What color is the underside of the car supposed to be? I知 painting a W-45. Not sure what it was from factory. I was gonna go with black. I知 not planning on undercoating it.

 

This is SEM Trim Black shot last week. Looks great

 

Looks good. What did you use for a primer? I

 

SPI epoxy, I use nothing but

 

That is my plan with my undercarriage as well, but I was considering a urethane paint. I am a novice, but curious as to why you picked SEM trim over a urethane or chassis black?

 

I have some DAR black ready to go but the flattener is $125 a QUART now and my hardener was out of sight too. I heard good things about the SEM and gave it a try. Very pleased

 

epoxy needs to be top coated. It has poor resistance to uv and abrasion. Not good for anything that痴 going to be exposed. I would use body color on the underside of the body and a 2k urethane satin black for the chassis.

 

Why would anyone paint the underside body color?? That's just wrong on many levels...I have several cars with bare SPI black epoxy bottoms and firewalls and all look and perform fantastic. These of course are non UV exposed areas and on cars that are 100% garaged (driven a couple times a year). It is tricky to get the right sheen, it is altered by spray temp, humidity, reducer ratio, number of coats, flash time between coats.... so on this GTO I figured I would step out of my box and try the SEM topcoat over the SPI epoxy. Laid down great and looks super. There are many ways to do this right

 

Basically everyone who paints true show cars does it that way. The only reason GM didn't paint the underside is because they were cheap and always trying to save money. Most of these cars left the factory with primer and overspray underneath. If all you care about is replicating originality, then by all means you should do it that way.

Even the bottom of a car is exposed to uv. It may be much less than the top and therefore the degradation may take a lot longer. However epoxies by nature are very intolerant of uv and should never be used in applications where they are exposed to elements. If you don’t drive it and keep it in the garage, I’m sure anything will hold up fine. The fact that you did it and it hasn’t failed in your circumstances doesn’t make it right. Especially for someone who may use it in different circumstances.

I agree there are many ways to do it right, but exposed epoxy isn’t one of them.

 

I do see that spi adds uv inhibitors to their epoxy. I would assume this is why you haven’t experienced a failure. I’m sure they do this because epoxies are so notoriously prone to uv degradation. Even in a garage uv exposure will kill epoxy, so diy’ers who might have a project, or parts of a project in epoxy for years can use spi with peace of mind. There’s still never a scenario where you will convince me, a professional painter of nearly 3 decades, that any primer is a better topcoat than something like a urethane that is intended to be a topcoat.

I'm not trying to be argumentative. I just can't in good conscience condone a novice seeking advice to be encouraged to leave exposed primer as a finished topcoat on any part of a car. The only exception would be cases of accurate restoration where the factory did it this way. But like I said, they didn't do it because it was ok, they did it to save money at at the expense of the consumer.

 

I have used SEM black trim paint several times and it looks better than anything else I have used.