Peeling paint on plywood dome.

[Rusted]

My DIY, 10' birch plywood dome paint is peeling badly after only one winter.

I used a cheap primer instead of painting directly with the "wood protection" paint.

How can I avoid fibre-glassing the whole thing?  Access is very dodgy due to the height.

Sand the rough paint down all over and then paint a couple of coats with the good stuff?

The summer working window is opening up and I really have to make a decision before the dome is ruined!  😱

Thanks..

 

[Bruce Leeroy]

Roofing felt either torch on or nail on? The torch on would add a fair amount of weight if that's an issue.

[mikeDnight]

If you did fiberglass it, it would last forever. It might be worth hiring a scaffold and doing it once for all time!  You can coat it in sections, then rotate the dome to access all round.

[Stuart1971]

Paint on plywood will always peel due to the movement in plywood material....the temperature plays havoc with the expansion and contraction of the outer surface of the wood, unfortunately this is pretty much unavoidable, I would bite the bullet and get it fibreglass befor you waste any more time and money, and then still need to do it anyway.... 😀 

Edited June 4, 2020 by Stuart1971

[Davey-T]

Lots of expensive paint claims to be weather proof, I've used Dulux Weather Shield and Sikins  and both give up eventually.

Dave

[Stuart1971]

3 minutes ago, Davey-T said:

Lots of expensive paint claims to be weather proof, I've used Dulux Weather Shield and Sikins  and both give up eventually.

Dave

Yes, in my experience no matter how good the paint, if there is movement in the painted surface, then it will eventually crack, then water will get under the edges, and then it will peel....🙁

[Swoop1]

Couldn't you paint it with a coupkle of coats of resin?

[steppenwolf]

That is a beautiful dome you have constructed and it deserves the best you can do for it - I believe that a glass fibre coating would be the best solution here. Not what you wanted to hear but this will future proof it for you.

[Davey-T]

This stuff designed for flat roofs but maybe able to use on dome shape with overlapping joints.

Dave

https://www.wickes.co.uk/Skyguard-10-x-15-ft-Lifetime-Garden-Building-Roof-Kit/p/223181

Or this

https://www.wickes.co.uk/IKOpro-Acrylic-Roof-Coat-Mid-Grey-20ltr/p/139076

Edited June 4, 2020 by Davey-T

[Rusted]

Thank you all for your excellent advice. 

I have discussed this so often [with myself on my blog] I can't remember whether I have actually raised it here before.

Too many options! 

[Skipper Billy]

As long as its dry and you remove the loose stuff then 2 coats of 2 pack polyurethane paint should give you 10+ years

https://www.international-yachtpaint.com/en/gb/boat-paint-products/topcoat-finishes/perfection

 

[Stuart1971]

9 minutes ago, Skipper Billy said:

As long as its dry and you remove the loose stuff then 2 coats of 2 pack polyurethane paint should give you 10+ years

https://www.international-yachtpaint.com/en/gb/boat-paint-products/topcoat-finishes/perfection

 

Will that paint expand and contrast with the wood...? If so then all good... 👍 as plywood does move a lot, with varying temps...

[saac]

Instead of paint why not oil it.  My obsy (cedar wood throughout walls and roof ) is re-oiled each summer and does the trick , nice and watertight. 

Jim

[saac]

3 hours ago, Skipper Billy said:

As long as its dry and you remove the loose stuff then 2 coats of 2 pack polyurethane paint should give you 10+ years

https://www.international-yachtpaint.com/en/gb/boat-paint-products/topcoat-finishes/perfection

 

Billy, I take it that is a specialist marine paint (high performance).  Would you recommend it for non marine applications? My house has dormers in the roof and I've been using Deluxe Weathershield but it does not last any more than 2 years and it peels off. The roof is south facing so it gets a lot of uv incident on it.  I wonder if your International paint would be worth a try ?

Jim

Edited June 4, 2020 by saac

[Rusted]

Many thanks again for the continuing input.

Black roofing felt is simply too heavy and too absorbent of hot sunshine. I have lately become a solar imager by obsession.

The dome is leaky at the seams despite spending literally hundreds of pounds on "the highest quality, marine, flexible and long lasting" sealant in cartridges.
Which means that not only does everything flex and move but is is damp both inside and out in heavy rain. The "high quality" sealant has cracked in lots of places.

Fibreglass is the most obvious route to happiness but has several major downsides:
Smelly, messy and very time consuming working at such a height.
It also spoils the crispness of once, sharp corners when  externally applied.

Being trapezoidal the plywood panels could be replaced with thin aluminium in full "gore" drops.
No distortion trying to make 2D into 3D curves. It could be overlapped sideways and pop riveted.
Still haven't found a Danish stockist who sells the suitable lengths to private customers.

I thought of tarpaulin drops heat welded. Heavy and of limited life. I have no experience with heat welding PVC.

Non-black pond liner/roofing rubber would be very heavy. I know because I used it for a dome skirt.

Not sure about yacht finishes. I have no experience and doubt it could cope with my dodgy seams.

Thanks again

[Davey-T]

You'd be better off with zinc rather than aluminium although it weighs more it would be a proper job.

In the meantime it's worth trying something quick like the acrylic roof coating as if it fails you can easily go over it with another system, nothing to lose, only money 😁

Dave

Edited June 5, 2020 by Davey-T

[Stuart1971]

A rubberised roofing paint may work, I have used it on a felted garage roof, when the felt started to wear, it works very well, and stays very flexible, but provides a good waterproof finish...

In fact it would be ideal for your application...it’s about £30 a tin and you would probably need two...

[Rusted]

16 minutes ago, Stuart1971 said:

A rubberised roofing paint may work, I have used it on a felted garage roof, when the felt started to wear, it works very well, and stays very flexible, but provides a good waterproof finish...

In fact it would be ideal for your application...it’s about £30 a tin and you would probably need two...

Interesting! II just need to source something like it over here. Amazon won't deliver.

I thought it would only be available in black but they also list a white!

Thanks.

[Rusted]

1 hour ago, Davey-T said:

You'd be better off with zinc rather than aluminium although it weighs more it would be a proper job.

In the meantime it's worth trying something quick like the acrylic roof coating as if it fails you can easily go over it with another system, nothing to lose, only money 😁

Dave

Thanks Dave.

Zinc is likely to get hot in sunshine as well as being more expensive. Polished aluminium is relatively cool.

Reflects the sky and surroundings so is less visible than white paint.

Not sure what acrylic roof coating is compared to liquid rubber. I'll do some homework.

Thanks again.

[Stuart1971]

10 minutes ago, Rusted said:

Interesting! II just need to source something like it over here. Amazon won't deliver.

I thought it would only be available in black but they also list a white!

Thanks.

Yes, also Grey, which is what I used.....and maybe good for your application....

[Davey-T]

Nice thin copper sheets and copper nails then it will go green and look like a proper observatory 😂

Dave

[Astro-Geek]

I know you said you prefered to not use fibreglass, but if it was me, I'd certainly do it that way.

As Mike said, you could do it in sections and rotate it.  The beauty of fibeglass is the way it confirms neatly to that awkward convex shape, (with the segment joints). When the matting is "wetted out" with the resin it flattens against any shape, and clings to it.

Fibreglass sheathing is so easy to do and makes such a permanent job, and could be quite neat too.  You could mix a pigment of your choice in the layup resin so you'd never have to paint it either.  (even simulated green copper !)

I did my flat garage roof 10 years ago with a kit, and it's as good as the day I did it. (and that's the bare fibreglass, pigmented grey, so never needs painting.)

Prior to that I'd used roofing felt twice, which was actually harder to do, and only lasted 3 or 4 years before cracking somewhere, rendering the whole thing useless.

Edited June 5, 2020 by Astro-Geek

[Rusted]

Thanks. I've done quite a bit of GRP and know exactly what is involved.

The entire dome is eventually accessible from a very tall ladder cantilevered over the handrail.
The question is whether I want to be the one up there again.
I bought a scaffolder's snap-on hook, lanyard and harness just to paint it.
Pictures are on the PC indoors. Even that did not feel very safe.
It's a long way up and the ladder sways all over the place! 
The base ring is 4.3m or 14' off the ground! The dome is another 1.5m or 6' to the top.

[Skipper Billy]

15 hours ago, saac said:

Billy, I take it that is a specialist marine paint (high performance).  Would you recommend it for non marine applications? My house has dormers in the roof and I've been using Deluxe Weathershield but it does not last any more than 2 years and it peels off. The roof is south facing so it gets a lot of uv incident on it.  I wonder if your International paint would be worth a try ?

I have used it extensively on wooden boats which flex a LOT and are dipped in and out of sea water - freezing cold then baked in sun - it is very tough stuff.

I painted the south facing wall of our wooden garage with it 11 years ago and it is still perfect. Avoid red if it gets a lot of UK.

[Rusted]

2 hours ago, Skipper Billy said:

I have used it extensively on wooden boats which flex a LOT and are dipped in and out of sea water - freezing cold then baked in sun - it is very tough stuff.

I painted the south facing wall of our wooden garage with it 11 years ago and it is still perfect. Avoid red if it gets a lot of UK.

What sort of preparation is required? Bare wood? Just sanded?

Primer? Undercoat?

How would it cope with filled joints? Not silicone.

Thanks.