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Posted by: ptravnic May 28 2003, 08:42 PM

My pops is sold on $6 per gallon roofing tar for undercoating. Its worked on his cars for years - held up on my teener pretty well. Well, some structural work was just done in the typical areas & I'm proably gonna put some of the stuff on there.

I've heard the POR-15 ravings - is it really that much better. That stuff is expensive.

Pete

Posted by: Gint May 28 2003, 09:15 PM

Huh? They're two entirely different things. I suppose if even my roof was rusty I would probably use POR-15 on it first before applying the roofing tar.

Posted by: seanery May 28 2003, 09:22 PM

"Roofing Tar"

Run, Run, Run....That stuff will collect all the road debris you pass!

Do the right thing! POR-15

Posted by: Hawktel May 28 2003, 09:44 PM

Be safe. Do both!

And let us know how it works out.

Posted by: campbellcj May 28 2003, 10:37 PM

Undercoating is evil....

Posted by: MarkV May 28 2003, 11:48 PM

How would you apply it? Would you use a trowel?

Posted by: GWN7 May 29 2003, 01:41 AM

Most undercoatings only work on new cars. The reason is the undercoating is applyed to a clean, newly painted surface. Even when new, the applicators wash and steam clean the underside of the car, to give the undercoater a clean surface to stick to.

POR15 and its counterparts create a chemical bond with the metal.

All the tar will do is cover the metal. If there is a small hole in the tar it will hold water and cause rust.

Most roofing tars don't "dry" compleatly. They are designed not to. They form a hard surface and are pliable underneath, so they can expand and contract with the shingles or as your house moves. Ever remove 20 yr old shingles? The tar they used around the flashings is usually still pliable.

GravelGuard/under coater is a sprayable tar designed to protect the sides and underside of your car from rocks. It is thin, but the reason it works is that it "moves" when struck by the rocks. It still needs paint over it to protect it. If the surface the GG/undercoater is put on isn't compleatly clean, rust will form & it will fall off. Might take a year or two, but it will happen.

Use a product for what it was intended.

Why paint your whole house, when only the neibours look at the front? Because you will know that it's done right

If your keeping the car, spend the extra $$, do it right. If your selling, spray/tar away.

Posted by: Gint May 29 2003, 07:46 AM

Unless I'm buying, in which case I will run far away.

Posted by: SirAndy May 29 2003, 11:14 AM

i hate undercoating.
it'll crack eventually and you can't see the rust behind it until it's too late.

i'll remove all of it when i get to the underside of the car.

actually, i will apply a new coat to the underside of the fiberglass fenders! that will protect the top paint from chipping when the underside is hit by pebbles ...

other than that, just the paint, so i can see the rust when there's still time to do something about it ...


Andy

Posted by: ptravnic May 29 2003, 11:22 AM

Surprisingly, general road debris does not stick to the tar. I do believe that if there is a small hole it may capture the very moisture (which is the devil) it is intending to prevent. An undercoating is not optional in this area. I don't have the luxury of a garage so something has to protect the undercarriage.

I'm beginning to believe POR-15 applied directly to the bare metal, then the tar over top would be a good mix. The tar has held up incredibly in the wheel wells!

The tar can be applied not so easily with paint brushes - kinda like spreading peanut butter.

For the POR-15, is the 3 step process necessary or is the POR-15 fine on its own applied directlly to somewhat clean bare metal???

Posted by: SirAndy May 29 2003, 11:41 AM

POR-15 can be applied to the bare metal. but i prefer to use "Metal-Ready" on the bare metal first, let that dry, then rinse it of with water (yes WATER!), let it dry again, then apply POR-15. that should do the trick. then put tar/undercoating over that. this way, if the undercoating cracks, the water still can't get to the metal ...

Andy

Posted by: meursault May 29 2003, 01:05 PM

Uggh. Roofing tar makes me cringe. Makes me think of how a PO sealed up the cowl on a parts car to deal with the rust there. Ugly. I'd almost prefer to see big bubbling mountains of rust.

Posted by: BenNC May 29 2003, 02:18 PM

POR-15 forms a very non-porous surface. I know they sell a special primer to get paint to stick it. Will the roofing tar or other undercoating have problems sticking directly to the POR-15?

Posted by: GWN7 May 29 2003, 07:06 PM

It will stick to anything.

Try using it sometime. Have plenty of solvent to wash your hands, hair or whatever else touches it. Wear throw away clothes, Trevak suit recomended.

There is 3 types of roofing tar that I know of (in Gal cans)

Fiber-has fiberglass strands init. Put it on with a stick.

Gel- works like peanut butter, can be painted on with a brush.

Liquid- paint on or spray it.

A buddy of my dads used to save his old oil, put it in a yard sprayer and spray it on the underside of his cars to prevent rust. It works too, but don't let the EPA catch you doing it.

Posted by: Mark Henry May 29 2003, 07:54 PM

DRIP, DRIP, DRIP

Everyone oil their cars, so all the parking spots look like a Porsche or old V-dub lives there!

Posted by: tracks914 May 29 2003, 08:13 PM

Most body shops can get a yellowy/clear K-Y type undercoating for your car. Here in Canada I have used it for about 15 years and get it done at the local WalMart. It never hardens and will weep out from your car for two or three years. (never enough to drip but enough to know it is still there and has to be washed off when you wash your car) For the amount of salt we use here I am very impressed with the way it holds out. I will never drive my teener in the salt but I will still get it sprayed too when I am done restoring it. I goes everywhere, inside the trunks lips, doors, fenders, rocker panels etc. Well worth the $75 for them to do it and cleaner too.

Posted by: ptravnic May 29 2003, 09:47 PM

I am beginning to see a distinct difference in attitudes when comparing the Californians vs the Northeasterners & Canadians.....

I must admit, I envy the California sun and lack of rust-consideration. Maybe, I'll strike it rich on Wall St, retire, and move to So Cal where snow and salt are non-issues. ahhh, its good to dream

Posted by: driver66 May 29 2003, 10:03 PM

anyone ever consider rhino lining for truck beds I hear its indestructable.

Posted by: SirAndy May 30 2003, 10:39 AM

haha, you don't have to "strike it rich on Wall St" to move here.
in fact, all the people i know that made enuff money around here are gone,
they all moved somewhere else. go figure ...

Andy

Posted by: GWN7 May 30 2003, 03:14 PM

Bed liners are usually a epoxy based thick paint. It won't do a thing to stop rust unless it's applyed to a rust free part.

If it has rust on it now you have to stop the rust first, not cover it over.

The 4 "C's" of rust...cut it out, clean it off, convert it, cover it.