Compounding painted plastics, fiber glass, and carbon fiber

RAG · 01-27-07, 07:27

Kind of an experts topic here...so bare with me.

I was wondering if anyone has every had any problems polishing plastic, fiberglass, or carbon fiber painted surfaces with respect to over heating and causing the paint to shrivel (of course this applies to rotary usage)? This issue was pointed out in Brazo's recent "A guide to rotary polishing" thread.

Personally, I have only seen issues with heavy scratch removal on bumpers - one time was on my own bumper and another was on a bumber that had been in an accident and I was trying to make look better...and both times I was using a lambwool pad aggressively (lots of pressure)...and both times I was polishing a ridge/corner of the bumper were the pressure per square inch in obviously amplified many times.

But when it comes to polishing and heavy compounding vehicles with predominently fiberglass or plastic panels (like Corvettes, Camaros, Phaetons, etc.) I don't even change my techniques. In Brazo's write up, he suggests making only one pass then letting it cool, but I have performed countless 3- and 4-step buffing process on the aforementioned vehicles (using high speed and heavy pressure with both wool and foam pads...typically 4 passes each step) and have never had a problem; question is...am I possibly pushing the envelope too much and thus "setting myself up for a potential disaster someday"? Or is Brazo's advice to make only one pass and then let cool a little on the "conservative side"?

Brazo · 01-27-07, 08:11

My advice is always conservative - after all it reaches a wide audience

I feel it also varies with paint types and yes will probably only become a problem when compouding hard, however that is the risk the user takes. In have seen paint wrinkle up trying to remove deep swirls rather than scratches an dthat was with a soft foam polishing pad.

My tecnique while slower will still give the same results but as I said its only one tecnique and you have to find what works best for you

wannafbody · 01-27-07, 08:59

proper auto care has pads designed to run cooler for painted fiberglass. I'm not sure if they really make much of a difference tho. My TA has plastic fenders and a fiberglass hood and I haven't had any issues with standard LC, Edge and Megs pads.

Setec Astronomy · 01-27-07, 09:06

Different materials have different thermal conductivity. I'm sure it's possible that the urethane bumper covers you had a problem with have different thermal conductivity than say, RIM fenders or 'glas hood.

RAG · 01-27-07, 10:19

Quote:

Originally Posted by wannafbody

proper auto care has pads designed to run cooler for painted fiberglass. I'm not sure if they really make much of a difference tho. My TA has plastic fenders and a fiberglass hood and I haven't had any issues with standard LC, Edge and Megs pads.

The green foam (particularly the Green P2s/American Buffing pads) are the best I've tried for this and generate almost no heat...but then again you're gonna have a heck of a time getting out heavy defects with these soft pads too.

RAG · 01-27-07, 10:20

Quote:

Originally Posted by Setec Astronomy

Different materials have different thermal conductivity. I'm sure it's possible that the urethane bumper covers you had a problem with have different thermal conductivity than say, RIM fenders or 'glas hood.

Agreed. And the flex additives in the paint on bumpers don't help either...in fact, I think they make paint much less "correctable."

RAG · 01-27-07, 10:22

Quote:

Originally Posted by Brazo

My advice is always conservative - after all it reaches a wide audience

I feel it also varies with paint types and yes will probably only become a problem when compouding hard, however that is the risk the user takes. In have seen paint wrinkle up trying to remove deep swirls rather than scratches an dthat was with a soft foam polishing pad.

My tecnique while slower will still give the same results but as I said its only one tecnique and you have to find what works best for you

In light of the fact that you've had a problem with panels other than bumpers, I'm going to make it a point to generate less heat when working on non metal surfaces - open celled pads, larger buffing area, and quicker passes ought to increase the safety significantly.

Picus · 01-27-07, 10:35

Bumper can be tricky but fiberglass/cf have never given me a problem; I treat them normally.

RAG · 01-27-07, 06:49

Quote:

Originally Posted by Picus

Bumper can be tricky but fiberglass/cf have never given me a problem; I treat them normally.

Yeah, I never really even thought about treating it different before and I haven't had any problems...and I've really thrown down on some tore up Vettes. I think as long as one doesn't really work a small isolated scratch real real hard, it'll all be fine.

HenrikP · 01-27-07, 07:28

From my experience paint on plastic burns through a lot faster than on sheet metal.

rydawg · 01-30-07, 09:43

on plastic zaino zpc is one of the best polishes that I have used. Secret: spray some detail spray on the plastic or rubber bumpers and this will break down your polishes better and disipate the heat.

AMDin93103 · 01-30-07, 03:46

I had a little experience with the rear bumper of an E46

White Propel, HTEC with a fifth of OP around 1300. The very last panel I was doing on the entire car. The beveled edge of the pad didn't have the polish build up of the rest, I brushed a high point and the paint literally separated from the primed plastic and pushed about an inch and a half. I was a little pissed to say the least.

I have had no issues with Carbon Fiber.

I found the nose on a Plymouth Prowler to butter soft. Irritatingly so. It was a pigmented "plastic" material that was (almost) the same as the rest of the vehicle. If someone could help me identify this material, I'd appreciate it.

Quote:

Originally Posted by Setec Astronomy

Different materials have different thermal conductivity. I'm sure it's possible that the urethane bumper covers you had a problem with have different thermal conductivity than say, RIM fenders or 'glas hood.

Qué es RIM Fender?

Regardless, I have no doubt that you are correct. There have to be a ton of variables during manufacturing of one material-type that would influence heat conductivity. Also, as Brazo stated, you have to take into consideration the variances in paint on these panels.

Quote:

Originally Posted by RAG

..generate less heat when working on non metal surfaces - open celled pads, larger buffing area, and quicker passes ought to increase the safety significantly.

I have found that lowering my RPMs, swapping out my pad for one less aggressive while easing up on the pressure are fairly effective in removing said defects. even stick with the same polish if it's working with the rest of the car. It definitely takes longer but the cost of repairing the E46s bumper was hard to stomach.