Diablo

Help Needed With My Leaky GRP Roof

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All,

 

today's torrential downpours have resulted in a leak in my living room roof.

 

When the OSB boards were originally put down, it started to rain before we could get them covered.  The roofer did his best to dry the boards out and put down the GRP roof.  He did warn us it was not ideal, but we were desperate to move in, so I told him to just go for it.

 

3 years on and the top coat is flaking badly and the roof has started to leak.

 

I intend to go up tomorrow morning, clean up the roof and put down some repair product that my brother swears by.   Has anyone got any advice on how to clean up the flaking topcoat as it is really tough stuff and cannot simply be pulled away?

 

Thanks in advance, Narinder 

 

 

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Sadly, polyester resin and even the slightest trace of moisture is a recipe for failure of the GRP.  The "topcoat" should be a waxed gelcoat, and will be equally susceptible to poor curing from any moisture inhibiting the cure of the underlying resin.  The gelcoat with the added wax tends to seal in moisture during the early stages of the curing process, as the added wax is there to float to the surface and exclude the inhibiting effect of moisture in the air during the cure.  This has the unfortunate effect of trapping any moisture that's already underneath the GRP, and this moisture will then end up staying in the partially cured laminating resin in the GRP itself.

 

Any over-coat won't fix the problem, and will be, at best, a stop-gap repair.  I'm near-certain that you will find that the GRP isn't bonded to the substrate.  As you almost certainly can't replace the GRP at this time of the year, because of the weather, I'd be inclined to just try and do a temporary fix with a bitumen-based repair solution.  This will preclude you putting anything permanent on top of the failing GRP, but should get you through the winter without costing an arm and a leg.

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JSHarris

As usual, I think you are spot on.  After all the blood, sweat and tears, it is a bit soul destroying to see water dripping into the living room…. However, I need to get through the Winter for now…

Any thoughts on the best way of scraping off the flaking top coat so that we can get a relatively smooth surface on which to apply the repair solution?

 

Thinking forward to next year, do you think we would need to replace the OSB boards?  I am really hoping we can get away without having to go to that extent…

Thanks again.

 

 

 

 

 

 

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31 minutes ago, Diablo said:

 

Thinking forward to next year, do you think we would need to replace the OSB boards?  I am really hoping we can get away without having to go to that extent…

Thanks again.

 

 

 

 

 

 

I think that depends on several things, including the physical form of the roof, and the condition of what is there already when you come to repair it.

 

One thing you could consider would be a whole new roof, including OSB, on the top. If the roof is between parapets that may work, but may leave you hostage to further deterioration of the existing (eg if the old OSB is wet and swells). 

 

Or you could take it off and start from scratch - or switch to a different type of roof. Is the physical form such that you could eg go right over the top with a membrane? (Perhaps not or you might not have used GRP anyway.)

 

I have seen fibreglass repairs work for years and years, but if it is nearly new and you are planning to be there for decades, it sounds like a bite the bullet and start from scratch may be the way.

 

Ferdinand

 

 

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I second all above, yes any damp on laying the GRP is a no no. Yes, bodge it to get over the winter and if we get a good summer or extended dry period next summer rip the GRP off and see what’s below, OSB is not expensive in the scheme of things .

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Gents,

 

Thanks again for the replies.

 

We spent all of Sunday on the roof, mostly cutting out the really bad areas of the topcoat.  The source of the leak was a particularly bad area where, once we cut through the GRP, revealed a rotten piece of OSB. This was cut and replaced. 

 

I cannot have this hanging over me (literally), so as has been suggested, we will take the plunge and replace all of the underlying OSB.  I cannot believe that the single board we replaced was the only rotten one, so I am budgeting to replace the entire lot.

 

Much appreciated.

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I'm really sorry to hear this, but sadly I can't say that I'm surprised.  The slightest bit of moisture seriously degrades the cure of polyester resin, and it's probably been gradually breaking down under the gelcoat and becomy more and more porous, most probably has been letting water through gradually ever since it was laid.  The problem then is that this result in more trapped water within the laminate which then tends to accelerate the rate of degradation.

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Sorry for slight hijacking of this thread, but I was about to fiberglass my balconies. I was actually planning to post on this topic today or tomorrow, but seeing this thread I thought I'd keep it all together.

 

The OSB unfortunately got a decent soaking over the weekend when I forgot to cover it. I'm allowing it to dry during the day when it isn't raining, and am covering it up at the end of the day, to keep any dew off it and reduce the condensation.

 

I know that there are both temperature and moisture issues when laying fiberglass. Regarding temperature, I was planning to wait until we had a couple of clear days with expected temps in the mid teens, and then do the work on consecutive afternoons (base one afternoon, gel coat the next). The balconies get sun in the morning, which will help.

 

Based on the comments above, I'm now a little concerned that perhaps I shouldn't be considering doing this until spring next year when things have warmed/dried up.

 

I really don't want to wait though. Short of getting heaters involved, is there anything I can do to allow me to crack on with this in the next week or two, assuming weather permits?

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Is there any waterproof material that can be applied over the osb before fibreglass works go on top ? Something that WILL adhere to the damp osb but provide 100% separation in regards to moisture.... and then still be able to take The fibreglass on top..... ? 

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3 hours ago, jack said:

Sorry for slight hijacking of this thread, but I was about to fiberglass my balconies. I was actually planning to post on this topic today or tomorrow, but seeing this thread I thought I'd keep it all together.

 

The OSB unfortunately got a decent soaking over the weekend when I forgot to cover it. I'm allowing it to dry during the day when it isn't raining, and am covering it up at the end of the day, to keep any dew off it and reduce the condensation.

 

I know that there are both temperature and moisture issues when laying fiberglass. Regarding temperature, I was planning to wait until we had a couple of clear days with expected temps in the mid teens, and then do the work on consecutive afternoons (base one afternoon, gel coat the next). The balconies get sun in the morning, which will help.

 

Based on the comments above, I'm now a little concerned that perhaps I shouldn't be considering doing this until spring next year when things have warmed/dried up.

 

I really don't want to wait though. Short of getting heaters involved, is there anything I can do to allow me to crack on with this in the next week or two, assuming weather permits?

 

One option (costly, though!) would be to switch to something like epoxy laminating resin instead of polyester, as the cure of that isn't seriously affected by moisture, only really temperature.  I'm not sure if there are approved epoxy roof systems though, my experience has been just with making boat and aircraft composite stuff.  One downside with epoxy resins is that they are susceptible to UV degradation, so the roof would still need a topcoat of UV resistant resin.

 

Another possibility may be to look at vinylester resins.  They are a sort of half way house between polyester and epoxy, in that they aren't as badly affected by moisture as polyester, but not quite as forgiving as epoxy.  Again, I'm not sure whether there are any approved vinylester resins for roofing systems, but unlike epoxy, vinylesters are pretty UV resistant, much the same as polyester I believe.

 

One other key difference between polyester/vinylester and epoxy is that epoxy will bond very much more securely to the substrate, even if it's slightly damp.  Epoxy will also bond much better to itself once it has cured, as long as the surface of a cured layer is roughed up a bit.  Polyester and vinylester resins don't bond that well to anything other than a really dry substrate and only bond really well over a cured layup when the cured layer hasn't fully cured, so there can be a chemical bond.  Another advantage polyester and vinylester have is that the cure time can be controlled by the amount of catalyst used, so if the weather is a bit cool adding more catalyst will usually get around the problem (as long as the temperature doesn't drop below about 7 or 8 deg C).  Epoxy resins have a fixed ratio of the two components, which has to be accurately measured, and cure time depends on temperature, which makes them a bit less forgiving to use.

 

It may well be possible to use an epoxy primer to seal the substrate, though.  It's not something I've tried, but a company with lots of experience of roofing and GRP, like CFS, may well be able to give you some good advice.  I've been using them for resin and composites for well over 30 years now, and always found them very helpful.

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I agree with JS --having also been doing grp +epoxy for 40years ,and also built a europa which is full epoxy wings.

there is a special resin which may help 

it is used for emergency gutter repairs and is set by unltraviolet  light, preactivated  --it is sold with a 28 days use by date on it and once you open it you need to use it  sets in less than an hour

It is not cheap ,but does adhere to damp surfaces,so maay be one coat of this then on with  normal grp on top of it --20years later gutters are still water tight 

would copy you site --but changed ocmputer since then..

CFS will know all the different solutions for sure --i also use them  

Edited by scottishjohn
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Thanks for the comments.

 

I've already bought all the stuff to do everything, so would prefer not to repurchase an entirely new system's worth of coatings. However, if there's some sort of base coat I can get that will give me a dry surface to work from with the standard resin, that might work.

 

I'll give CFS a call.

 

thanks

Jeff

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PVA? that mixs with water then drys a;ways used to seal blockwork+ give a bond coat  before hard plastering ,

wheres the grp going to go once its a complete sheet any way .

you got some thin sheets of dry ply -nail that onto osb and bobs your uncle --osb will soon dry out under it

you could always mix up a very small amount and try an area and see if you pull it off next day --if its stuck no problem 

Edited by scottishjohn

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5 minutes ago, scottishjohn said:

PVA? that mixs with water then drys a;ways used to seal blockwork+ give a bond coat  before hard plastering ,

wheres the grp going to go once its a complete sheet any way .

you got some thin sheets of dry ply -nail that onto osb and bobs your uncle --osb will soon dry out under it

you could always mix up a very small amount and try an area and see if you pull it off next day --if its stuck no problem 

 

 

Absolutely not, I'm afraid, as PVA has a lot of water in it, which then has to dry out as well as any residual moisture in the substrate, so it makes the problem potentially worse, by partially sealing damp in.  GRP doesn't adhere that well to it either, as PVA is slightly moisture permeable when it's dried, so moisture trapped underneath (because the PVA only dries from the exposed surface) will gradually migrate through it to the GRP. 

 

Using a moisture-curing primer will help to draw moisture out of the substrate as it cures (and G4 cures, rather than dries), which is one reason G4 is used such a lot as a primer before applying GRP.

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so go to plan 3 try a small area today and try to peel it off tomorrow,

he don,t want to spend money he already said that 

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1 minute ago, scottishjohn said:

so go to plan 3 try a small area today and try to peel it off tomorrow,

he don,t want to spend money he already said that 

 

The snag is that it may take a year or two for the GRP to start breaking down internally from trapped moisture, so a quick test may well not do very much.  If there's enough moisture around a quick test will show the problem, as the first coat of resin will take a long time to partially cure and will remain a bit like a gel for a long time, but it's hard to judge this unless you've done a lot of polyester GRP work and seen what moisture curing inhibition looks like.  Some resins will blush if there's too much moisture present, which is a good clue, but it's not a guarantee that it is all OK, unfortunately.

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7 minutes ago, JSHarris said:

 

The snag is that it may take a year or two for the GRP to start breaking down internally from trapped moisture, so a quick test may well not do very much.  If there's enough moisture around a quick test will show the problem, as the first coat of resin will take a long time to partially cure and will remain a bit like a gel for a long time, but it's hard to judge this unless you've done a lot of polyester GRP work and seen what moisture curing inhibition looks like.  Some resins will blush if there's too much moisture present, which is a good clue, but it's not a guarantee that it is all OK, unfortunately.

yes its very hard cos his idea of just slightly damp might not be our idea of slightly damp-- yes most resins will blush if alot of moisture present --the wee test might show that and then he knows he gotta wait till its all dry .some of my gutter repairs did that ,but doing in mid winter its not suprising ,but i did use 2% hardener to make to go off quick due to temp--still there holding the rusty old gutters together and water tight --maybe the exothermic reaction dried it out a bit .LOL

 

Edited by scottishjohn

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I don't mind spending some more money on a primer. It's just I'd rather not spend a lot of money replacing all of the materials I've already bought.

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2 minutes ago, jack said:

I don't mind spending some more money on a primer. It's just I'd rather not spend a lot of money replacing all of the materials I've already bought.

but if you look at cfs site it says apply to DRY clean substras --not to damp surface --.still say a wee test --if it drys clear and a bugger to pull of it should be fine --or just wait till its all dry thats 100% fix

 

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Just now, scottishjohn said:

or just wait till its all dry thats 100% fix

 

Which is exactly my original question: will it get "dry" in the current weather, assuming I cover and uncover it as described above?

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on further reflection i think i,ve  been talking nonsense so I checked with my expert grp roofer friend

its a balcony so it must be flat ?

i guess you did not tape the osb joints ,so the water will have gone to underside as well ?

 the  roofer always lay board and grp  it the same day .

so if you want perfect --its strip them off and start again , anything else will be  open  to  possible problems later on .

 he won,t even put grp on old osb  after stripping off a roof felt  -always needs new  t&g roofing boards + then the grp 

hes done hundreds and not one comeback 

 he uses t&g so there is no area where there could be a joint problem + even adds a little pva glue to each joint as he puts them together.

hope this helps 

 

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12 minutes ago, scottishjohn said:

its a balcony so it must be flat ?

 

No, there's a slight fall to a drain.

 

12 minutes ago, scottishjohn said:

i guess you did not tape the osb joints ,so the water will have gone to underside as well ?

 

Good guess! It's all completely open underneath though, so it isn't as though water can pool anywhere.

 

12 minutes ago, scottishjohn said:

so if you want perfect --its strip them off and start again , anything else will be  open  to  possible problems later on .

 

I do want it perfect - we'll be here for a long time, I hope, and this is exactly the sort of job I don't want to be revisiting in three years.

 

Most of the boards are easy enough to take up - they're just screwed down with stainless screws. I can bring them inside for a week and allow them to dry in the warm, then bung them down and fiberglass on a day when the weather is good enough.


There're a couple of small end pieces that can't easily be taken up, as they have trim pieces nailed and glued in place. I can cover those though, and will consider flaming them as well.


Thanks for your help.

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