undercoat

Folks,

I remember that comment has been made on the use of spray truck bed liner material as an undercoat.

What are the best brands for this use? Any cautions?

thanks,

Mike, a friend of mine restores early Corvettes professionally & after years of trying all sorts of approaches for painting f/glass cars has settled on the following for finishing over raw f/glass or gelcoat :

- block back the whole car with 80 grit.

- paint with a fairly thick coat of sprayable polyester resin - he uses "Radirol" brand (this might be a local brand).

- leave it for about a month (absolutely critical, he tells me).

- block back with 120 grit, then again with 320 grit, then again with 600 grit (if you are a fanatic !).

- paint with 2-pack primer

- paint with 2-pack base coat

- paint with 2-pack clear coat

He has now settled on Spies Hecker brand paint(not sure about the spelling here) - it is the one that has given him no trouble at all.

Mike, let me know if you would like further details on resin/paint brand/types.

Kind Regards,

Peter D.

Peter,

Very valuable and appreciated information ... when i get that far. Would appreciate further info on the resins.

Was actually looking for information on undercoat for the chassis.

Wouldn't hurt from the corrosion and sound deadening points of view.

Mike, the chassis is another story ! If you are not obsessed about having a show-car finish, one of the best approaches is to use POR-15 as the base coat, then POR's "Blackcoat" to finish. The POR-15 is just about the best rust-proofing you can use, & when overcoated with Blackcoat, provides a surface that you can lay into with a hammer & have nothing to show for it but some dents. The only drawback is that it does have some "inclusions" in it - tiny little lumps that show up as dots on the surface. I have done the chassis & underbody of the '40 in this & am very pleased with the results - I intend to drive it on a regular basis, so am more concerned with rust-proofing & chip resistance than a mirror show-finish.

I have a '71 Vette under reconstruction, & before I found out about the POR products, made the decision to go 2-pack on the chassis. After linishing it all back, we prepped it with X-Trol (similar to Penetrol - a clear, paintable rust preventative), then 2-pack primer, the 2-pack gloss black. It looks stunning & resists just about every chemical (even acetone-soaked rags !). I am told that it is quite resistant to stone chips, but we'll see when it finally gets back on the road !

Cheers,

Peter D.

DARN! Let's try this again.

Peter,

The plan was to use POR-15 on the chassis with the top coat. Then use something like the bed liner on the bottom, and dynamat extreme on the inside of the driver's compartment. Hoping to provide very good rust proofing and sound deadening.

The POR-15 is in progress.

Thanks,

How are you guys applying the POR-15? I know it comes in cans, have one, is this a good method for the underside of the car?

Ron

Ron,

I am using a HVLP gun. Tried a bristle brush, a foam brush, and (for small areas) an air brush.

Most important ... read the directions, read the directions, read the directions. and did I forget ... read the directions. Stir, don't shake!

I prepped the steel either with sand blast or by sanding and wire brushing.

Pretty amazing stuff.

Laquer thinner works to clean up the guns. Don't put extra back into the original can. Use the extra within 24 hours.

Thanks,

Brian, I tried to have all the holes drilled before painting, but Murphy's Law always strikes - hence a number of extra holes later. I found that drilling these was fine - no chipping or peeling of the POR. After cleaning up the holes, I just brushed a little POR in & around the holes with an artist's brush. The nut/bolt,etc hides any sign of manual painting.

Mike, if you are going to overcoat the POR-15, I don't think you need the BlackCoat - it just provides the UV protection for the POR-15 (which doesn't have any). However, I think you need to use TieCoat over the POR-15 to get a good bond with other paints.

Kind Regards,

Peter D.

Peter, What happens to POR-15 if you have to drill a hole in to mount something? Does it chip? can it be repaired? or is it best to drill and assemble the whole car, then breakdown for finishing? I have used POR-15, but only on small items and am impressed with it's durability. Would like to consider using it on the whole frame rather than a powder coat shop as I have had powder coatings (factory ones)fail in the past.. Brian

Joining the discussion a bit later, but I think the initial question still remains. The POR-15 appears to be a moisture-cured urethane. These tend to be very good products for adhesion over marginally prepared steel and also as tie coats. I am using a product of my companies manufacture prior to attaching aluminum chassis panels to protect the chassis as best possible.

However, I too am interested in what people are using as undercoaters on the street side of the floor pan as well as a coating for the interior of the wheel wells. I know POR says their product is resistant to rock chips, but that only goes so far. Applying additional coats of finish coat(s) od moisture-cured urethanes will help, but these are inherently 'brittle' coatings that will not be able to withstand point-load impact from rocks and so forth. Anybody using a rubberized coating, an elastomeric polyurethane or polyurea like Rhino or similar? Can these be applied at home or do I need to transport the chassis?

Best,

Pat Barry

I have seen a few fiberglass Cobras and GT40's that had taken a rock hit from inside the finderwell causing a crack viewable from the top. Not good. I was wondering about ruberized coatings or bed liners for the finderwells to eliminate this possiblilty. Has anyone tackled this issue?

I used a gallon of duraliner on my cobra project. I put 4 coats on the underside of the wheel wells. Never had an issue with star cracks or dimples and not for lack of trying ! It can be found at any autoparts store. Rhinoliner is a dealers sprayed finish that also works well.

My 'Vette expert (20 years in the game, made all the mistakes !) now recommends using a product called "Stone-Guard" over the primer, then 2-pack polyurethane (with a plasticiser added) over that. This gives a slight "orange-peel effect" like you often see in exposed areas under the sills of many modern cars.

I have already done the steel parts of the 40's underbody with POR, but I think I'll go with the Stone-Guard / 2-pack under the fender areas.

Dupont's website has heaps of tech info on "paint systems" (what goes over what, with what prep) & their tech helpdesk is really good at providing any extra guidance.

Peter D.

Mike, in my research on this subject I talked with several people who are into competition automotive sound installations. The brand that they view as the best as do others who use it as a bed liner is Line-X. It is not something you can get and spray yourself, to my knowledge; you must go to a dealer and have them do it, but it is supposed to be the absolute best. If you get one of the self applied liners (the guns to do it are getting cheaper) the urethane based ones seem to be the best.