Any GRP roofing experts out there?

[nothanks]

As part of a small extension I needed a "hidden" flat roof section. I got builders to do the groundwork, blockwork and roofing - although their work in most areas has been good, the GRP roof did not go well and they've run out of ideas, so I need some advice. The flat roof slopes back (and sideways) to an existing tiled roof and water then spills down a valley. The problem is that the GRP seems to be porous where the flat roof meets the old roof, this despite appropriate flashing and 3 layers of mat. The cure would be fairly easy (with another layer of GRP) if the weather was dry and warm, but it isn't now and probably won't be until the Spring. Once the area is dry I think the answer will be to cut-out this section of GRP and to glass-in some new mat, taking care to thoroughly impregnate it with resin. The question is: what can I/they do to make it watertight until it can be fixed properly? It needs something that can be applied to a damp surface.

[harry]

You can buy a liquid roof seal that can be applied even underwater.

There are other manufacturers too.

[tabbypurr]

bitumen is fairly usable in wet conditions. Or you can often dry things out temporarily with a heating, tarp, etc. I've no idea whether GRP & bitumen are compatible.

NT

[newshound]

The Aquashield MSDS is a bit weasely but I'd not be surprised if that isn't, in fact, bitumen based.

Shouldn't be a problem with bitumen on GRP, especially for a short term fix.

[Tim Lamb]

In message [e-mail]>, [e-mail] writes

Have a look through this and you will know as much as any in here:-)

I take it your construction involves a shallow valley. The video above advises one layer of glass mat (if it is not a trafficked area) plus a gel coat on top.

They show how to *bandage* joints in the roof boarding and close off any apertures. One point of interest to you is that the recommended cleaning solvent, acetone, is soluble in water which may make drying off the surface ready for a re-coat easier. Lots of rubbing down with 60 grit glass paper!

Connecting *pin holes* through three layers seems unlikely and you don't mention a gel coat.

No leaks found in my d-i-y one, yet!

[Brian Gaff (Sofa)]

That sounds very handy. I can think of few uses for that. Brian

[Dave Plowman (News)]

Aquapol ain't cheap but worked very well on this felt flat roof that is nominally well past the usual life. It has cracked where it was bent up under the flashing. Used their reinforcing gauze too. Only intended it as a temporary fix, but it's done three winters so far.

[T i m]

<snip>

Quite, especially as many boats are lighter built than that. ;-)

Excellent, but then I know how much attention to detail you generally apply to such things.

I have laid up quite a bit of fibreglass in my time and also come across some pretty poor example of both amateur and professional work (too 'dry' being the worst).

Many seem to put the resin on like a paint, rather than stippling it through with the right sort of brush, therefore not 'wetting' the mat / roving out properly.

You don't want to over-work chopped-strand-mat either or you can start to impact the consistency too much.

Re gel-coat, I've only ever applied it directly to a mould where it's then followed by the resin / fibreglass and because std gel is anaerobic (?), you don't need to prep the gelcoat to get the resin to bond effectively.

I think you can apply gelcoat to the outside of some (cured) fibreglass but I think it's different or needs further coating (wax?) to get it to fully cure?

I am lucky that I don't seem to react to fibreglass itself, lucky because I spent much of my youth stuck in lockers or other confined spaces glassing stuff up for Dad on our various boats. It was like a modern day version of the kids used to sweep chimneys. ;-)

I was thinking of putting a fibreglass roof on my (10x6') shed that is still in Mums back garden but I imagine the materials would cost quite a bit these days?

Cheers, T i m

[nothanks]

Thanks

It's slightly difficult to describe the roof. An existing single storey pitched roof runs into an existing vertical wall. The new roof is 90 degrees to the single storey bit and has a hidden flat roof (middle dotted line, below). This flat section slopes back to the single storey roof and also slopes away from the vertical wall, so the water runs back and then down the valley (V). All pitches are 62 degrees'ish. The problem area is where the flat roof meets the original pitched roof, along the middle dotted line. __________ | | -------------| /\ | V/ -\---| V/ \--| ---V/------\

I checked this morning, and found that I'd got that wrong. I don't know why I thought it was 3 layers, but it's only 1. The top coat isn't on yet because the guys want to first make sure the main layer isn't leaking.

[Tim Lamb]

Sadly that doesn't display well on my set up.

After 24 hours, any further coats (including the gel coat) require a thorough sanding followed by a wipe off with acetone.

I think the video suggests a second layer of *thin* mat if there is any doubt.

I ended up with 2 gel coats because it is much slower to cure than the resin and it rained that night:-(

If you do seal it with bitumen you will need to start over for a fresh glass fibre job. Resin and any sort of tar/grease do not go well together.

[Tim Lamb]

In message [e-mail], T i m [e-mail]> writes

It needs to go on within 24 hours or you have to abrade the surface before applying.

Ah! I have a can of resin, some accelerator about 4m2 of heavy chopped strand matt and enough gelcoat for about 5m2. Plus the tools for which I will have no further use.

I planned to offer it as an inducement:-) The telephone engineer is booked for the afternoon of the 12th Nov!

[nothanks]

We've decided to construct a tent over the flat section and, if this works, they will then re-do the GRP. If that fails then it will be Aquapol or TekCryl to get through the winter and fix it properly in the dry weather.

[tabbypurr]

I patched a split felt roof with 1 layer of bedsheet & bitumen just to get it through the winter before a full reroof. Plans changed & more work was never done, about 6 years on the patches are still fine. As for the rest... entire sections have gone.

NT

[T i m]

<snip>

That sounds familiar. ;-)

<snip>

Ok ...

No 'inducement' needed mate, happy to pop over any time (but thanks very much for the kind offer. With that in mind I'll leave the 'temporary' DPM on there (that seems to be holding for now) and wait for the nicer weather). ;-)

I'll get her to put it in her diary.

I can't see there being any issues as we tested all we could from different directions and I can't see anyone complaining about not having to run cables. ;-)

Cheers, T i m

[T i m]

Does Turnpike have the option to display Fixed Pitch font (or not), as Agent does Tim? My default on Forte Agent is proportionally spaced as it makes it easier to read but as it sounds like you have seen, it screws up any ASCII art. By checking 'Fixed pitch font' makes it all appear as intended. ;-)

Cheers, T i m

[Dave Plowman (News)]

I was told 25 years was good for a felt roof. But on this one, the majority of it looked to be just fine at over this. It was done by a local company with an excellent reputation, though. And with decent ply decking.

[Andrew]

If you mean Acrypol, then my experience of it, when used over Isoflex is that is expensive and useless. Lasts about a year.

[tabbypurr]

would that be an apocryphal story?