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Old 04-28-2021, 04:42 PM   #1
WHN
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Default Undercoating would like your comments.

Back in 1981 when we were doing over our 1929 Sport Coupe we had it under coated.

The undercoating has really held up. No rust at all on frame or under fenders. Fenders, and running boards were coated off the car.

Has anyone else done this. Also, what comments do you have on it having been done.

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Old 04-28-2021, 07:36 PM   #2
Model A Ron
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Default Re: Undercoating would like your comments.

I came across many cars with undercoating that looked good only to find rust under. This was a popular thing to do in the rust belt to help prevent underbody rust. the sad thing is it only helped to rust the cars out and have them look pretty as they rot.

i would remove the undercoating, fix any rust that you may find, and paint the underside.
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Old 04-28-2021, 08:37 PM   #3
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Default Re: Undercoating would like your comments.

I live in the northeast and learned the hard way to avoid undercoating likes its the plague. I use fluid film now with excellent results. It does need a annual application but it works great! Its not something i would use on my model a since it stays like a tacky oil. Undercoating would work for a fair weather driver but avoid it on daily drivers, especially if it will see salty roads.
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Old 04-28-2021, 08:48 PM   #4
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Default Re: Undercoating would like your comments.

Also, do not use undercoating on a undercarriage that already has rust. Undercoating will not stop rust that is already there. Most likely will make it worse. Only benefit i see to undercoating is that it wont chip from stones like paint will. Maybe undercoat the bottom side of the fenders but i would paint everything else.
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Old 04-28-2021, 09:23 PM   #5
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Default Re: Undercoating would like your comments.

Had been working on a coupe that had "EVERYTHING", except the running gear, on the underside even in the the trunk behind the curved panel front to back undercoated. What a pain in the A$$!
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Old 04-29-2021, 09:07 AM   #6
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Default Re: Undercoating would like your comments.

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In my opinion, the following is a corrosion control scheme for a restoration that is better than undercoating:
> Frame & Running Gear: Powder coat all that gets a black finish. If powder coating is not doable, coat all bare parts to be black with POR-15 Chassis Black and overcoat with a light coat of satin / gloss black Krylon;
> Body: Strip to bare metal, repair corroded panels with new metal welded into place. Use a welding compatible primer on surfaces that will be hidden. Coat all accessible bare metal with an epoxy primer. Do this to interior metal as well. On panels directly exposed to rain, use a paintable sealer on all faying surfaces during installation;
> Wheels: Powder coat them if they will be black, otherwise paint with an epoxy primer and single stage polyurethane color coat;
> Wood: Sand surfaces to open the grain and coat the wood with a petroleum based modern wood preservative. Avoid water based preservatives;
>Hardware: There are many pieces of hardware that were originally bare, and these need to be primed & painted.


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Old 04-29-2021, 10:13 AM   #7
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Default Re: Undercoating would like your comments.

Undercoatings were advertised to reduce road noise and some may have advertised corrosion protection but that would be false advertising in most cases.

I have two 1951 Mercury cars. Both came from the St Louis, plant in December of 1950. One was undercoated and one was not. The one that was undercoated rusted out in both inner and outer rocker panels with a lot of floor rust as well. The one with no undercoat rusted in only a few places on the inner and outer rockers with virtually no major rust on the floor. What happens is the undercoat hardens and starts to get fractures in the coating over a period of around 5 to 8 years and it starts holding moisture between the coating and the steel. If a car is driven in winter where salt is used then the salt brine starts getting in there too. This can literally eat the steel up and leave nothing but an undercoat shell with iron oxide in there.

If the car is garaged and never driven in inclement weather then it may still last a very long time as long as all the steel that it is coated has good primer and paint adhesion at the time of the coating deposit.
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Old 04-29-2021, 01:15 PM   #8
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Default Re: Undercoating would like your comments.

Back in the day I worked at the local Cadillac/Pontiac dealer and got one dollar for every car I undercoated and there were al lot. My Mother bought a new 62 Bonneville 2dr h//top. It must have weighed an additional 100+ lbs when it was delivered to her. Paul in CT
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Old 04-29-2021, 01:28 PM   #9
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Default Re: Undercoating would like your comments.

I use the fluid fine on daily drivers, wouldn’t recommend on a restoration,the undercoat was a big profit option for Dealers at one time , I have a 49 Buick that was dealer under coated and was quite a project to remove it ,along with parts of the floor.Chip guard is used on newer cars to protect from chipping, its clear and applied over paint, may be a option on underside of Model A fenders, for a driver it has a texture finish like heavy applied enamel.
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Old 04-29-2021, 08:40 PM   #10
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Default Re: Undercoating would like your comments.

Undercoating is only as good as the prep done for it. Steam cleaning and wiping down with prep solvent and it will last the life of the vehicle.

Would you spray undercoat on after driving the car through a mud bog?
Even a new car that has not been on the road has enough dirt film on it to make undercoat adhesion marginal.
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Old 04-29-2021, 08:49 PM   #11
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Default Re: Undercoating would like your comments.

Don't drive your car when there is salt on the road. Wait until the spring rain has washed it all away. If you have to drive your modern car when there is salt, pressure wash the underside as soon as you can.

I experimented with using Flex Seal Rubber Sealant, the stuff that was advertised on TV for a while. It can be bought in spray cans or cans for brushing. I coated the underside of a pair of front Model T fenders, after pressure washing them. The coating was still on and not cracked when I took the fenders off to replace them with new fenders. The Flex Seal can be found at the major hardware stores. Being rubber, the stones kicked up by the tires just bounce off. I did not see any new rust in the couple of years they were coated.
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Old 04-30-2021, 10:26 AM   #12
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Default Re: Undercoating would like your comments.

Quote:
Originally Posted by Bob Bidonde View Post
In my opinion, the following is a corrosion control scheme for a restoration that is better than undercoating:
> Frame & Running Gear: Powder coat all that gets a black finish. If powder coating is not doable, coat all bare parts to be black with POR-15 Chassis Black and overcoat with a light coat of satin / gloss black Krylon;
>Hardware: There are many pieces of hardware that were originally bare, and these need to be primed & painted.


I am not a big fan of power coat. I would not power coat anything under a car. Any rock chips will let moisture and rust under the powder coat then it flakes off. Paint may get chips also but is much easier to 'touch up'.

For the hardware, I spray a clear coat of Krylon Acrylic Satin to prevent rust.
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