clay Posted July 5, 2009 Share Posted July 5, 2009 away at Brynych this weekend in kon tiki. sat. afternoon it was raining so sitting in van listening to some music, says to wife that drum seems to be out of tune, thats no drum she says its water. jumped up and before my eyes water was dripping through the roof vent and onto floor, placed bucket under it and scuttled up ladder to roof, seems that fractionally the centre of the roof is just about the lowest point causing small amounts of water to pool. rain stopped so got some towels and formed a bund. hoping all alright carried on, 2 am on sun. morning drip, drip again nothing to do but lie there and listen. when it got light i took bottom half of vent off and by feeling around inside to my surprise this vent has been fitted with no upstand and just a mastic used to seal. in all my years in h&v i never fitted a roof vent/ fan without fitting an upstand . fed up, packed up and came home will get outer vent off next weekend and re seal incorporating an upstand . do a better job than swift will ever do. >:-) Link to comment Share on other sites More sharing options...
Derek Uzzell Posted July 6, 2009 Share Posted July 6, 2009 Clay Could you explain what "fitting an upstand" entails, please? As far as I'm aware roof-windows normally just sit directly on top of a motorhome's roof and rely on sealant to maintain water-tightness. Moulded GRP roofs may be designed to incorporate raised areas to support roof-windows and this will undoubtedly minimise the likelihood of pooled rain-water leaking past a roof-window's seal. But roofs with flat aluminium skinning won't have this feature. I've got several magazine articles on installing roof-windows (made by various manufacturers) and all of these articles show sealant being employed as the sole means of obtaining water-tightness. Link to comment Share on other sites More sharing options...
Brian Kirby Posted July 6, 2009 Share Posted July 6, 2009 Your problem, Clay, is you're used to the building trades, where waterproofing is (usually :-)) done proper.The comedians who make motorhomes are only aiming for a life somewhere over 5/6 years, which is where most of their water ingress warranties expire, so can just about get away with using sealants for everything. Most use good sealants, but the way the sealant joints are designed and executed would never pass muster on a half competent building site! Ticky-tacky is, I'm afraid, what you get.I doubt your attempts at creating an upstand will bring much benefit, because all you will be able to do is bond the upstand to the aly roof covering, in just the same way the rooflight frame is now bonded (one dodgy joint being better than two!). You will get just as much success by removing the outer rooflight frame, then cleaning away all the old sealant from both frame and roof, an re-bonding the frame to the roof with an good quality sealant. Sikaflex (from Sika) is one favourite, Teroson (from Loctite) another. Contact either firm's technical dept and ask about removal of the existing stuff, what they recommend as the new sealant, and where to get it. They will probably be able to send a data sheet with full instructions for use. Properly used, these sealants have a life expectancy of around 25 years, so the trick is to use it properly. In the meantime, dry off the roof and use duct, or gaffer, tape for temporary sealing - though I guess you'll already know that!!Good luck. Link to comment Share on other sites More sharing options...
clay Posted July 6, 2009 Author Share Posted July 6, 2009 Hi bryan, i certainly take your point about 1 possible leak source being better than 2. as far as an upstand is concerned i intend to cut a square out of a piece of 1/2'' marine ply, i have a roll of pure ptfe cord, (not tape, which we used to used a as a sealent between flanges on a refinary i used to work. i will sandwich between and screw the ply to the roof joist . this should form a sound joint on the plastic roof. then i have the base to fit the vent. i will do this on the w/end and let you know how i get on. Link to comment Share on other sites More sharing options...
Brian Kirby Posted July 7, 2009 Share Posted July 7, 2009 When you get the rooflight frame off, I suspect you will find that it is held in place by clamping its inner, and outer, portions, with the outer sitting on the bed of sealant. Although this is probably not the most satisfactory way of sealing a rooflight frame to the flat roof, it has one great advantage. There are no screws, or bolts, penetrating the roof. If I understand your proposal correctly, you will have to make quite a few holes in the aluminium, which I think a potential source of future trouble. I think you may also find the "joists" aren't quite what you are expecting! Remember, you said the rooflight corresponds with a low point in the roof, and good as marine ply is, it is still ply, an so prone to expand and contract somewhat with moisture and heat. I really think you would be better off replacing the frame as it is currently installed, but doing the job properly, rather than introducing a different material that involves a lot of screwholes. You need to achieve about a 3mm bed of the sealant between the frame and the aly roof sheet, let it fully cure, and then just give the clamping screws a gentle nip all round, so that the sealant bed is very slightly held under compression - not flattened but just held firmly. Done properly it will last for years. However, if you still don't trust that method, at least make absolutely sure you use only aluminium, or stainless steel screws. Whatever you do don't use brass - you'll turn the roof into a battery - and bright zinc or galvanised won't be much use either! Link to comment Share on other sites More sharing options...
Derek Uzzell Posted July 7, 2009 Share Posted July 7, 2009 As clay mentions, Kon-Tiki roofs (and body panels) are GRP. I think the idea of using marine plywood to raise a roof-window above the roof's surface is unwise, as the material's projected life-span when sat in a pool of water is likely to be significantly less than that of the type of adhesive/sealant Brian suggests. It also needs considering whether introducing a thick 'spacer' between the roof-light and the roof will prevent the original roof-light being easily refitted. Roof-lights are designed to cope with a range of roof thicknesses and, if the Kon-Tiki's roof is already near the maximum thickness that the existing roof-light was designed for, then increasing that dimension via a spacer may well cause problems. Conversely, if the Kon-Tiki roof's thickness is shallow, certain components (like roof-light hold-down bolts) may have been reduced in length and need replacement once the spacer has been introduced. I agree wholeheartedly with Brian that it would be preferable to reject the plywood spacer concept and refit the roof-light using a method that that follows the roof-light manufacturer's instructions exactly and employing a modern adhesive/sealant that has been designed for this type of task. Link to comment Share on other sites More sharing options...
Brian Kirby Posted July 7, 2009 Share Posted July 7, 2009 Derek Uzzell - 2009-07-07 8:36 AM As clay mentions, Kon-Tiki roofs (and body panels) are GRP. ............... How right you are, Derek, indeed he does. I'm afraid I was think of the roof on our van while writing, which is aly, and forgetting what Clay had said.Apologies Clay: though I would still advise against the ply.My comments about brass screws are therefore redundant, though I would still say avoid bright zinc or galvanised - neither will survive without the underlying steel beginning to rust. Link to comment Share on other sites More sharing options...
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