Block sanding epoxy.

[DoubleNickel]

I'm blocking my car using SPI epoxy and have no plains on using any primer, the epoxy works great and I don't need any guide coat to find low spots which is kewl. I was told the best technique is to apply 2 coats epoxy (I applied three heavy coats), block sand with 120, fill low spots apply another coat of epoxy, block with 180, fill low spots if any remain, block with 220 and then finally last block sand with 320. This sound about right? Thanks!

[Rick_L]

I know that some guys love the SPI epoxy and don't use primer surfacer. I've never used the stuff but I really can't see how it can build as well or sand as well as primer surfacer. Especially the build.

The other thing you might think about if you have a lot of bodywork/low spots is Slick Sand or one of the other sprayable polyesters like Featherfill or Rust Defender. They will build a low spot faster - they are essentially sprayable filler.

[DoubleNickel]

Rick_L, thanks for the reply. How about my procedure and sand paper grit, am I doing that right?

[BAM55]

Personally I would not spray a basecoat on 320 . I would finish blocking with at least 400 grit, and if I'm shooting a light metallic color I block to 600. I also use SPI epoxy primer and it is great stuff, but I do use a primer surfacer for more build. I only use the epoxy primer to protect the bare metal.

[Geoff]

You are getting some great advice. You definitely want to build with a primer/surfacer and then block, block, block. The materials available these days are awesome and the results will amaze you.
If you are doing it yourself and want it super atraight, it will be a lot of work. If you are paying someone, it will be a LOT more money than you think because there are no real shortcuts. Laser straight costs big bucks or time.


As a kid i worked in a body shop and painted my '68 Camaro twice within 18 mos. The first time it looked good but I didn't know how to block it correctly. The second time I painted it I blocked it to death and it was as straight as an arrow. Same car, two totally different results....

[DoubleNickel]

Geoff, what did you do different the second time to make it straighter? Any techniques or tricks you care to share.

[DoubleNickel]

I decided to use 2k primer over the epoxy because it takes too long to dry and does not build very thick. My question is, after applying primer and while block sanding and I sand down to bare metal ( this has happened a few timers mostly on the edges) do I apply more primer or will it need epoxy on the exposed metal for corrosion protection?

[Rick_L]

It's ok to use primer surfacer on bare metal, but epoxy is the best barrier/sealer. I usually spot primer any bare areas with epoxy and then primer surfacer over that, over the whole panel again, or at least over a larger area.

You have to make that call.

[BAM55]

I always apply epoxy over the bare spots and then spray the whole panel with 2k again as was said above.

[DoubleNickel]

Epoxy over bare spots and beyond, got it. Thanks for the help! I just finished watching Overhauling, they do not use epoxy at all, primer over bare metal. I hope my wife never surprises me and lets them do my car. lol

[BAM55]

Some people still use etching primer over bare metal. It has worked for years and I don't really have a issue with those who still prefer it. I just believe that epoxy has better corrosion protection. The epoxy vs etching primer debate has been going on for years.

[chevynut]

I stay away rom etching primers. A lot of fillers and other primers are incompatible with it. You can't put fillers over or under most etching primers, so what good are they?

[Rick_L]

You can't put fillers over or under most etching primers, so what good are they?

They are good for priming your trailer or engine hoist or whatever. The stuff works great on steel tubing or structural shapes.

[BAM55]

I stay away rom etching primers. A lot of fillers and other primers are incompatible with it. You can't put fillers over or under most etching primers, so what good are they?
Chevynut I will first say that I agree with you that I like epoxy primer better. I think it is great for the home builder who may take awhile to get to a panel. I like its corrosion protection, I like the fact that I can use filler over or under it. I'm a fan of epoxy.

I was only stating the etching primer to explain that they may have been using it on the overhauling show that the original poster was talking about.

As a person who has used etching primer in past. I used etching primer over filler and never had an issue. I was taught to always use it over filler. Actually epoxy is the only primer that I was taught could be used either over or under filler. I still know old school body men who would never put filler over epoxy and get mad at me because I do.lol Never had an issue with that either. That is another debate filler over or under.

I find that if you ask 10 people a question you will have as many answer when it comes to this stuff. I think people should follow their comfort level. So filler over or under epoxy, etching primer vs epoxy primer I've done all of those and never had an issue. Oh I've have had paint issues but it was for other reasons.

[Rick_L]

Not all etch primers will cause a problem over filler. I agree with you that epoxy is the only primer to use under filler, and even then the filler needs to be applied within the recommended time window.

The best advice is to read the p sheets for the materials you might want to use, and pay attention to the apply over recommendations. Or stick with what you know works.

And when there is a failure, there's almost always a logical reason. Professional materials applied as directed rarely fail.

[BAM55]

Not all etch primers will cause a problem over filler. I agree with you that epoxy is the only primer to use under filler, and even then the filler needs to be applied within the recommended time window.

The best advice is to read the p sheets for the materials you might want to use, and pay attention to the apply over recommendations. Or stick with what you know works.

And when there is a failure, there's almost always a logical reason. Professional materials applied as directed rarely fail.

Nothing really to say other than I agree with everything you stated 100%