I'm in the process of replacing outer wheel houses and am wondering, what would be the best way to seal the bare metal flange areas before welding in order to prevent rust later?

Use a weld thru primer.

Your best bet would be to use a panel bonding adhesive or seal the joints completely after welding. On verticle joints I sometimes seal the bottom of the joint and fill it with epoxy primer till the void is full, then follow up with cavity wax like 3m rustfighter.
Weld through primers are a nice idea but really don't help much, confirmed from the testing I've done.

Baddbob 71, are you saying you would rather use adhesive than weld these pieces? But if you weld, you would leave everything bare untill after welding, then apply epoxy primer? The weld through dosen't help at all? Did you have to repair any of the dash under the windshield in the Nova? Thanks for your replies everyone.

The weld through coating offers minimal protection IMO. I tested some different brands years ago trying to determine which worked best. The tests were done with saltwater because that's what cars are subjected to up here all winter long, roadsalt. I think in a mild environment the weld through coatings may offer enough protection to slow the corrosion down long enough to get a reasonable service life out of a vehicle but the conditions up here require more attention. If you want this work to last a very long time I would suggest using panel adhesive or weld them in with or without the weld through coating then apply primer and seamsealer to the exterior surfaces then treat all the pinchweld areas internally with epoxy and or a cavity wax like 3M's rustfighter or cosmoline. These waxy coatings will seep into nooks and crannies and are self healing. Filling the void between the lapped metal is number one for fighting corrosion in these areas. The panel adhesives do this in one step and most offer a parts and labor warrantee. Do not use the adhesives for any structural repairs. I do use the weld through coatings for doing structural repairs on unibody vehicles but mostly for liability reasons- (I-CAR and all OEM guidelines suggest it's use). A better option/product would be nice. I have used another product totally unrelated to the automotive industry as a weld through coating that worked extremely well, it actually flowed to the weld, but the fumes were deadly requiring a fresh air supply system while welding and I wouldn't suggest it to anyone. :eek:

Thanks again, for the info.

On any area that will recieve welding its suggested yu apply weld thru primer. Is it a perfect product NO but its way better then nothing. Every car manufactor wants weld thru applied to panels, expect for Dodge on new Rams, they DO NOT want weld thru. :confused:

Once welding is done you need to remove any excess weld thru, like overpsray etc. It has poor adhesion, so topcoating over it is a bad idea.
Also Ive found 3M weld thru to be a very poor product. SEM makes about the best weld thru.

Here's an example of internal corrosion on a two year old vehicle with only 16,000 miles. It is an 03 Ford Taurus. At the factory this vehicle was welded together and then Ecoat was applied to the galvanized steel- just think of how bad the corrosion would have been had they just coated it with weld through coating and welded her up. This project is a builder that I'm doing for a good friend, I took care of the corrosion before the replacement panel was installed. The replacement panel I installed will outlast the life of the car, but I expect the Quarter panel on the other side of the car will be showing external corrosion within a year or two-depressing. Does the factory engineer a lifespan into the body of these cars? Other seams on this particular vehicle like the rear panel and the horizontal seam midway on the rear panel are sealed very well-it seams they really didn't want water problems in this area and the related warranty problems of water in the trunk. This is typical of most models up here, untill the advent of adhesives doorskins were corroding on new cars before they left the lot. Bob

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