Primer or filler on bare metal? (3 Viewers)

Joined
Jan 6, 2003
Messages
973
I did a search but didn't see this discussed or I missed it. When doing body work, what is the order of repairs after welding? Is it better to use body filler on bare metal or primer?

Also, for repair patches that won't be painted for a while, what's the best way of protecting it from rust? For now, I've been using a spray can primer just to get something on bare metal, but I already see some rusting in the seams so maybe I wasn't putting a thick enough coat on. An epoxy primer is probably better, but not always feasible when doing small areas. These are areas that may sit around for months or even a year before I'm ready to paint. Can anyone recommend a good spray can primer, some thing I can use for spot repairs?
 

PAToyota

Keystone Cruisers
SILVER Star
Joined
Oct 4, 2009
Messages
2,275
Location
South Central Pennsylvania
My standard procedure is to lay down a coat of epoxy primer over everything to get it all sealed. Many of the body fillers are porous, so you want that sealer under everything to protect the bare metal. If you're still doing welding and patch panels, you can get 2K epoxy primer in a spray can. It's expensive, but you can do your body work on an area, clean it all up, and then seal it up with the spray can. When you're all finished, clean it all up and lay down a coat of primer surfacer over everything to start blocking things out.
 
Joined
Jan 6, 2003
Messages
973
Thanks for the info. Are there any other primers can be used as a base to seal the metal? One of the reasons I haven't used the epoxy primer is the shelf life is a matter of days once activated (from the ones i've looked at). So unless I do a very large repair that needs an entire can I'd be wasting most of it.
 

Jdc1

SILVER Star
Joined
Sep 9, 2013
Messages
3,788
Location
Akron, OH
Thanks for the info. Are there any other primers can be used as a base to seal the metal? One of the reasons I haven't used the epoxy primer is the shelf life is a matter of days once activated (from the ones i've looked at). So unless I do a very large repair that needs an entire can I'd be wasting most of it.
Epoxy is best. Just mix up a smaller amount. It’s worth it to invest in the DeCups starter pack for your HVLP gun.
 
Joined
Aug 22, 2015
Messages
1,576
Location
Ohio
I've had good results with a Harbor Freight touch up gun and mixing small amounts of 2K epoxy. If you do it right there's little waste, and I would think more economical than anything in a rattle can. Lasts years in the can prior to mixing.
 

FishNinJay

SILVER Star
Joined
Jun 8, 2009
Messages
807
Location
Orange County, CA
My standard procedure is to lay down a coat of epoxy primer over everything to get it all sealed. Many of the body fillers are porous, so you want that sealer under everything to protect the bare metal. If you're still doing welding and patch panels, you can get 2K epoxy primer in a spray can. It's expensive, but you can do your body work on an area, clean it all up, and then seal it up with the spray can. When you're all finished, clean it all up and lay down a coat of primer surfacer over everything to start blocking things out.
That’s interesting. I need to tackle some surface rust spots and just figured I’d hit it with wire wheel, sand it and clean. Then figured I’d use any filler or finish bondo then primer. What’s etching primer vs epoxy? Sorry for the basic questions! Also, was considering after sand and clean, doing a spray coat of VHT Rust Reformer to treat tiny rust pinholes my eyes might miss. Then filler bondo? Sand, primer, more sanding, paint. Thanks!!
 

Jdc1

SILVER Star
Joined
Sep 9, 2013
Messages
3,788
Location
Akron, OH
That’s interesting. I need to tackle some surface rust spots and just figured I’d hit it with wire wheel, sand it and clean. Then figured I’d use any filler or finish bondo then primer. What’s etching primer vs epoxy? Sorry for the basic questions! Also, was considering after sand and clean, doing a spray coat of VHT Rust Reformer to treat tiny rust pinholes my eyes might miss. Then filler bondo? Sand, primer, more sanding, paint. Thanks!!
Epoxy is a direct to metal primer. It’s pretty bad ass. You want to seal the metal before using any filler to prevent any moisture getting through the filler to the metal.
 

FishNinJay

SILVER Star
Joined
Jun 8, 2009
Messages
807
Location
Orange County, CA
Epoxy is a direct to metal primer. It’s pretty bad ass. You want to seal the metal before using any filler to prevent any moisture getting through the filler to the metal.
Cool.. I'll look for that 2K epoxy primer. Any thoughts on these rustoleum or VHT "rust reformers"? or just snake oil nonsense? Thanks..
 

Jdc1

SILVER Star
Joined
Sep 9, 2013
Messages
3,788
Location
Akron, OH
Cool.. I'll look for that 2K epoxy primer. Any thoughts on these rustoleum or VHT "rust reformers"? or just snake oil nonsense? Thanks..
The rust reformers will only stick to rust, if you get some on clean metal it just wipes off and paint won’t like it. after sandblasting you can hit it with a wire wheel if you need to. Make sure not to touch the bare sheet metal with bare hands as the oils in your skin will make it rust.

Eastwood has a lot of decent videos on body work.
 
Joined
Aug 4, 2009
Messages
7,516
Location
New Hampshire
The rust reformers will only stick to rust, if you get some on clean metal it just wipes off and paint won’t like it. after sandblasting you can hit it with a wire wheel if you need to. Make sure not to touch the bare sheet metal with bare hands as the oils in your skin will make it rust.

Eastwood has a lot of decent videos on body work.

Rust converters work, but will never provide the same results as blasting to white metal. If you’re going to use a converter, do so before blasting so that the converter will treat the areas you can’t blast and the excess will be removed during blasting. Do not use a wire wheel after blasting. It will remove the surface profile created by blasting and defeats the purpose of blasting.
 

Jdc1

SILVER Star
Joined
Sep 9, 2013
Messages
3,788
Location
Akron, OH
Rust converters work, but will never provide the same results as blasting to white metal. If you’re going to use a converter, do so before blasting so that the converter will treat the areas you can’t blast and the excess will be removed during blasting. Do not use a wire wheel after blasting. It will remove the surface profile created by blasting and defeats the purpose of blasting.
Agree to disagree on this one. The process that I am learning(show car finish) is.

Heavy rust repair
Mock up
Blast
Wire Wheel
Epoxy Primer
Filler
Primers
Color/Clear

There’s usually sanding between every step.

The difficult thing about paint and body is that everyone does it there own way.
 
Joined
Aug 4, 2009
Messages
7,516
Location
New Hampshire
Agree to disagree on this one. The process that I am learning(show car finish) is.

Heavy rust repair
Mock up
Blast
Wire Wheel
Epoxy Primer
Filler
Primers
Color/Clear

There’s usually sanding between every step.

The difficult thing about paint and body is that everyone does it there own way.

Yes, but not everybody does it the right way. In fact, many people fail to read the tech sheets for the coatings they’re applying.

Epoxies (like most coatings) require a surface profile for proper adhesion. Applying coatings to a smooth wire wheeled surface WILL result in less adhesion than a properly prepared surface.

One of the primary benefits of using epoxies is their excellent adhesion to a properly prepared steel surface. By compromising the adhesion, it defeats the purpose of using that product.

If you need to create profile again after doing sheet metal work, you can blast again (not practical in most cases) or sand using the grit specified in the product tech sheets.

Also, avoid creating too much profile by using too heavy of a grit when blasting or sanding. It can lead to just as many problems as not enough profile.
 
Last edited:

Jdc1

SILVER Star
Joined
Sep 9, 2013
Messages
3,788
Location
Akron, OH
Yes, but not everybody does it the right way. In fact, many people fail to read the tech sheets for the coatings they’re applying.

Epoxies (like most coatings) require a surface profile for proper adhesion. Applying coatings to a smooth wire wheeled surface WILL result in less adhesion than a properly prepared surface.

One of the primary benefits of using epoxies is their excellent adhesion to a properly prepared steel surface. By compromising the adhesion, it defeats the purpose of using that product.

If you need to create profile again after doing sheet metal work, you can blast again (not practical in most cases) or sand using the grit specified in the product tech sheets.

Also, avoid creating too much profile by using too heavy of a grit when blasting or sanding. It can lead to just as many problems as not enough profile.
I clarified today, we do sand with 180 prior to epoxy.
 

FishNinJay

SILVER Star
Joined
Jun 8, 2009
Messages
807
Location
Orange County, CA
Epoxies (like most coatings) require a surface profile for proper adhesion. Applying coatings to a smooth wire wheeled surface WILL result in less adhesion than a properly prepared surface.

One of the primary benefits of using epoxies is their excellent adhesion to a properly prepared steel surface. By compromising the adhesion, it defeats the purpose of using that product.

Also, avoid creating too much profile by using too heavy of a grit when blasting or sanding. It can lead to just as many problems as not enough profile.
so.. a wire wheel is smoother than sanded? And by "profile" you mean the roughness, or grit? of the surface? What's the best grit sandpaper to use prior to epoxy primer?
And then, is there a proper grit to wet or dry sand the epoxy primer, before final paint layer?

Ok, thanks!
-J
 
Joined
Aug 4, 2009
Messages
7,516
Location
New Hampshire
so.. a wire wheel is smoother than sanded? And by "profile" you mean the roughness, or grit? of the surface? What's the best grit sandpaper to use prior to epoxy primer?
And then, is there a proper grit to wet or dry sand the epoxy primer, before final paint layer?

Ok, thanks!
-J

wire wheeling is WAY smoother than sanding. IN fact, it smoothes the surface. Surface profile is a technical term that refers to the roughness of the surface after blasting or sanding. It can be measured with instruments when things matter most (like million dollar bridge painting projects), and is specified by the coating manufacturer to match the particular product you're using. Download and read the tech sheets for the products you're using and you'll find the recommended grit to achieve the best profile.

You typically don't sand and paint epoxies. You typically either coat with a surfacer primer or paint within the recoat "window" (period of time) specified by the manufacturer, or sand and apply another coat of epoxy and then topcoat within the recoat window. Most epoxies only have a 3-5 day recoat window. After that they can no longer rely on chemical adhesion and need to rely on mechanical adhesion (have to be sanded). The Tech sheets will specify the correct grit paper for the next coat.

Sanding epoxies sucks. They gum up your paper and are not fun to sand. It's best to avoid it when possible.
 

Users who are viewing this thread

Top Bottom