Sealing Wooden Ply Cabin Roof

[gregich]

I'm looking into sealing a ply roof on my cabin, the roof is not leaking but some of the wood is darkening and it looks like water is getting between the sheets of ply (3 in total overlapping). I'm assuming that some of the screw holes are leaking and the joins between sheets as it took 10 sheets of ply to do an 11m cabin (30 in total for 3 layers). I'v been treating the ply with Osmo uv wood seal and Osmo decking seal once every 2 years and using uv resistant silicon every year on the joins to try and preserve the original wood finish. This was a tad optimistic/romantic as the wood has darkened in patches over the years and now i want to seal it properly before it becomes a big problem. Any pointers from experience welcome.

Edited August 11, 2018 by gregich
details

[Neil2]

Ideally you would want to seal it with epoxy but that would involve a lot of work stripping back to bare wood and maybe it's not possible anyway if you've used a lot of sealer on it over the years.  

 

Something like Owatrol D1 might be a better approach - AFAIK you can apply this without any sanding/stripping. 

[Murflynn]

use the ply roof as a mould and laminate a GRP roof over the top.  no need for epoxy - polyester is much cheaper and fine for that type of job.

[WotEver]

4 hours ago, Murflynn said:

use the ply roof as a mould and laminate a GRP roof over the top.  no need for epoxy - polyester is much cheaper and fine for that type of job.

I’ve seen similar done with canvas instead of glass fibre mat. Used exactly the same way, laid over the roof and wetted with the resin. A couple of layers, then painted with your paint of choice. 

[TheBiscuits]

If you are all taking that approach, for goodness sake take a look at EDPM roofing sheet.  20 year guarantee exposed to the weather and a damn sight cheaper than epoxy.

[gregich]

On 11/08/2018 at 15:05, Neil2 said:

Ideally you would want to seal it with epoxy but that would involve a lot of work stripping back to bare wood and maybe it's not possible anyway if you've used a lot of sealer on it over the years.  

 

Something like Owatrol D1 might be a better approach - AFAIK you can apply this without any sanding/stripping. 

I wouldn't say iv used a lot, the roofs only been on 5 years but taking it back to bare wood would be an enormous job by sanding and i would lose some of the wood to boot. it is possible that there is a remover for the sealants from Osmo so i'll look into it. Thanks

[gregich]

On 11/08/2018 at 21:49, TheBiscuits said:

If you are all taking that approach, for goodness sake take a look at EDPM roofing sheet.  20 year guarantee exposed to the weather and a damn sight cheaper than epoxy.

My mate who built the roof recomended that when we replaced the old roof. I boat single handed though which means theres a lot of jumping on and off the roof at locks, would also need to store stuff on there. my worry is how it would fare with this after a few years.

[gregich]

On 11/08/2018 at 21:45, WotEver said:

I’ve seen similar done with canvas instead of glass fibre mat. Used exactly the same way, laid over the roof and wetted with the resin. A couple of layers, then painted with your paint of choice. 

Iv read that canvas was for tongue and groove and to allow for movement. Canvas was my original plan till i looked into it. Still open to it if it solves my problem.

 

On 11/08/2018 at 17:35, Murflynn said:

use the ply roof as a mould and laminate a GRP roof over the top.  no need for epoxy - polyester is much cheaper and fine for that type of job.

Wouldn't that be a bit messy and difficult to get a smooth finish without bumps?

Edited August 14, 2018 by gregich

[TheBiscuits]

37 minutes ago, gregich said:

My mate who built the roof recomended that when we replaced the old roof. I boat single handed though which means theres a lot of jumping on and off the roof at locks, would also need to store stuff on there. my worry is how it would fare with this after a few years.

All the ones I have seen say it's fine, and some of them are over 10 years old. 

[WotEver]

1 hour ago, gregich said:

Iv read that canvas was for tongue and groove and to allow for movement. Canvas was my original plan till i looked into it. Still open to it if it solves my problem.

All wood will move to some extent so I guess that’s the advantage of canvas. 

[smileypete]

Could also try skinning it with decent 1/4" WBP or marine ('marine') ply.

 

If the boat is liveaboard it may be that moisture from inside is condensing between the sheets of ply, what's on the inside of the roof?

 

Maybe try the lumpy water forums for ideas, bear in mind that fresh paint is better than neglected varnish, and covers funky wood nicely. ?

Edited August 14, 2018 by smileypete

[koukouvagia]

You can get a really good smooth finish using fibre glass mat and resin.  

I've also used polyester, but found that this tended to crack.

It is often said that fibreglassing a wooden boat is a death knell.  Either the wood can't breath and rots or, as in my case, the back cabin often was very hot. The wood then dried out thoroughly and shrank and crumbled.   The fibre glass and resin sheathing then began to crack and there was little I could then do but remove the cabin and start again.  

If the underlying wood is sound, resin and fibreglass is proabably as good a way as any.

 

 

 

All the back cabin was coated with fibre glass and resin, including the slide.

 

For more details see my website buttyhampton.com and go to "Problems - external wood and roof".

 

Have you consulted the West System Guides? They tell you everything you need to know about using resin and fibre glass to repair boats.

[gregich]

On 14/08/2018 at 22:18, koukouvagia said:

You can get a really good smooth finish using fibre glass mat and resin.  

I've also used polyester, but found that this tended to crack.

It is often said that fibreglassing a wooden boat is a death knell.  Either the wood can't breath and rots or, as in my case, the back cabin often was very hot. The wood then dried out thoroughly and shrank and crumbled.   The fibre glass and resin sheathing then began to crack and there was little I could then do but remove the cabin and start again.  

If the underlying wood is sound, resin and fibreglass is proabably as good a way as any.

 

 

 

All the back cabin was coated with fibre glass and resin, including the slide.

 

For more details see my website buttyhampton.com and go to "Problems - external wood and roof".

 

Have you consulted the West System Guides? They tell you everything you need to know about using resin and fibre glass to repair boats.

Thanks for the info, only the roof is wood and its very well insulated with 1in reflective multi foil & micro fiber before the 3 layers of ply so is unlikely to get very hot and also is 36ft long so heat would dissipate from directly above burner. I think i could possibly leave the sides of the roof (over 100mm depth) as wood and that would allow it to breath. Also there is some overhang on the cabin sides allowing more breathing. Food for thought.

[gregich]

On 14/08/2018 at 19:42, smileypete said:

Could also try skinning it with decent 1/4" WBP or marine ('marine') ply.

 

If the boat is liveaboard it may be that moisture from inside is condensing between the sheets of ply, what's on the inside of the roof?

 

Maybe try the lumpy water forums for ideas, bear in mind that fresh paint is better than neglected varnish, and covers funky wood nicely. ?

I dont want to skin it again as i only skinned it 5 years ago, i'm looking for a more permanent solution. T&G matchboard is on the inside and 1in multi foil insulation on top of that, then the 3 layers of ply.

[Mike Adams]

Best solution if you can get the roof really dry and it is solid is to sand to bare wood, coat with west epoxy resin, sand coat with a layer of composite glass mat/cloth inpregnated with resin then sand and coat with 2 pack filler primer, sand and finish with 2 pack paint. I have done this three times and it lasts for years and years. costs about £1k in materials for 30ft roof.

[koukouvagia]

13 minutes ago, Mike Adams said:

Best solution if you can get the roof really dry and it is solid is to sand to bare wood, coat with west epoxy resin, sand coat with a layer of composite glass mat/cloth inpregnated with resin then sand and coat with 2 pack filler primer, sand and finish with 2 pack paint. 

Excellent advice provided the underlying wood is dry and solid.

[gregich]

On 16/08/2018 at 13:59, Mike Adams said:

Best solution if you can get the roof really dry and it is solid is to sand to bare wood, coat with west epoxy resin, sand coat with a layer of composite glass mat/cloth inpregnated with resin then sand and coat with 2 pack filler primer, sand and finish with 2 pack paint. I have done this three times and it lasts for years and years. costs about £1k in materials for 30ft roof.

1k!!! cough splutter. Thanks, this is probably what i'll run with, shame it's so pricey but hey ho.

[gregich]

On 11/08/2018 at 21:49, TheBiscuits said:

If you are all taking that approach, for goodness sake take a look at EDPM roofing sheet.  20 year guarantee exposed to the weather and a damn sight cheaper than epoxy.

I'm seriously looking into this, do you know anyone who has painted over it? And if so what was the outcome? I realise its meant to be the finished product but wondering if this would be possible as a black roof would absorb heat and not really my choice of colour.

[Sabine]

Hello, I'm reviving this thread as I'm having a similar problem to the OP. My boat's a Norfolk Broads cruiser from the 70s. It has a canvas-lined, painted wooden roof that's got water seeping in through the hardware fixings. My intention was to follow the West System advice here, however today when I removed a strip of the canvas I found that the wood isn't how I expected, and now I'm not sure what sort of approach would work. The roof wood seems to be several layers of ply, which are coming apart from each other. The wood seems sound otherwise - I'd expected it to be soft and rotten in the wet spots, but actually it's been saturated in some kind of resin/glue/varnish, meaning the actual wood fibres are apparently impermeable, but the water can get in through the spaces between the fibres. (I don't mean the ply layers - it's the actual fibres.) It's weird. The wood is acting like a water filter rather than a sponge, so the water flows through without damaging the texture of the wood. It dries out quickly, even after a huge rainstorm. As far as I can tell, the entire depth of the roof is like that; the wood is impregnated with this varnish stuff. 

 

I'm wondering if the West method will still work in this case, because it seems impossible to sand the roof to an exposed surface as the varnish goes all the way through. Does anyone have advice about how to fix the leaks?  

 

Thanks.

[Tony Brooks]

1 hour ago, Sabine said:

Hello, I'm reviving this thread as I'm having a similar problem to the OP. My boat's a Norfolk Broads cruiser from the 70s. It has a canvas-lined, painted wooden roof that's got water seeping in through the hardware fixings. My intention was to follow the West System advice here, however today when I removed a strip of the canvas I found that the wood isn't how I expected, and now I'm not sure what sort of approach would work. The roof wood seems to be several layers of ply, which are coming apart from each other. The wood seems sound otherwise - I'd expected it to be soft and rotten in the wet spots, but actually it's been saturated in some kind of resin/glue/varnish, meaning the actual wood fibres are apparently impermeable, but the water can get in through the spaces between the fibres. (I don't mean the ply layers - it's the actual fibres.) It's weird. The wood is acting like a water filter rather than a sponge, so the water flows through without damaging the texture of the wood. It dries out quickly, even after a huge rainstorm. As far as I can tell, the entire depth of the roof is like that; the wood is impregnated with this varnish stuff. 

 

I'm wondering if the West method will still work in this case, because it seems impossible to sand the roof to an exposed surface as the varnish goes all the way through. Does anyone have advice about how to fix the leaks?  

 

Thanks.

 

This sounds like one of the Sonesta cruisers we fitted out at Maidenhead apart from the  several layers of plywood sheets.  Rather than chopped strand mat we used woven glass fibre mat (also called roving). This is far easier to get a decent finish on because the glass strands do not keep pooping up on the "mashing" equipment.  If I recall it was then painted with several layers of epoxy paint. I met one on the GU some 40 odd years after building and the owner did not mention any water leakage through the roof. The roving looks rather like very coarse canvas or sackcloth when painted/resined.

[Sabine]

5 hours ago, Tony Brooks said:

 

This sounds like one of the Sonesta cruisers we fitted out at Maidenhead apart from the  several layers of plywood sheets.  Rather than chopped strand mat we used woven glass fibre mat (also called roving). This is far easier to get a decent finish on because the glass strands do not keep pooping up on the "mashing" equipment.  If I recall it was then painted with several layers of epoxy paint. I met one on the GU some 40 odd years after building and the owner did not mention any water leakage through the roof. The roving looks rather like very coarse canvas or sackcloth when painted/resined.

That's helpful, thank you. Didn't know about 'roving' - I think you're right.

[koukouvagia]

On our butty I removed the top layer of ply which had been laid over the original wooden roof.  I quickly realised that original roof would not provide a smooth surface so I added a thin layer of ply (8mm, I think); I covered this with fibre glass matting, poured on resin and then sanded it down.  

The result was aestheticlly OK, but as I've mentioned before, the underlying problem was not really solved.  Still it gave me a few more years of a leakproof roof.

 

 

 

 

[blackrose]

14 hours ago, Sabine said:

Hello, I'm reviving this thread as I'm having a similar problem to the OP. 

 

As long as you're not using similar methods as the OP....

 

Silicone to seal joints? Use a good polyurethane sealant. Sikaflex, Marineflex, Stixall, CT1, etc. 

[Mike Adams]

If it was 1960s/70s it may well have been 'cascover' sheathing. This was a system using glue and a nylon sheath. It lasts well and epoxy will stick to it. If it is just leaking at the joints you could cover the joints with glass fibre tape and epoxy after sanding and where it is leaking around the fittings remove them and fit with new sealant after drying the area and soaking with epoxy.

[Sabine]

On 09/07/2022 at 09:12, koukouvagia said:

On our butty I removed the top layer of ply which had been laid over the original wooden roof.  I quickly realised that original roof would not provide a smooth surface so I added a thin layer of ply (8mm, I think); I covered this with fibre glass matting, poured on resin and then sanded it down.  

The result was aestheticlly OK, but as I've mentioned before, the underlying problem was not really solved.  Still it gave me a few more years of a leakproof roof.

 

 

 

 

 

 

Thanks Koukouvagia, that's food for thought. Happily, after we exposed more of the roof ply yesterday, the surface looks good enough to re-skin. 

 

What method/adhesive did you use to lay the new ply? Did you use screws or staples to attach it during the cure time?

 

22 hours ago, Mike Adams said:

If it was 1960s/70s it may well have been 'cascover' sheathing. This was a system using glue and a nylon sheath. It lasts well and epoxy will stick to it. If it is just leaking at the joints you could cover the joints with glass fibre tape and epoxy after sanding and where it is leaking around the fittings remove them and fit with new sealant after drying the area and soaking with epoxy.

 

Thanks for this advice Mike. Do you happen to know whether the cascover glue is compatible with other adhesives? It's penetrated well into the substrate, and I don't think practically I'll be able to sand it back to new wood.

Edited July 11, 2022 by Sabine