Rust in the roof

[peterbylt]

Removing the Ceiling panels on the 1989 MCI 96A3.
 
I came across a couple of areas where the Steel ribs have surface rust on them.

I cannot find anywhere that looks like a leak, I was out looking for a leak during one of the rain bands from Mathew and did not see any leaks.

Some of the old insulation looked pretty good, some was pretty deteriorated, all of it now removed.

The large percentage of the roof looked good without any rust on the ribs.

The Bus itself has been mostly rust free.

Could this rust have been caused by condensation?







Peter

[brmax]

Looks like a bit more than condensation, though where anything is coming in is a study.
Where are you at taking the pic, curious minds ya know.
Might this be next to a roof opening? or inline with any sort of condensation.

good day there
Floyd

[gumpy]

Roof hatches leak. If it runs down the framing, it gets absorbed by the insulation. No air circulation to dry it out.

Clearance lights also leak, but they're lower than that framing. Clearance lights are often responsible for rust in the lower wall, just forward of the drive axle.

[bigred]

Had a similar issue on my American Dream .Kept getting rusty "RUNS" down the outside of the white coach.Had it calked from one end to the other ,still had those rust runs down the side finally was on the roof one day and looked at the little "Rubber Ducky "cb antenna and there was the same rust on that thing .Got a tube of caulk and calked the heck out of that thing .End of problem !!!

[Astro]

More than likely it is condensation. If the bus had original ceiling and insulation, the cold transfers directly through the rigs and stringers to the inside heat and condensation forms towards the warm side. Fact of nature and general manufacturing/industry lack of awareness or care as these busses were built as business economic tools, not long term motorhomes. The bus design lacked adequate corrosion protection, condensation drainage and durable, water-proof insulation thick enough to make a difference.

I still suggest, whilst one is that deep in structure to correct as best one can the deficiency and make due.  In other words, check for leaks too, clean the metal and move on.

As one with 40 years of aircraft construction experience, I am appalled at the lag of the bus construction technology in regard to known factors.  Its water, air and heat that causes the damage. remove at least one.

[peterbylt]

Cleaned up the area, still don't see where it could be leaking.

Rust cleaned off pretty good, just surface rust, no deep corrosion.
 
That picture of the rusty rib is taken just to the driver's side of the rear escape hatch, didn't see any leakage around the hatch.

The rain band from Matthew was as good a torrential, wind driven rain as you're likely to get and there was no leaking, I will try a high pressure hose in an attempt to simulate rain at interstate speeds.

If that don't leak I will paint it up and move on. The roof is going to be insulated with closed cell Spray Foam.

Thank You for all your suggestions.

Peter

[Jim Eh.]

One consideration before you spray foam the roof is noise transfer. Although probably the best way to insulate, it is the worst for noise transmission. Makes a rain shower sound like hail. If noise is not an issue or if you are going to put secondary insulation layer then no probs.

[peterbylt]

While cleaning the surface rust off the roof framing I found this one piece of channel with some rust all the way through.

My initial thought is to cut off the bottom of the channel where the rust holes are and clean out and evaluate the inside of the channel, if all looks good cut and weld a strip back on to the channel.

The rest of the roof looks to be in pretty good shape, some spots had some pretty good surface rust but nothing like this.
I have tested the roof with a pressure washer and found no leaks.
 
The moisture must have been from almost thirty years of high Florida Humidity and condensation from air-conditioning.
 
The OEM insulation was pretty deteriorated in places. 90% of the roof was perfect without any rust.



Peter

[eagle19952]

if i were to do anything, i would plate right over it. i would not cut it out.

further investigation is warranted get your ice pick out then a nice sharp steel punch and 8 oz hammer, there is probably a lot more metal/structure there than meets the eye

[brmax]

I was told the major strength in something like that channel is its sides.
One could focus first on carefully checking the rivets for turnable movement, maybe finding a few loose ones.
That rivet issue on bottom or top side, could be fixed pretty quick then I would holesaw holes on bottom flat giving enough to provide a means of spraying something like rust kill, but cleaning first inside with wire brushing possibly. Ive worked through them holes with some cheap engine block brushes before as most are 3' long on twisted wire, they come in handy couple times a year. HF I'm sure has something to help.

Floyd

[JDWood]

Peter...I agree with Astro.  I just observed this happening in my bus this Saturday while getting ready to go out for the weekly ride. We don't have all the original seats out yet and my wife observed several seats with moisture on them. Quick glance up and there was the answer....drip at the rib line.  I expect I may find the same thing you've discovered when I peel our ceiling out. Thanks for posting!
Jon

[BIG DOC]

   HEY, JUST A THOUGHT. I HAD A TRUCK SHOP IN NEW YORK,SO YOU KNOW WHAT WE WENT THRU WITH WATER LEAK'S IN CAB'S.WE USED TO SPRAY SOAP & WATER ON THE AREA WE THOUGHT WAS COMING IN, RUN A AIR HOSE WITH A CHUCK INSIDE. WHERE WE JUST BLEW AIR IN THAT AREA & HAVE SOMEONE OUTSIDE LOOKING FOR THE BUBBLES.WORKED EVERY TIME. EASY TO SEE AROUND LIGHT'S OR SEAM'S. TRY IT. I BET YOU WILL FIND ANY LEAKS. PLAY NICE.DOC

[daddysgirl]

Nice ride 
I don't know if they still observed the same practice in 1989, but on my MC8 (74) all of the structural beams were coated in a rust colored paint. Oddly enough, that coating was to prevent rust. It seems to have worked as I only have one place under my windshield that I need to replace.
But that old insulation is nothing but a nice moisture retention system.

[daddysgirl]

Oh, another thing.
You might want to consider giving all the exposed members a coat of liquid truck bed coating before whatever insulating you use. It will provide an extra layer of waterproof.

[stanton]

Couple things-
Cold Short(s)    insulation can be your friend .I am sure that is what is going on there .(lack of)
Next,  the self-made drains in bottom of channel will not hurt, but now will allow a rust killer  to be sprayed up inside.
.Dont waste your time doing much else.
For plugging holes  where necessary ,  or bedding nuts and bolts As in a roof, holes etc-      Use    3M 5200.  (available at most places that sell marine stuff).