Plywood

Plywood

I am using plywood for my layout in a 14' x 20' space in the Vancouver BC area.  While it is temperature controlled (basement) I have had concerns about humidity.  This is controlled with a dehumidifier which also circulates the air when humidity is low.  Several other layouts in this area use plywood for the benchwork, no issues reported that I am aware of. 

Marc Simpson

Engineering can make all the difference

Geometry is key. A long straight board, regardless of its makeup, will warp eventually. Build your benchwork like a bridge. Follow the stress load. Triangles are magic!

FWIW I am a fan of the aforementioned birch plywood. Straight off the table saw you get clean, straight boards with no warp, twist, or bow. And if your labor is considered free, at a lower cost than dimensional lumber.

operating in an uncontrolled space in the Pacific NW

More than the materials you should be worrying about how to control that space. Everything in there is subject to the climate change including the people. Don't try to build a layout in a space that lumber can't stand because you and the equipment will like it less. I don't have heat or cooling in my shop and despite a very mild climate here I lose about 25% of the days to either too hot or too cold to go out there( that's why I'm building a backup N scale layout in the house) In a suitable space lumber or plywood are equally suitable for layout framing, depending on the design, tools available, builders experience,etc.......DaveB

My vote is for metal studs!

I have been using Metal Studs since 1993! They don't warp, they don't mind the drastic temperature changes, and per linear foot they are cheaper than lumber OR plywood!

Ken L.

Sometimes we use what we have...

Several of you have said really useful things here. Sometimes needs must and we use the space we have.

DaveB: I can put insulation in this space, and I plan to do so. That will go a ways toward controlling the temperature range, and it will buy me enough thermal containment that I can use a heater when necessary, but it won't do anything about humidity. I'm in the Redmond, WA area. The humidity here ranges from about 44% to as high as 87%. The space can't be entirely enclosed, so dehumidifying isn't going to be an effective option.

Alan: Thanks for mentioning the warping issue. I was aware of it. but I appreciate the thoughtful response. In addition to triangles, it's been my experience that if you glue your L-girders in addition to screwing them together, they resist warping more effectively.

Unfortunately, I'd already bought the framing lumber. In the past I've done L-girder framing with 1x3 and 1x2. Given the humidity issue, I'm now thinking that I'll use that 1x3 for the "depth" members (about 27") where the shrinkage and expansion won't be overwhelming, and use 3/4" ply for the length-of-room framing pieces.

Forgive me, but there's a lot of experience-derived wisdom out there regarding expansion and sealing that just ain't so. Is there any way to quantify the expansion difference? I know that ply will expand less, both because of the way the grains go in different directions between layers and because of the laminating glue. I'd just feel more comfortable understanding that issue better in quantifiable terms.

If I do decide to go with the ply, I'll inevitably need to attach to the end of a piece at some point. Anything special I need to know there about putting screws into the end of the plywood? My usual practice is to drill pilots and then use drywall screws. Anything beyond that I need to think about? Oh, and is L-girder still effective when the framing is done with ply?

Pelsea: are you talking here about expansion joints in the wood, or in the track work (or presumably both)? I haven't had to deal with that issue before in my framing, so if there happens to be something you can point me at that would be greatly appreciated.

Plywood

My layout is constructed of modular sections (dominoes) which use 3/4"plywood for framing and 1/2"plywood for tops.

Expansion joints

The way to deal with the possibility of expansion is to anticipate it and control where it happens. With wood construction of any sort, there will be enough motion to produce cracks in any hard scenic material that bridges the joints in the top plywood. The best solution is probably a layer of extruded foam over the ply-- that is flexible enough to absorb any motion of the underlying structure. If you want to use hard shell plaster construction, you should place the joints so that the inevitable cracks will be hidden by ground foam or grass or something easy to touch up. In any case favoring short runs of lumber over long ones will produce more expansion zones, but each will move less and the scenery is less likely to crack.

Track expansion is a temperature related problem, but easily handled by leaving an unsoldered 1/32" gap here and there. (Be sure to provide power feeders.) I've never built anything big enough for that to be a problem, but some of the empire builders on this forum will soon share their experience.

When you need to attach to the end of plywood, use a 1"x1" corner block or a framing angle at the joint.

pqe

Corner blocks, expansion

Pelsea: thanks. I saw the corner blocks on Jim's photos as well. If I go ahead and use conventional lumber for my 27" length I might not need those. Historically I've gone with 6' segments that I've connected together with butt plates and carriage bolts. What I'm pondering now is whether I should do that again but put some kind of foam or rubber strip material on the edges between the segments to allow for expansion. That'll leave a bit of a plywood gap at the connecting segment edges, which can either be filled with a rubber-like fill material or just sanded and tracked over. Then I can deal with track expansion gaps as a separate issue. Given the framing of the space, my segments want to be some multiple of two feet.

Jim: It looks to me like you went with a mostly flat-top approach and so you didn't need to bother with L-girder. How would your approach change if you were going to do open benchwork? Would that make it harder to use the 3/4" ply for framing?

where the shrinkage and expansion won't be overwhelming,

Lumber expands and shrinks most over the width and very little in length. So you don't want to use the width in places where a crack would matter.  If you frame a box grid with 1 X 4's set on edge and covered with plywood the 1 X 4's will all shrink or expand the same and since the width is the vertical dimension in this case the change in width will not affect the layout top. Now frame it with plywood runners and lay the 1X4's flat on the top and you'd have big problems as the width would be where it could do the most harm.    Plywood is not a cure all for poor construction but it can be easier to find stable plywood than stable lumber in many cases. The plywood has to be decent quality with more glue lines better than less( 5 layer is ok, 3 layer usually not so good) . Plan the joints so you are not dependent on end grain nails or screws, glue and nail a plywood top on a box grid frame for instance, or use metal framing clips in the corners if you can't figure out a good wood to wood joint. I'd take a good look at that layout space and see how the wood in the building is holding up and just go with what has been working in there, the wood don't care if it's in the building structure or in the layout structure it will act the same. If you buy lumber buy lumber that's been in the yard for a while so it's seasoned to fit the climate, if it looks good after seasoning in the yard it should stay looking good in the shed. I'd seriously be more concerned with my creature comforts and the possibility of mold or mildew than with my layout warping.......DaveB 

Open Frame Modular Benchwork

Some kind of foam material on the edges ?

I'd just go ahead and bolt the modules together as you did before. Some folks use alignment dowels so you don't get the slight sliding motion that often happens with bolts. Any cracks in the scenery (and we are talking cracks, not gaps) will happen at the joints, so avoid putting things there that would be difficult to patch, like a river or lake.

Better still, add a layer of 1/2" pink foam. Everything above that will be stable.

pqe

I used plywood for my bench construction

Here are some links to my blog on MRH of my sectional benchwork constructed of plywood:

http://model-railroad-hobbyist.com/node/14384

http://model-railroad-hobbyist.com/node/14424

http://model-railroad-hobbyist.com/node/14677

If I can answer any questions please let me know.

Plywood hands down.

Found the Chinese 3/4" 4x8 on sale at Home Depot for less than the cost of anyones white wood 1x4. 13  8' pcs from each sheet. 23 sheets will be all I need to fill my 24x13 room. This was a no brainer. 

Blayne

Chinese plywood..

Double check. Last time I bought some, it was from Chile. The Chinese stuff had too many problems!

One thing you can do to prevent warping or anything like that is paint to wood. That seals out the moisture and keeps it from doing anything. And plywood is great for stable benchwork!

A tip from Holmes

If you are using dimensioned lumber for your framing, I'd like to pass along a tip I got from my favorite program on the DIY channel.

Any piece of 1 by or two by lumber has a "crown" on one edge. That is where the board curves laterally-- the crown is the outside of the curve. When you set up your frame, always place the crown up, so that screwing the plywood down tends to straighten the board. This puts some tension on the joint. It's not enough to break loose, but the glue will be extra strong, and any flexing will have to work against this. Like wise, if there if any bow in the board, place the board so the bow is in, putting pressure against the cross brace instead of pulling on it.  Reject any board that has too much crown or a twist in it. The plywood should be flat, but if there is any bow, place it bow down.

pqe

Metal studs too

My steel stud table frames have been in use for more than a decade with no sags or warps and have remained level.  The wood legs system is conventional lumber (2X2's) brace in both directions, sealed with varnish and then painted.  Sub roadbed is 5/8" plywood.  All risers and cleats are 3/4" plywood.  I am very pleased with how this has worked for me.;

Bob Bochenek

metals studs too - picture

Here is a photo of steel studs in use on my layout under construction:

Bob 

Rivets or screws?

Bob-- Is your framework held together with screws or pop rivets? How do you cut the pieces?

pqe

Another vote for ply

The steel studs look intriguing! After building a few layouts I am a huge advocate of 3/4 ply ripped into 3" strips for framing.

steel studs

I used self drilling wafer-head 1/2" screws to hold the pieces together.  Cutting was with tin snips.  For straight cuts, I would cut the short sides on each side to the length needed and then fold the section back on itself back and forth till it would break.  T
This results in a very square cut.  Always be careful working with sharp metal.  I guess no more hazardous than splinters from wood.

dimensional lumber

I have a piece of layout made from dimensional lumber-16 x 2.5 ft.  I have had no expansion/contraction on this in over 30 years.  It was built in Beaverton OR and lived there for 20+ years.  It now resides outside Klamath Falls OR and worked fine after cleaning rails last year.  Temp range is from 110F to approximately -15F.  Humidity has ranged from approx 80% to less than 10%

The only time I have had problems with dimensional lumber is when I used green lumber straight from the lumber yard and then only in the first year.  It shrank.  No problems after air drying lumber for a month or two before use. 

Moisture content in wood is measured by weight with 100% moisture content is where the water in the wood equals the weight of the wood fiber in the board.  Green lumber can have over 100% moisture content.  Kiln dried lumber is usually between 8 and 15% moisture content.  Relative humidity is a measure of how much water the air can hold and is a lot less than that wood can hold at the same percentage.

Air drying takes 10-20 times as long than that of a solar kiln to get from green lumber to about 12% in our climate regardless of the atmospheric humidity during that time.  There is not much dimensional change for either drying method over several years afterwards--Yes I have the sawmills and solar kiln to verify this.

I either use plywood or lumber I have cut and milled for new construction as I know how to control warpage in the drying process and some lumber at the local outlets makes pretty good rocking chair rockers.  I've got some of them, too--they make good kindling.

Terry

That's really nice work, Rick

I'm just enough of a woodworker to understand that you're a lot better than I am. That's really nice work, Rick. Thanks for sharing that.

Shap, thanks for your kind words!

My dear old Daddy taught me basic woodworking skills (along with metal fabrication, electrical, plumbing and other things) when I was a little boy.  I was truly blessed to have such a wonderful Dad!