Paint for the underside of a fiberglass body

[Bearwolf]

I'm getting ready to bond the body on my ERA 289 FIA car and I want to paint the underside of the fiberglass body black before I permanently bond it to the frame. I'm no paint expert but it looks like a flat or satin black Acrylic Enamel spray paint wouldn't require primer to spray it to the underside of a fiberglass body and should hold up okay from what I've been reading. For those who know a little more about fiberglass and paint than I do, does this seem like a good choice or would you recommend something else? Keep in mind, this won't be a focal point. In fact, the main reason for the black paint would be just to cover any raw fiberglass and make it blend in to the background while looking under the hood or any other angles where it would be visible.

[DanEC]

For what you are trying to achieve you don’t need primer. Just wipe it down good with Prep Sol or lacquer thinner and spray away. I lightly sprayed the bare underbody of my 66 Vette 25 years when I had the body off the frame, with semi-flattened black lacquer to blend in a fiberglass repair and for easy of cleaning and it has held up fine. Another option is spray bed liner which is what I used on the underbody areas of my ERA. Correction - I sprayed the wheel well side of my panels with undercoating and rolled/brushed bed liner protection on the body underside.

[Dwight]

I have been told by a painter that fiberglass needs to be sealed on the back side to keep water out.

Water can wicks through the fiberglass and lifts the paint.

I have seen several paint flaws in my Cobra and others that we could not explain how they happen.
So it's easy for me to believe what the painter said.

Just in case I had the back side of my GT 40 primed / sealed.

I don't know what type of sealer he used.

[DanEC]

Yes, migration of contaminants from the underside of fiberglass that lifts patient or creates pimples in the surface is a very common issue for old Corvettes and very difficult to remedy. That’s one of the reasons I used bed liner on my ERA instead of lacquer paint. I also rolled and brushed it on. Most old Corvettes have press molded, smooth on both sides panels (except for earliest years) and have a more tightly sealed underside surface than most hand laid or chopper gun fiberglass which is fairly rough and porous by comparison. So if battery acid, brake fluid, accessory oil can get through a Vette panel it potentially could do so even easier on a hand laid body. Paint alone may not seal the underside glass without applying a lot of it.

Cobra fiberglass bodies do have one advantage over old Corvette bodies which is the gel coat surface which should keep most contaminates from migrating to the surface. Old Vettes never, ever had gel coat surfaces. It was not practical for early, mass produced, match mold, steam cured fiberglass panels.

[Bearwolf]

So the way I read it that's 2 votes to just put bed liner on the underside if the body to seal it. I guess I'll start looking into that over paint unless someone has a good paint alternative that will stick and seal. Maybe I'll stop by the auto body paint store on my way home from work and see what they say now that they are open. I'll report back here with my findings. Until then I'm open to all the information that anyone else wants to post here.

[Karl Bebout]

I used rubberized undercoating figuring a good seal and padding resistance to picked up gravel. I'm happy with it. Fresh over spray cleaned up easily with paint thinner. My 2¢ worth.

[1985 CCX]

I used std aluminum Rust-Oleum no prep, lasted 10 years …..

[letsboogie351]

Black stone guard will do the trick

[CHANMADD]

I coated the whole underside with lizard skin..same color as the car...Actually mixed it all myself..Buy the ceramics and out it in the paint. Stops all the heat.andblooks great..

[Bearwolf]

Thanks for all the great recommendations. After all of the input I figured it's only fair to stop back in and update you guys on what direction I went with it. My body guy and our local auto paint store guys both ended up telling me that I'm going to want to seal the underside with an epoxy primer and then paint it with any old flat black paint that I want to. I'm told the key is to use an actual 2 part epoxy primer with an activator. Our paint supply store had some Spray Max 2k epoxy primer that came in an aerosol. This stuff had a button on the bottom of the can to break a canister on the inside of the can and allow the activator to mix with the primer. It only came in beige, so I had to run some flat black over it to make it look right. If you're looking to do the same you can probably get away with 3 cans of the primer if you spray it on just right but you should probably use 4, 5 if you want to get thicker with it. It was about $25 a can from the paint store but it's probably cheaper online. I'll probably still put a little rubberized undercoating above the tires. If I remember I'll stop back at this post 10 or 20 years from now to let everyone know how it holds up.

[Dwight]

Thanks for the update