin holes, the heat from the welding process will burn out any rusted thin metal and "show" you how extensive the rust damage is. You could find that you chase the holes out well past where they appear to be OR merely weld in the holes and be done.

I would consider welding the holes up first and if they burnout horribly proceed to cutting out and patching in. I say this because the roof is a complex curve and my sheet metal shaping abilities are novice at best. Also, my builds do not see day-in and day-out weather. So, the likelihood of the inner rust resurfacing is minimal.

On the flip side, by cutting a section out, you could do a more thorough inspection and see just how far the pitting extends past what is showing.

[Livrat]

In order to prevent issues down the road I personally would cut off the entire roof skin at the drip rails and across the back forward of the factory seam, treat the inner with Ospho, then replace it with a good skin. (the reason the inner is also cut out was to delete a sunroof)

[landarts]

Originally Posted by sick472

On the flip side, by cutting a section out, you could do a more thorough inspection and see just how far the pitting extends past what is showing.

I have really thought about doing this for sure, maybe even get a inspection camera snake in there to see what else might be going on.

Originally Posted by Livrat

In order to prevent issues down the road I personally would cut off the entire roof skin at the drip rails and across the back forward of the factory seam, treat the inner with Ospho, then replace it with a good skin. (the reason the inner is also cut out was to delete a sunroof)

Livrat I thought about this also and that might be where this is heading depending on what I see after removing the area in red in the photo.