Sealing an aluminium Caravan roof
  I hope this article will make life easier for somebody. I don't claim to be an expert on sealing water leaks but I have learned a trick or two by listening to those who are experts and from my own mistakes.  
     
 

Finding the leak

 
 

The location of the drip is only a rough indication of where the water is entering the roof. Having penetrated the 'vans outer skin, water will flow above your ceiling according to the gradient; where it drips could be some distance from the actual leak. Place your spirit level against the ceiling and turn it around until you determine the direction from which the water will be flowing. That will give you an idea of where to start looking when the rain stops.

 
     
  Finding A ladder  
  Not many caravan parks will loan you a ladder these days due to liability concerns but you might be lucky. Alternatively you can buy your own, it'll come in useful again and again.
"Where on earth am I going to carry a ladder when we're travelling?", you're probably asking.
I researched this problem and Bunnings provided the answer. For a little over $300 (Ouch!) they retail an "i.Q Telescopic Ladder".
 
     
   
  As the pictures show, this i.Q Telescopic Ladder reaches the caravan roof with ease yet collapses down to 85cm (2' 10").
It retails from Bunnings and is rated to carry up to 100kg. A tradesman wouldn't use it but it's ideal for a caravan.
 
     
  Be aware that this ladder is sensitive to water and grit entering the telescopic sections. It must be cleaned and dried before collapsing for storage. Also, on page 7 of the booklet that comes with the ladder, it states: "The ladder is built for a maximum load of 150kg (fig. 12)". Figure 12 shows a man on the ladder with 100kg printed in bold type. The ladder itself also has "100kg. max" printed on it. If I weighed 150kg I wouldn't go near it.  
     
  Locating the leak  
  Our caravan roof is made up of five aluminium sheets which are turned over at the edge. Each sheet hooks into its neighbour and is sealed with silicone. These joints are unlikely to leak. However, where the roof meets the caravan side panels the joint is covered by a rigid, right angle strip and sealed with silicone. Pressure on the roof here will cause the thin aluminium to sag and break that seal. Then next time it rains . . .  
     
   
  Our roof during preparation for re-sealing  
     
 

A bit about the roof construction. The roof is supported by cross beams spaced irregularly along the 'van. The roof is only load-bearing directly above these beams. You can 'feel' where they are by depressing the roof panels with your hand. (I marked the location of each one with a black, indelible marker.) If you stand between the supports there is only a thin sheet of aluminium beneath you. That aluminium is probably ribbed, as in the photo above, and your weight will stretch the metal, leaving a hollow forever more. If you stand on an unsupported area near the edge of the roof, the seal between the roof and the edging strip will break. This doesn't just apply to you, of course, but to anyone else (such as an air conditioner engineer) who tramps around on your roof.

To locate a leak, stand on your ladder and lean over the roof while you press on the aluminium adjacent to the rigid edge strip. If there is any movement between the two, the site needs to be re-sealed. Move the ladder around the 'van and check the whole roof in this way, marking any suspicious places.

The seals around roof vents, your television antenna, the air conditioner, etc., may require you to climb onto the roof. Now you'll need a couple of short planks, strong enough to hold your weight and just long enough to straddle the gap between the roof supports. As you move you pick up the plank just vacated and place it ahead of you.

 
     
 

What you'll need.

 
 

Depending on the condition of the seals you may decide to just repair the suspicious area(s) or to re-seal the whole roof. I decided on resealing both edges, front to back. Most other seals looked perfectly sound. Before you start you'll need the following:

Some form of scraper to get under the old seal and lift it, then to scrape away all the remaining seal from both sides of the repair. A Stanley Knife works well, but using the end of the blade, not the sharpened edge.

A bucket with a little water, some scouring powder such as Jif, a washing up brush and a sponge. This is to thoroughly clean the area that the new seal will contact. If you examine the photo above you'll see that the roof is dimpled and it's in those dimples that the dirt settles. A sponge skims over the dimples, a brush cleans them out.

A degreasing agent that does not leave any residue. (Not turpentine, for example, though turps is invaluable for cleaning silicone off hands and tools.) I used acetone but it's very harsh and too much rubbing dissolves the paint. Again, thoroughly clean the surface to which the new seal will adhere. Like decorating, the success of the finished job depends largely on the quality of the preparation.

You'll need a quantity of clean rags. A discarded bed sheet or towel cut into 30cm. squares works well. Once silicone is smeared on a rag it tends to get in all the wrong places if used several times, so pop it in a supermarket bag (or similar) for later disposal and use a fresh rag.

Finally, you'll need cartridges of new silicone sealer and not just any old sealer:

It must have a neutral cure. (I don't know why this is important but I'm told it is.)
It must be impervious to U.V.
It must be impervious to heat and cold.
It must be impervious to water.
It must remain flexible and never harden.
Finally it must have strong adhesive qualities.

I spent ages going through the dozens of sealers that Bunnings stock and found only one which satisfied all the above criteria. Bostik Roof and Gutter Sealer retails for between $5 and $6 a cartridge. Don't forget to pick up a nozzle for each cartridge - and an application gun if you don't already have one.

 
     
  Sealing the Roof  
  Okay, the suspicious areas have been located, thoroughly cleaned, degreased and are ready for sealing. When the caravan was built, the sealer was applied between the edge strip and the roof. Removing that strip to seal beneath it would be a huge task; having tried on a small section I wouldn't entertain it. The only option, therefore, is to construct a fillet across the join between the edge strip and the roof. Similarly, between any other roof fixtures and the roof metal.

Prepare the cartridge and nozzle as per the instructions on the cartridge. Press the nozzle hard into the junction to be sealed and pull on the trigger. As the sealant oozes from the nozzle, move it slowly along the junction for a distance of about one metre, moving the nozzle back and forth slightly to work the silicone well into the joint.

Next I used my index finger to further press the silicone into the joint and smooth it out. If necessary I added more silicone so that the fillet of new sealant stretched about 2 cm on either side of the join and formed a 'hump' over it. The silicone skins over after five minutes so work it as quickly as possible.

Don't try and make the end result look pretty, you won't succeed. Besides, it's on the roof where nobody will see it. The important thing is that you want it to remain water tight for a number of years. It must withstand temperature change expansion and contraction, and flexing during travel.