Undercoat, or full on paint?

hoagster · Jul 6, 2021

I'm fixing to roll the cab on it's back. Going to strip a coat on rattle can primer, prep and spray epoxy primer. Question is after the primer is cured does it get base and clear? Or 3m 544 rubber undercoat, or some other undercoat and a finish?

Grit dog · Jul 6, 2021

Personal opinion, I’d paint it first. Then undercoat it if you wish.
If it’s as nice as it sounds, I’d want to paint it same color you’re doing the truck.

ali_c20 · Jul 6, 2021

I say paint. Some primers and fillers are not 100% water proof and without the paint layer rust starts to grow under the primer. Have seen it on a few projects that sit only with primer for a few years. I would not use the rubber undercoat. Water can get under it if it's not perfectly applied or when it ages.

Bennyt · Jul 6, 2021

Showcar: Paint
Anything else: Raptor liner. Almost every custom shop I know has been using Raptor Liner on the undersides of the cars/ trucks that actually see street use for the last 10-20 years. Holds up well and has a nice even coating. Costs about $150 with the schutz gun to do a cab.

Grit dog · Jul 6, 2021

^ Agree, if going for ultimate durability in rough conditions, off roadin, slingin rocks, driving on salted roads all winter, epoxy with serious chip resistance is preferable. But the truck’s already made it almost 50 years on its own. Doesn’t seem like Hoagster is doing a frame off, damn near nut and bolt resto on the truck to go see if he can bury in mud up to the doors!

But remember, rust doesn't usually proliferate first in the nice open areas, but rather the hidden areas that collect full of dirt n **** and don't dry out. The $250 raptor kit is double or triple that much by the time you do under the bed and all the wheel wells too. A gallon of 2k urethane chassis paint with rust inhibitor is $131.99.
The best looking job on an undercarriage is for naught if the hidden areas are bare or not protected. Cabs rust out mostly from rocker panels not draining, cab corners packed fill of **** and carpet padding holding ,moisture on top of the floor pans for years on end.

Again, unless its a boonie basher or going to live in the rust belt and be daily driven in the winter, I'd paint it up nice however you want and save any undercoating/rock schutz for the high wear areas like just behind the wheels, if warranted.

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All the rough spots are 35 year old "aftermarket" undercoating. It's an asphalt based half hearted attempt to undercoat the old truck, back when it was new. Stuck very well except in the wheel wells in some spots. I gave up after the initial thought of stripping it all off for a clean look!
Old bed was pressure washed and sprayed and the paint is well adhered.

hoagster · Jul 6, 2021

You are right there, I'm not going to go bury it in the mud! But we do get some snow and lots of rain most years in Shasta county CA. Thanks for the inputs.

Raider L · Jul 16, 2021

Krylon makes many paints these days just for what you want to do. Go to the Krylon site, not Walmart, although Walmart Super Centers do carry a huge assortment of many different spray paints for different applications. You'll get the type of paint you're looking for at the Krylon site. There are paints you won't see at the stores.
And if you can't get it on the Krylon site it will tell you where you can get it in your area. And it's less expensive.

Then there is POR 15 for "painting" a "coating" on the underside that's not one of those rubbery spray on coatings. They probably do have a spray on paint that's like a "under coating". Also, Eastman makes paint for a under coating that's not like one of those rubber under coatings people do to the underside.

I say paint it, but with a modern paint for under the truck.
I did my entire engine compartment and frame with a Krylon semi-gloss spray paint and I followed the directions for multiple coats. I put three coats on it all and it's still holding up. That was 25 years ago!
I washed the engine compartment two days ago and the paint still looks great. And I'm talking hot soapy water with wash cloths, sponges, and brushes. I use Dawn dish washing liquid detergent and it cleans it good. I might wash my engine compartment maybe once a year. I don't like dirt, oily sludgy filth in a engine compartment. Of course my engine compartment doesn't ever look like that.
And fortunately we own trucks where you can almost stand down on the ground next to the engine. Not like these modern engine compartments where you can't see anything but a mass of hoses and all kinds of stuff. You can forget getting down anywhere to clean anything. Last year I had a chance to wash the underside of the truck from front to back. That way if something is going on I can tell where it's coming from.

SirRobyn0 · Jul 16, 2021

I cannot really comment on on what's best, I just wanted to say that my truck is not undercoated and does not have rust issues. I'm not saying it wouldn't hurt, but personally I believe that washing the underside a few times a year and making sure drains stay open go a long way to reducing rust issue regardless of what paint or coating is used.

Grit dog · Jul 17, 2021

SirRobyn0 said:
I cannot really comment on on what's best, I just wanted to say that my truck is not undercoated and does not have rust issues. I'm not saying it wouldn't hurt, but personally I believe that washing the underside a few times a year and making sure drains stay open go a long way to reducing rust issue regardless of what paint or coating is used.

That’s why the vehicles here in the PNW are among the most rust free in the country.
6 months of daily free undercarriage washes are a great thing!

K5ride · Jul 17, 2021

Some of my side job mechanic work, I get cars covered in grease and grime. I put the casters on my 4 post lift and roll it outside so I can pressure wash the underside of the vehicle to make working on it easier. While I have it set up outside, I make sure to wash the underside of my truck too. I do this at least every year or so. My C10 is not a daily driver and living in So Cal, we don't have the weather issues. No undercoat and everything still looks okay after 46 years.

Rumbledawg · Jul 17, 2021

have always had good results wit por15. did my frame, susp, bottom of the box and cab with 2 coats por 15 and 2 coats por chassis black.
some real life testing. new tanks in 2010 painted with por...

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and 11 yrs later, still lookin' not bad. pretty much zero rust except for the leaf springs

You must be registered for see images attach

AuroraGirl · Jul 17, 2021

Raider L said:
Krylon makes many paints these days just for what you want to do. Go to the Krylon site, not Walmart, although Walmart Super Centers do carry a huge assortment of many different spray paints for different applications. You'll get the type of paint you're looking for at the Krylon site. There are paints you won't see at the stores.
And if you can't get it on the Krylon site it will tell you where you can get it in your area. And it's less expensive.

Then there is POR 15 for "painting" a "coating" on the underside that's not one of those rubbery spray on coatings. They probably do have a spray on paint that's like a "under coating". Also, Eastman makes paint for a under coating that's not like one of those rubber under coatings people do to the underside.

I say paint it, but with a modern paint for under the truck.
I did my entire engine compartment and frame with a Krylon semi-gloss spray paint and I followed the directions for multiple coats. I put three coats on it all and it's still holding up. That was 25 years ago!
I washed the engine compartment two days ago and the paint still looks great. And I'm talking hot soapy water with wash cloths, sponges, and brushes. I use Dawn dish washing liquid detergent and it cleans it good. I might wash my engine compartment maybe once a year. I don't like dirt, oily sludgy filth in a engine compartment. Of course my engine compartment doesn't ever look like that.
And fortunately we own trucks where you can almost stand down on the ground next to the engine. Not like these modern engine compartments where you can't see anything but a mass of hoses and all kinds of stuff. You can forget getting down anywhere to clean anything. Last year I had a chance to wash the underside of the truck from front to back. That way if something is going on I can tell where it's coming from.

I’m allergic to your cleaning methods.

SirRobyn0 · Jul 18, 2021

Grit dog said:
That’s why the vehicles here in the PNW are among the most rust free in the country.
6 months of daily free undercarriage washes are a great thing!

I agree, but also and maybe because I'm around the farms so much, my truck will still get a build up of mud in the inner fender wells and such. Our well has a hard time keeping up in the summer so I run mine though the car wash, probably once a week or so. (Keep in mind I put a lot of miles on it). I know you likely already know this, and folks that don't live around here won't know who Brown Bear Car washes is, but I'm a big fan of their tunnel washes. And I'm sorry to the OP for getting sort of off topic.

Grit dog · Jul 18, 2021

@SirRobyn0 For sure. There’s places stuff is caked up a little on our 2016 pavement princess truck and a well placed blob of muc rusted out a tank on the ‘86 just last year.
No substitute for proper cleaning, but merely an observation that the big time rain season up here is more helpful than detrimental to vehicles.

Undercoat, or full on paint?

hoagster

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