Securing 2" Foam to Plywood Sheet

If you choose to use an adhesive, be sure it is recommended for use with foam board, as some adhesives with melt the foam. I've used the Pl series adhesive made for use with foam products. I would also recommend using some type of evenly distributed weight to insure a good bond.

I would guess with all the different types of hot glue available, there is one suited for foam, but I've never used it for that purpose. I would be reluctant because of the relatively short set time as you mentioned.

Don

Depending on the size of your foam, hot glue might harden too soon prior to your applying it.

I use 1" foam on top of plywood and use 1" drywall screws.  I barely counter sink just enough to penetrate the plywood.  Nice and quiet too.  As a matter of fact, I used 2" foam to make a 6 foot span.  It is constructed with Elmer's glue.  Watch the 1st minute of the below video and listen when the train departs the plywood/foam for the ALL foam part.  It surprised me the first time.  I thought it would be quieter on all foam.

Of course, when it came to redoing my layout, the foam came up easy and I was able to re-use it all again.

So you might consider 2" screws with 2" foam.  It's easy to install.

Ron

From both replies, it would seem that adhesive is the way to go over hot glue.

Ron... When you attached the 1" foam sheet to the plywood with drywall screws, did you also use any adhesive or was it strictly screws?  How closely did you apply the screws?  I like this idea of no adhesive if I ever want to take the foam up and change things around.  I definitely hear the difference going over the strictly foam section... Actually it sounds pretty good... like going over a actual bridge you can hear a difference.  By the way, nice video!

They make a construction adhesive for foam.  Comes in a caulking tube.  Just ask at the store.  I recently purchased a six pack of tubes and have used three on the layout so far.

I use carpet tape. It is very strong, but you can separate the foam from the wood if needed.

Regular liquid nails heavy duty is foam safe. There's also the dedicated foam adhesives. If you lay the adhesive down in lines, you should be able to get it off if you need to, as the foam will still break loose, and then its a matter of scraping it off the plywood. I suppose you could also use dots rather than lines. You just need to immobilize it... shouldnt need much adhesive. Weigh the foam down while the adhesive sets so the glue flattens out.

Loctite PL Construction Adhesive(or Liquid Nails). Apply in a small bead in a wiggly fashion, apply pressure and slide it around in a small circular pattern and then then slide to the proper position.

A roofing supply house will have 2"-3" washers that are used for holding down roof deck insulation, which happens to be foam board in some applications. You could use them with deck screws. Screw just tight enough to sink the washer into the foam.

Either way will work. The screw method will give you the option to replace the foam easily if you want to change an area's landscaping. Photos attached.

PaulG,

I did not use adheasive... Only the drywall screws. 

On another note, while I believe the foam on plywood to be quiet, I recently ballasted a section of track and was surprised to hear that section get even quieter.

Ron

I didn't realize that so many people were simply screwing the foam to the plywood and avoiding the use of adhesives.  This seems like a much cleaner solution especially if you want to pull the foam up for some reason.  I think I will give screws a try for the base layer of foam.  However, for the buildup of mountains, I believe that I will have to use an adhesive.

Thanks to all who responded... This helped me make my decision on how to attach foam!

They make a special screw for securing foam board. It looks like a plastic washer on a screw.

Anything that restricts, reduces, or dampens the transmission of vibration will also reduce sound.