Weatherproofing and sealing a building roof?.

  spuds 12:29 07 May 2013

I recently raised a question about Warping on timber fencing structure, and some very good results came from that, so here's another topic possibly for discussion?.

Have ever used or possibly know anything about Fibreglass type or GRP roofing resin, and if you have, would you care to share any experiences on that product or something similar for roofing and weatherproofing?.

  wiz-king 17:31 07 May 2013

All my experiences with that type of product have been dire. I have had corrugated GRP stable roofs and they havent lasted more than a few years before needing repair. Either they get a build up of crud and go opaque or the crows peck holes in them even with a fair slope on the roof. I have also tried butyl sheet but again it may be OK for a new build but once the roof gets old, wrinkled or any water ingress in the winter it is hopeless and you have to strip the roof off and start again. A good slope and sheets of corrugated iron on top of sterling OSB boards is best for shed and stables.

  spuds 17:45 07 May 2013


I think that I might need to agree with you about corrugated iron, but not so sure about the OSB boards though, unless it is well sealed and protected.

Thanks for the crow suggestion, I had never thought about that, but then again crows are not our main concerns, more with feral pigeons messing the place.

  Forum Editor 18:24 07 May 2013

"A good slope and sheets of corrugated iron on top of sterling OSB boards is best for shed and stables."

Sheds and stables maybe, but hopeless for any habitable structure. Even so, I would still prefer to use a torch-on thermofusible bitumen membrane. Properly installed this is a superb, good-looking, long lasting material, and will not wrinkle or creep. The drawback is that it must be laid by someone who knows how to handle a Propane torch, or trouble will ensue.

18mm WBP ply is infinitely preferable to Sterling board as a substrate, but if the roof is to be what's called a 'warmdeck' construction the covering will go on top of ply-faced Celotex (or similar) insulating boards.

Chopped strand matting and Acetone can be combined with a coloured topcoat resin to provide an excellent, good looking surface that should gibe many years' service. The matting is bonded to the ply substrate with the acetone, and the topcoat fuses to the resulting hard surface - it's pretty easy to do, provided you are reasonably handy with tools, and you take care with the corner and edge details - always areas of potential problems for DIY roofers.

  oresome 20:16 07 May 2013

I worked for a company who had 1970s premises with a roof that forever leaked after the first 15 years or so.

They got quotes for a once and for all fix and chose the cheapest because it came with a 25 year guarantee.

The company put a membrane over the entire roof which originally consisted of corrugated sheeting. Needless to say, it didn't stop the leaks and the roofing company then went out of business after a few unsuccessful attempts at rectifying the faults.

Subsequent attempts to get anyone else to look at the roof proved futile as they couldn't see under the membrane to estimate what was needed and wouldn't quote.

The roof still leaked in 2002 when we vacated the premises.

  carver 20:53 07 May 2013

just what are you trying to do, re roof an existing building, patch a roof up , is it a flat roof or pitched roof.

I can tell you how to do a complete roof but unless I know what you are intending to achieve I don't know what to tell you.

I can explain how to put a GRP roof on or even the best way to sheet a roof, what sort of area are you covering, an out building or part of a home. Will people walk on it after wards, have you got sufficient purlins and are they the correct size.

These are the things we need to know.

  Aitchbee 21:36 07 May 2013

My verandah and my next door neighbour's adjoining verandah, which are on the first floor level, overhang and are 'for all intents and purposes' are the roof[s] to our downstairs' neighbour's living rooms.

About 4 years ago the total surface area of the 2 x 1st floor verandahs were resurfaced or re-roofed, so-to-speak, with a 'liquid plasic' compound called DECOTHANE. The final look of the verandahs looked like 'a lunar surface', but, in all fairness, the water ingress to our neighbours' living rooms, directly below the treated balconies, was fixed.

Total cost for 2 X 8m X 3m verandahs was about £3,200.

PS. The 2 verandah were restored to the original tiled finish [on top of the DECOTHANE], free-of-charge, eventually.

  Forum Editor 23:07 07 May 2013


it's obviously a flat roof - see my response. You don't have purlins in a flat roof construction,and you wouldn't use a resin-based covering on a conventional pitched roof.

In general terms the two materials of choice for a flat roof are a torch-on membrane or a resin-based covering. Both are effective, and both can be walked on if necessary.

  spuds 00:26 08 May 2013

My main question open to discussion was about Fibreglass or GRP roofing resin, and whether anyone had used this type of product, and what was their experiences.

One of the reasons why I asked the question, is due to having a number of outbuildings with various roofing construction, both flat and pitched, and GRP had been suggested as a sealing and weatherproofing compound.

  carver 06:54 08 May 2013

F.E Thank you for your reply, you obviously know far me than I will ever know even after working in the industrial roofing trade for a fair number of years.

Rule number one/ do not take any thing for granted, ask first.

  carver 07:02 08 May 2013

F.E "it's obviously a flat roof - see my response. You don't have purlins in a flat roof construction,and you wouldn't use a resin-based covering on a conventional pitched roof."

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obviously you should inform these people and god knows how many more you can't use their product on a pitched roof

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