Special Primer

[DoRight]

Last year I visited an auto restorer and noticed he used a special primer after removing rust and old paint, which he then would weld "through". I'd not seen that before. Is that an ok practice? If ok, does anyone know what it's called and where to get it ?

[enlpck]

There are several of these products. One I have used is bloxide from Tempil (th heat crayon people). It isn't so much a primer as to protect prepared surfaces from rusting. Doesn't have any effect on weldability or weld quality AFAIK. The inspectors are happy as cn be with it. Very useful, as prep can all be done in one shot and protected. Seemd to take paint over it ok.

[Sberry]

I am not sure what that might be, but most primer doesnt weld "too bad". Still, its got to be better to clean it especially on thin steel with wirefeed.

[Sandy]

Most true 'weld through' primers are loaded with zinc. Like enlpck says, they are mostly for auto body folks who strip areas then need to protect the metal between then and when it gets attention again. High humidity areas, salt environment, long gaps between sessions and so-on. They aren't necessarily just "for" welding and they aren't necessarily a good primer. Low VOC is a must if nothing else no matter whether it's a cheap knock off or high quality.

[gocirino]

Try eastwoodco.com or better yet try http://www.eastwoodco.com/shopping/search/searchresultsmain.jsp?fresh=1&searchType=advanced&iMainCat=0&iSubCat=0&attribute14=0&attribute15=0&attribute16=0&RS=1&keyword=weld+through

[enlpck]

Sandy: Depends on the prep. The stuff I'm talking about doesn't have significant zinc. Allows code welds on boilers, boats, etc. and can be TIGed over without a problem.

Some of the auto body products ARE zinc loaded and are unsuitable for most structural and pressure vessel work without specifically qualifying a procedure, due to the zincs effect on the weld metal, and you can not TIG over the zinc preps.

Of course, the good stuff costs a bundle....

[Sandy]

Originally posted by enlpck
Sandy: Depends on the prep. The stuff I'm talking about doesn't have significant zinc. Allows code welds on boilers, boats, etc. and can be TIGed over without a problem.........................................
Of course, the good stuff costs a bundle....

Makes it tough without a bunch of research to know what your getting for sure I guess. Crap at the rattle can store isn't famous for accuracy in labeling.:p From what I've seen Weld Through on the label is about all they tell you and you go research from there. The stuff you are talking about is probably "the" weld through primer as intended. As always the phrase catches on an away we go.

I haven't seen any hardware store variety yet that could really explain why I should use it. I know there probably won't be one out there that will enhance the weld, that's for sure. The way I see it you pros know what you're doing and know how to deal with different chemical and metalurgical make-ups. Guys like me should just stick to the simplist way of doing things, like weld first, prime after.

Thanks for the info..

[enlpck]

It's actually pretty simple: any of the 'weld thru' are ok in a situation where galv is ok, such as much sheet metal work. The expectation is that the process is either tolerant of the zinc, or it won't affect weld strength enough to matter (do you really need a 70000PSI weld on a car trim panel? exhaust pipe? As long as it doesn't crack off, it's ok) Flux-core wire and some sticks have fluxes that will help keep the zinc from affecting the weld, either by flushing it out or binding it harmlessly.

The other type seems to be principally ultrs fine aluminum flake and a binder. The binder needs to cook off without introducing any contamination to the weld (especially carbon or hydrogen) The alum flake will oxidize, obviously, but small quantities of alum help flux the weld area, and net percentage that can get to the weld at all (if properly applied) is very low. In practice, you can see it float off the puddle, probably because the aluminum oxide provents the flakes from melting, and is insoluble in the molten metal.

[Sandy]

Originally posted by enlpck
It's actually pretty simple: any of the 'weld thru' are ok in a situation where galv is ok, such as much sheet metal work. The expectation is that the process is either tolerant of the zinc, or it won't affect weld strength enough to matter .................................................. .................................................
The other type seems to be principally ultrs fine aluminum flake and a binder. The binder needs to cook off without introducing any contamination to the weld (especially carbon or hydrogen) The alum flake will oxidize, .................................................. ....................................


Alrighty!! (blink, blink my bulb comes on). Put that way it makes a lot of sense now. For me that translates to= If I don't know or can't tell which type it is don't use it unless structural integrity isn't a real concern.

Thank ya sir.

[DoRight]

Thanks so much. I'll bet its the Bloxide. The link gocirono provided above jumps right to a site with it. It runs $14.99/Qt on that site ... Quote from the info there, "Bloxide - The preferred weld-through primer. This Aluminized de-oxidizing primer insures x-ray quality welds. Promotes the formation of Aluminum oxide at the weld site to reduce porosity. Prevents corrosion of coated steel surfaces for several months of outside storage."