I pulled off the headliner and trim to figure out why my headliner was warping. I discovered that condensation was forming on the inside of the cab roof (Hence, my waaavvvyyy headliner) and eventually dripping on the back of the cardboard material. Some of the condensation trickles down toward the cab's perimeter which is showing surface rust. This seems to be why alot of these rigs rust out the leading edge of the roof.

I don't have any rust-through (yet) but is there anything I can do to prevent the condensation and stave off the electrolytic action? I figure insulation but with what? I've heard of some FTE'ers shooting expanding foam where it is inaccessible but will that really prevent rust-through? It seems to be all that would do is hold any water that might form... and be a PITA if and when it comes to replace the metal if preventative measures fail.

What about that stuff that looks like carpet underlayment? Or should I LizardSkin it since it's shootable?

Also when I pulled out the headliner, I discovered a broken weld on the roof bracket (connects back to front) so that needs fixin' on my rig (No problem). Yall might want to check yours.. the weld was tiny and weak.

 

I wouldn't use the expanding all that will do is hold moisture and rot it out real quick.
The roof of my new cab has surface rust all over the whole inside of it so I'm in the same boat as you, not rotted through but I'm trying to prevent that.

I'm gonna sand it all the loose stuff off and por15 it I think.

I plan to get the box type dehumidifiers that have the gel beads in them and stick a few under the seat when I finish the truck to prevent the condensation.

 

he's right - foam is your worst enemy

the bottom line is, if your truck doesn't leak there won't be any water to condense. Every car on the road can potentially have this problem, but not all cars are old and leaky. the ones that are.... well the roofs are all rusting up like yours and mine.

I'll be putting in new glass and getting a quality seal kit for every single seal on the dumb truck. I'm sick of the rust.

 

That may or may not fix the problem. Some of these trucks have a problem with the seam sealer not being applied well or it is just rotted away and the truck is leaking at the cab seams.

 

Yeah, I didn't think foam would be the right option.

I beg to differ...The condensation forms from the ambient humidity in the air contained inside the cab.... Like a glass of cold water on a warm day, the moisture in the air condenses and forms moisture on the glass.

Using the above case to be analagous to the phenomenon, I theorize the air is warmer in the cab than than outside therefore condensing on the cab roof.

Observing the cab today, there were only small droplets that formed on the ceiling... not like when I pulled off the headliner when there were gobs and gobs of water literally ready to drip. I think the open exposure of the cab roof helped somewhat to reduce the temperature difference between the cab's interior and the outside. Then again, it's still condensing.

I am befuddled... vent the roof with an open cell headliner or insulate the hell out of it?

 

Amazon.com: Hydrosorbent Silica Gel Dehumidifier 200 Gram Reuseable: Home Improvement

That's what I was talking about earlier. Not sure how much it would help but it's just a thought I've had.

 

I also have a similar problem...my drip rail thingys are rusted badly where they are welded to the roof...any ideas how to fix/prevent this?

 

Be sure to check under the fllor mat. The insulation in mine years ago was sopping wet (used to play in the mud and water a lot.) The wet insulation was a constant supply of moisture in the cab. Got rid of all the insulation and it helped. When I would get the interior real wet, I would crack the window (weather permitting) just about 1 inch and the sun beating on the cab would evaporate the moisture and the open window would let it out instead of condensing on the cab roof. This way will dry a cab out quicker than just leaving doors or windows open.

 

With the headliner down , leave it out and let the roof dry out for a couple days, the use a good petroleum based undercoating and spray it around the entire roof and above the windshield. Painting it, sealing it will only speed up the rust, it will look good but it doesn't work. Rust check is avail. in sray cans and 2 would do the job quite well. If you look in my profile under albums on the right side you will see that I know way too much about roof rust.

 

I asked a guy who does foam insulation about condensation on a metal roof. Basically the foam keeps the air from the metal. No air = no condensation. A lot of foam has been sprayed in metal buildings in NY with good results.

 

If you want to permenantly fix this problem you will have to start on the outside of the roof and get the old sealer out of the drip rails, you need to get them down to bare metal and apply POR 15 and then new urethane self leveling seam sealer, then replace your window gaskets, your getting water in there somewhere it usually starts on the drip rails