The 1/8" to 1/4" gaps are horizontal gaps between sheets. The actual top (layout) surface of the foam has about a 1/16 to 1/8" gap vertically at several joint locations. The plywood benchwork is all 3/4" on 2x4 frame and as mentioned earlier, all within 1/8" in height while travelling around the entire layout: i.e. very flat.
The issue here is not with the benchwork but with the slight differences in the thickness of individual foam sheets. I read that Bill Darnaby plans to use a 1/4" sheet of plywood on top of his foamboard next time he builds a layout due to the slight imperfections (waves) he has found in some foamboard pieces. I have noted this too. Sometimes I find slight depressions or “waves” near the edges of foamboard. I’m guessing this is where the banding is placed to sandwich sheets together for transport. Perhaps the Woodland Scenics foam putty can also function as a sort of transition “ramp” between sheets that are reasonably close in height at the joints (like mine), and can even fill in some of these depressions when needed where cork and track will cross them.
In any case, before I started placing any foamboard I went over every joint in the plywood benchwork and made adjustments for smoothness, in some cases sanding out 6" on each side of the joint with an orbital sander. Whatever is going on here is due to some manufacturing tolerance range allowed by Owens-Corning and the way they ship their product to stores.
Dunno, maybe it will all work out, but it doesn’t sound good to me. Before I start laying track, I want my subroadbed as smooth and level as possible. The more you screw with it, the worse things become. If you have solid benchwork, maybe start over with the foamboard.
I’m not sure that I would recommend using PL300 to fill gaps between the foam sheets. I did that about two weeks ago on my own layout which I am building in my insulated garage, and the larger gaps are still quite soft to the touch. I should mention that I am in southern Ontario, Canada so the garage is normally cool at this time of year. I have had a small electric heater running for close to 10 days and it is keeping the garage at a comfortable temperature (I won’t say warm) but apparently isn’t helping the PL300 much. If I was doing it again I would use low expansion foam.
By the way, I think the Woodland Scenics foam putty is a bit pricey. Walthers regular price is $9.99 and they have it on sale for $7.98 right now. A 16 oz. tub is about the size of a container of cottage cheese. I haven’t tried mine yet but I hope a little goes a long way.
Now that y’all mention it, I don’t think this foam board is manufactured to be dimensionally precise. I can think of a number of logical ways this could be economically manufactured for ‘least material waste for a guaranteeable R-value’ that would produce exactly the edge variation being described.
Has anyone gone to the trouble of taking depth measurements on a ‘grid’ of different points on the sheet? I have to wonder if the same approach with rolled steel might be used here – cut off and use ‘for other purposes’ a certain amount of the edge to assure proper quality.
I don’t remember a truly dimensional thickness insulating panel … I confess I’d never carefully thought about checking.
What could be a great deal of fun is determining if there is any tool or technique that could practically accomplish what a planer does for lumber or plywood. Perhaps something with cutters if you chilled the foam down? An additive method, with floats or rollers?
Probably extreme overkill, though. I think the consensus so far, which is to tape, dutch, or butter over the edges and gaps, and be precise only where the subroadbed goes, would be the wisest approach.
I like your idea of cutting off a certain amount of the edges to assure proper quality. That may well be the best solution. The edges may be curling a bit, creating unevenness at the joints.
I suggest the extruded stuff is continuous sheet cut with a knife device into 96" lengths as it is made. The two edges are moulded and the ends obviously physically cut somehow. Chopped I would say.
I have several sheets of the blue styrofoam in 1/2" thickness, nominal. Actual thickness is around 0.53 to 0.54". This tolerance is exhibited everywhere, I have a number of cut sheets so a random point of measure “sampling”. No difference at the cut edge but the moulded edges are quarter rounded very slightly. Butting those edge to edge would result in a shallow gulley.
The stuff is amazingly consistently oversized by about 10% in thickness at room temperature. Of course ours is made in Canada so precision is expected. We make ours in metric and mm are far more precise than inches. Your stuff may not be as accurately made, maybe in Mexico even?
I also have Woodland Scenics 1/2 bead type styrofoam, the white stuff, claimed to be more precision moulded. It is. It varies only by thousandths of an inch and only by less than two tenths thicker than 1/2" nominal. It averages about 0.51" which is pretty good quality control. Again, I have several sheets with some cut pieces for random sampling.
I only sampled ten or so times on the blue and maybe 5 or 6 on the white.
Generally speaking the thickness does not vary by enough for us to be concerned about.
I expect maybe some consistent variation in thickness if the styrofoam you buy came from different factories but I doubt the “step” resulting could be anything we would worry about.
THis seems like the obvious answer. Rather than grind and make a mess, just shim under the piece that is lowest to bring it up to level to the higher piece. Snicker snack!
I’m not understanding why this is so complicated. Maybe boredom is alleviated by overthinking stuff.
Secure subroadbed to the benchwork so that it doesn’t move.
1a. Now that you have determined a fixed and exact amount of “offage” at the joints…
Build up the top of the lower sheet at the joint only where the tracks are going, ensuring the slope does not create a short but still severe grade.
2a. This can be accomplished any number of ways. Cardstock, various lengths of construction shims, scrap styrene, new styrene, old credit cards, your wife’s current credit cards…etc.
Affix said build up with appropriate adhesive suitable for foam such as silicone caulk, construction adhesive, etc.
Lay roadbed
Lay track
Scenic the sides
Scenic the rest of the sharp joint where the track isn’t…to taste.
Me neither. Cut and level or slop on something to raise the terrain. Use spackle or wood or plastic shims or whatever. I have used caulk as a leveller before, I just made a dam out of painters tape or the foam itself does the job. I have flooded entire rooms with floor leveller and don’t understand how levelling up a few square inches of foam seems to be such a chore.
After reading this thread I completely agree. Thousands of words about a solution as easy as a few swipes with a coarse rasp or the installation of a couple of carpentry shims.
I’m not sure that I follow your objections, guys, or your rationale in this regard. I don’t see where anybody is overthinking anything. Everyone is making suggetions to help the OP, and it seems that both of you are doing the same thing.
We had a very similar discussion about overcomplicatizing soldering. Same applies there, too.
In (partial) defense of wall-o-text firehose threads: I think it’s valuable to get the different options ‘out there’ quickly so the people needing assistance, knowledge, enlightenment or whatever won’t miss critical options. If it’s something they don’t need (or don’t like) they can hit the back button.
No different in a sense from healthy eating. Good to have the vitamins, trace elements, and a proper mix of food groups … but you can always opt to eat less, and you don’t have to digest things your metabolism rejects…
Appreciate the thoughts guys. I was just looking for best practices. I decided to cut several pieces and layers of thicker cardstock and glue them under the portion I was concerned about. I had a little PL300 left in my last tube so I went ahead and glued the piece down and placed my weights on it. The card stock leveled it up nicely. I will get around to the gaps at some point, and maybe I will just try using tape like some have suggested!