Plywood disaster

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Paul Willis
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Re: Plywood disaster

Postby Paul Willis » Tue Nov 12, 2019 7:16 pm

davebradwell wrote:To pass by the original thread briefly, isn't it good practice to stack the wood for a job in the room it's to be used for a few days before starting? I'm no joiner but I seem to have this in my head from somewhere way back. Perhaps it was just a strategy my Father used to delay a job.


Yes, you are supposed to do this. Good quality timber, such as solid oak floorboards, may even have this as part of the instructions on the packaging.

And also pay attention to the storage, so it doesn't lean and bend in any plane. Either flat (as in on the floor) or as near vertical as you can manage. Anything on an angle will cause problems when you come to use it.

I take good care of the timber stack at the back of my garage!

Cheers
Flymo
(and no criticism intended of Bob's preparation for his baseboards - that sounds most unfortunate)
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Philip Hall
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Re: Plywood disaster

Postby Philip Hall » Wed Nov 13, 2019 9:44 am

Dave and Flymo’s thoughts about timber ring true for me too. I bought some very long lengths of 2x1 many years ago and left it on the stairs leading up to the (then) workshop. It didn’t get used for the layout in its new location, but when we used it for supports and suchlike it was still dead straight.

My new boards are indeed on a substantial ply frame, with some old bookshelves here and there for some of the cross bracing, but screwed to the walls. Longitudinal runners are two strips of thinish ply glued together, over 20ft long and have remained dead straight, baseboards the same and dead level within 0.5mm all around the room.

Philip

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John Bateson
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Re: Plywood disaster

Postby John Bateson » Wed Nov 13, 2019 12:07 pm

May I offer an option for ply surfaces apart from a good coat of traditional varnish. I have used double sided carpet tape directly on the ply. This acts as a waterproof barrier.
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Re: Plywood disaster

Postby Enigma » Wed Nov 13, 2019 4:04 pm

Philip Hall wrote:Dave and Flymo’s thoughts about timber ring true for me too. I bought some very long lengths of 2x1 many years ago and left it on the stairs leading up to the (then) workshop. It didn’t get used for the layout in its new location, but when we used it for supports and suchlike it was still dead straight.

My new boards are indeed on a substantial ply frame, with some old bookshelves here and there for some of the cross bracing, but screwed to the walls. Longitudinal runners are two strips of thinish ply glued together, over 20ft long and have remained dead straight, baseboards the same and dead level within 0.5mm all around the room.

Philip

I had some bundles of 2x1 lying around my layout room for several years and they remained straight - and they also became very much lighter. Goes to show how much of the solid mass of newly bought timber is actually moisture.

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Re: Plywood disaster

Postby bobwallison » Sun Nov 17, 2019 5:43 pm

Well that's sorted at last. I eventually coated the bottom surface with the same glue as the top surface, together with a polythene sheet to emulate the waterproof properties of the Exactoscale underlay on top. The ply is now restored to a very small uneven-ness, which is probably more realistic for my sorting sidings than dead flat (whatever that means).

I think that I will revert to 12mm MDF for future trackbeds, except where they need to be portable. Notwithstanding warnings from various folks on this thread, it has always worked well for me and continues to do so. Oh, and it's about half the price of 9mm ply.

Bob

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Re: Plywood disaster

Postby Terry Bendall » Mon Nov 18, 2019 8:49 am

bobwallison wrote:I think that I will revert to 12mm MDF for future trackbeds, except where they need to be portable. Notwithstanding warnings from various folks on this thread, it has always worked well for me and continues to do so. Oh, and it's about half the price of 9mm ply.


In the last 45 years I have been involved in the construction of 8 layouts built to P4 standards, all of which have used 12mm plywood for the baseboards with no problems and with close to 60 years experience of working in wood I would not use anything else. What people do is of course up to them ( :) ) but we often see on here reports of problems where experience shows an alternative course may have resulted in fewer difficulties. Sometimes choosing a cheaper material may turn out to be a false economy without considering the time used in building something that turns out to cause difficulties. :)

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Le Corbusier
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Re: Plywood disaster

Postby Le Corbusier » Mon Nov 18, 2019 12:38 pm

In this instance it would appear that it is the ply rather than the MDF which has caused the issues? So investing in the more expensive option following on from advice taken seems to have caused issues not experienced before?

Or maybe I have this wrong :?
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Re: Plywood disaster

Postby nberrington » Mon Nov 18, 2019 1:44 pm

I have mixed feelings about ply. I have used Baltic birch - 12mm for trackbed and 18mm for the chassis. It is light and very strong. Unfortunately will chip a bit in the CNC machine if you use the wrong bit!

The boards I’ve made have been done with sturdy stuff and is assembled as to be bomb proof with gorilla glue and screws. It doesn’t move a bit.

I’ve noticed it will twist wickedly if you leave pieces lying stacked against something. Folks in our worker space often have to throw entire boards out. Store flat, machine with care, secure solidly.
I’m expecting it to last forever.

Here in North America foam insulation seems to be the order of the day. Mark S on this forum has his layout made out of the stuff. Amazingly light. Poses its own challenges.

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Re: Plywood disaster

Postby nberrington » Mon Nov 18, 2019 3:49 pm

Somewhat over engineered.

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bobwallison
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Re: Plywood disaster

Postby bobwallison » Tue Nov 19, 2019 12:07 pm

Le Corbusier wrote:In this instance it would appear that it is the ply rather than the MDF which has caused the issues? So investing in the more expensive option following on from advice taken seems to have caused issues not experienced before?

Or maybe I have this wrong :?

No Tim, you are spot on. Whilst I agree with Terry that buying cheap materials is often a false economy - both of time and money - in this instance the exact opposite was true. I cannot match Terry's 40 years experience, but varnishing both sides of plywood, providing extra bracing and the like are all solutions to a problem I have never experienced in a decade of using MDF for my trackbeds.

But then I have never built a portable layout.

Regards,
Bob

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Re: Plywood disaster

Postby Alan Turner » Wed Nov 20, 2019 9:57 am

bobwallison wrote:
Le Corbusier wrote:In this instance it would appear that it is the ply rather than the MDF which has caused the issues? So investing in the more expensive option following on from advice taken seems to have caused issues not experienced before?

Or maybe I have this wrong :?

No Tim, you are spot on. Whilst I agree with Terry that buying cheap materials is often a false economy - both of time and money - in this instance the exact opposite was true. I cannot match Terry's 40 years experience, but varnishing both sides of plywood, providing extra bracing and the like are all solutions to a problem I have never experienced in a decade of using MDF for my trackbeds.

But then I have never built a portable layout.

Regards,
Bob


You are all making these comments without any details or photos of the OP work. Properly constructed 9mm ply baseboards do not warp in this manner so I would like to see some details.

I have just built some Birch ply baseboards using 9mm framing and 6mm top. They are flat and have remained so after attaching track bed material to the top.

regards

Alan

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Le Corbusier
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Re: Plywood disaster

Postby Le Corbusier » Wed Nov 20, 2019 10:11 am

Alan Turner wrote:
bobwallison wrote:
Le Corbusier wrote:In this instance it would appear that it is the ply rather than the MDF which has caused the issues? So investing in the more expensive option following on from advice taken seems to have caused issues not experienced before?

Or maybe I have this wrong :?

No Tim, you are spot on. Whilst I agree with Terry that buying cheap materials is often a false economy - both of time and money - in this instance the exact opposite was true. I cannot match Terry's 40 years experience, but varnishing both sides of plywood, providing extra bracing and the like are all solutions to a problem I have never experienced in a decade of using MDF for my trackbeds.

But then I have never built a portable layout.

Regards,
Bob


You are all making these comments without any details or photos of the OP work. Properly constructed 9mm ply baseboards do not warp in this manner so I would like to see some details.

I have just built some Birch ply baseboards using 9mm framing and 6mm top. They are flat and have remained so after attaching track bed material to the top.

regards

Alan

Guilty as charged m'lud :D But then my comment was simply an observation with no advice or thoughts added.
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Re: Plywood disaster

Postby bobwallison » Wed Nov 20, 2019 4:14 pm

Alan Turner wrote:You are all making these comments without any details or photos of the OP work. Properly constructed 9mm ply baseboards do not warp in this manner so I would like to see some details.

Benchwork.jpg

Alan,
Hopefully the picture above will make things clear. The L-girders are 153mm deep overall, bearers 68x18 and risers are ply - in this instance 6mm thick at 300mm centres. The ply trackbed is in the foreground, under the black underlay; in the background on the shallow embankment is the MDF trackbed which I have used hitherto. I normally fix the trackbed in place at the ends only, relying on gravity to hold it down in between. Before I coated the underside with glue, the ply trackbed was effectively supported on the two outer risers at 1200mm centres and had bowed upwards in the middle by at least 10mm.

I would be very interested to see the arrangement of your own baseboard and to know how far the 6mm trackbed can span before it begins to sag. Also, what kind of glue did you use to fix the underlay? I am fairly sure that if I had used a foam or carpet spray adhesive the ply would not have distorted.

Regards,
Bob

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Tim V
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Re: Plywood disaster

Postby Tim V » Wed Nov 20, 2019 7:15 pm

So, it was 4' long, screwed down at the ends only.

I'm not surprised it bowed.
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jon price
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Re: Plywood disaster

Postby jon price » Wed Nov 20, 2019 8:26 pm

My understanding is that to be effective as a girder there would need to be an L or T brace directly under the trackbed board thus making the trackbed the top of the girder. The transverse beams do not provide that kind of rigidity to the trackbed.
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Re: Plywood disaster

Postby Tim V » Wed Nov 20, 2019 8:57 pm

Here is a drawing of the L girder principle. Note that the trackbed does not float on the supports, but is screwed to every support, thus providing rigidity. Homasote (Sundeala in this country) is laid on top of the roadbed, for the track to be pinned to.
L Girder.jpg
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Re: Plywood disaster

Postby Alan Turner » Mon Nov 25, 2019 11:14 am

bobwallison wrote:
Alan Turner wrote:You are all making these comments without any details or photos of the OP work. Properly constructed 9mm ply baseboards do not warp in this manner so I would like to see some details.

Benchwork.jpg
Alan,
Hopefully the picture above will make things clear. The L-girders are 153mm deep overall, bearers 68x18 and risers are ply - in this instance 6mm thick at 300mm centres. The ply trackbed is in the foreground, under the black underlay; in the background on the shallow embankment is the MDF trackbed which I have used hitherto. I normally fix the trackbed in place at the ends only, relying on gravity to hold it down in between. Before I coated the underside with glue, the ply trackbed was effectively supported on the two outer risers at 1200mm centres and had bowed upwards in the middle by at least 10mm.

I would be very interested to see the arrangement of your own baseboard and to know how far the 6mm trackbed can span before it begins to sag. Also, what kind of glue did you use to fix the underlay? I am fairly sure that if I had used a foam or carpet spray adhesive the ply would not have distorted.

Regards,
Bob


Well all I can say is that I would have been utterly amazed had it NOT sagged.

regards

Alan

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Re: Plywood disaster

Postby Terry Bendall » Mon Nov 25, 2019 3:35 pm

Alan Turner wrote:You are all making these comments without any details or photos of the OP work


Scalefour News numbers 171 to 177 which covers February 2011 to May 2012 contains a series of articles on baseboard construction which may be useful to some. No fancy stuff but they work. :)

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Re: Plywood disaster

Postby bobwallison » Mon Nov 25, 2019 5:44 pm

Alan Turner wrote:
Well all I can say is that I would have been utterly amazed had it NOT sagged.

regards

Alan

Except it didn't sag, it bowed upwards. That's why it was only in contact with the supports at the outer end of the board, even though supports are provided at the usual 300mm centres.

I wonder if people are making insufficient allowance for the fact that this is a permanent layout. It is not subjected to any of the twisting or wracking loads that must effect portable layouts as they are dismantled, moved around the country and re-built somewhere else, so I don't see the need to provide rigidity to resist - what, exactly? If it is to resist a built-in tendency of the materials to twist and warp that would seem poor engineering - much better to use an inert material, such as MDF, which is more inclined (at least in my experience) to stay put once it is seated on supports at reasonable centres.

There are parts of my layout which will need to be portable, so I still plan to use plywood for these, and I will take on board the various comments about strength and rigidity for these, and re-read Terry's articles on baseboard construction.


Regards,
Bob

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Noel
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Re: Plywood disaster

Postby Noel » Mon Nov 25, 2019 7:38 pm

bobwallison wrote:Except it didn't sag, it bowed upwards


Which would seem to imply that it had expanded. Possibly an issue with humidity being higher than when installed?
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Re: Plywood disaster

Postby grovenor-2685 » Mon Nov 25, 2019 7:46 pm

It bowed because it was coated with glue on one side and not the other, commo0n enough problem which we went through in the first few posts.
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jon price
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Re: Plywood disaster

Postby jon price » Mon Nov 25, 2019 9:29 pm

the l girder design as depicted seems inherently flawed. Apply pressure on the trackbed between supports (or differential expansion through gluing one side) and it can fairly cleary bend in the vertical plane as there is plenty of scope for the transverse supports to twist. Fasten the L girder vertical directly below the trackbed and it can't.
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Re: Plywood disaster

Postby Le Corbusier » Mon Nov 25, 2019 9:46 pm

Speaking with my joinery/carpentry - design, detailing and specification hat on ..... from what I have learned over the last 30 years of practice - from the joinery firms and cabinet makers I have worked with ....

My two penn'orth would be to advise sealing whatever substrate is used to limit any tendency towards movement via absorption or humidity - and make sure that the sealant is not microporous. I would also observe that if the intent is to bond to one face (particularly if you are bonding a material which might tend towards shrinkage on drying), then it would be wise to either counter-balance the other side, use a thickness which would make such bonding all but immaterial, or brace to achieve the same effect.

As a further observation, my experience with thinnish non exterior grade plywoods is that the top face will absorb water and expand, but that the glues prevent significant penetration to the lower layers so a marked bowing occurs. This would be another reason to avoid waterborne products in this instance.

Exterior grade and moisture resistant MDF are both available, are stable and are not subject to this kind of bowing. However MDF does have a tendency to 'flow' due to its internal structure and so if used horizontally will almost always sag over time (dependent upon the thickness used and centres of support). It will do this due to its self weight without loading.

Beware of block boards. In the old days blockboard was often lipped, veneered and used for shelving ... but the BS has changed and the internal bonding is much cheaper and less effective, meaning it will now sag quite alarmingly.

Having said that ... if something has been working for you over time, then you must be doing something right, so why change?

I observe the guidance above because I can be sued if it goes wrong and so better to be safe rather than sorry. :thumb
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Re: Plywood disaster

Postby davebradwell » Mon Nov 25, 2019 10:20 pm

Good to have a professional explain the basic rules to us. Thank you Tim. I will copy your guidance to my notes for future reference.

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Re: Plywood disaster

Postby Le Corbusier » Mon Nov 25, 2019 10:42 pm

davebradwell wrote:Good to have a professional explain the basic rules to us. Thank you Tim.
DaveB


The caveat being ... I am an architect, so this is the advice I have gleaned from the real experts I have worked with over the years (joinery shops, cabinet makers etc). I detail up the work initially but always ask for rods and then go into the workshops to work with the joiners to develop the final construction details - each shop tends to have its own foibles. I will always defer to someone with greater hands on experience ... after all they work with the materials day in day out and have to put things right if they go wrong - but generally nowadays we tend to be in agreement. Things generally go wrong when know it all architects tell craftsmen to do something they are uncomfortable about or know won't work ;)
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