Old Son Posted September 26, 2017 Report Share Posted September 26, 2017 I am going to build some timber covers that will sit over my roof hatches. I plan to paint the covers to match the roof. What do you think I should use as a water proofer for the new cover. The top will be waterproof plywood. I was thinking of using the potable bitumen paint and then paint over with an undercoat and colour. I could put some self adhesive roof felt but that would look like a botch and I want it to look neat and tidy. Thanks Link to comment Share on other sites More sharing options...
Murflynn Posted September 26, 2017 Report Share Posted September 26, 2017 wherever I have used plywood for a roof or cover I have found it worthwhile to sheathe the top and any exposed edges with glass mat and polyester resin, finishing with a gel coat applied with a squeegee. fit and forget. Link to comment Share on other sites More sharing options...
Bee Posted September 26, 2017 Report Share Posted September 26, 2017 34 minutes ago, Murflynn said: wherever I have used plywood for a roof or cover I have found it worthwhile to sheathe the top and any exposed edges with glass mat and polyester resin, finishing with a gel coat applied with a squeegee. fit and forget. Did that with wheelhouse roof, bit heavy for a whole roof but as you say, fit and forget. I also built a canoe from cheap and thin ply then covered it with glass tissue and clear gel, very thin, very light and looks as though its varnished. 10 years later it still looks pretty good. Link to comment Share on other sites More sharing options...
WotEver Posted September 26, 2017 Report Share Posted September 26, 2017 And always remember that it’s the edges of plywood that are the most vulnerable. You can seal the surface 100% but if the edges are even slightly porous it’ll delaminate in short order. 38 minutes ago, Murflynn said: polyester resin Is this as good as epoxy for UV resistance? Link to comment Share on other sites More sharing options...
rusty69 Posted September 26, 2017 Report Share Posted September 26, 2017 18 minutes ago, WotEver said: And always remember that it’s the edges of plywood that are the most vulnerable. You can seal the surface 100% but if the edges are even slightly porous it’ll delaminate in short order. Is this as good as epoxy for UV resistance? I've used epoxy resin to seal ply,pay particular attention to the edges as Wotever advises. Although more expensive epoxy resin is vastly superior (dunno about the uv bit) Link to comment Share on other sites More sharing options...
Neil2 Posted September 26, 2017 Report Share Posted September 26, 2017 2 hours ago, Old Son said: I am going to build some timber covers that will sit over my roof hatches. I plan to paint the covers to match the roof. What do you think I should use as a water proofer for the new cover. The top will be waterproof plywood. I was thinking of using the potable bitumen paint and then paint over with an undercoat and colour. I could put some self adhesive roof felt but that would look like a botch and I want it to look neat and tidy. Thanks Epoxy. Then paint over with whatever you like. Don't use bitumen you won't be able to paint over it the bitumen will bleed through unless you seal it with aluminium based wood primer first but what a faff, just use epoxy. Link to comment Share on other sites More sharing options...
Old Son Posted September 26, 2017 Author Report Share Posted September 26, 2017 Thanks. Just epoxy resin, no glass mat? How many coats is recommended? Link to comment Share on other sites More sharing options...
Murflynn Posted September 26, 2017 Report Share Posted September 26, 2017 minimum 2 coats but I would use polyester and glass if I wanted a more robust job. You can buy white polyester gel coat which is not bothered by UV. Polyester resin has the advantage that it seems to gel as soon as it is applied and doesn't run, while epoxy runs all over the place. also remember that epoxy is not UV resistant. I only use if for brightwork (varnished hardwood) and then I have applied Epifanes UV resistant varnish over the well-sanded epoxy, but it needs to be re-varnished every year. Link to comment Share on other sites More sharing options...
David Mack Posted September 26, 2017 Report Share Posted September 26, 2017 If the covers are going to be near horizontal you need good quality plywood. DIY store exterior ply will quickly delaminate, whatever you coat it with. Link to comment Share on other sites More sharing options...
Old Son Posted September 26, 2017 Author Report Share Posted September 26, 2017 The hatches are 600 square. I thought I would use ply because it wont move about and crack like individual pieces of timber would. Would waterproof MDF be better or maybe some sort of cement board? Link to comment Share on other sites More sharing options...
BWM Posted September 26, 2017 Report Share Posted September 26, 2017 57 minutes ago, rusty69 said: I've used epoxy resin to seal ply,pay particular attention to the edges as Wotever advises. Although more expensive epoxy resin is vastly superior (dunno about the uv bit) I have used an epoxy called Timber seal ps which is uv stable, can be painted or varnished, excellent stuff. I have found that sealing the cut edges can be improved by using the last bit of mixed resin as it starts to thicken, The build up gives a glass like finish when rubbed down. Link to comment Share on other sites More sharing options...
rusty69 Posted September 26, 2017 Report Share Posted September 26, 2017 1 hour ago, BWM said: I have used an epoxy called Timber seal ps which is uv stable, can be painted or varnished, excellent stuff. I have found that sealing the cut edges can be improved by using the last bit of mixed resin as it starts to thicken, The build up gives a glass like finish when rubbed down. You can also thicken epoxy with colloidal silica or micro balloons Link to comment Share on other sites More sharing options...
Murflynn Posted September 26, 2017 Report Share Posted September 26, 2017 additives for thickening epoxy are not intended for sheathing, but for filling, filleting and glueing; thickened epoxy is not rock hard like the real thing. Link to comment Share on other sites More sharing options...
rusty69 Posted September 26, 2017 Report Share Posted September 26, 2017 I wouldn't bother sheathing if using epoxy in this case. Link to comment Share on other sites More sharing options...
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