Blocking spi epoxy

T

tylercr423

New Member
Hey guys first time post. I've been doing a ton of reading and have about got everything sorted out but I'm stumped.

I started with a bare metal truck that I sand blasted, then da'ed with 80 grit, sprayed two coats of spi epoxy, then laid body filler in troubled areas and sanded flat, today I sprayed two coats of evercoat feather fill g2 over everything. I plan on blocking it with 180-220 and then I'm a little lost. I see it as I have two options.

option 1
guide coat the poly primer, block with 180-220 then shoot a coat of 2k primer, block with 400-600 and then shoot a reduced coat of epoxy and spray my base with in a couple hrs.

option 2
guide coat the poly primer, block with 180-220 then shoot a coat of epoxy (reduced or unreduced?) let dry to the next day and wet sand with 600 and then proceed to spray base.

I'm spraying a metallic base so I'm nervous about leaving a coarse scratch and the metallic falling into the scratches.

I don't have any 2k primer right now and would really prefer to use spi 2k if that's the route I should go but I'm hoping to shoot color this week and I'm a 2 day ship time from spi so I need to order asap once I hear from you all.

Thanks in advance for the advise!
 
Sanding poly primer with 180-220 is not easy initially. It will tend to make you put more pressure than you should because it is not cutting. I start with 80-120 on the initial cut, then guide coat and finish with 180. Then either 2 coats epoxy unreduced (if it looks really nice) or 2-3 coats of Turbo if it needs a little more leveling. If epoxied, block with 320 and finish with 600. If 2K, start with 180-220, 320, then 600. The key is getting the previous grit scratch out using guide coat so when you finish with 600 there is no coarse scratches left. The reduced epoxy as a sealer will fill 400-600 scratches easily.
 
Just to update this in case any one comes across it.

First off thanks for the advise guys.

I ended up guide coating and blocking my polyester with 180. Then I shot two coats of 2k and guide coated again, wet sanded using a block and 400, then wet sanded again using 600. Washed everything and wax and grease removed using spi 710. Then shot one wet coat of epoxy reduced with a double shot glass of reducer per quart. Ended up shooting 3 coats of S-W ultra 7000 and 3 coats of Spi universal clear. Absolutely could not be happier with the results!

This was mine and my father's first bare metal complete vehicle paint job, he has painted a few motorcycles but never an entire vehicle. Everything I needed to know to properly do this job was found on these spi forums.
 

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Last edited:
Totally out of curiosity... Been reading a bunch on the forum about the epoxy (my gallon is still unopened). Can someone explain why bare metal gets an 80 grit sanding before epoxy, but then 600 grit sanding is fine before using the epoxy as a sealer?

Yes. That paint job looks GREAT!
 
FunThumbs said:
Totally out of curiosity... Been reading a bunch on the forum about the epoxy (my gallon is still unopened). Can someone explain why bare metal gets an 80 grit sanding before epoxy, but then 600 grit sanding is fine before using the epoxy as a sealer?

Yes. That paint job looks GREAT!
Click to expand...

My take...bare metal will only have mechanical adhesion, thus a deeper scratch. Plus the added viscosity..as a sealer it also has chemical adhesion to the undercoat..plus less viscosity allowing it to penetrate a smaller scratch.
 
FunThumbs said:
Totally out of curiosity... Been reading a bunch on the forum about the epoxy (my gallon is still unopened). Can someone explain why bare metal gets an 80 grit sanding before epoxy, but then 600 grit sanding is fine before using the epoxy as a sealer?

Yes. That paint job looks GREAT!
Click to expand...

I believe Rbm is correct. The bare metal is a mechanical bond and once there is product there is a chemical bond that forms. Barry would be able to better answer your question however I believe that's what it boils down to.
 
Also, 600 is a good grit to put metallic base on but I would not have sanded with 600 if I was going to seal it with epoxy afterward. I personally would have used 400.

John
 
Thanks for all the replies! *thumbsups*

Yea, it wasn't jiving in my head why the two different grits would both work for mechanical adhesion if 80 grit was needed for metal. But I was assuming if you were sanding that you were out of the chemical adhesion window and back to relying on mechanical. I'm still learning.
 
Bare in mind, metal is extremely hard. 400 grit would not hardly knock the,shine off of it but will cut into a lower level of paint. Metal is non porous and there is no grip what soever except the mechanical adhesion. Any one of us here who has done much paint work will testify that a good tooth for your first layer is absolutely imperative.

Years ago, I painted a car I had cleaned up with 3m brown conditioning pads. The epoxy (not SPI) I shot on it blistered and peeled off to bare metal leaving bright shiny metal under it. Some mistakes you only have to make once.

Do the 80 grit! ....Always! It takes no time and is the best insurance you can buy.

John
 
Thanks for helping me wrap my head around it! 80 for tooth on metal made alot of sense. It was 600 being acceptable for sealer that was confusing to me. Thanks again! *thumbsups*
 
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