From my experience, it is

From my experience, it is more do do with the subroadbed. I made the error once of having my around the walls shelf layout (made out of plywood) its sections snug up against each other and tight to the walls corners. It caused an area to bow upwards in the hot summers. As for rail, allowing gaps or cutting gaps will resolve rail expansion.

My current layout's subroadbed consists of extruded rigid foam glued to hollow core doors. Five years of the subroadbed exposed to cold and hot temperatures indoors and I've had no problems. The rail was installed on the subroadbed back in December 2016 and has been exposed to heat and cold as well with no problems.

its the Lumber

...from another forum, and experienced model railroader as well as house builder...

 

My trainroom at our old house

Didn't vary by more than 10 degrees Celsius summer to winter, and humidity was reasonably well controlled with a dehumidifier in the summer.  Never had any issues I was aware of.  Bare plywood, bare lumber, bare MDF spline.

Then we had a sump pump failure, with 1/4" of water on most of the floor, and it was unmonitored for a day or so before we got at it.  The basement was 2 weeks drying out.  The railroad was toast.  I didn't take a lot of pictures, but here's one (I have no idea why it rotated 90 degrees on import).  This was half way through the demolition.

  It's by no means the worst of what happened, but it's illustrative.  The 12 track staging yard was actually comical, after I stopped beating my head against the wall.  Some of the tracks literally alternated left and right swerves at every nail.  The tracks that were still accessible could have been fixed, but we had too much buried track.

The irony is, I think the damage was done by drying it out.  Everything made of wood must have expanded like crazy at the humidity peak, but as it dried again, nothing returned to where it was; the flextrack accommodated the shrinking roadbed by bending - around every track nail.  Tragic.

Blair

No real issues

I have not had any issues that can be directly related to expansion and contraction. My layout is in the garage (Florida), the temp and humidity varies a lot over the year. Parts of the layout are over 30 years old. I only run my AC when I am out there. The frame work is open grid with cross members every  18 inches. On the lower level I used half inch plywood and homasote, the helix and upper level I used door skin to reduce weight and homasote. I used liquid nails between the homasote and plywood or door skin. Everything is screwed to the frame work or risers. Except for a few industrial tracks the track is on cork roadbed, all track is Peco or Shinohara. 

For Blair:

For Blair:

Thanks

But how?  I imported an image that was in that orientation.  The resultant image was rotated.  Why, I don't know.  What did you do to fix it - rotate it in some other program?  Or is there a step, or setting, I missed in the import?

B

I think it's the roadbed

First winter on my new layout.

My fault for soldering all the joints. Went back and cut in expansion joints, and did not use track nails through the ties but rather over the flange of the rail. Have not had any problems close to this severe since. 

Jim

Makes sense...

I bet your humidity dropped in the winter, causing the roadbed to shrink in all directions.  The damage in my photo above was IN SPITE of having inserted 1/32" gaps in all the trackage, AND having laid it all in the winter when humidity was lower than summer, anyway, so we had some extreme movement.  I can well understand how soldering all the rails would make it extremely vulnerable to any dimensional change in the layout structure.

Blair

Logging Tracks

I thought maybe you were converting your layout to a logging scene  .....isn't that what their tracks look like sometimes.

Sorry for your problems.

Gaps in track and don't glue everything

I'm living in Belgium, well know to be a relatively wet country.

For the story, this year, is raining nearly everyday since october including today morning.

When we have fine weather it's only for three or four days, after it's raining again.

So or trains suffer from humidity in Belgium and plywood didn't like to much humidity and variations.

I use only plywood for my train structure 3/4 pine plywood cut in form for the track roadbed  and yard, like the benchwork, I have a few spline roadbed made for a test, but I obtain the same effect by tracing the track with the yardstick method on plywood and find easier and quicker to do. 

Most roadbed  is screwed on riser but not glued and  some parts of the benchwork aren't glued too, not because I forget to glue them, but just to give some play in extansion and contraction of the structure; this was an idea of my late father.

These "forget gluing parts" give the  expantions needed.

For track I use  N scale flex track but on straight track I didnt solder the pieces of track toghether and don't glue them, just nailed here and there with invisible pins, the on glued ballast glue everything in place and it's really enough.

Gaps in track aren't filed with anything; I use jeweller saw to make gaps.

Part of my layout are 40 years old now and never had problems with expansion or contraction on the layout and track.

Marc

Two types of track gaps

The incredible shrinking railroad.

Your layout is shrinking, at least if it is made from wood or wood products. There is a continual loss of moisture within the cell walls that will result in a reduction of volume that can be up to 15% from living plant to totally dry.  If the wood is subjected to high humidity, moisture will be reabsorbed, returning the wood to the original state.

This shrinkage is not uniform-- it is mostly oriented on radii of the original tree. The long dimension of a board hardly shrinks at all.  The shrinkage of thickness vs. width varies according to how the board was sawn. Quartersawn wood is first ripped into four sections, then each section sliced more or less perpendicular to the growth rings. This means the the majority of shrinkage will be in thickness. Plainsawn wood is just sliced directly into boards and will change primarily across the width. You can spot plainsawn wood by the "cathedrals" or arcs of grain visible on the side. Quartersawn wood has generally straight grain.

The layers of plywood are oriented with the longitudinal directions at right angles. This will reduce shrinkage in width or length, but does not stabilize thickness so much. Also, if one side is exposed to more moisture than the other, plywood will warp spectacularly. This will also happen if one side is dried by exposure to direct hot sun.

Fibreboard will not shrink so much, since it has already been through a complex drying and cooking process. It will expand with exposure to moisture, and does so in all directions more or less equally.

The best step you can take to give your layout dimensional stability is to paint it, including the parts that don't show. Polyurethane varnish is an excellent sealer. Next best thing is to use high grade lumber-- that means poplar, select pine, or AB plywood.

pqe

PS The expansion coefficient of nickel silver is 0.000009/F°, which does not seem like much, but amounts to a 0.0324" change in 10 ft of track over a 30 degree temperature swing. That's enough to put interesting kinks in your rail.

Sealing the wood

That's my plans with TOMA Siskiyou Line 2 -- to apply a gray primer followed by a matte urethane to all the wood and cork roadbed used in its construction. This includes the roadbed, which will be pine lath.

Cork is a kind of wood and needs sealed as well.

SL1 performance

So I have to ask, Joe - did you have performance issues on the old railroad?  Did it move around with humidity?  We didn't have problems until our flood, so I'm not terribly worried, but I haven't run an empire for 25 years, so what was your experience?

Blair

Yes

The short answer is yes, I had some expansion/contraction problems -- two specific instances in fact. Not the entire railroad by any means, but not zero either.

Both instances were humidity related although the second one probably had a thermal element as well. The first was track I laid during the dry summer, and then later when the roadbed expanded as the winter humidity hit, the track on a curve buckled.

The second one, the track was directly under a ceiling furnace vent (upper deck of the mushroom, track was about 15" below the ceiling vent). The track again buckled badly. Once the heat was removed (the furnace vent closed), the track remained buckled -- so it appears the constant heat drove all moisture out of the roadbed and benchwork making it extremely dry (and making it shrink badly). So while heat was involved in this second incident, it appears it was the humidity change that made the damage permanent.

I did not use much cork on SL1, but I plan to use more cork on SL2 because it's lightweight. I have nightmares about cork expanding/contracting due to humidity, so I plan to seal everything just to be very sure all the module joints likewise don't move around.

Cork roadbed

The only cork product I have been able to buy lately, by Midwest products, seems to be a mix of cork chips in a binder of black stuff reminiscent of recycled tires. When burned, it gives off the distinctive odor of burnt rubber. If it is rubber, the stuff should be pretty stable. I’ve dropped a piece in water and will check it in the morning.

pqe

Our recent experience

Our club layout has suffered a couple of expansion kinks recently. Our room has a moisture problem so one member ran a dehumidifier there for several months so I am wondering if that has caused the benchwork to shrink.

Bill

Treat, Treat and Retreat

Furniture makers have been dealing with the expansion and shrinkage of wood for a few (hundreds) of years, and the the general consensus has been to "treat, treat and retreat" wood where variations in humidity are expected. For furniture I usually use something like Tung or teak oil, but having spent a significant amount of time "treating" wood on sailboats, for the last few decades my approach to stabilizing modules (and boats) has simple: apply a very, very thin coat of polyurethane or epoxy (generally I prefer the epoxy), followed by a thin coat of poly or epoxy, followed by a couple of coats of poly or epoxy. The initial thin coats do a better job of sealing the wood and preventing moisture ingress.

The length of one eight foot N scale filler module varied almost 1/4 inch. For modular layouts this would not normally be a concern; however, the variation caused buckling of the track which often did not show up until the later in the show. After all surfaces were treated (sprayed) with poly, we did not experience any more track buckling.

Most layout builders do not want to "seal" every bit of wood on the layout (due to additional costs and labor), but sealing the wood could reduce or prevent future humidity related problems (belts and suspenders).

Bench Work Concerns for Stability

In the beginning I was seriously considering 2" foam subroadbed shelves held up with some pretty nice metal brackets from Home Depot. The 2" foam is not so readily available here in FL, so I looked around for options.

Found what I thought was some decent plywood (called Blondwood) at Lowes. I monitored a stack of it at their store and i became less impressed,...and thought perhaps 3/4" rather then 1/2". I had also inherited a 1/2" piece of 4x8 from a friend and stored it in my carport, both on its edge and flat on the cement floor. I became even less impressed. It went thru all kinds of gyrations.

Then I ran across some 7 ply, 3/4" plywood from Chili being sold at Home Depot. It was the best looking stuff I had seen,....Radiata Pine

It was a little thicker (and heavier) than I had originally planned, but then again I am not supporting it with 3" wood framework on its edge as in many conventional benchworks, so a little extra thickness could be helpful for both stability and extra cantilivered strength. And if I paint it all around that should help seal it against some of the moisture of humidity.

So next my staging area track plans expanded, and began to interfere with those metal brackets I had selected originally. Got a new idea that I would weld up my own out of surplus (scrap) steel bed rails/frames.

oops, I was over at my local metal scrap yard this past Fri and noticed some hollow square steel tubing they use to mount street signs with. Its 2" square verses my flanged 1-1.25" bed rails, and its really strong, and its galvanized. So now I am definitely considering this stuff.

In the past I have critiqued that I often see benchwork for our model trains 'overbuilt'. Funny how I seemed to be headed in that same direction.

Joe..

Thanks for outlining where you had problems.  Our seasons are the reverse of yours, I guess - summers are moderate, but winters are dry indoors (we have to heat incoming air from temperatures between 30 F and -30 F, to house temperatures; as you warm a given volume of air, it's RH drops dramatically).  Our old house was a sieve, so RH could drop to 30% in the winter, and reach 65 in the summer, though we battled that with a dehumidifier.  Now, in the new house, our RH runs between 35% in the winter, and 50% in the summer.  Basement temperatures run from 65F in the winter, to 75F in the summer, unless we run the AC.  So I'm expecting better performance in the new house.  Of course the layout is much bigger, so I guess I'm just going to have to see what happens. 

Blair

Marine plywood

Marine plywood is not actually waterproof, (the glue is) but the pressure treated grades will be more stable then the bargain bin stuff. Finish it with polyurethane and it should be trouble free. The downside is the stuff is really expensive.

pqe

My Thoughts and Experience

It is usually recommended to allow your wood to acclimatize to the area it is going to be used in for 2-3 weeks. This helps to minimize changes once you cut the wood. My railroad is in a basement that does experience some heat and humidity changes. I only had one issue with rail kinking. It was some time after I had laid my staging yards along a long (15-20') wall. These particular tracks all developed nice "mini curves". But no where else on the layout.

I had used a different brand of code 100 track for these yards ( I think it was Model Power)( I got a good deal) and I always wondered if it didn't have a different blend of metals than the Atlas that was the major cause of the problem.

Anyway, a Dremel tool and some wire to jump the gaps solved the issue with no further subsequent problems in over 20 years.

Espee over Donner

Cork immersion test

After spending 12 hours in water, the Midwest cork roadbed expanded about 3%. So it should probably be sealed too. I suspect the caulk and Elmer's treatment it usually gets would do that.

pqe

Acrylic Based Paint, Oil Based Paint,...sealers?

I had plans on painting all of my good quality plywood roadbed shelves (technically subroadbed I guess you would call it) to attempt to 'seal it' against moisture/humidity absorption. 
 

My general feeling was that oil based paints would be better at this job, but how about acrylics? Someone on another forum has offered that acrylics do NOTHING to prevent moisture absorption by the under laying wood ?
 

Anyone care to offer their experiences?