Thursday, January 20, 2011

Sealants & Undercoating


If you keep any motorhome long enough, no matter how well it's maintained, you are going to have a leak that wasn't anticipated. That said, most leaks can be prevented if your maintenance is comprehensive enough. The problem is knowing about all that should be done. For example, a window leak in driving rain. I had never read or heard of cleaning under the window tracks and the LD manual has no instructions. It may be obvious now but it wasn't before. My neighbor's RV developed a leak in the TV antenna, a hidden seal went bad. The owner's manual had no maintenance instructions. The ceiling on my LD developed a roof leak in the summer with the A/C running. After tearing the unit apart, I found the evaporator condensate drained was plugged, overflowing the tray. No mention of this in the owners manual and it is hidden from view.

Most leaks enter at the roof seams, roof appliances, end caps, or window frame seals. Where the water travels after that before settling and causing damage is less obvious, but gravity is the key. Inspect carefully the walls below all windows, especially at floor level. In general, move stuff to see the floor-wall seam everywhere you can, even inside cupboards, around the bunk mattress. For outside compartments above floor level, inspect inside carefully. Check compartments below floor level from underneath. And, from the outside, look carefully at all walls for signs of vertical compression due to wood rot - visible by horizontal ripples in the aluminum skin.

Most leaks occur because the owner doesn't want to or have the time to yearly go through the whole RV looking for problems. We need to to find and use more effective sealants with longer lifespans.For many years Lazy Daze used Parlastic or PR-255 sealants; both are polyurethane sealants. The factory also tells you to NEVER use silicone based sealants on the exterior of your motorhome. This is also what RVCG says. Silicone sealants tend to develop hairline fractures between the surfaces being sealed that draw water in by the same capillary action that the window sealant you used on your rig uses. This is becoming a more well known fact about silicone sealants adhering to metal and several other surfaces.

Suggestions by fellow LD'ers

- I switched over to marine polyurethane several years ago. It last longer than silicone but still needs replacing every few years.A commercial debonder is available for removing and cleaning polyurethane. Silicone does not have a product like this that I know of.

- Eternabond: See the Eternabond FAQ on this product which many have used to re-seal roof seams. The advantage of Eternabond over Parlastic is that you can apply it over an old seam with minimal preparation--whereas with Parlastic, you must clean off ALL the old sealant, right down to the metal.

- I had a rear window leak. The water was coming between the rubber seal and the glass. Instead of a using a messy sealant, I used "Captain Tolleys"s Creeping Crack Cure"....great name.It is a very thin sealant that used capillary action to pull it into fine cracks.It cleans up well.

- While wandering about the vendor area at the Tampa RV show the other day, I came across this RV roof coating company that I found quite interesting. After reading the many post by LD owners that are faced with 10-year period roof seam re-sealing project, I was wondering if this would be a viable alternative. The company rep said that the coating can be applied not only to rubber roof, but also to fiberglass and aluminum roofs. He removes all the old caulking around all roof openings, replaces any damages sub structure, primes the surface, and sprays on a thick (3/16") Dow vinyl-type flexible material. Then a non- slip granular layer is sprayed on followed by the final white coating. The demo model showing the sealing around roof vents was impressive. I asked about the additional weight which was around 100+lbs. He charges by the linear foot. You would have to call for the price. Here is the web site.

Treating Wood Surfaces

A while back I replaced all the wood around my propane tank because it was rotted out. I finally got around to covering the wood with a coat of undercoating spray.

I found two kinds at AutoZone, both from Dupli-Color, the same company that makes those cans of "matching" automotive spray paints. The cheaper can was about $2, I think it was a 16 oz. can. The more expensive can was $4, and included rubberized "soundproofing", and was a little bigger can at 17 oz. It was labeled "Professional Undercoat and Sound Eliminator".

I kind of wondered/worried that if this stuff was made to adhere to metal, it might not be effective on wood. The rubberized stuff said on the label it was good for protecting trees after pruning, so I figured it would work, the $2 stuff didn't have any mention of anything but covering metal. So I went with the $4 stuff.It worked great. There were a couple places were there was a seam between 2 panels and I wanted a "bead" between them. I just got the can close and went slow and it made a nice bead in the crack. It dried to a nice tough rubbery consistency. Kind of like the spray on bed-liner. I wouldn't be surprised if it was the same stuff.

A couple of things I noticed or would do differently:

1. The wood was new so there was no need to clean it, this made life very easy. So, the sooner you cover the new wood the easier it will be on you.

2. I would wear disposable gloves. I didn't and wish I had. When I sprayed in tight spots, the back of my hand hit a panel I had already done, and there was some backsplatter when I got in close. Anyway, I got some on my hands and it took Acetone, Carb Cleaner, and WD-40 to
get this stuff off. After trying to get this stuff off my hands (it wasn't even fully dry) I feel pretty confident it is going to stay on that wood.

Things I did correctly: I wore old clothes I use for "grimy" work. A long sleeve shirt, and goggles. I didn't cover my hair, this might be a good idea too. I almost didn't wear the long sleeve shirt because it would be hot, so I decided I'd wait and work in the morning. The reason the long sleeve shirt turned out to be important is that you get an occasional glob that drops off onto the ground (and you don't always notice it), and then your arm hits it as you roll or slide over it to get a new spraying angle. I had some good smears on the back of the arms and forearms of my old shirt.


On our 2001 LD MB, there were only two under-body locations where wood was exposed with porous black paint as the finish. One was a wood strip across the back of the coach between the under-body floor and the rear bumper pan, and the other a wood strip running forward – aft at the intersection of the under-body floor and the left rear lower storage compartment. All other wood used in the under-body area on our LD was extremely well sealed and protected during original build.

I waited until the wood in the above two under-body locations was fully dry and then undercoated the exposed strips, using a pressure can of automotive undercoating, available at automobile accessory or NAPA parts stores. This is a messy job because the undercoating spray is not easily contained. I used plastic sheeting on the storage area concrete, an old pair of coveralls, hat, plastic gloves and plastic safety goggles. All had to be discarded after three coats of undercoating had been applied. All the under-body wood on our LD is now well protected.

Contributors: Chuck, Andy Baird, Don McG, Mike Coachman

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