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.