Preventing flash rust after blasting

motley911 · 09:37 PM

I am in the process of restoring a 1974 911. I made the ultimate mistake of buying the car sight unseen off the internet - and it wasn't quite what I expected - it needs a considerable amount of metalwork.

A "short" list of issues include:
- the seat mounts and inner sills / longitudinal's have been cut out so the PO could mount a set of BMW seats

- a number of large holes, some as big as 6" diameter have been cut in the firewall
- the RHS footwell (the panel between the footwell and the smugglers box) has been cut out
- 27 holes (3/8" diameter) have been drilled in the floor pan
- the front trunk has all sorts of holes cut in it
What makes it worse is most of the holes look they have been cut with either a cold chisel or an oxy torch.

I have removed all of the bolt on parts / windows and mounted the chassis on a rotisserie. In order to streamline the metalwork I am going to have the chassis sandblasted (dustless blasting) so that I can start welding up all of the holes.

I can handle the metalwork myself and will farm out the painting. As the metalwork will likely be carried out over the next few months (I have a day job

) I am concerned about flash rusting after sandblasting. The car is in my basement garage that is climate controlled.

I have done some searching on how to prevent flash rust starting after sandblasting but couldn't find anything recent. What suggestions do you guys have for preventing flash rust after sandblasting?

Thanks in advance,
Richard.

motley911 · 09:40 PM

Here are a few pictures of the car - I will post some pictures of the areas needing repair later. Oh - I realized that I never mentioned it is a 935 replica.

This is the car in the process of being mounted to the rotisserie.

You can see one of the many "holes" in the inner fender to smuggler box in the picture above. Notice the "rough" edges

911Cabrio · 911Cabrio's Garage

Once you are finished with the blasting. Apply a good epoxy primer (PPG DP40/DP401) to protect the steel.

motley911 · 03-15-2018, 07:09 PM

Thanks for the reply. For the primers you suggested - can I weld through them or will I have to grind the epoxy primer off before welding?

If that Is the case I may as well just remove the existing paint in the areas that I am needing to weld (wire wheel in a grinder) and not sandblast the car until I am ready to paint.

onboost · 03-22-2018, 04:18 AM

Quote:

Originally Posted by motley911

Thanks for the reply. For the primers you suggested - can I weld through them or will I have to grind the epoxy primer off before welding?

If that Is the case I may as well just remove the existing paint in the areas that I am needing to weld (wire wheel in a grinder) and not sandblast the car until I am ready to paint.

You're gonna end-up havening to remove the epoxy primer off before welding. So yeah, may just want to wire-wheel, fix, spot prime and move-on until done. Looks like an interesting find/project.

Good luck!

boosted79 · 03-26-2018, 05:32 PM

This stuff is great, but holy crap it's like doubled from when I bought it last.

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962porsche · 03-27-2018, 06:55 AM

just spray one coat of a epoxy primer down.
once you have picked what product line you are going to use stay with in that product line .
so if your going to use glasurit for your top coat use all glasurit from your undercoats right thru to your top coats . do not mix and match your product line. so if your go with PPG stay with that line.
personally i do not like any other products other then BASF. it's what most top auto makers use for there coatings and it's what your porsche came with new.

with epoxy primer you should be able to do your body filler work right over the top of it. but check your TDS to be sure the epoxy you pick you can do that.
some people like to do there body filler work over bare metal but most times it makes no difference if you do or not. again just check your TDS to see if you can.

as for welding.
you have to remove the epoxy were your going to do any welding. a stripped disc works good for removing the primer. i tend not to grind the primers off as the grinding marks could bite you later on after your all finished painting the car.
a stripped disc will give enough of a tooth to have a body filler bite into it.
i like the orange norton strip and clean discs best. they seam to last longer then the 3M's discs and will not fly apart if you catch an edge.