Gravel guard/noise control

[haris]

Was the 1970 911 was applied gravel guard/noise control over bare metal and then spray painted over it with exterior color? This applies to wheel wells, underbody, engine compartment and trunk.

Should I take the factory coating completely off and start over again? Once I sand blasted, the color has come out exposing a grey rubbery material which could only be stripped off with heat and scrape. Very labor intensive and time consuming besides the fumes! Confused, and need direction here please.

[962porsche]

if there is nothing wrong with the stone guard and your not having any rust problems under it there should be no reason to remove it.
it's not uncommon to need to remove it in some areas to do rust repairs. in a case like that you remove the stone guard to clean metal then feather edge it out repair the rust then blend new stone guard back in over the repair area.

[haris]

Was the engine compartment sprayed with gravel guard at Karmann and painted finish color over it ?I think that it is prudent to clean the gravel guard at panel junctions to inspect as i found concealed rust under the gravel guard. Is it OK to epoxy primer and apply gravel guard over it?

[962porsche]

it's very common to find rust where the panels meet.
yes once you do your rust removal repair work epoxy primer over the bare metal then spray your stone/chip guard.
the chip guard sticks best when there is no bare metal under it.

[haris]

What did the factory use? Wurth?

[962porsche]

worth doesn't make there own products!
by license they relabel other brands to sell as there own.
your cars stone/chip guard was 3M solvent based rocker schutz discontinued many years ago now.
now stone guards are water based not solvent based.
worths was and maybe still is U-pol gravitex plus.

3M when they discontinued the beige solvent based stone guard didn't replace it right away with a water based beige so restoration shop like mine were at a lose needing the proper color for any cars.
Us like many other shops started using the U-pol as it could be tinted with enamel paint to match the beige in our case also the gray of the fuel tanks.
after a number of years 3M did come back out with an other water based beige we tried it on a bunch of cars and the match was terrible.
we quickly just went and stayed with the white colored U-pol and having figured out what color/s we needed to tint it to match the OE beige just kept using it with very good results. this just made sense for us as we were always using the u-pol tint to restore the fuel tanks. so we found no need to have 3m and u-pol in stock.

if you do not have the ability to tint the stone guard you could just use the 3M. the color most likely will not be the same beige as on the car but only a discerning eye would be able to tell.
personally for us this wasn't good enough of a match.

[haris]

Thank you for your kind advise and information. Now I have stripped this to the 'bone', I am witnessing 'crap' welding by Karmann in the drivers and pass wheel well areas and on the door hinge post supports. There is some kind of black mastic coating on the fire wall besides the asphalt sheets which I removed. I presume I could use the Wurth products here? I am doing this for the first time. An eye opening experience. I will use the PPG DX579 & 520 before I prime with 2K epoxy? Am I on the right path?

[Dpmulvan]

That black mastic is called seam sealer, replace it with seam sealer if you removed it. The ppg metal cleaner and phosphate is ok to use but pricey for what it is. I use it whenever I can’t sandblast pitted areas but it’s not needed on clean bare metal. 2k epoxy primer is fine spray a couple coats let it flash then spray gravitex over top. Check tds sheet for your epoxy flash times. Chemical bond easier than having to rough up epoxy for mechanical bond.

[haris]

Thank you for your expert advise. I have to change course as I cannot get the PPG DX products in Edmonton readily. My paint store gave me POR15. I have to use their rust inhibitor paint with it. I am told that once I have done that, I do not need 2K epoxy. I am advised to use 2K urethane as I will be starting my sheet metal work after the body is sealed. That will be my Winter project. Please tell me whether I am on the right path. Much appreciated. Axalta paint tech advisor does not seem to know what he is talking about. PPG was better. She informs me that the PPG DX cleaner and prep is not meant to be for sandblasted cars. I am really lost here!

[962porsche]

if your metal is clean you do not need a metal wash product.
if it's sandblasted your going to want to sand the sandblasted areas with a 80 or 180 check your TDS to see what they say the best sanding grit is for the product.
personally I'm not a fan of the por product line. it's over priced and only and ok product that takes for ever to get to full cure before you can put anything thing over it. a product that's pretty much equal to what's on the floor pans is SEM rust shield with the rust shield hardener mixed 8 to 1 part hardener. spray two coats 24 hours later you can apply the chip/stone guard over it.
por you apply it and hope that in two weeks it's cured enough to apply stone guard over it.
if it's not 100% cured it will off gas and the stone guard will lift off it.
with the por or sem you would not need epoxy under or over it. with the sem you can just go over it with the stone guard with Por you will need to buy there tie coat to apply another product over it. just more money and time for a product that doesn't give any better rust protection.
with sem all you need to do is scuff it to give it some tooth for the stone guard to bite into. you can use a red scuff pad or 180 to 220 sand paper. personally I use a red pad on a 6" and 3" DA sander then a red pad by hand to get into all the nooks and crannies.
Por is popular because of there marketing so people know the name. SEM markets to only the body and restoration shops so the general public doesn't know much about SEM.

[haris]

Oops! too late now. I sprayed a coat of POR15 Rust inhibitor8hrs ago. It is dry to touch now. The car is outside to bake in the sun. In any case I will be doing the body work over the next 6 months. I just wanted to protect the sand blasted metal. I had to use the wire wheel brush all over to get off the flash rust after the wet blasting. From this point on it will be BASF paints and primers. When I figure out how to, I will post some images. It is strange that POR uses Varsol as their solvent. I could not clean the gun with gun-wash. Once it is hardened I will check what solvent will take it off on a test patch. I would like paints which would flash with the previous coat instead of depending on mechanical interlocking. My preference would be a 2K urethane. I am not a fan of water based colors. Clear coats give a nice depth, but I like to do it the old way.

Thanks a million for your advise. I have printed all these in case I lose it.

[Dpmulvan]

I use a product called hold tight 102 it keeps wet blasting and bare metal from rusting.