Lightweight SWB: Undercoating or no undercoat?

[911hunt]

I am falling deep down the slippery slope of a lightweight SWB project and currently the chassis is off being cleaned and dipped in Oregon. I am doing EB Motorsports fiberglass front fenders, bumper, hood, rear bumper, and deck lid. I will also do lightweight perlon carpet. My question is whether or not to do undercoating or simply paint the bottom of the chassis body color. This car will be 99% street with spirited driving. I know shaving ounces off a car using and it for street driving is like taking crazy pills but I have already started and there is no going back. Is the car going to sound like a tin can inside without undercoating or is it going to sound like that even with undercoating? I would greatly appreciate any opinions or feedback!

[Bill Douglas]

It sounds a fun project.

Underseal, I guess that's what's meant by undercoating, is low density stuff so wouldn't add too much weight. You could put on just a thin layer to keep weight down. Also it stops stones etc bouncing up and chipping the paint off, and letting rust gt in.

If you really do mean undercoat, you've got to have undercoat to get the top coat to stick to the primer.

[safe]

Undercoating, not so much for the sound (but you will need ear protection no doubt) but for the rock chipping.
Defiantly in the fenders, small stones will make sharp little dents in metal fenders and easily crack the gel coat on fibreglass fenders.

A small weight penalty for keeping the car looking fresh and making the driving more enjoyably.

[K24madness]

Look for the textured material used on rocker panels. It’s designed to be painted but will also protect against rock chips and subsequent rust under the car. Not sure on weight but given the consequences and location (very low) I would not be worried about weight.

I don’t know what to suggest on the fenders. I didn’t put anything under mine and it looks like crap in no time from flinging rocks on track. I heard artificial turf is the most effective but damn that mist look like hell. I may opt for bed liner on that.

[1QuickS]

I stripped my 67S to bare metal and never regretted it.

[Matthew Barnes]

Went down the same road a few years ago....and the car is still not finished! I live in a dry climate but would be very wary of not giving the underside a proper protective coat that can handle stones and road debris and dirt.

The modern water or xylene-based undercoat / stone guard coatings are much lighter than the factory bitumen they layered on. I pity the poor bugger that has to remove the crap...break out the dry-ice, chisel, face-off disk, aircraft carrier, small portable nuclear device.

My process was bare-metal then 2k primer. Then the xylene-based stone guard. I used the stuff that comes in a tall tin and is sprayed on with a special screw-in fitting (not an expensive fitting). Once it dries, I sprayed topcoat in the 24 hour period stipulated. Otherwise, if you leave it longer then you have to key it with a light sand. You need to mask the car properly - more so than when spraying paint - as this stuff goes everywhere. Literally. A body suit also helps to keep the stuff our of your hair and eyebrows and beard and and.....