Repairing/improving a fibreglassed wooden roof

[Giant]

Although we've now patched up the main problem area with this roof we're still not quite happy with it, so I'm throwing this one open to the CWDF nitpicking brigade / peanut gallery.

 

This is our wheelhouse roof, from outside and inside:

 

 

It is in three sections which lift off to allow the wheelhouse to fold down, with two aluminium drainage channels sitting under the joins. The roof construction is tongue and groove laid over an iroko frame, then ~5mm plywood glued on top of the tongue and groove, then the whole top fibreglassed over and gel coated.

 

One corner had developed a crack:

 

 

It's not clear whether the crack came first and let water in, expanding the wood and worsening the crack, or if water got in first and caused the crack. Either way it was wet in there. After cutting further along the crack and peeling back it was clear the plywood was wet and rotten:

 

 

I had to cut a long way back to get back to sound material:

 

 

Fortunately, the tongue and groove didn't seem to be much affected and dried out nicely with some time in the sunshine. I cleaned things up, and we cut and glued in a new section of ply to fill the gap:

 

 

Finally we glassed it over, which turned out to be a lot harder than expected and was looking pretty messy, but eventually cleaned up sort of OK:

 

 

It still needs gel coated, but I guess it will keep the rain out for the time being whilst we figure out how to do that (advice welcome, never touched the stuff).

 

Our main worry with the whole thing though is the overhang under the edges of the roof. The fibreglassing comes down the side but doesn't extend round the corner to the overhang, and I think it would be a bugger of a job to make it do so. The underside of the overhang is basically just painted with what I guess is more gel coat, and there are a lot of cracks in it:

 

 

My best guess for how the water-damaged area started is that water was gathering under the overhang, and propagated up a knot in the tongue and groove which appears just under where the crack started, eventually getting into the plywood.

 

So even assuming this repair holds, we still have an open question of how to seal under the overhangs better. Hopefully with a solution that isn't be too labour intensive, as between all three sections there is 30 metres of edge to be dealt with.

 

Thoughts welcome.

[Tiggs]

 

If you look at an old wooden window cill you will see underneath channel or groove which the water drips from. If your roof had something like this it might help preserve the wooden frame and may help the sealing.

Edited September 26, 2016 by Tiggs

[Seti-Yeti]

I was about to suggest a drip bar but the groove will do just as well. As for GRP on wood roof... hmmmm, I'd not. Wood expands naturally and in effect "breathes", GRP doesn't. As a result the two will part company. My cabin roofs were T&G but caulked in the gaps to allow for movement. SikaFlex is good at this job. They were then covered with a canvas type material fixed with a flexible rubber based glue. Tough enough for foot traffic, waterproof AND flexible.

[Giant]

If you look at an old wooden window cill you will see underneath channel or groove which the water drips from. If your roof had something like this it might help preserve the wooden frame and may help the sealing.

 

That's a good idea, and would be reasonably easy to cut down the long edges after setting up the right jig. A bit harder for the short edges, which are curved, but should be doable.

 

Still leaves the question of how to protect the bit of wood that forms the outer part of the groove, though. I guess whatever one paints a wooden windowsill with, although I expect those are usually hardier wood than this tongue & groove stuff.

[Giant]

I was about to suggest a drip bar but the groove will do just as well. As for GRP on wood roof... hmmmm, I'd not. Wood expands naturally and in effect "breathes", GRP doesn't. As a result the two will part company. My cabin roofs were T&G but caulked in the gaps to allow for movement. SikaFlex is good at this job. They were then covered with a canvas type material fixed with a flexible rubber based glue. Tough enough for foot traffic, waterproof AND flexible.

 

You may well be right, but this is the roof we have and we'd rather not have to completely rebuild it unless we really have to. Fortunately this roof doesn't get walked on, so the requirements are a bit less demanding. For what it's worth, I don't see any evidence of damage from mismatched expansion so far, except in this one spot where the plywood obviously got wet.

[WotEver]

Instead of routing a groove all around why not affix a bead to the outer edge? Say a piece of 12x12mm which you could probably pick up in a DIY shed in Ramin or some other hard wood.

[Phil Ambrose]

Ref the overhang, yes a bead should do the job and for protection against wet, why not go alone the side (thickness of the roof) with GRP tape, carrying it on under the overhang, easy enough to do with GF tape. Then a swift woosh over with gel coat and jobs a good 'un.

Phil

[Giant]

Instead of routing a groove all around why not affix a bead to the outer edge? Say a piece of 12x12mm which you could probably pick up in a DIY shed in Ramin or some other hard wood.

 

That's an option but it would have to be a pretty thin bead, the overhang at the sides is only about 20mm including the thickness of the glass & gelcoat on the edge.

 

Ref the overhang, yes a bead should do the job and for protection against wet, why not go alone the side (thickness of the roof) with GRP tape, carrying it on under the overhang, easy enough to do with GF tape. Then a swift woosh over with gel coat and jobs a good 'un.

 

By GRP/GF tape, do you mean woven glass fibre tape for use with resin, or something self-adhesive? Do you have a particular product in mind that you think would do it?

[WotEver]

 

That's an option but it would have to be a pretty thin bead, the overhang at the sides is only about 20mm including the thickness of the glass & gelcoat on the edge.

This would work: http://www.wickes.co.uk/Wickes-Dark-Hardwood-Glass-Bead-Moulding-9x9x2400mm/p/121237

 

One flat edge facing up and the other flat edge to the outside.

 

Tony