Painting and then varnishing ply

[klare123]

Hello. I have a project working with kids at a school. They would like to make 4ft x 8ft ply sheet panels to fit to exterior walls. To be decorated by stencilling / painting and adding mosaic. Then the whole panels sealed to withstand English weather.
My question is what materials to use?!
6mm ply good quality
prime with wood primer
One block colour of paint - emulsion?/ acrylic? (I will only need 500ml of each colour at the most)
layers of stencilling using stencil brush -acrylic?
Add glass/ mosaic -using silicone??
Then to seal so it doesn't brown with time ?- is there a varnish or lacquer that you would recommend?
Thanks so much

 

[bonobobrown]

Is there any reason why you are not painting directly onto the wall - is this so that the children can work on it when it is flat and then be moved ?

Marine ply is more suited for outdoors than standard - I have used boat varnish and off the shelf varnish intended for front doors and it seems to have lasted well.

You can get sample paints from diy stores that are intended for children's rooms - so less of a worry about what the paints are made from. But they are intended for interior use. (my kids selected all of them so I had to paint a stripy wall ). Sealing them with the varnish should work though. Probably worth doing a test first though in case the varnish smears the paint.

You could seal the art behind a perspex sheet - but might need to be smaller panels. This would allow for some areas of paint and mosaic that have been applied with enthusiasm and stick out loads to be covered without having to pour varnish over to cover all the cracks.

 

[Burnerman]

I think one of the big problems here would be protecting the ply edges.....you would need exterior quality WBP (water and boil proof) ply, but even that is prone to letting water in through the edges and delaminating.
Anyway, you'd need exterior grade primer followed by a quality exterior gloss.....maybe from the International Paints range? Interior paints simply won't last.
Silicone is fine for fixing the glass / tile though.
As for the varnishing, again exterior grade products are required, and certainly not cellulose based...maybe a yacht varnish could be best?
Anyway, good luck with your project, and lets hear what the others say!
John

 

[klare123]

Thank you both . The project is next month so need to work flat and inside then once all sealing is dry the panels will be attached to walls.
Ok, great wbp ply
Followed by acrylic exterior primer?
What about acrylic paints and then an exterior polyurethane varnish?
Then all layers are water based / acrylic .
Thanks so much

 

[Burnerman]

No problems with your proposal there! Presumably vandalism isn't an issue?
Putting the art behind a plastic screen would be best, but hugely expensive.
John

 

[klare123]

Hello John
Vandalism not a prob and plastic would be costly . Thanks do much ! I think I have a system !

 

[Burnerman]

Meant to say - its probably best to treat both sides of the ply, this will minimise weather damage and also prevent warping.
Send us a photo of the finished article?
John

 

[klare123]

Ok
Does that mean prime & varnish the back side? Thanks

 

[Burnerman]

Yep, it sort of 'balances' the treatments and should be done.
John

 

[foxhole]

You will probbaly need 12mm ply to avoid warping, 6mm would need lots of fixings.

 

[AronSearle]

The quality of the plywood is important as well.

Don't buy cheap chinese plywood, you run the risk of buying dodgy plywood, and make sure it doesnt have a .2mm decorative veneer, but that the face veneer is "proper".

FYI WBP is defunct, it's now called EN636-3 plywood - Or - EN636-2 but marked with a class 3 bond.

You tend to find the cheap chinese **** still uses the WBP "branding".

 

[klare123]

Really helpful. Thanks so much.

 

[klare123]

one more question! How many coast of primer would you recommend and how many coats of varnish? (both sides?) Thanks

 

[Burnerman]

Look at the absorbency of the primer once on the timber....if it soaks in well, give it a couple of coats.
As for the varnish, again a couple of coats should be fine - again its important not to miss anywhere as the weather will get underneath.
John