Epoxy on steel? Or primer first?

[rebar]

Hello new here. I would like to use epoxy filler to repair a non structural steel wall above water because I cant weld it.

Should I apply epoxy directly to the rough clean mild steel? Or should I prime if first with epoxy primer or a rust converting paint like por15 or rust bullet before applying epoxy?

Thanks

 

[gm280]

:welcome: aboard rebar. Always glad to have a new member...

Not knowing or seeing what you are dealing with, my simple opinion, is make absolutely sure the metal is clean, oil and rust free and then use the epoxy first. JB Weld is an extremely good epoxy for things like that. And my uneducted opinon would be that the epoxy would adhere to the bare cleaned metal better then adhering to the primer. But after using the epoxy and allowing it to thoroughly cure, then prime over it along with the rest of the metal. Should be good to go. JMHO

 

[harleyman1975]

GM 280, What about priming with DP 40? They used to say to DP40 before applying any type of filler. He could brush it on if not wanting to spray.

 

[rebar]

:welcome: aboard rebar. Always glad to have a new member...

Not knowing or seeing what you are dealing with, my simple opinion, is make absolutely sure the metal is clean, oil and rust free and then use the epoxy first. JB Weld is an extremely good epoxy for things like that. And my uneducated opinion would be that the epoxy would adhere to the bare cleaned metal better then adhering to the primer. But after using the epoxy and allowing it to thoroughly cure, then prime over it along with the rest of the metal. Should be good to go. JMHO

Thanks GM280.
Essentially, I'm doing some body work but don't want to use polyester resin aka bondo glass. It's a flat steel exterior wall with a good size dent which by the time I feather it out, will be around 24" across. But what I forgot to mention was its rust pitted, so I'm leaning towards Rust Bullet paint and then the epoxy filler. But its hard to decide.

GM 280, What about priming with DP 40? They used to say to DP40 before applying any type of filler. He could brush it on if not wanting to spray.

That's great primer .

Another thing I'm wondering about is the filler ratios I should use. Iv used [FONT=&quot]cabosil, micro balloons and milled fiberglass, but don't have it down to a science.. Are there any guide lines regarding these fillers or does everybody just wing it? Iv read no more than 1/3 as much cabosil as filler, whether it is milled fiberglass or microballoons.
Because Iv never mixed a batch intended to defy gravity on a wall which will need to be sanded flat and skimmed a few times.[/FONT]

 

[gm280]

rebar, I have done a lot of body work on project cars and such. And the very first thing you need to do is clean the metal to bare metal. And then use the body filler next, followed by high build sandable primer coats. If you do it the other way around, the body filler will only attach to the primer. And the only thing that will keep it from coming out later on down the road will be how well the primer adhered to the bare metal.

For actual auto body work I used Every Coat products. And it will tell you to make sure the metal is clean and rust free to start with. However, it this is a boat, then I would mix up Polyester 435 Resin, Cabosil, MEKP, Glass Bubbles (not Micro-Balloons), Surfacing Wax and Acetone. The percentages vary per weather and temperatures.

Here's the recipe for making Fairing Material. This isn't my recipe but Woodonglass's mixture. However it works very nicely and sands easy as well. And I will give it two thumbs up! You can scale this up or down and even deviate from the amounts however you please. The mixture isn't really too critical. .

250ml Polyester Resin,
60ml Cabosil,
250ml 3M Glass Bubbles,
2.5ml MEKP (Methyl Ethyl Ketone Peroxide)
15ml Acetone
3ml of Surfacing Wax.

Apply this like you would typical auto body filler using the same type spreader. Cures in about a half to one hour and is ready to sand at that time. Hope this helps. JMHO

 

[Woodonglass]

I'd strongly advice AGAINST using any coating on the metal prior to filling and fairing. If you do then the filler and fairing are adhered to the coating and NOT the metal. Do as GM280 has advised and you'll have a successful repair. If it's rusted steel then clean it well then wipe it down with acetone and I'd use thickened
epoxy to fill and then use epoxy fairing using the recipe GM280 listed above. Don't use Polyester resin it won't stick to the epoxy. Same recipe but use epoxy. Also NO surfacing wax is needed

 

[Scott Danforth]

Years ago, i would have said POR15 putty and POR15 paint. However the product is no longer what it once was.....

I recommend a portable welder, repair/replace as required with metal

 

[rebar]

Years ago, i would have said POR15 putty and POR15 paint. However the product is no longer what it once was.....

I recommend a portable welder, repair/replace as required with metal

I was against using anything under the epoxy, but have been told epoxy primers like SPI's epoxy primer adheres to steel just as well as epoxy.

West systems epoxy published a pull off strength test of around 7000 psi. And I looked up a paint I have and they published 1100 psi, but it's a single stage paint.

I cant seem to find any numbers published for well known epoxy primers and when I asked one of the best was told "of course they did pull off strength testing but go ask PPG... Like I was asking for their proprietary secret formula.

Is a pull off strength test a common test for paint companies to perform and publish?

 

[gm280]

rebar, most body shops that I know about usually grind down any body issue to the bare metal first. Then pull dents to as close to level as they can get. Then use fillers to build up to a flat level surface before any priming is done. And I have done that myself and it works perfectly. However, this is your project and you can do it however you like. I personally can't verify one way over the other because I never done it any other way. JMHO