1/2" rigid foamboard on top of a 3/8" plywood base (primed) for a ‘L’ shaped N scale shelve layout:
I’m thinking of instead of using some type of adhesive or caulk, why not screws w/ washers to hold the foamboard in place? Enough to do the job w/o going overboard.
At least, if there is any reason (that I couldn’t imagine) to lift or remove the foam, you could do so w/o ripping things apart. (My argument for screws vs nails)
Bruce,
As long as you can access the screws easily, that should be fine. However, If you end up having to tear apart things to get to the screws, I’d prefer caulk and using a putty knife to pry the foam board up.
The other thing you could do is make pockets for the screws and washers and disguise them with scenery - i.e. dirt, ballast, structures, trees and shrubs, etc. Just make sure you map out where they are so that you don’t have to try and recollect or guess.
Tom
As good as foam is, I would not nail or screw it, as it does break rather easily, and you would indent the foam where ever the screws sink in. Glue is best, LION would use (does use) silicone caulk. You need not cover the whole thing, just a few patches to hold the foam in place. If you have to lift it up in the future it will usually pop right off, although in this case it may tear the foam a little, but this should not be a problem.
ROAR
Remembering where the screws were and then ‘digging’ them up would be a issue which I did think about. It’s just that caulk is sometimes messy.
How about cheap basic caulk vs silicone? Or is the flexibility important?
LION used cheap latex painters caulk, and it works very well, but when dry seems to be far more aggressive. If you are thinking about pulling it apart in the future, the silicone is far easier to clean up.
The silicone is also stronger while it is till wet. LION uses the silicone to hold tortoise machines in place without ever using screws. They pop right off when you finally need to move them. The cheaper latex would not hold them when wet, and the machine would have to be propped in place until the caulk sets. Then if you need to remove the machine, you will have a lot of work in front of you before you can reuse it.
or at least those are my findings, your own results may vary: there are many different kinds of caulk and other adhesives.
ROAR
Bruce,
I use the DAP Alex Plus Latex Caulk w/Silicone. It’s ~$2/tube at Lowe’s or HD and can be used in a caulking gun. I find it very convenient to use and control this way. I like it better than the more expensive foam adhesives because it doesn’t contain all those nasty chemicals. Since it’s silicone, it uses acetic acid to cure, which smells like vinegar.
As Lion suggested, just tack down the foam board at regular intervals with a bead of caulk. I would think every foot or so would be just fine.
Tom
I would be a little concerned about the structural rigidity of the sandwich if not glued. If not very closely supported, neither 3/8" plywood nor the 1/2" foam by itself is sufficiently rigid to prevent subtle sagging between supports. The combination when glued together probably does have enough rigidity. Remember that a sag of 1/16" between 16" supports is a 2% grade from the center of the sag. Rigidity over the long term is not the same as not sagging when 1st installed.
The experience of our modular group is that caulk and white glue for gluing foam to plywood tend not to stand up to the handling, transporting, and widely varying environments of modular layouts. The glue joint breaks, and the rigidity created by the combination of plywood and foam is no longer there. Only the polyurethane glues (think Gorilla) seems to last over time. But because polyurethane glue expands as it cures, clamping during the cure is a necessity. Clamping is not always easy to do with foam.
my thoughts and experiences
Fred W
Dexter,
Since I’m assuming you just updated to Internet Explorer (IE)9, you’ll need to click the torn paper icon to the right of the URL (web address) box at the top of the page. This will run an emulated version of IE8 so that your post will show up.
You can also install and/or use Mozilla Firefox or Google Chrone as a browser. I have both IE and Firefox on my desktop in cases such as this.
Hope that helps…
Tom
Cheap caulk will work, no need for the expensive silicon stuff. However, in the rather sealed environment of a piece of extruded foam on top of a shet of plywood, it may take a long time to set up - could of days. Keep it evenly weighted to hold things in place.
I use yellow glue, works just as well.
–Randy
Really agree w/ Fred, bonding the foam to the ply with your choice of adhesive will produce a far superior structure for the layout. Also those DW screws will protrude making the plywood bottom a nasty “porcupine” to tear into you. Trying to size a screw and find the depth so this won’t happen and/ or hoping that screws into only 3/8" of ply will hold can be a PITA.
The Lion has some good ideas methinks [Y]
For myself, I would say that both foam and plywood are unnecessary.
If you’re going to use foam, though, I would use at least 1", and maybe 2", which will give you enough depth to carve terrain features into it.
Attach with adhesive latex caulk. One tip – since foam doesn’t breath, and plywood only barely does, apply caulk in a bead straight across with gaps in between beads, or use an “S” pattern. If you enclose a bead of caulk completely with another bead, the one on the inside will take forever to cure.
That I would agree with. Good point.
Dito.
Then you are saying I should use both screws & glue??
I have glued 2" foam board to 1/2" plywood with Titebond II yellow wood glue. I put the glue bead down in a zig zag pattern on the surface of the plywood so air can reach all of it. I put the foam board in position and then place scrap pieces of foam board on top to protect the surface from being damaged. I then place old sidewalk pavers on top of the scrap foam pieces to hold the foam tight to the surface of the plywood. I also place a line of “C” clamps along the free edges. I put scraps of plywood under the clamps to keep them from digging into the foam board surface. I would allow the glue to setup for at least 24 hrs. 48hrs was the usual time that I allowed for setting. When the glue sets, the foam is going nowhere.
Bob
Normally, I prefer to present facts and anecdotes, and let folks draw their own conclusions. But since you asked, I’ll connect the dots my way.
To solve the rigidity issue and prevent sagging in the long term:
use 1/2" or thicker plywood, supported at 16" intervals. No foam needed. That seems to be about the minimum recommendation for plywood by itself. Many experienced modelers prefer 3/4" plywood, believing 1/2" plywood - especially today’s quality - isn’t good enough.
OR
use 2 layers of 2" foam, without plywood. Top layer is for carving, bottom layer is for structural strength. Support should be 16" -24" spacing for 2" foam, based on all reports I have seen. I personally use 18"-20" support spacing with a 1/4" plywood/2" foam sandwich where the top layer gets carved in many places.
OR
use your 3/8" plywood and 1/2" foam glued together. The glue is essential to get the combined rigidity of the sandwich.
IF you use the sandwich construction, and IF
Normally, I prefer to present facts and anecdotes, and let folks draw their own conclusions. But since you asked, I’ll connect the dots my way.
To solve the rigidity issue and prevent sagging in the long term:
use 1/2" or thicker plywood, supported at 16" intervals. No foam needed. That seems to be about the minimum recommendation for plywood by itself. Many experienced modelers prefer 3/4" plywood, believing 1/2" plywood - especially today’s quality - isn’t good enough.
OR
use 2 layers of 2" foam, without plywood. Top layer is for carving, bottom layer is for structural strength. Support should be 16" -24" spacing for 2" foam, based on all reports I have seen. I personally use 18"-20" support spacing with a 1/4" plywood/2" foam sandwich where the top layer gets carved in many places.
OR
use your 3/8" plywood and 1/2" foam glued together. The glue is essential to get the combined rigidity of the sandwich.
IF you use the sandwich construction, and IF
Transporting is no issue. The layout is a 9x19’ ‘J’ shape in N scale. I was just thinking of for some unknown reason if I had to remove the foam, I could do it.
Would typical acrylic latex caulk work instead of silicone? I have been using the ‘clear’ since it applies white and turns clear when set.
Yes, latex caulk works fine, this is what I use for everything, although if there’s a price difference, use th cheapest color to glue the foam and plywood together since you won;t ever see it. I use the clear to attach my track to the roadbed, works great because you can see it while still wet, when it disappears you know it’s cured and can move on to the next step.
–Randy
That’s what my 1st choice would be. I like that feature (if you can call it that).
Loctite PL300 in 50 cent size dots…Weight it down for overnight - works great, easy to work around, and removes easily. Cheers!