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Fri Jul 25, 2014 8:25 am

Having used at least over a dozen cans of spray can undercoating already, I tried using Henry's roofing mastic yesterday. It is much better than the spray can because it is much thicker, cheaper, has fibers in it and dries pretty fast with a fan on it. I found if you set the can in hot water and get it to at least 100f it will brush on and smooth pretty well. Will dry to touch in 4hrs with a fan blowing on it.

Fri Jul 25, 2014 8:57 am

Personally, I have seen too many problems with undercoatings and wish my cars PO's had not used any. Only place I would use it, is in the wheel wells and only in-line with the tire rotation.

Fri Jul 25, 2014 9:26 am

1967250s wrote: Personally, I have seen too many problems with undercoatings and wish my cars PO's had not used any. Only place I would use it, is in the wheel wells and only in-line with the tire rotation.

Could you elaborate on the problems you've had? I've had some awfully smart people recommend it especially for our very valuable (to us) German steel, but only when surface prep has been extensive and meticulous. My 72 Super Beetle still had its dealership undercoat, and was in phenomenal condition, so I'm be interested to hear your experience.

M

Fri Jul 25, 2014 9:41 am

This is what I would recommend.

Fri Jul 25, 2014 9:48 am

My bus is running now but I don't want to drive it until the undercarriage undercoating is completed. Right now the undercarriage is super clean an rust free. I won't be able to apply the undercoating once it gets dirty. I'm shooting for at least a 1/8" or more in the wheel well areas for sound mitigation.

Fri Jul 25, 2014 9:54 am

Brionp wrote: This is what I would recommend.

Good stuff, but too pricey, costs 4X more than Henry's and its the same type, rubber and asphalt but without the fiber. I'm using 1 gallon just for the front fender well areas.

Fri Jul 25, 2014 10:16 am

the wax-oyl VW used works well. It is mobile and recoats when heat moves it. Places where it stayed were dry and rust free. Cosmoline is similar.

Rubberized sprays are bad news. It can delaminate just enough that water gets pulled in through osmosis between it and the metal. It looks pretty but my body shop guy makes a lot of money fixing damage caused by it. It did not stop rust from forming under it on my jeep CJ7 front fenders either.

Fri Jul 25, 2014 10:43 am

What SGKent said. All the joints and crevices in the chassis and lowers on my Bus rusted because of the either incomplete, heavy, or cracked coating. The places where you cannot coat also rusted because the coating retained water. A good coating of paint would have been better.

Fri Jul 25, 2014 11:22 am

I thought the purpose of undercoating was to protect the paint underneath?

Fri Jul 25, 2014 11:41 am

VW Bus Cavity Preservation - March, 1972

Fri Jul 25, 2014 12:06 pm

mojogoat wrote: I thought the purpose of undercoating was to protect the paint underneath?

Fromy the factory, maybe. Now with the youngest German Baywindow being 35 years old, we have rust to deal with. Road salt. Greater road debris. POs. :wink:

My factory undercoating under the main chassis is in great (and thick) shape, but near the battery trays, wheel wells, and front bumper, the original coating has turned to flaky sheets that do nothing but trap water and encourage rust. Water needs to drain, and dry out quickly. Scraping away the flaky sheets left me with surface rusted paint. So I treated it with formic acid and applied rubberized paintable undercoating.

Fri Jul 25, 2014 12:17 pm

mojogoat wrote: I thought the purpose of undercoating was to protect the paint underneath?
No, no -- Like many products, the purpose of undercoating is to sell undercoating!

I'm with Steve (SGKent) on this. I hate the stuff. The only undercoating that I have seen eventually peel off and leave pristine metal behind it is the factory stuff.

Otherwise, I have seen it trap water and cause rust, unseen until you actually dig in there and get rid of the chthonic stuff.

Fri Jul 25, 2014 2:42 pm

I used Rustoulm spray can undercoating on both side of my pan. Somewhere in the neighborhood of 30k on it in 3 years and it still looks great. Unlike most of the people here I don't just drive when the weather is nice. I drive it everyday even in the rain and snow. I know everyone wants to be more technical then the next guy but there's nothing wrong with the rattle can undercoating.

Fri Jul 25, 2014 3:50 pm

Jeez.....the "purpose" of undercoating has been widely documented. It comes in hard or soft...regardless of chemical make up. It has two main purposes:

1. To make a surface that does not chip easily from rocks and dirt to keep from exposing bare metal which will rust.

2. In the case of rubberized undercoating...same as above except its more flexible and "generally" shrinks less with age (whether it adheres or not is a different argument)....but its main claim to fame is that is blocks more road noise.

That being said.....I hate both of them. The factory undercoating on 411 and 412 cars....is just plain awesome in its bullet proofedness. Hard as a rock and super long lasting and an absolute B*tch to remove. Aircraft stripper and most other chemicals will not touch it and at best make it gooey....and then it hardens up again when it dries.

I would be happy to leave it alone.....if it were not the fact that where it gets thick in corners and crevices...are the only places it cracks with age and shrinkage....and thats where it absorbs water and rusts.

I'm taking mine down to metal.....and I am applying epoxy with ceramic.

Over the last two weeks I have been experimenting with the VHT rattle can epoxy suspension component/metal spray. Just awesome tough stuff.

While i would be happy to do the whole underside in rattlecan the way this stuff lays down....I think Eastwood has an epoxy underside paint product that comes in quarts or gallons...which may be quite a b it more cost effective. Ray

Fri Jul 25, 2014 3:55 pm

While this subject is up and alive I thought I'd chime in with a question.

My 72 still has 80% of its undercoating. Its starting to peel or has peeled away in some areas exposing the metal/paint. I was debating patching these areas with an undercoating but now just debating using a rustoleum type paint. What would you guy suggest?

Here are some pictures:
http://www.thesamba.com/vw/forum/album_page.php?pic_id=1224200
http://www.thesamba.com/vw/forum/album_page.php?pic_id=1224199

Should I strip it all then just paint it, or leave it and just patch the bare areas? I want to do it right within reason.

Also I wanted to ask if I should just leave the dirt/dust thats under there, or should I clean it off with a brush and some water on a nice warm day so it dries up? Auto Carwash (scares me, but might work)?

Fri Jul 25, 2014 4:08 pm

In areas where you don't get much rust to start with undercoating is fine and will quiet up the ride a bit. In areas with high salt use it is just going to hold the corrosive salt moist and in place longer and keep clean water from washing the salt away.

Fri Jul 25, 2014 4:32 pm

I spent many hours chipping and cleaning the undercarriage. Treat the rusty areas with rust treatment, paint with POR15,Rust bullet, or Rustoleum hammered paint. I treated the rusty areas, rust bullet and painted with rustoleum hammered over the areas not rusted then undercoated. some of the areas I put rubberized seal tape for extra sound proofing. If you are in a hurry, rustoleum hammered works pretty good on its own. The Qt cans go along way and you can put it on thick. I have a gallon of the rust converter acid stuff I keep some in spray bottle to pre treat areas before painting.

Fri Jul 25, 2014 5:33 pm

Here is my plan for the front fenders once the Euro gets devalued and the exchange rate evens out. http://www.lokari.de/epages/62716287.sf/en_GB/?Vie...3%9CGEL%22 They sell them for ALL air-cooled VWs, even type 4s lol. I already knocked the old rubberized undercoat off and treated the rust and repainted. Now I just have to wait for that dang Euro to get devalued.

Also Master-Series paint and primer is an excellent water curing epoxy paint with sacrificial anode in it that is guaranteed not to rust beyond a chip. I've used it for many years and it is very expensive but probably the best paint there is. The primer must be applied to bare metal, no rust. Don't apply it to rust if you want it to really last, even though they say you can.http://www.masterseriesct.com/

Sat Jul 26, 2014 10:36 am

For inner panels (doors, nose, dog legs etc) this works great, and has a 'new car' smell http://www.noxudolusa.com/product/noxudol-750-aerosol/ I use the qt size in a Harbor Freight cheapie gun. Good on seams too due to it's ability to creep - on a warm day it is like water until it cures. Cheapest through Ebay I found.

In Europe VW, like all manufacturers, has had an anti-perforation rust warranty for many years and will cover any areas under their cars likely to rust to avoid this problem. Old underseal on our VW's wasn't designed to last 35+ years and is best scraped off with a plastic spatula if flaking. Trapped road salt is a real metal killer.

I love Henry's plastic roofing cement inside doors to cut the noise - stipple the surface with a short bristle brush to get the best results.

Sat Jul 26, 2014 12:07 pm

alikatcraig wrote: For inner panels (doors, nose, dog legs etc) this works great, and has a 'new car' smell http://www.noxudolusa.com/product/noxudol-750-aerosol/ I use the qt size in a Harbor Freight cheapie gun. Good on seams too due to it's ability to creep - on a warm day it is like water until it cures. Cheapest through Ebay I found.

Hummm seems interesting, how does it hold up, how often do you need to apply? Id rather do this then spray paint over my exposed metal.

I wonder the difference between it and this one:
http://www.noxudolusa.com/product/noxudol-900-aerosol/

It almost seems like the 900 is for what were talking about at the 750 is more for exposed metal, cavitys, engine bays, drainholes etc?