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    • CommentAuthorowlman
    • CommentTimeMay 12th 2012
     
    Does anyone have any experience of GRP as a lead roof substitute. It's for a small pitched roof.
    For instance does it look OK, and how does it weather? The longevity seems fine, and all the components/mouldings etc are readily available. Is it easily applied? What about flashing to a house wall?
    Any advice greatly received. Mike
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 12th 2012
     
    Posted By: owlmandoes it look OK

    Can look like anything you want almost.

    Posted By: owlmanhow does it weather

    Very well if applied right, dreadfully if applied wrong.

    Posted By: owlmanIs it easily applied

    Has to be very dry, not to hot, not to cold, not sunny if possible.
    Easy when you have worked with the material for years.

    I think (started using this stuff in the mid 70's) it is easy to fall into a trap with GRP if you think that it is an easy material to use correctly. But if used correctly it is an excellent material that is under used in the building industry.
    If you want to 'give it a go', go and get a few kilos and do some test runs outside in the garden. Find the pitfalls and find ways around them.
    Oh and make sure it is absolutely dry, not even damp.

    And get ready for itchy arms and hands, face and legs, neck and torso.

    Make sure it is absolutely dry, don't let the matt lay on anything even remotely damp.

    Buy lots of hand cleaner and acetone for cleaning things up with.

    Make sure nothing gets wet or damp.

    We have discussed this at length somewhere else on here.

    Have I mentioned that it has to be dry?
    •  
      CommentAuthorjoe90
    • CommentTimeMay 12th 2012
     
    As per what ST said above but also It has to be dry . Our local supplier even does free 2 hour lessons including materials to point you in the right direction.

    I have used it many times to replace lead gulleys, small flat roofs etc and found it marvelous stuff. Unlike lead you dont need step ups and expansion gaps.

    It looks exactly like lead from a small distance.

    Also no-one is going to nick it:devil:
    •  
      CommentAuthorJSHarris
    • CommentTimeMay 12th 2012
     
    Anyone just used it (DIY) to replace a small felted flat roof, by any chance?

    I have a small porch (maybe 2 m²) where the felt is at the end of it's life and have thought about ripping it off and doing it with GRP. I've done a fair bit of composite work over the years, but never on something like a roof.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 12th 2012
     
    Make sure it is dry Jeremy, apart from that it is just the same. Painting on Cobalt Accelerator onto the timber can help it to adhere very well (I would not recommend an Amine based one though, bit too quick)
    •  
      CommentAuthorjoe90
    • CommentTimeMay 12th 2012
     
    JSH, a man of your experience will find this a piece of cake, lots of advise on you tube.

    But make sure its dry (have we mentioned that)
    •  
      CommentAuthorJSHarris
    • CommentTimeMay 12th 2012
     
    <blockquote><cite>Posted By: SteamyTea</cite>Make sure it is dry Jeremy, apart from that it is just the same. Painting on Cobalt Accelerator onto the timber can help it to adhere very well (I would not recommend an Amine based one though, bit too quick)</blockquote>

    Thanks Nick. What do you finish the surface with, just a gel coat (with wax so it cures properly) or is there some other way of getting a durable finish?

    I have a part roll of CSM, a the best part of roll of 300g/m² rovings, so was planning on getting some resin, waiting till the weather right and just ripping the old felt off and having a go.
    • CommentAuthortony
    • CommentTimeMay 12th 2012
     
    Lead is better, longer lasting, recyclable, probably cheaper in the long run if done properly
    • CommentAuthorCerisy
    • CommentTimeMay 12th 2012
     
    Years ago it was pushed in the trade as the answer for flat roofs, but it's all down to the detailing and the companies involved couldn't be bothered with such small issues so it faded away. You have to remember to allow for expansion / contraction, especially at junctions. The early stuff was also badly affected by sunlight, so you need to properly specify or protect.
    • CommentAuthorowlman
    • CommentTimeMay 12th 2012
     
    Thanks fellas I guess it has to be dry then.
    I had a look at a suppliers website and all the mopstick mouldings, upstands, downstands, corner detailing, etc. to pre-apply are all readily available. Is the colourant in the resin or do you apply a patinating liquid or gel. Any ideas about how to get a nice flashing detail,- presumably adhere an upstand moulding to the brickwork.
    • CommentAuthorowlman
    • CommentTimeMay 12th 2012
     
    Posted By: Cerisy................ You have to remember to allow for expansion / contraction, especially at junctions.

    Good point Jonathan.


    The early stuff was also badly affected by sunlight, so you need to properly specify or protect.

    How?........This job is South facing.
    • CommentAuthortony
    • CommentTimeMay 12th 2012
     
    UV kills it
    • CommentAuthorowlman
    • CommentTimeMay 12th 2012 edited
     
    I figured that tony, but it was the properly specced bit I was after. It can't be that bad they build boats from the stuff.
    •  
      CommentAuthorjoe90
    • CommentTimeMay 12th 2012
     
    Posted By: tonyUV kills it


    Why dont boats fall apart then?

    Expansion is only a real problem with large flat roofs
    • CommentAuthorMike George
    • CommentTimeMay 12th 2012 edited
     
    Posted By: tonyUV kills it


    The gel coat stops the effects of UV doesn't it?
    • CommentAuthortony
    • CommentTimeMay 12th 2012
     
    No but slows it down.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 12th 2012
     
    As for the top coat a 50/50 mix of gelcoat and a self etching resin, some wax additive and a colour of your choice. Sand the glass resin matrix as well as you can, get rid of all the dust and then, with a very stiff brush, fill all the little holes and before then resin cures (this happens in a few minutes as you have to keep the catalyst ratio high), finish of with long smooth strokes.
    Takes practice.
    •  
      CommentAuthorjoe90
    • CommentTimeMay 12th 2012
     
    This from the countries largest supplier of GRP:-

    "Many glassfibre laminates made during the early days of GRP production in the 1940s are still in use today. Extensive testing has demonstrated the typical life expectancy of a GRP roof product to be well in excess of 50 years. And, tests conducted to date have shown 'no deterioration' infrastructure or performance throughout the testing period. Additionally, because GRP products or use in extreme conditions such as underwater, when used in the manufacture of boats, a GRP product applied by a specialist company could be expected to last a lifetime.

    The entire area on a GRP roof is encapsulated into one single continuous GRP membrane and there are no seams joints or welds. It is also completely UV resistant."

    A local company advertise GRP roofing to last in excess of 35 years.
    •  
      CommentAuthorJSHarris
    • CommentTimeMay 13th 2012
     
    Thanks Nick.

    As for longevity, all I can say is that there are an awful lot of 30 to 40 year old GRP boats around that haven't fallen apart from UV exposure. I know that some of the gel coat pigments are (or were) badly affected, as the body of an orange beach buggy I owned about 35 years ago went a bit chalky on the surface. On the other hand, a friends knock about GRP dinghy is around 30 years old and still looks fine, despite having lived outside in his garden for the whole time he's had it (his kids learned to sail in it and are now grown up with kids of their own who are also learning to sail in it).

    Hot tar and felt only has a 10 to 20 year life, so if GRP is double life that for little difference in cost it seems to make sense to me.
    • CommentAuthorCerisy
    • CommentTimeMay 13th 2012
     
    Just one issue with "Hot tar and felt only has a 10 to 20 year life, so if GRP is double life that for little difference in cost it seems to make sense to me." The more expensive "felts" have lifespans far in excess of 10 to 20 years ... back in the days of my CLASP involvement we were putting flat roofs up that were lasting over 25 years and still looked excellent. It's back to the old chestnut - the right material for the right location properly detailed.
    •  
      CommentAuthorJSHarris
    • CommentTimeMay 13th 2012
     
    <blockquote><cite>Posted By: Cerisy</cite>Just one issue with "Hot tar and felt only has a 10 to 20 year life, so if GRP is double life that for little difference in cost it seems to make sense to me." The more expensive "felts" have lifespans far in excess of 10 to 20 years ... back in the days of my CLASP involvement we were putting flat roofs up that were lasting over 25 years and still looked excellent. It's back to the old chestnut - the right material for the right location properly detailed.</blockquote>

    That's interesting, thanks. I was going on an observation our surveyor made in his report when we bought this house, and assumed all felt flat roofs were much the same.
    •  
      CommentAuthorjoe90
    • CommentTimeMay 13th 2012
     
    Not sure you can DIY hot tar? Lots of loft conversion companies here in Bristol use GRP for flat roofs quoting min 35 years, the cost of repair/replacement goes up a lot 3 floors up with scaffolding!!!
    • CommentAuthortony
    • CommentTimeMay 13th 2012
     
    I have seen tar flat roof 80 yea old, my first 45 yrs ago still hasnt leaked

    Did lots of torch on ones (possible for DIY) with high performance felts, always and crucially with a fall ot 1:40 or steeeper. No probs yet.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 13th 2012
     
    Posted By: CerisyIt's back to the old chestnut - the right material for the right location properly detailed.

    Yes, and application of those materials.

    I like GRP, but can see lots of limitations to using it on site.
    The main one being having everything very dry.
    The other one being not letting just anyone 'have a go'.

    And did I mention making sure everything is really dry.
  1.  
    I've heard rumours that GRP coated OSB is now available, though not managed to source it yet. It may just be that contractors are pre-coating the OSB in a dry environment and then 2nd coating or bandaging the joins on site prior to the gel coat. Not sure what I think of this, as there will be lots of 'bandaged' joins on site. Though I guess the theory is that this is fine, apart from the aesthetics of it.

    Anyone else have a view on this?
    • CommentAuthortony
    • CommentTimeMay 13th 2012
     
    I can see it cracking on the joins eventually
    •  
      CommentAuthorjoe90
    • CommentTimeMay 13th 2012
     
    Tony, I get the impression you dont like GRP!!!!

    Not sure about GRP coated OSB as the fixing nails would puncture the GRP which means you would have to bandage all the nail holes as well as the joins. Usually roofs only have one coat of matting unless used as a walkway so dont see the point. It could be a way of keeping the OSB dry (did we mention keeping it dry?) but any rain etc would get in the joins before it was bandaged/gel coat.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMay 13th 2012
     
    Posted By: joe90Usually roofs only have one coat of matting

    That worried me, I would use 3 layers of 450 g/m^2 (or once and a half as we call it). It may also be necessary to put a second glaze on it depending on how well the first one goes on.

    I like the idea of pre-laminated boards and it does reduce the risk of moisture affecting it, have I mentioned just how awful it is to do when it gets wet, may have slipped my mind.
    Would require careful fitting and very careful jointing on site, and if any water got in, it could cause havoc.

    But if they are going to the trouble of covering 8 by 4 sheets of OSB from the builders yard, they better make sure that the have only been stored inside, don't want them getting wet. But then again if they are doing it this way, why not just make a cheap mould and lay it up correctly with a decent jointing design, used tt work on the steam rooms a treat (for a list of some of the ones I have installed, join the RAC club, most of the THF hotels, SaunaWorld in Colchester, did the saunas too, just timber framed buildings really).
    If you want to use a resin that has both good chemical resistance and can take high temperatures, and a way around the moisture problem, it starts costing a lot of cash :wink:

    Forgot to mention, everything needs to be dry, bone dry, not even that slight cold damp feeling.
    • CommentAuthorowlman
    • CommentTimeMay 14th 2012
     
    The small pitched roof ( porch type ),I had in mind was about 3m x 1.2M hipped at each end. The thought occured to me of cutting and fitting the OSB or ply covering, (4 pieces at most), and then removing them undercover where I can control the first coat, and joint the edges . The subsequent coats applied after final in situ fixing. Joints to be covered with the purchased mouldings and overcoated. It also occured to me to construct a small hidden box gutter around the edge using ply and purchased mouldings. I havent figured that out yet especially the soffit detail. Do you think it's do-able?
    •  
      CommentAuthorjoe90
    • CommentTimeMay 14th 2012
     
    From ST

    That worried me, I would use 3 layers of 450 g/m^2

    I have been on the roofing course given by the supplier and one coat of matt 450 with resin followed by one coat of coloured top coat is the norm. They mentioned a second coat of matt and resin if the roof had foot traffic. I must admit I thought it a bit "thin" but as long as you are not mean with the resin the result is very good. None of mine has leaked in 10 years.

    P.S. why cant I quote from a previous page?
   
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