Morning all,

I am about to embark on a complete teardown of my layout.  It's been 'under construction' for the last 12 years, in that time I've made many mistakes due to poor (no) planning and it's now time to correct that situation.

My current setup has chipboard baseboards (15ft x 9ft with central well) topped with Sundeala, which I now understand to be completely the wrong choice for a loft layout 

I have learned from bitter experience that the moisture level in my loft has led to the Sundeala absorbing most of it, giving me massive issues with track all year round.  So, with that in mind I want to replace it with marine plywood (9mm seems to be the most suitable).

My question is, is the marine stuff really that good at resisting damp?  The ambient conditions in my loft are between 60-80% humidity (max), I do have a dehumidifier, but I've stopped using it all the time since the our energy prices went through the roof.  So I really need the wood to 'hold its own' where possible.

For information, my loft is insulated in the normal fashion (wool) under the floor and has foil blanket on the inside of the roof and down to floor level.  I realise this isn't ideal, but I don't have the time, nor money to have a full conversion done in my current house.

Can anyone tell me if marine ply will be my saviour here, before I start the heartbreaking process of pulling my existing setup apart?

Any advice is welcomed!

Thanks,

Simon

Hi Simon

It's not so much the humidity level, it's the fluctuations that make the difference. When I lived in the States, people still built stable wood structured layouts in sheds without air conditioning and pretty extreme humidity levels, worse than your attic for sure. Most people that did this made sure they sealed all surfaces of anything absorbent such as wood, card or paper with shellac, wax or varnish before using it though.

From what I understand of it, the glue in marine plywood prevents the individual plys that make up the sheet delaminating when wet, it doesn't mean it won't absorb water. However it's normally made with better quality wood which should be denser and less absorbent than cheap plywood but you'd still need to seal it to make absolutely sure it doesn't absorb moisture.

There's not a massive difference in price between marine and good birch plywood and as you'd probably want to seal both anyway maybe consider good birch plywood too, the slight price difference might pay for the sealant. I'm just gluing up some nice birch ply for my own boards now and it's really nice to work with, solid, no voids or delaminated areas, no noticeable if any warping and it's been stored in all kinds of environments and dampness levels (indoors, unheated garage, damp garage, back to relatively dry house etc) since I bought it years ago.

Another tip if you do come to rebuild, let your wood whatever it is (sheets or timber), acclimatize to the new environment before using it, it could well have been stored in different conditions than your attic and will then either shrink or expand as it adapts to the new environment.

Also Simon 

I would agree that 9mm ply is your best option but you don't necessarily have to buy premium quality ply providing you use it correctly.  The 1200x600 sheets available from Wickes are pretty good and easy to manage.  Being smaller they don't seem to warp so easily.  It costs a bit more to buy the smaller sheets but makes life much easier, especially if you have to use smallish pieces anyway to get them into your loft. 

The critical things are:
1) store it flat on the floor, never on its side leant up against the wall.
2) fix it to a sturdy frame (ideally 75x25 PSE - which comes out at about 70x20mm and try to have battens at around 600mm centres with similarly spaced cross braces.  If you get that right and then screw your plywood tops down to it (screws every 150-200mm slong each supporting batten) you won't have any issues with it twisting.
3) once you have cut a section of ply to size give it a coat of paint on both sides and on the edges with a vinyl emulsion. A dark colour like brown on the top is ideal and some people paint the underside white to make it easier to see when wiring underneath.

In addition to glue quality and the type of wood in the laminates, one of the major differences in marine ply is that voids are not allowed.  I doubt that is relevant for our hobby, and I'd just go for a good quality birch plywood.

Jon

I use MDF in my loft. Made sure to seal with brown paint and as @devonjames says, I created a secure frame with 2x1 PAR and screwed it down securely. Remember to drill some 1/2" holes in the cross members to allow for cables.

Quote from: NScaleNotes on February 11, 2023, 11:31:08 AM
Hi Simon

It's not so much the humidity level, it's the fluctuations that make the difference. When I lived in the States, people still built stable wood structured layouts in sheds without air conditioning and pretty extreme humidity levels, worse than your attic for sure. Most people that did this made sure they sealed all surfaces of anything absorbent such as wood, card or paper with shellac, wax or varnish before using it though.

From what I understand of it, the glue in marine plywood prevents the individual plys that make up the sheet delaminating when wet, it doesn't mean it won't absorb water. However it's normally made with better quality wood which should be denser and less absorbent than cheap plywood but you'd still need to seal it to make absolutely sure it doesn't absorb moisture.

There's not a massive difference in price between marine and good birch plywood and as you'd probably want to seal both anyway maybe consider good birch plywood too, the slight price difference might pay for the sealant. I'm just gluing up some nice birch ply for my own boards now and it's really nice to work with, solid, no voids or delaminated areas, no noticeable if any warping and it's been stored in all kinds of environments and dampness levels (indoors, unheated garage, damp garage, back to relatively dry house etc) since I bought it years ago.

Another tip if you do come to rebuild, let your wood whatever it is (sheets or timber), acclimatize to the new environment before using it, it could well have been stored in different conditions than your attic and will then either shrink or expand as it adapts to the new environment.

Also Simon 

Thanks for the comprehensive reply.  That has cemented my decision to go for the rebuild and use marine ply to do it, I'm not hugely bothered about the cost if I'm honest, I'd rather do it right this time around.  I'm pretty sure that since I stopped dehumidifying 24 hours a day, the expansion of the sundeala has gotten worse and caused more extensive damage to my track.  That being said, last summer's extreme temperatures also created havoc (38C in my loft at the hottest).

I had read that acclimatisation and sealing of the edges is essential - nice to have that confirmed.

Next up will be to start the dismantling process, not something I'm looking forward to, but exciting to be able to start working towards a new layout nonetheless!

Thanks again.

Simon
PS Also thanks to everyone else who replied!

One thing I've noted of late in videos and commercial baseboards is that the traditional 1" x 2" or 2" x 3" softwood frame has been dropped in favour of using plywood framing of 3" or 4" strips often with holes in to reduce weight but retain rigidity.  I used this method for my small 240cm x 75cm base board as the previous one that used 9mm MDF screwed and glued to a frame made from 38mm x 63mm studding had bowed in only a year, and that was in a bedroom and not in a loft environment.

Here is an example form a commercial manufacture.

I used 9mm shuttering plywood to keep cost down but 'sealed it' with leftover emulsion paint on the underside and brown Shed & Fence on the top surface. It's an unheated garage and hasn't moved in 3 years sitting on the frame - outer is 4" x1" with 9mm x3" plywood webs.
I think @malc-c and @Malc have similar experiences.

I'm a great believer in avoiding a solid top "train set" baseboard unless it's appropriate for the intended scenery or for a fiddleyard. I much prefer an open frame approach with scenery above and below the track bed.   I build my layouts in manageable sections for portability and ease of maintenance and working on one section at a time on a table.

I use 9mm ply to create the sides of a deep box, with less cross-bracing than @malc-c shows in that commercial baseboard kit but enough to tie the sides together and provide support for risers up to the track bed.   The box sides are later cut down to the scenic contours.


I've not gone for marine ply as such, just the standard DIY store sheets.  The baseboards live in a garage except when at exhibitions or brief periods set up indoors. So there's certainly some degree of temperature and humidity fluctuation but probably not quite as bad a a loft (not an environment I'd choose to build a layout in tbh). The oldest boards were built in 1994 and have suffered no warping in that time, I've just put them back together after 6 years of storage and everything's gone together perfectly.

I too didn't go with so much bracing as the commercial example,  and I've opted for a closed frame with a 9mm top, but it's still very sturdy once glued and nailed

Interesting to see you use copper foil tape, @malc-c . Have you had any problems?

@Malc no, its all been fine.  Easy to solder dropper wires to, and for this sized layout there is no signs of voltage drop or loss of DCC signals etc.

Hi Malc, I just wondered about the "stickiness" of the adhesive, in case it came unstuck during the summer.

Here in the US all exterior grade plywood, typically graded CDX and smooth on one side, uses waterproof glue.  It sounds like your layout was built of cheaper interior grade.

I would not use marine plywood due to the cost and the toxicity of the sawdust..  It has zero voids and is treated against rot.  The treatment here used to be arsenic based but is now copper, a less toxic (to people anyway) heavy metal.

Quote from: Malc on February 13, 2023, 12:53:41 PM
Hi Malc, I just wondered about the "stickiness" of the adhesive, in case it came unstuck during the summer.

Well it's still stuck after last years 40c heat :-)

So far it's been fine.  How good it is after a few years only time will tell.  The layout is small enough that should it become an issue I can replace it with traditional wire and Wago connectors without too much inconvenience