Patched and Painted the FloorPan, NOW Undercoating on the Inside?

Hey all,

Anyone use Rubberized Undercoating on the inside of the vehicle, on the floorpan (inside) under the carpet?? The instructions on the can says its NOT for the inside of the car, but no reason why. What is there some reason not to use it? Does it smell, how bad? What would be a better coating against liquid (soda, etc), that is also cheap, quick and easy to apply?

I had several rust holes in the floor pan of my '95 XJ. I finished welding in sheetmetal patches and sealing the edges on both inside and outside with autobody sealant. I'm doing this on the cheap side, so I painted the inside of the floorpan using a hand brush, 2 coats of Rustoleum Clean Metal Primer and 2 coats of Rustoleum Tough Enamel. The last coat is drying now.

It appears the rust holes may have begun from the inside out. (Previous owner never cleaned the vehicle, oh what a spectacle it was cleaning the carpets). The biggest rust hole just happened to be directly under the inadequate cup holder that would let drinks spill on the floor.

So, ontop of the paint, I'd like to coat the floorpan with something super liquid resistant (especially soda) to prevent this rust out again.

Truck bed lining (RINO or eqivilant) works great. It is also not that expensive.

DO NOT USE UNDERCOATING!!!!!!!!!! I got an 87 not too long ago that someone had sprayed undercoating all over the inside, and I've been trying to remove it since I got it. The undercoating does not harden like the bed liner does. Every time something scuffs it, it will smear and in the hot summer it turns to goo.

I think most use a roofing tar to seal the inside of the patch, however I have not done it myself.

So it gets gooey and oozes? Now that you mention it, I've seen undercoating get soft like tar (which is an ingredient, isn't it?). Yea, I could see it getting into the padding under the carpet, even oozing up thru.

Ok, I'll look at Truck Bed Liner, I have almost no experience with it. I'm assuming if it says its truck bed liner, it will be hard and not ooze into the carpet or padding over top it. Is that correct, or is there cheapo Truck Bed Liner that would do that?

I'm talking $20 worth of Truck Bed Liner here, to coat the low spots that liquid would collect, to prevent it ruining the paint and starting the rust again. If the truck bed liner is too expensive, I'll just get another $9 can of Rustoleum and do 2 more coats on the floor.

I think most auto parts stores carry truck lining and you can buy it in spray cans for about $5 a piece. Its for touchups but it should work like you want. Good luck. If you look in the pictures page here there are several pics so you can see what it looks like. Most of us buy the kit and doo the whole floor.

Thanks guys.

I would do the whole floor if this was an actual 4 wheeling off road machine. BUT, its a 2WD 4 Cyl for my daughter to drive on the street. It looks cool and has enough heft, that I won't worry like most of the little econo-box's that we would have had otherwise. Unfortunately, I returned the welder before I remembered to weld up the back seat in the upright position, that thing can NOT be allowed to go down into the improtu bead in the back. :lol:

This experience has wet my whistle a bit for 4wd, I may trade in my Poor Man's Sports Car (Neon R/T) for my own 4WD Cherokee for some off-roading on weekends. In that case I would do the whole floor with the Kit and No carpet. I helped my Brother do his Jeep Wrangler floor with the kit. My first experience with the Jeep "Snap Off any Bolt under the car because its siezed."

HOW TRUE GOOD LUCK!!

Jess said:

The undercoating does not harden like the bed liner does.

Click to expand...

Well ... don't forget there are two types of undercoating. There's the rubberized kind, and the tar-oil kind. The rubberized kind of undercoating dries up pretty hard and flexible ... not a bad solution I think. I've never used it to line a floorpan, but I have used it under the body, and it dried up good and hard (rubbery).

How will it act above the cat? That's anybody's guess.

Funny, the floorpan just above the CAT is great, the rust holes were just in front (the biggest one) and behind it.

Maybe it was the heat from the exhaust that helped, but rust holes were almost symmetrical from left and right side of the floorpan, and the larger were low points on the floor pan that would pool any spilled liquids. Like I said before, the largest hole was exactly below the 1/4" deep cup holder, that was next to the shifter and hung out over the passenger side foot well. Judging from the condition of the carpet, this was the cause of the rust and it rusted from the inside out. Lots of soda spilled into the carpet over my biggest rust hole.

From underneath, the rust was totally hidden under intact undercoating, until I tapped on it with a hammer. Once I lifted the carpet, it was quite obvious. That might also just be the difference between paint and undercoating also.