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Randy Roberson
Prolific User
Username: wascator

Post Number: 105
Registered: 5-2009
Posted on Tuesday, 26 March, 2013 - 02:01 am:   Edit PostDelete PostView Post/Check IP

Hi, In reviewing a Factory sales brochure from 1970, I ran across a claim that the underbody was coated with a material which would never harden or deteriorate. Quite a claim, as "never" is a long time! As my Car SRH 9391 was I think undercoated with some sort of black mastic or asphaltic substance, possibly when new, I am not certain, but there seems to be a thin hard coating that was maybe similar to (or exactly like) the urethane coatings which are now popular in the USA for pickup truck beds. It is most evident at the bottom of each side rocker panel, like it was intended for stone chip prevention. Does anyone know more about this? There is some asphaltic substance in the inner floor, as I discovered when removing the rugs to install updated seat belts. This was not a lot and it was not completely over the floor surface, as both primer and the original Seychelles blue were both readily visible. The black substance might have been part of the sound attenuating padding under the rugs.
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David Hughes
Experienced User
Username: wedcar

Post Number: 34
Registered: 7-2004
Posted on Tuesday, 26 March, 2013 - 07:44 pm:   Edit PostDelete PostView Post/Check IP

Hello Randy
I am not certain what the product is that is applied to your vehicle, however there is a product produced by 3M named Body Shutz, that has similar properties that you refer to.
Trust that helps.
Regards
David Hughes
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Jan Forrest
Grand Master
Username: got_one

Post Number: 466
Registered: 1-2008
Posted on Tuesday, 26 March, 2013 - 10:21 pm:   Edit PostDelete PostView Post/Check IP

I undersealed SRH24518 with that Schutz twice the year before last as the first coat all but disappeared! I got it for a song in what turned out to be a closing down sale. I wish he'd told me that he was closing down as I would have bought his entire stock at the price I paid! You can get a similar substance called (in the UK) 'Waxoyl' in either clear or black to do the same thing. At least in the latter case they claim that not only does it stay flexible 'indefinitely', but it also has the ability to flow sideways to heal minor pits and scratches.
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Randy Roberson
Prolific User
Username: wascator

Post Number: 106
Registered: 5-2009
Posted on Tuesday, 26 March, 2013 - 11:13 pm:   Edit PostDelete PostView Post/Check IP

I have been underneath my 1951 Buick recently, cleaning the underneath and preparing it for paint. I have owned this car for 40 years, so I know whatever is there is at least that old. It has a very small amount of a mostly hardened black asphalt substance sprayed underneath the floor along and just inboard of the rocker box on each side. In scraping it off, although it is hard, there is bright steel underneath it; solid surface (but no perforating or flaking) rust elsewhere. Why they used such a small amount, I don't know. Probably a combination of cost control, poor quality control, etc.
I think my Rolls-Royce has two substances coating the underside: the hard, plastic coating which seems pretty thin; and this covered by the thicker, gooey bitumen or asphalt coating which I figure was probably a dealer-applied or aftermarket application. That's why I asked about what the Factory was using: was it urethane?
I can see that, if the black gooey stuff were properly and completely applied, it would have to do a good job of keeping water, and maybe the salt carried by water, off the steel. if there were voids or uncovered areas, though,they would not be protected, plus the coating could make it worse by trapping water/salt. My Shadow is in good solid shape, though, after 42 years, so I can only complain about getting black goop all over me and in my hair when performing maintenance and repairs!
My '86 Mercedes seems to have been sprayed underneath with a clear-amber wax of some sort. It repels water completely and has remained somewhat pliable after 26 years, and it makes less mess, so it might be a good product also.
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Bill Coburn
Moderator
Username: bill_coburn

Post Number: 1501
Registered: 4-2003
Posted on Wednesday, 27 March, 2013 - 10:04 am:   Edit PostDelete PostView Post/Check IP

From the dregs of my memory the paint used on the Shadows' undersides was thixotropic. That explains their claim that Randy mentions. Underbody 'sealers' were quite an innovation after the war the most popular as I recall was 'Prufcote' which was quite popular. Please Google thixotropic - it is quite an interesting concept!
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Randy Roberson
Prolific User
Username: wascator

Post Number: 107
Registered: 5-2009
Posted on Wednesday, 27 March, 2013 - 11:21 pm:   Edit PostDelete PostView Post/Check IP

Thanks, Sir. I found this on a website of a company in Sweden who makes underbody and other anticorrosion products:
"Noxudol UM-1600 is a highly thixotropic, fiber reinforced product, based on bitumen, waxes and low aromatic solvent."
The site is www.auson.se and there are others. I suppose because I read British car magazines, I think of "Waxoyl" first but there are many brands of undercoatings and anticorrosion sealers.
In reflection I think maybe the plastic or hard coating is just on the bottom of the outer rockers, maybe to resist stone chips.
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Randy Roberson
Prolific User
Username: wascator

Post Number: 108
Registered: 5-2009
Posted on Thursday, 28 March, 2013 - 02:09 am:   Edit PostDelete PostView Post/Check IP

Update: I was thinking about the different products' descriptions I have been reading. I think the 1986 Mercedes-Benz I have is completely coated underneath with one of the fiber/fibre reinforced bitumen products. Several of the descriptions mention that their product is paintable, and the coating underneath my 420 is definately painted over in body color. It is pretty firm and has fibres in it and the black bitumen appearance. The older cars seem to have a tendency to develop cracks as might be caused by long-term shrinkage,and I have read in the past about rust forming underneath this coating when it allows water/salt/whatever underneath; but I doubt the cars were meant to last 25 years anyway. One of the dealer maintenance tasks is to periodically inspect this coating and repair as necessary, and of course most older cars don't get to the dealer's shop very often for the expensive going-over! (annual teardown-inspection).
One manufacturer states that thixotropic means that it skins over yet remains pliable underneath and will slowly flow to heal damage and restore the sealing effect. That sounds like a good feature.
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Jan Forrest
Grand Master
Username: got_one

Post Number: 467
Registered: 1-2008
Posted on Thursday, 28 March, 2013 - 05:08 am:   Edit PostDelete PostView Post/Check IP

According to a friend Waxoyle, once allowed to dry for a few days, will take an overcoating of Hammerite paint. Whether this affects the thixotropic properties I couldn't say for certain, but it seems to me that it might help keep the Waxoyle soft for longer due to the reduced tendency for the lighter fractions to evaporate over time.
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Randy Roberson
Prolific User
Username: wascator

Post Number: 109
Registered: 5-2009
Posted on Thursday, 28 March, 2013 - 12:19 pm:   Edit PostDelete PostView Post/Check IP

I can't judge if the coating underneath Her Majesty is original or has been added to by post-sale vendors/applicators. I know that in most places it is still soft and will get all over you during maintenance and repair activity; in places like the boot floor over the spare wheel, it has dried out and was falling off in places and some surface rust had set in (since cleaned up and recoated by yours truly). The only really rusty spots I had concern about were the inner sides of the rockers, immediately behind the front wheels (there was flaking rust there but not perforated when I removed the inspection plate) and the right-rear corner where the bumper support passes through the rear valence (a common rust spot) and both rear bumper corners are perforated but still presentable.
I read some interesting tech articles today; also found some great videos on Youtube; the best were in German but clearly showed blast-cleaning the underside with dry ice, and application of various products. Also examination of rockers and other hidden areas with a borescope was interesting.

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