Baseboard - 6mm marine ply or 6mm MDF?

 
  Gremlin Assistant Commissioner

Any benefits/disadvantages of either?

To go on top of a proper frame, 60cm*120cm and 60cm*240cm sections.

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  wobert Chief Commissioner

Location: Half way between Propodolla and Kinimakatka
Marine ply handles moisture, I think the other stuff can warp pretty bad
  DJPeters Assistant Commissioner

Any timber based product can warp but some do it worse than others, also some man made timber substitutes not only warp but disintegrate or swell given the right conditions. Adding moisture on top of a bare piece of standard MDF or Chip board is just asking to have the the board do anything and every thing. However some seem to get away with using it provide the board is all sealed with a coat of paint usually the brown of bare earth or something similar. This has to be all round though top, bottom and all edges.

Marine Ply is expensive though but is probably the best bet. How ever a properly made frame with either MDF or Chipboard on the top should be just as good provide you do what I said up top and paint the board before installing it on the frame, you could paint the whole sheet to start with and just touch up wherever you make a cut or cuts.

But no matter what you really use if the base framework is not good and strong enough it will move and adding the board on the top will not fix it. Like a house a good foundation is needed if you want it to last.
  dthead Site Admin

Location: Melbourne, Australia
Agree, Ply is better -  and the better it is the more it costs. thickness is another factor - too thin you will need more supporting framework. You do not want to flex the board.

If using MDF, seal it well with paint, every surface. It will need more support / framework too.


Regards,

David Head
  Clyde Goodwin2 Chief Train Controller

If you realy must go with MDF Please Ensure you wear a very good quality respirator/dust mask when cutting or shaping it.

Another good thing that is not overly pricey is Form ply the thing that is used for forming up by Concrete form workers.
  yogibarnes Locomotive Fireman

I agree with main points above.
For a given thickness, ply much better than MDF (which is basically dense cardboard).  Even chipboard is better than MDF.
No need for the cost of formply.  Biggest threat of moisture (unless you are in an open shed) is under the track whilst ballasting.  Avoid the potential moisture problem by painting, preferably all surfaces of MDF, especially the edges of ply, and especially under the (yet to be laid) track.
6mm ply too thin.  Go with 9mm ply (or 16mm MDF) with 450-500mm spaced joists.  Always try to span any cut pieces across three joists.
  Gremlin Assistant Commissioner

I agree with main points above.
For a given thickness, ply much better than MDF (which is basically dense cardboard).  Even chipboard is better than MDF.
No need for the cost of formply.  Biggest threat of moisture (unless you are in an open shed) is under the track whilst ballasting.  Avoid the potential moisture problem by painting, preferably all surfaces of MDF, especially the edges of ply, and especially under the (yet to be laid) track.
6mm ply too thin.  Go with 9mm ply (or 16mm MDF) with 450-500mm spaced joists.  Always try to span any cut pieces across three joists.
yogibarnes
I am surprised that 6mm is too thin...I have made some test frames and it seems rigid.  Would you recommend 9mm for any particular reason?
  gordon_s1942 Chief Commissioner

Location: Central Tablelands of NSW
I think much will depend on what sort of layout your planning, like the 'good old 6 X 4 foot' panels or is it a 'skeletal' type or around the wall shelf type, all of which require their own form of support.
Watching some of these Home renovation shows on TV where they are converting older style housing to open plan that alters what was load bearing walls before may help you even though your layout stresses are Horizontal and those others are vertical.

Another is to see how they are building bridges like the Milleu Bridge in France and the one over the Bosphourous in Turkey.
  LaidlayM Chief Commissioner

Location: Research
I am surprised that 6mm is too thin...I have made some test frames and it seems rigid.  Would you recommend 9mm for any particular reason?
Gremlin
I use 19mm or lamitations to make up similar.  That's for a shelf with 400mm spacing

Mark
  DJPeters Assistant Commissioner

You need to stop the frame from twisting and a thicker top piece of board will help this immensely. You can make up reasonably light sections of board able to be picked up by one person if you make a modular type of board or boards. A thicker top surface is really needed here to stop the boards from twisting and throwing your track alignment way out. Even if sections are bolted together one section can twist out of alignment it only takes a little bit to throw a spanner in the works so to speak.

I have used 42 X 19 Pine PAR for my modular layout where each section is approx a metre long by about 600mm wide but the top of it is made from chipboard about 15 mm thick and the boards are extremely rigid but reasonably light weight that I can carry one in one hand if needed. The legs to support it are also 42 X 19 Pinus PAR.

It has been well over 20 years now and probably closer to 30 actually but the boards are still flat and usable! I just wish I had the room to put them all up again though!
  yogibarnes Locomotive Fireman

I agree with main points above.
For a given thickness, ply much better than MDF (which is basically dense cardboard).  Even chipboard is better than MDF.
No need for the cost of formply.  Biggest threat of moisture (unless you are in an open shed) is under the track whilst ballasting.  Avoid the potential moisture problem by painting, preferably all surfaces of MDF, especially the edges of ply, and especially under the (yet to be laid) track.
6mm ply too thin.  Go with 9mm ply (or 16mm MDF) with 450-500mm spaced joists.  Always try to span any cut pieces across three joists.
I am surprised that 6mm is too thin...I have made some test frames and it seems rigid.  Would you recommend 9mm for any particular reason?
Gremlin
Only that I know 9mm works well and I haven't tried 6mm extensively.
  G Train Locomotive Driver

6mm MDF or 6 or 7mm Plywood can be used successfully depending on the short span & how it's framed/supported. Plywood comes in various grades/strengths. Does the 6mm MDF or Ply deflect (sag) too much when you have all your scenery and rollingstock on it? Testing it as you indicated is a good idea.
I'd definitely echo sentiments of using respiratory protection if cutting MDF but a good idea with any fine airborne particulates if you value your health. Also sealing all faces and edges at the same time.

Here's my experience in building a diorama:
I asked a local hobby shop who suggested MDF...
My short span is typically 350mm to 390mm by 1800mm and I used 6mm MDF. I painted the underside and edges of the first one, laid foam to support the track then painted the rest. Hmm, a while after ballasting I noticed slight curling at the long edges. I have since managed to arrest this somewhat.
For the second one I painted all the board left it inside to dry, then laid track. This is very flat and has been my best effort to date.
At this point I felt confident using MDF so built a third, reinforced the edges and decided to spray paint one side (to make it quicker) and leave it in the sun to dry. Well, that turned into a banana! So judicious clamping and steaming was required and I eventually straightened it out and coated the other side.

I still have some leftover MDF and will use it, but the next time I build something or if I want to extend it into something resembling a layout I think I will use Plywood around 6 to 9mm thick. If it's painted before any scenery you shouldn't get too many problems but extensive holes that may need to be drilled may mean that Marine Ply is a better choice.

One other thing, Ply is easier to pin track into than MDF.

Happy building!
  Tom66 Assistant Commissioner

I'm a carpenter and can tell you with confidence that mdf and moisture do not go well together and is never used in any wet areas of a house. If it gets wet it swells and warps like you wouldn't believe and is not designed to absorb and deflect water. Marine ply is a good product but generally only used to form concrete and has a nonstick/wax type coating that is designed so as not to stick to concrete when it is being stripped so you might struggle trying to glue foam or scenery to it. Normal ply is fine but I wouldn't go any less then 12mm in thickness, as long as you use PVA fly and acre it off to your frame at 100-150 mm centres you should have any problems but the thicker the better.
  meh Chief Commissioner

Location: Sydney
I'm a carpenter and can tell you with confidence that mdf and moisture do not go well together and is never used in any wet areas of a house. If it gets wet it swells and warps like you wouldn't believe and is not designed to absorb and deflect water. Marine ply is a good product but generally only used to form concrete and has a nonstick/wax type coating that is designed so as not to stick to concrete when it is being stripped so you might struggle trying to glue foam or scenery to it. Normal ply is fine but I wouldn't go any less then 12mm in thickness, as long as you use PVA fly and acre it off to your frame at 100-150 mm centres you should have any problems but the thicker the better.
Tom66

Just to clarify, marine ply and form ply are two different products.

Marine ply is like typical plywood, however it is made from much higher grades of veneer with higher finish quality. Structural grade plywood surfaces are graded from A - D; an AA rating (marine ply) is a high quality finish on both sides, whilst CD is more rough with higher number of imperfections. The higher the quality of the surfaces, the more resistant it is to moisture and other contaminants. Needless to say, marine ply can be almost double to price.

Bog standard plywood from Bunnings is usually CD finish; check the price difference:
'Standard' structural plywood
2400x1200x12 CD Plywood

Marine Plywood
2440x1220x12mm Marine Plywood

Form-ply is a different product altogether. It is structural, usually high-grade and at least 17mm thick, but the outer layers have a resin coating to, as you mention, prevent the concrete from sticking and giving a smooth finish to the concrete surface, and then it can be re-used. The edges are also painted to reduce moisture absorption (even still; after about 5-6 concrete pours most form-ply should be disposed of).
1800x1200x17mm Formply

So Gremlin to answer your original question; for a baseboard marine-ply is the much better choice. That said; 6mm is rather thin, so make sure you install regular cross-pieces (say at 300mm spacings) to the frame to support the board; this will prevent warping/sagging and give it a lot more strength. The cross-pieces can even be the simple 19x38mm pine lengths you can buy from Bunnings.

Cheers and all the best with it; keep us posted Smile
  railmod Chief Train Controller

Gremlin,
My layout is made using L-Girder topped with 12mm (C-D grade) Ply, braced every 450 odd mm, in one spot I have a a siding where the ply is only the width of the track + 10mm, this was not braced as well & did warp/bend somewhat (now has extra bracing & seems OK) - the rest has lasted OK with little, if any sagging - on that basis I'd go with Ply - I did use some MDF & Chipboard on an early module, but that did warp & was replaced. - I have not sceniced the layout as yet so not sure what impact that will have.

Cheers Alex.
  Iain Chief Commissioner

Location: Concord, NSW
I think the general opinion is ply rather than MDF. I have used ply and the reasoning was a concern that in high humidity such as we get in Sydney MDF might absorb moisture, it is also heavy. I opted to go with the skeletal frame - egg carton approach with 6mm ply and this produced a rigid but light frame with little to no distortion. I also painted the frame just to make sure.

Iain
  SA_trains Deputy Commissioner

Location: ACT
I am a fan of a monocoque building style.

For my modest shelf layout, I used 6mm plywood. Just the bog standard type of ply. I painted all surfaces. Each module is 1200x450mm. It has a modest internal frame. Each module is very light, very strong and very stiff. There is no flexing/twisting in the module.

The photos below shows the modules.



and inside:



And here is a photo showing a somewhat more advanced module with wiring going on!



Each module came from a single sheet of plywood which was quite economical. Not shown is the bracing that goes on the bottom which then makes the modules a monpcoque structure. That said, the modules are quite stiff even without the bottom brace.

This an alternate suggestion for you. If you have a look at the UK model railway scene, they use a lot of monocoque structure techniques. It has a number of significant advantages in light, strong, stiff construction and is usually quite cheap. It is highly suitable for layouts that are likely to be moved a lot, like an expo layout. It is a method that is highly commendable.

Cheers,

Dan

Images fixed! bloody pain in the fundamental orrifice getting them to work.... Smile
  sol Assistant Commissioner

Location: Evanston Gardens SA
Dan, Photobucket is not allowing photos to be displayed unless you have a paid account with them..
  sol Assistant Commissioner

Location: Evanston Gardens SA
Still not working - clicking on the links takes you to the Photobucket site but still NBG. the dreaded square...
  dthead Site Admin

Location: Melbourne, Australia
10mm ply is better than MDF any day. 6mm is rather thin unless you have extensive bracing, something we learned the hard way with our former layout Murranbilla.

Regards,
David Head

(Eltham Model Railway Club member)
  SA_trains Deputy Commissioner

Location: ACT
Thanks for letting me know Sol, I'll figure out a different way of posting photos.
Cheers

Dan

Sol, photos fixed...
  sol Assistant Commissioner

Location: Evanston Gardens SA
Thanks Dan

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