Adhesives

Jeff,

For something that is structurally more durable and secure than caulk, I would look at Liquid Nails.  They have a couple of construction adhesives:  Original "Liquid Nails" is super.  It even can glue your fingers together, but it's not to be used with plastics or foam.    Second is their foam and plastic safe adhesive (I don't remember the name of it; read the label).

I don't have a hot knife, but I bought a really long blade for my sawsall, and it does a nice job on foam.  I can cut to 1/4 inch accuracy, then surform to finish.

Working foam

I worked with foam for the first time when I started making a static grass diorama recently.  I did lots of the carving with a drywall saw, a wire brush and a utility knife.  then I used an abrasive bit in my dremel to contour the foam in the tight spots.

I used Great Stuff expanding foam as adhesive because it's what I had on hand that I knew was foam safe.  To say it is not ideal would be an understatement, but it does work.  I applied it fairly sparingly between the layers being joined and added weight to hold the pieces together.  Later there is some "flash" to trim because of the expansion but the foam is glued really well.

Messy

Sounds like you made a big mess with the debris.

Mess...What Mess?

Oh heck yeah!  I should mention that I did ALL of my carving and cutting of foam in the garage where the mess was not an issue.  I probably threw away as much foam as is left in the base of the diorama now.

If you are carving the foam like I did, keep the Shop Vac handy and don't forget to vacuum yourself before wandering around the house!

I had fun with it and it makes a great base for my diorama but I think I'll stick to hard shell for layout scenery.

Working with foam

I have used foam on numerous occasions. For cutting I used a homemade hot wire cutter that I could form the wire to various shapes such as a round end to cut out a drainage ditch, or a long straight wire to cut a straight edge.

Where I did not use the hot knife approach, I use a carpet knife, utility knife or exacto knife depending on the size and detail of the cut.

Carving with a knife or the hot wire approach produces much less mess than a saw or "surefoam" tool.

With melting the foam you need to be aware of the fumes, and be working in a ventilated space.

For glueing Loctite Powergrip Foamboard adhesive works very well, and it has an extremely long life in the caulking tube even after it is opened.

If you are the DIY type person, there is info on the web on how to make a hot wire cutter, they are also available commercially at Hobby stores.

Latex liquid nails

Jeff,

I've used latex liquid nails to glue pink foam layers together. Yes it works, but...

One the layers are together, the glue on the interior portion of the joint doesn't have access to air. Air is required for the adhesive to set. I've pulled apart pink foam layers that were glued together several years ago and found the adesive in the center of the sheets was still wet!

You'll need to be very careful to manage the thickness of the glue layer. A notched trowel, like those used by linoleum installers might be a good idea. A thick glue layer will make alignment of multiple pink foam layers tricky.

I'd recommend letting the glue sit in the air for 10 minutes prior to putting the pieces together. *Maybe* this will give the adhesive a head start on setting avoiding the glue-is-still-wet-in-the-middle-of-the-joint syndrome.

I've considered but not yet attempted using latex contact cement. This would have the advantages of not staying wet and of having a nearly zero glue thickness. The drawback of course is once the two pieces touch each other you have no further opportunity for adjustment (unlike the construction adhesive method which gives lots of adjustment time). Is there anyone out there who has actualy used latex contact cement to glue large sheets of foam together?

For attaching relatively small pieces of foam where structural strength isn't a big issue, I've used hot glue. This works especially well for bonding foam to wood, masonite or other non foam substances. When gluing foam to foam too much glue tends to melt the foam (from the heat) and the foam is such a good thermal insulator it can take quite a while for a hot glued foam-to-foam joint to become rigid. On the positive side it does tend make construction go pretty quickly.

Cheers,

Charlie

Hot stuff

If you are the DIY type person, there is info on the web on how to make a hot wire cutter, they are also available commercially at Hobby stores.

Yes, barring the fumes, I agree that heat is the best way to deal with the foam.  I remembered seeing a DIY hot wire cutter made with a soldering iron.  This one might be it.

Soldering Gun Cutter

My old soldering gun gave up the ghost recently or I would have tried this method.  I saw some fairly cheap cutters at Michaels but didn't get one. On my diorama I used a bit of heat from a torch to shape a couple of areas with some degree of success.  Hot wire seems like the way to go.

For glueing Loctite Powergrip

Agreed. This stuff is great for foam to foam, and foam to wood. Easy to apply, strongly recommended.

Jeff, I have a hot knife (the fancy pants one from Micromark, and I don't recommend it), a D battey hot wire cutter, and a very long, dull straight edge knife. I also use a sureform, and a sharp utility knife on occasion.

They all have their uses, but I dont like working with the stuff regardless of the method. I have done so extensively in the past, and I realize that I can't avoid it totally.  It makes a mess seemingly no matter what, the shop vac advice is good.

One thing I also due when gluing layers is drive toothpicks into the two pieces at various places in order to hold the sections in alignment while the glue dries. You'll never know they're there...

Gluing and cutting foam

 I've recently redone part of my scenery for the third time! This time I stuck the foam with a cheap No-nails type adhesive. I layered the foam horizontally,mistake.

I carved it with a surform and long knife to get the basic shape and then used a snap off blade knife to carve the rocks. I did shallow cuts in one direction to provide a "grain" to the surface. I then cut deeper to produce the fault lines. I then used a small nylon brush to open out the faults and give a finer grain. I painted it with artex followed by a grey paint and then black / brown washes of emulsion / latex paint. I've still to dry brush highlights, add soil and vegetation.

It took more work to try and hide, not totally successfully, the joins between foam blocks. Next time I'll stack them vertically, so I will not get horizontal lines from normal viewing angles.

Mike Ruby

The glued boards.

The first carving

After a second carving, painting and washes.

A close up of almost finished

I read the article to make

I read the article to make your own wire cutter. Has anyone made these because I wanted to know if you can make the cutting area longer or would this cause an issue. Not sure if it would make it to cold to cut or even hotter and not safe. 

Love to make one and I would like to know the limits before I get this unsafe. 

Dave

Has anyone tried an electric

Has anyone tried an electric carving knife on foam? Seems like it would make less mess because of the thin blades..

Carving knife

yes.. Works great on cushion foam, but real bad on XPS board. 

I have used an undulating blade for my jigsaw (see pic below) and it works great for foam AND homasote.

 ​

It's funny seeing this post...

The original swinging bridge never happened as conceived, failed as implemented, and was replaced by a solid aluminum duckunder... which has since been removed. 

I'm working on a related liftout in a nearby location instead. 

Foam cutting devices

John you should see the most recent 'What's Neat' video from Ken Patterson... He was using a CHAINSAW to cut and manipulate the foam into hills and ridges! 

I've also just started filming a video tutorial about making your own wire foam cutting device. There are plenty of videos on YouTube but most of them don't tell you the whole story about what is actually happening with regards to wire length and power source needed to heat the wire...

It's very easy to destroy batteries and transformers so you need to understand what is happening based on the gauge of wire and length of wire. It's much easier than it sounds once you have a basic understanding and that is the information I'm hoping to deliver in the video.

I'm waiting for some components to arrive by mail but once they are here on Friday I should have the video filmed and edited fairly fast.

LOL... Jeff

Jeff I too was surprised seeing this post come to life! 

About 3 days ago I was doing some research on making wire foam cutters and came across this post in my search! It's amazing how old posts randomly come to life considering I was just looking at it a few days ago.