You are correct that it is best to avoid the White “Beaded” Foam board. The “extruded” Foam, ie: pink or blue stuff and some other colors including some brands that are white, is better for what you are trying to do. I assume this is for the Hogwarts? To answer your question of how much?? You can do a lot of scenery with just one 4’ x 8’ sheet. I would start with one sheet and see how much you need as you go along. The purpose of the foam would be to provide an easily shaped base for scenery that can then be finished with plaster, paint, and other decoration.
When using foam products and hot knives, be sure to use a lot of ventilation (as in cut it outside or with windows open and fans) as most brands can create toxic fumes when the material melts.
How much you need will depend on what you make out of it. If you are going to build the mountains, it will take a bit . If you just use it to cover the 4x8 ply wood I would use 1" foam board (the pink stuff) . Purpose: sound deadening and allowing you to model areas lower than ground level with out having to cut up the plywood, like rivers or Hogwarts lake. On my own layout, I am using cookie cutter 1/2" plywood with 1" foam (Home Depot). None of my tracks are on the same level. I am trying for a narrow gauge feel using HO track, lots of vertical scenary. 7 inches of separation with up to 2.25% grades. Ask about the damaged pieces. Some times you can get the stores to mark them down a little. See if you can find a real lumber yard (one the home buliders use for supplies) as they may have foam cheaper. I to had sticker shock, when I check about two weeks ago. Home Depot has the 1" 2x8 sheets (pink). 2 x 8 sheets seam to be a little cheeper than 4x8 in this area Woodbridge VA. Well 2 sections of bench work done 6 to go. I still ran a homemade Thomas and a repowered Duck on my old layout until it came down, and they will run again on the new one. Made Thomas for my 5 year old Daughter , she’s 13 now. any how Hope this helps
Any new construction in your area? Every now and then I get lucky, find all kinds of blue styrene in the dumpsters. I usually only find the 3/4 inch, but collect enough and you can stack it up glued together.
Another way is to stand the styrene on edge (works best on open benchwork, you can attech it directly to the joists on a girder system). then cover it with alluminum screen wire, and finally cover with plaster cloth. This method should be drescribed more fully in those book that you are waiting for.
I am rebuilding my layout right now and have about 3" of foam board on my table. I may add another inch so I can create a deep vally in my table. I am planning to have a river run through my layout. In KY where I live, the rivers are in mostly in deep valleys. Also, the railroad tracks are frequently found up on hills that run through the bluegrasss area (because of the potential for flooding in this area) That is why I designed my layout the way I did so it will look like it is from my area of KY.
I at first used two 4x8 sheets of 1/2" blue foam since my local Lowes doesn’t carry anything bigger. I found this week at Home Depot a half hour north of me some 2" pink foam. Stay away from the typical white foam–it is messy.
I have been using a cheap razor blade knife with break away sections for cutting the foam. The mess has been minimal. What I like about this knife is you can extend it out a little more than 2" and be able to slice carefully even 2" foam. The knife you can usually get at a hardware store.
Wish my Home Depot had 4x8 sheets for $28. Over on this end of the state I pay $17 for a 2x8 sheet of the 2" foam.
It’s STILL cheaper than plywood - plywood that is thick enough to support itself AND has at least one very smooth side.
If I had a truck or trailer big enough to full contain many 4x8 sheets it would be worth it for me to drive out there and pick up a big stock of foam at those prices. As it is, I can’t even enclose the 2x8 sheets (too long) so bringing those home is an adventure. I managed to squeeze 4 sheets in once, luckily the closest HD is only about 3 miles away.
Check at the Lowes & Home Depot and ask if they have any broken pieces of foam as they can not sell this stuff and most times they throw this stuff away. The most you will get is a no!
Another place is scraps from remodeling jobs. If you know anyone that does construction you can find a lot in the dumpster.
Ask around at the Club if they know where to get some foam!
The Clarion bunch should be coming down for a visit sometime in the next couple of months.
$28 is about right for a 2" sheet of foam. You want sticker shock? Take a look at the sheets of 3/4" BC plywood!
How much you’ll need all depends on what you want to do. If you want a fair amount of scenery that heads below track grade (like real life) then you’ll want at least 2" of foam under the track. And how many hills or mountains do you want? There’s a fair amount of wastage in carved foam hillsides, so figure at least 1/2 of a sheet of foam for every 4" up you want to go, if you’ve got a lot of terrain to build.
From what you are saying, since the major part of the layout is flat, I can go with the 3/4 there. For the hills on the edges, go with the 2".
I planned a deep river bed on my larger layout and had planned to make that happen in the framing stage of the layout. You guys and the price of the foam have helped convince me I made the right decision.