Saturday, 26 April 2014

Quick Cheap Terrain - Expanding Foam Hills in 30 minutes

Most people use dense insulation foam (either pink or blue) for modelling but for some reason I have found it impossible to get hold of.

However, whilst in the hardware store I found some expanding sealant foam.  You know, the stuff that comes in a can for about $7.  You spray it into cracks and it swells up to 3x the size.

                                                 Ingredients: Foam can, craft paint, sand, PVA glue.

#1. I sprayed the foam into messy heaps, chuckling in an immature way (you could also make a good fake dog poop from it I think!).  It takes about 4 hours to dry.

#2. Then, I used my wife's serrated kitchen knife (after a bit of experimenting, I found this was the best cutting tool) to cut flat sections to rest the models on. I also had to cut underneath to level out "bulges" of foam that appeared under the foam lump.  This took the longest time to do.

#3. I painted the sides with a single coat of $2 acrylic craft paint (remember, don't spraypaint foam unless you want it to melt!)

#4.  The hardest bit was painting the top with PVA glue. It was pretty messy.  I sprinkled sand on top and "voila!"

You can see how the foam does not quite sit "flat" on the table.  I can pile sand up around it, but this could be an issue on a "normal" table.

A few thoughts:
The foam on the bottom of a piece "bulges"  as it dries so you have to cut it flat underneath as well.  This was a bit of a pain to cut level.  I considered using a hot wire cutter but the foam is apparently "highly flammable" and I didn't want to "gas" myself with poisonous vapours.

Obviously, a second coat/drybrush would make the painted sides look WAY better. However I was already pushing my 30 minute deadline.  

By the way, the can made double as much as what I pictured here - this was the first half I did as a "trial run."  One can of $7 foam made enough "hills" to easily fill a table, so I reckon it is good "value."

Some close-ups so you can see the finish, warts and all. Miniatures are a 15mm hovertank (GZG) and Iron Winds mecha (they stand about 15mm tall).
Obviously as second coat of paint and a drybrush in a lighter shade of brown would make it look 100% better.  However this was a quick trial run before my wife forced me to go shopping...

Here is what is looks like with 28mm models with the whole table set up. 

13 comments:

  1. Maybe use a file or a fine sandpaper to level the bottom. wear a mask.

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    1. I did give it a few experimental rubs (that didn't sound good) with the sandpaper but yes, the fine dust was a bit concerning...

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  2. Because the expanding foam can and will, sounds like you need to devise a way that controls the expansion? How about this?:
    Create a mold cavity out of clay and build a 3/4 inch box frame, nailed and sealed to a base plate around it. Clamp an over sized piece of wood on top that has a hole,(not much bigger than the nozzle of the applicator). Insert nozzle and spray away until you figure you have filled the mold half to 2/3rds full. Allow the foam to harden then unclamp the box. (You will probably have to use that serrated blade to cut off the button formed of foam extruding itself from the hole.) What you should have is your hill with a flat bottom, only having to saw off the feed sprue formed. You should also notice that the foam is denser and maybe even firmer than your current method.

    Hope this helps and good luck with your project! Let me know how this worked for you. It was how it was done in the "early" days when this material first came out and Limeys and Slimeys ships were done this way.

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    1. Sounds like a much better method than I used. You could make much "finer" and better quality pieces.

      My only concern is that setting it up properly would take longer than the time I took to actually make the terrain.

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    2. Foam is made to adhere to anything - maybe use impermanent adhesive to stick plastic wrap to the inside?

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  3. Before I crack open a can and try this myself I was wondering if you'd tried spraying it on a piece of thicker paper; might be a potential solution to get a more level bottom. Once it dries you could just tear the excess from around the edges maybe?

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    1. I did try it on newspaper and (admittedly thinnish) card. The problem is the foam expands or "pushes up" in a U shape and does not "ooze" and sit flat like a liquid. So the sides naturally seem to curve up and out.

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  4. It's likely the flammable warning was for the propellant in the aerosol can rather than the foam its self... but you can light just about anything on fire so take that with a grain of salt I guess. Most insulation is at least somewhat fire rated.

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  5. Great stuff! How do you think it would go if the expanding foam was sprayed onto bases (CDs, corrugated card, MDF, plasticard, sticky tile) and allowed to spread over the edges? If you carved it off, I suppose you'd have flat-based pieces?

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    1. No. The foam "pushes up" off whatever surface it is sprayed on; it does not sit flat unless you spray waaaaay over the edges of the MDF then cut it back to fit.

      I try not to cut the foam too much because it has bubbles and a rough texture. In fact, the bigger the piece of expanding foam, the worse problems you have.

      A dinner plate size chunk might have a huge bubble and be hollow inside.

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  6. I've also used this method for terrain. There are 2 things I've discovered that might help you. Firstly I used the powder based type filler to get the foam terrain both smoother and flatter where and when it was needed since both cutting and sanding the foam filler was rather inexact. Secondly it is possible to shape the foam where you need flatter or more even terrain. Simply let the foam dry slightly for about 5 minutes, then spray it with water (if you can get a water spray can that can manage a reasonable mist). The 5 minutes allow the foam to form a skin that won't tear too easily while the water helps to stop it from sticking to your hand, or a moist sponge if you don't want to use your hand.

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  7. If you could put a flat piece of plyboard on top, just after you spray out the foam, it would control the "U" type vertical tendencies and direct the expansion out to the sides. Maybe put some 2x4's well out beside the foam to support the top board and keep the top surface even. A heavy object on top of the board would help keep the board in place if the foam pushed it up. This would be quick to set up and eliminate all of the cutting. Construction sites are always throwing away scrap boards and 2x4's that are too small for them, but perfect for you.

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