Plywood Plywood and more Plywood

[GNRi1959]

Over a period of several months i’ve used various types of plywood in my garden shed layout. As a carpenter I tend to go for quality over cost and was surprised by the behaviour of the various options. 

9mm birch ply that I used cupped across the width of a 350mm board whilst 9mm Malaysian was quite coarse on the surface when primed.

I normally avoid DIY stores (Homebase) but their 9mm ply, described as ‘hardwood’, was very flat and took two coats of Rustins grey primer on the edges and surfaces leaving a really smooth finish. On close inspection the hardwood is on the finished veneers only.

I’m sure many layouts are built on what’s cheapest and easily obtained but it would be interesting to hear if primed plywood can withstand many happy years in an insulated shed before I starts to show its age.

 

 

Edited April 3, 2018 by GNRi1959

[brianmcs]

It is the nature of plywood that it will warp of it's own accord if not well supported/fixed

For some years I have been using ply on flat roofs where it is expected to survive at least 30 years.

We always regarded 416mm as the maximum safe span for 18mm ply.

So I am not surprised at the 9mm cupping. 

The " hardwood" ply sold here in Ireland is visually very pleasing but now has a bad reputation in the roofing trade because it tends to delaminate .

The birch is usually very good quality ( especially the scandinavian ones ) but it still needs to be well supported/fixed

 

[GNRi1959]

9mm ply with 2 coats of primer 450mm wide screwed to a 60x20mm framework should be fine.

Edited April 3, 2018 by GNRi1959

[warb]

1 hour ago, GNRi1959 said:

9mm ply with 2 coats of primer 450mm wide screwed to a 60x20mm framework should be fine.

I have used 9mm birch 1800mm x 600mm wide with 12mm x 120mm frame to allow for  tortoise motors with no problems

[GNRi1959]

There has been a surge in sales of cheap Chinese ply which peels and   Is poor quality. 

[Mayner]

I can claim that I have used ply for baseboards in three different countries on two continents!

Scandanavian birch ply is probably the best option, we had major problems with Canadian ply on an Irish site, most of our home produced ply in New Zealand is from Radiata Pine warpps and twists into wonderful shapes unless securely fixed down.

I 1st used ply 9mm ply as a baseboard material on a 4mm shunting yard layout in the UK with an open top trackbed busing the technique in Barry Normans Landscape Modelling of fabricating the baseboard framing laminated from 75mm wide strips of ply laminated into "beams" X 75mm spacer blocks cut from 75X25 (nominal) softwood. The baseboards were very strong and stable despite using cheap ply, the main drawback was that the 9mm ply trackbed sagged between supports and noise with glued Woodlands Scenics ballast. I eventually fixed reinforcing strips under the track bed.

I used 12mm ply for baseboard framing and top for an American N gauge layout in Ireland, the framing was simply 75mm strips of ply reinforced at the corners with 50X25 (nominal) stripwood. This was very strong and stable but again very noisy.

Being from a building background I am not above using 18mm construction ply on 100X50 softwood framing for baseboard framing. I tried this on my 1st 21mm gauge layout in Ireland in Ireland, but was hardly portable to get out of an attic so the less said the better. The current incarnation is on a 1200X4800 permanent baseboard on timber piles in the garden all in CCA H3.2 treated timber. The ply is capped with a damp proof membrane with a drainage channel on either side to drain rain water, track and ballast (real stone) is glued down with dilute pva concrete bonding agent.

Certainly strong enough to walk on no signs of delamination or decay after 3 years in a rainy extremly humid environment. This section of baseboard is slightly noisier than adjacent sections where track is laid on 250X45 softwood, main issue is water not draining away quickly and flooding the line after a heavy downpour.