Ideal board?

[Spookymooo]

I have a very large waterproof garden shed in which I am going to create a 00 scale model of Severn Tunnel Junction circa 1965.
I’m about to order plywood sheets but not sure which thickness to go for. Even though the shed is waterproof, I need to be realistic and accept that there will be varying humidity levels across the year and will probably need to treat the ply and supports with the right product...
Recommendations re ply thickness and treatment would be greatly appreciated
Cheers
Rob

[Steve M]

9mm or 12mm ply supported by suitable framing -either softwood or strips of ply cut to size. Glue and screw construction. For sealing either give it a coat of paint or dilute PVA.

[Maria]

we've recently built a board, 12mm ply on a frame, seems very stable but its indoors so not liable to damp.

post some pics!

[Walkingthedog]

I’ll second Steve’s recommendation.

[Tricky Dicky]

In conditions of variable humidity, plywood is the most stable. The traditional 2x1 softwood frame with plywood on top can still be subject to movement. I would advise using plywood throughout both frame and top. You will have to compensate for plywood’s thickness by making the frame deeper but we are only talking of a depth of round 100mm.

Richard

[shroomy]

Use 12mm birch ply or marine ply

[bulleidboy]

With a good framework underneath 9mm ply is fine - I used to walk on mine during layout construction. The underneath framework is important to stop sagging.

100_0371 by Barry Clayton, on Flickr

[Spookymooo]

Many thanks for all your useful replies
There will be 2 main board areas:
1) 18 feet x 3 feet.... (station area)
2) 14 feet x 3 feet.... (fiddle yard area)

These areas will be made of several framed ply boards.
What size framed boards should I make to suit...2x3, 3x3, 4x3???
Also, if I use ply for framing can these be screwed from the bass boards ... I’ve always been reluctant to screw into the thickness of ply...
Cheers
Rob

[Steve M]

Can you access both sides of the proposed layout or is it up against a wall? 3’ is a bit of a stretch without damaging things at the front of the layout - better to go for 2’ or 2’6”.
My layout is made of 2’x4’ modular units (although some have subsequently been extended) which makes for easily handled units when assembling. I use bolts to lock the boards together. I would suggest a size that is a) manageable and b) minimises cuts from an 8x4 sheet.
As for screwing into the ply either use 12mm for the sides or maybe glue and pin them or if screwing try predrilling the holes - Aldo allows you to countersink the screws for a neat finish.

[bulleidboy]

My boards have the tops screwed and glued onto a 12mm ply outer framework - inner framework was 9mm. All holes were pre-drilled into the tops - no problems with the sides splitting - screws about every twelve inches. All very rigid.