Thursday, 24 July 2008

Getting to the inevitable leaks

If you buy a second hand motorhome or caravan or whatever, you're likely to have inherited some leaks. The biggest sin of mobile living is not checking for these, and unfortunately, most previous owners have pretty much decided they didn't want the vehicle and have probably let this maintenance slide.

I've found two full on leaks, one through a cracked/rusted roof skin and the other through a very old and perished roof vent. The roof vent will get replaced (and sealed) the same time as the hot water system gets installed. The other - has been dealt with.

Here's a picture of the offending leaky spot. Sorry there was no before picture, but the long and short of it is that this Nissan Civilian bus has several seams in the roof, covered with a bonded-on plastic capping. This leak had obviously bothered the previous owners because there was some sealeant against one edge of the capping.

When I dug out the rust, there was a 2cm long, 0.5cm wide L shaped hole right through the roof. Sorry - I'd already hit the rust with passivator fluid so it's all turned black and hard to see. But it's there... And speaking of rust passivator, it, automotive body filler, and a can of spray paint form the backbone of your seek and eliminate mission.

Don't skimp on these - they don't cost all that much (about $8 for the rust convertor/passivator and $14 for the body filler) and will be all that stands between your belongings and a deluge. (The black duct tape was just there for emergencies, as the weather was varying between bright sunshine and rain showers, and if it had set in for rain I would have temporarily put tape over the spot.)

The first step is to remove the paint, the rust, and any flakes and crap around the "wound." I use a screwdriver for the first attack, then a hand wirebrush, and then a bit or emery paper or cloth if you're finicky. As long as the surface is clean and all the rust is exposed and the majority of it scraped off, you should be okay.

Apply the rust passivator with a bit of cloth, or a brush. USE RUBBER GLOVES. This stuff is generally a nasty acid like phosphoric acid, and you don't want to get it on your skin. If you have access to the leak inside, go inside now and remove the rust in there too, and also brush some passivator on this. Give the outside time to dry out completely, that takes a few minutes. Take a piece of wet paper towel or cloth and lightly wipe over the area to remove excess.

Dispose of the passivator-contaminated items responsibly. Washing out the brushes/cloths in water is perfectly acceptable as far as I'm concerned, you should not have used more than a few mils anyway, and water apparently breaks it down. Just don't get any on your skin nor let it go into your garden.

Mix the body filler (aka "bog" in bodyshop parlance) as per directions. This is important - don't try and hurry the setting by adding more hardener, or you'll end up with a less than ideal density of patch. I'd chiselled away a lot of the plastic capping so I elected to very roughly follow the profile of that capping, you can apply the bog as you like, as long as it's a little proud of the surface. That allows you to sand it back if you want to achieve bodyshop standards of finish.

I pretty much left it like that. I could have spent time sanding to profile and so forth but the rain was approaching and I just wanted to get finished before I had to tape over everything and then I'd have to probably start again...

Bog takes between 10 minutes and several hours to set, I go for the rapid cure type for preference. After 30 anxious minutes watching cloud banks scud to either side of me, the bog had set dry on the outside and was no longer flexible.

The last stage is - PAINT IT. Don't leave body filler and raw metal exposed to the elements, that's just asking for a recurrence of the rust. I use an enamel type undercoat white, because this gives a good surface that I'll be able to spray tropical white over at a later stage, you could use touch-up paint matched to your vehicle if you prefer. Faster drying is better, but this is up to you. While I was at it I sprayed a short distance either side of the repair, on the theory that filling minute crazing and cracks in the plastic capping with paint would protect against further rust developing.

I just lightly keyed either side of the capping with sandpaper, maybe a centimetre either side, and sprayed on a few thin films one after the other. The undercoat enamel dried within minutes so it was quite easy to apply three coats in about 15 minutes.

And that was it - repair effected in about two hours, the rain actually came in an hour later and the leak is gone.

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