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Just another modeller
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*** Actually I don't think the actual material is an issue:

The need to have it at a stable condition and seal every surface is the main issue. All timber products expand and contract far more than any metal in the rails - probably several times more in fact. If movement is enough for track bed to be shifted then its not rail... Its timber expansion and contraction!

Consider this - when its hot, rail expands and wood dries and shrinks / when its cold and damp, the opposite happens - the rail shrinks at the same time untreated wood epands quote a lot! We blame it on the rail, but we should look to the WOOD!

There are always screams of "beware" when anyone mentions customwood but its very consistent and stable if used properly. Ply is more user friendly but either MDF or ply will be equally stable if properly supported and painted on all faces and edges when used. MORE stable than any grained timber including all but top quality marine grade ply perhaps!

6mm is THIN for track bed and will need considerable support if the layout is not to become a roller coaster over the years. I would personally recommend never less than 12mm ply or customewood to lay the track on, with supports every 300mm.

the actual baseboard frame can be thinner, particularly if a sandwich style construction is used (two strips of wood with pine blocks separating them at regular intervals, reinforced by blocks at every gusset and join area).

My formula for a stable layout:

Keep timber in the railway room for a couple of weeks before using it. Preferably do all timberwork when its early in a dry period and not either extremely ot or cold.

Paint all wood before cutting it or assembling it - its easier. Use a standard household paint with a little flow aid and a small amount of thinning so it will soak into the wood well - I actually like using a little meths and water rather than plain water.

when the baseboard is cut and assembled, paint all exposed edges and ends before you start tracklaying.

Have a cheap low cost fan heater in the room when doing any glueing - set the heater part to low at most though - the idea is to circulate warm dry air all the while so glue goes off well and moisture is expelled. Leave it on for 24 hours after any work session - just the fan is OK as long as the atmosphere isn't damp.. if its cold and damp, leave the heater on low too.

Fix foam roadbed with good quality PVA full strength. Paint both the roadbed and the area it will be laid then weight it down for at least an hour over its full surface.

Fix track with full strength PVA, no pins (at least none that will be there permanently). weight it down evenly across its length for at least an hour to let the glue tack enough.

Leave a small gap each metre (0.5mm is more than enough if it is regular). Be careful to be sure these gaps are there for curves much more than straight track. never solder rail joiners, just feed every track section with droppers if DCC wiring.

BTW rail joiners aren't all that important if you use bullhead rail or very fine rail - I don't bother with them on bullhead for 4mm scale or code 40 and 55 in HO... but I do always have large radii (5' or more) - I use exactly NONE on my current layout and simply lay the (many many many metres) of track properly aligned.

For layouts with sharper curves and bigger rail sizes (above code 70) they are more important, and a sloppy joiner will cause problems so only ever use NEW joiners - never re-use old ones!

SAME fan heater procedure with ballasting and scenery: ANY water in the layout room should be encouraged to leave as soon as possible.

Use a mix of water and meths NOT water with the glue for these aeas - everything will dry quicker and more thoroughly and the meths will act as the best possible "wetting agent" - much better than dishwashing liquid. Thin the good quality glue at least several parts mths + water to one of glue!

Re a "hot/cold" room or attic. The enemy is changing humidit levels MUCH morethan hot or cold really, except that when things are cold, humidity becomes dampness!.

Leave the fan heater up there. Buy a small plug-in timer and set it to work for an hour at least 4 times per day EVERY day. That will keep humidity and cold stagble across the year and in check and at a low heat setting it will not kill te power bill.

Richard

PS: Its never too late to paint the baseboard timbers.... just more of a pain to do it later. Do a bit at a time thoug, and in no time at all it'll all be sealed with minimal hassle!
 
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