Glued 2' foam down to the frame but no piece of foam is truly flat/perfect when it is formed. Especially where they butt together at a joint. I'll use joint compound at the joint to fill in, but it is still pretty uneven. That stuff is very hard to compress to get the edges to meet flatly. I added some pics to show how the foam looks under a flat edge. Notice how the level bubble is perfect but the foam looks a little wavy under it. If I use joint compound to help take out some of the waves will it stick to foam? Thought of a belt sander to even the joints abit? Just concerned that the n-scale cars may unhook due to "excessive waves".
WOW! I haven't seen such in the foam I've worked with but then that quality is good enough for housing use. I would think that filling in is more advisable so that you don't break the "skin" on the foam board. Maybe a thin coat of drywall compound followed by block sanding as in auto body work. Keep it in the area of the trackage and let the rest of the terrain undulate as it does in nature.
I dont think I would use a belt sander to get the surface even and flat, one slip and you got a trench to fill in . I'd be more inclined to use a floor leveling joint compound ior something like what shortround mentioned if it is really vital you get a flat surface. I use 2" foam board for my 18" x 6' and will need to attach it a second section of the same size and I am not going to get obsessed with making the joints or the surronding area level , I doubt I will do any thing to the joint .If you go with just joint compound , screed it off with a 2-3 foot wide float and be done . Get the light weight as you will not be walking on it ... something that will give you a couple minutes work time before setting up. I do not recommend Plaster of Paris or Hydrocal or products like these as the work time is very narrow.
You could use 80 grit sandpaper glued to an aluminum square tube or "T" and sand it smooth. Foam sand pretty easy, should not take much to make it level. Might be able to use a nice straight 1X2 Alder too? http://www.amazon.com/Aluminum-6061...50220&sr=8-1&keywords=extruded+aluminum+angle http://www.amazon.com/Anodized-Squa...sr=8-2&keywords=extruded+aluminum+square+tube Buzz.
I'm using Lowes construction foam. The level touches the foam and sits level on the edges and center across the 4ft width. The dips are in the area of the 1st and 2nd third of the board running the length. This is on all the 4 x 8 ft sheets I got. My guess during production something pushes down on the foam like guide wheels while it's still warm leaving the slight depressions. I'll guess I'll go with a couple of light coats of joint compound where the track will run. It's about a 15" wide depression down each third of the board. Thx for the input guys.
First of all, I recommend removing the thin plastic film from the foam. It comes off fairly easily. If you don't remove it, you may find the it will lift away from the foam when you least expect, and anything glued to the film will come loose from the foam. As others have said, it is easy to shape the foam with a sanding block, which should allow you to smooth the transitions between sheets. You could possibly use a small powered palm sander for this, but a belt sander is overkill! Be sure to wear a dust mask; you don't want to inhale the foam dust. - Jeff
Looking at the second image, you can see that a long straight-edge shows the highs and lows easily. It turns out the best way to get your surface more even is using that very length with sandpaper, probably 100 grit or so. Find a way to fasten sand paper along one long side of a level or something like it, and then use long parallel strokes, with the direction of the strokes parallel to the long axis of the level, to let the sand paper wear down the weight-bearing places, which will be the highest ones. You don't want all one side covered in the sand paper, just a short distance that will allow you to erode the highs near it without also eroding nearby stuff you want left alone. This could take some time, particularly when you accept that just a few strokes and you will have to check to ensure you aren't now causing more problems. You'll have to then change the instrument and check with it oriented at an angle to see if other dips show up that way..or highs. Same thing. Eventually, placing the level in various positions/places/orientations, you will see that you have it pretty close and some vacuuming to do.
I'm surprised to see that much distortion. Have never encountered that much in any sheets of foam board I have bought. I do agree that some careful sanding is your best best.
I've had this happen on sheets of foam that were bowed during transit, storage, or movement for an extended period of time. The foam has "memory" and when it is bent in a slight curve from being placed between the wheel wells of cars (in my case) when it is put on a level surface the surface will have a similar effect. I normally try to take a vehicle that the entire sheet can lay flat in now.
I guess also it's a different manufacturer. I bought foam a couple of years ago from Lowes to insulate my basement of which I still have a few scrap pieces. It was colored blue was made by DOW chemical and has that plastic film on it that you can peel off. That is truly flat foam. This green stuff they have now is made by PACTIV and doesn't have that plastic film. Oh well, I'll make it work. It'll just take a little extra work.
