Beginner Questions on SPI Epoxy

F

Ferrino

I have some questions regarding SPI epoxy, if anyone can please help:

1. When applying polyester filler over SPI epoxy, is there any difference in adhesion of the filler if you apply it within the window, versus after the window and scuffing?
2. When you apply filler over SPI epoxy, should you then spot-prime over the areas of filler with epoxy or can you go straight to a 2K primer?
3. What would be the best way of covering up weld seams on the outside of the car (for example, where flares have been welded to quarters)? Would you shoot SPI epoxy directly on to the weld seam (after grinding/blasting/cleaning, of course) and then apply some short-strand fiberglass or polyester filler and then re-prime?

Thanks!
 
I've been told adhesion is always better within the 7 day window, but even scuffing beyond then it will still stick really well.

Best practice would be to prime epoxy over filler. If you've put filler on a panel, chances are you've sanded to bare metal somewhere anyways so I just reprime the entire panel with epoxy, and then come back 30 minutes later and shoot another coat just over the filler areas. Then 2k the next day.

Yes, epoxy over weld seam for sure. Then filler, then epoxy. The filler will stick to bare metal fine. But to me, best practice is epoxy first.
 
Two coats of epoxy over bare metal before anything else is a rule I follow, I think the optimum time to put filler over 2 coats of epoxy is after an overnight cure IMO but I also apply it without scuffing the epoxy for a few days with good results, after the epoxy is 3 days old I scuff it up with 180 just to be on the safe side. There's no real need to epoxy the filler before your surfacer primer is applied, you can but no major advantages IMO, if there's bare metal showing it needs to be coated with epoxy IMO.
 
Bob Hollinshead;n71716 said:
Two coats of epoxy over bare metal before anything else is a rule I follow, I think the optimum time to put filler over 2 coats of epoxy is after an overnight cure IMO but I also apply it without scuffing the epoxy for a few days with good results, after the epoxy is 3 days old I scuff it up with 180 just to be on the safe side. There's no real need to epoxy the filler before your surfacer primer is applied, you can but no major advantages IMO, if there's bare metal showing it needs to be coated with epoxy IMO.
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I always epoxy over my filler. I think it helps a lot against shrinkage, and I love to use it as a reverse guide coat, I epoxy in black, and 2k in grey. By doing this, I know when to stop sanding. When I hit black in spots all over the panel I know that I have used the 2k primer to it's maximum benefit while also keeping the mil built to a minimum. I then seal in epoxy, then go to base coat.

Here is a picture for reference.
 
Thanks all - great information. Which SPI 2K product are you using there, Chad?
 
I had a question along the same line. We sprayed my bug 2 months ago, then had some COOOOLD weather. I brought the car home and covered it up.
Now I am ready for filler. I bought some scotchbrite red to scuff up the fender I am about to work on with my friend. So, do I use the red scotchbrite or 180 to scuff it up?
He applied the SPI epoxy pretty thick. I bought the black, then was going to use filler (Evercoat Rage Ultra) then the SPI grey high build primer as a final coat. I was thinking if I did the black/grey then I would know if I sanded too far down if I hit the black. Am I on the right track?
 
I would scuff with 180 after a couple months of cure. Or shoot some fresh epoxy. Using different colors is a great technique. I also do this with filler, using different color hardeners
 
This might seem like a stupid question, but here goes.. Can you describe the scuffing technique? Do you scuff by hand or with a block?

thanks
 
TrevO;n74711 said:
This might seem like a stupid question, but here goes.. Can you describe the scuffing technique? Do you scuff by hand or with a block?

thanks
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Usually by hand, soft pad, or scotchbrite, although a large area could be sanded a little bit with a DA and still be part of a "scuffing" process. Basically scuffing means that a lot of material is not being removed, only enough to put a uniform scratch pattern on the surface for greater adhesion.
 
Ferrino;n71722 said:
Thanks all - great information. Which SPI 2K product are you using there, Chad?
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I always use Barry's favorite Turbo and do the same as Chad black or red epoxy followed by gray Turbo
 
Here's a handy chart that shows the Scotchbrite Pad Colors and the corresponding sandpaper grit. What we call "red" is technically Maroon. Sometimes we see references to Gray but they are usually referring to the 7448 Light Gray.
ScotchBrite%20Chart.jpg
 
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