Coating Underside of Mark IV Body

[DowenS]

I'm planning to coat the underside of my Mark IV body this weekend and I've got some questions
that I was hoping you all could weigh in on.

What is the best way to prep the fiberglass?
Should I be using an undercoating product or a bed liner product?
Will the final result be a smooth or rough finish, and does it matter? (not sure if much or any of it will be visible in the engine compartment)
What brand(s) have worked well for you?
Brush on vs Spray on?
How many coats?
How much will I need?

Thanks in advance for your help.

[PeteH]

Many use truck bed liner. I plan to use Body Shutz, a rubberized undercoating for sound deadening and chip resistance. I'll scuff with 80 grit, wipe it down with lacquer thinner. It will have a pebbly finish, as most bed liners will, and probably still see the glass texture as well.
The aerosol cans of undercoating go on very thin, probably not the best approach.

[DaveS53]

Lizard skin sound reduction coating is water based and can be applied to a very heavy thickness if there are areas where rocks can be thrown off the tires. That's what I used inside my fenders. Despite being water based, wipe off any excess quickly. Like latex paint, it quickly becomes waterproof and only acetone or lacquer thinner will remove it.

[phileas_fogg]

I brushed on my first coat of Duplicolor bed liner yesterday, and used ~3/4 gallon. I'll do a second coat because once the body was back on the buck I can see some spots that are too thin for my liking. I didn't do anything special to the fiberglass - just vacuumed the surface with a shop vac. That stuff is like tar!


John

[SingleMaltWSKY]

This is a good question, I'll be looking into the same thing next year.

Potential options:
Bedliner
Body Shutz (that's a new one for me, I will investigate for sure)

What about something like "Steel-IT" metal spray.....does anyone have experience with metalic sprays? (http://www.steel-it.com/polyurethane-stainless-steel-coatings-10)
Apparently products like Steel-IT are used in off-road frame coverage applications and it's supposed to be very durable.

Thoughts?

[DaveS53]

What's the goal of the coating - make it look pretty or protect against rock damage? A rock thrown against the inner fender of a car can cause significant damage that may require cutting a portion of the body out and rebuilding. I know because I had it happen, but fortunately it was before I had the final paint on the car. Thin coatings, even truck bed liner may not provide adequate protection.

[SingleMaltWSKY]

Thin coatings, even truck bed liner may not provide adequate protection.

OK - then I would have to say the purpose of the coating I want will be for impact protection and to look decent with the hood lifted.

Suggestions?

[ej95Cobra]

I used brush on bedliner after scuffing with 80 grit and wiping with acetone. Two coats but did 4 coats in wheel wells.

#8469

[GoDadGo]

I've used this stuff and it looks professional as long as you have a good water filter on your compressor.

Here are a few videos that may be of use to you.

https://youtu.be/b1fcntE6Ryc

https://youtu.be/Ua1DJyAw_D8

https://youtu.be/ezVsBjayjYA

[edwardb]

I agree with the others. No special prep is really necessary. But I still run over the inside of the body with 80 grit to knock off any loose edges, strings, etc. in the glass layup. Then wipe it out with some lacquer thinner and apply the bedliner. One overall heavy coat and several additional coats in the wheel wells. Agree it won't stop everything. Some have even gone as far as put padding in there. But I haven't found that necessary. Multiple coats of bedliner are going to provide way more protection than nothing at all. I've used several different brands of bedliner and haven't found a big difference. The water based ones are a little easier to clean up after when you're done. The solvent based ones dry faster. They're all messy. Be prepared for that. I'm probably going to try the U-POL RAPTOR that GoDadGo recommended the next time around. Looks interesting.

The coating in the wheel wells gives protection and also reduces "pinging." But it also is an appearance item. Looks nice with the wheel wells blacked out. The inside of the body can be seen a little when the hood is open. In the general area of the side louvers. The inside of the body is also visible a little from inside the trunk, and also in the front opening when the doors are open. A nice uniform color for all that gives the build a more finished look.

[rich grsc]

OK - then I would have to say the purpose of the coating I want will be for impact protection and to look decent with the hood lifted.

Suggestions?
You don't see any of the underside of the body unless you are laying on your back under the car. Rustoleum truck bed liner works great, doesn't require any prep to the body, a gallon is more than enough.

[edwardb]

You don't see any of the underside of the body unless you are laying on your back under the car...

OK, if you also leave the hood, trunk, and doors closed. Agreed it's not a lot, but the backside of the fiberglass is visible in the areas I referenced in my post. Without laying on your back. :o

[GoDadGo]

Regarding the coating and/or painting of the back side of the body.

It is the little details that make an okay car good, a good car great and a great car a show stopper.

It all depends on what you want your car to be in the end and what your intended use of it will be.

[SCFFR]

I also used the brush on bedliner (two coats) and was happy with it. However, I have a 700' gravel driveway that runs from my house to the county road so
I wanted a little more protection. Followed the recommendation of another member (think it was Gumball) and got a black high-density mat (actually a yoga mat)
from WalMart and cut and glued it in the top of all the wheel wells. Glad I did since the tires pick up dozens of rocks every time I take the car out. When I get on the county road and speed up, I can hear the rocks flying out of the tires however after many years, not damage to the paint or fiberglass.

[Jeff Kleiner]

Have not tried any of the spray on products but have used both Herculiner and Duplicolor Bed Armor roll on. Both hold up well, look exactly the same when applied and cost the same. Bed Armor gets my nod simply because it will clean up with soap and water before it's cured while Herculiner requires Xylene. A gallon is plenty.

Jeff

[DowenS]

Thanks everyone for your input. Once again the forum comes through with some valuable advice.

[DaveS53]

Bed liner materials are primarily used to protect against abrasion. A product like Lizard skin will not protect against abrasion, so it is not to be used as a bed liner. It will protect against rock damage.

http://www.lizardskin.com/sound-control-insulation.html

[BEAR-AvHistory]

There are also plastic fender liners available in the 3rd party market. I used Truck bed lines as a general undercoat then the plastic liners for thrown rocks.

[cfriedman67]

When is the best time to do this step? Before you fit the body, doors, hood etc... or afterwards.

[Dave Howard]

One gallon of truck bedliner is more than enough for the job. It comes on sale at Canadian Tire. I pushed the body buck out of the garage and flipped the body off onto the front lawn. Prep was minimal. You don't need to prep the body with any chemical cleaners. There's no release agent on that side of the body. The roughness of the underside is NO concern. NO ONE will see it. I used a 3 inch throw away paint brush and applied several coats to the entire underside. The wheel wells recieved many more. Dry time was pretty short in the sun and the end product looked much like you'd expect......truck liner.

[DaveS53]

Easy but worthless if the wrong product is used.

[GoDadGo]

Easy but worthless if the wrong product is used.

Back in the day (Early 2000's) I did a couple of truck beds with Heuculiner and it was an okay product; however, after using the U-Pol Raptor Liner on some other projects I've been impressed for a D.Y.I. application.
Just understand that if you tint this product then I strongly suggest you be very accurate with your tint measurements so that each bottle yields the same color.
The fact that you can tint this stuff allows you to create a colored non-skid surface on all sorts of materials and it is especially good for marine applications.

[WIS89]

... and it is especially good for marine applications.

I don't know Steve; I can never get the Marine to stand still long enough for me to cover him with paint. ;)

Regards,

Steve

[BTHWarrior]

I used a product called Monstaliner on a Jeep tub and it is IMO a better product then Herculiner (used this once on a truck). It is non abrasive since it doesn't have the bits of rubber added to the product like some DIY roll on liners. Two coats end up being about 40 mils thick. Can be tinted to 40 different colors. A one gallon kit cost about $150 (black) and tintable is same price plus the color tint that runs from $20 to $50 depending on color choice. http://www.monstaliner.com/monstaliner_features_techdata.htm

[GoDadGo]

I don't know Steve; I can never get the Marine to stand still long enough for me to cover him with paint. ;)

Regards,

Steve

Only Paint A Marine If He Or She Wants To Be Painted!

Then Thank Them For Their Service!

God Bless Our Armed Forces!

Especially The Marines!

[Hotyacht]

Are you guys applying the coating to the inside before or after painting the body? I am assuming before?? Where do you stop the liner and start the paint?

[GoDadGo]

Are you guys applying the coating to the inside before or after painting the body? I am assuming before?? Where do you stop the liner and start the paint?

Before Painting!

Just apply to the back side of the body on the Raw fiberglass, not the gel coated side.

[Hotyacht]

Before Painting!

Just apply to the back side of the body on the Raw fiberglass, not the gel coated side.

I understand that but I was thinking particularly in the wheelarches, there much be a join at some point and for sure this will be inside. Do you mask and paint the bedliner or whatever chosen coating and then lap the paint finish onto this or just butt the two coatings together?

[GKindle]

I just picked my kit up on Saturday at the factory. Very good information here on the undercoating. The U-POL Raptor that GoDadGo recommended looks like some really good material.