I have been asked about the stages in construction of these, so as I started another couple of boxes yesterday:
Making the structure.....
The document boxes come flat packed and have a built on folding lid. First stage is to cut off the lid top and lid sides. This offcut card is then used to double the thickness on the base and 4 sides of the now open box. Then cut out the openings/entrances as you need and glue everything together with a hot glue gun.
I then cover all the exposed edges of now double thick cardboard with masking (painters) tape.
I then mark the rough design I am aiming for onto the base so I can make sure I get the corner right angles in the correct place and can cut exactly to the openings as required.
The Insulation foam is cut with a simple 10" hacksaw blade, used without the handle. Held vertically and used with a sawing action. The blade is narrow enough that it will turn to cut fairly tight curves for the rock face. Where possible I use one single piece of foam for the long sections as hiding joins is quite difficult. If I have to have a join I tend to make that into a fissure. Any caves or deep cuts required can be roughly carved in at this time with a penknife.
On this one the foam sheet offcut I used was thinner than the previous one so I had to build up the height to match. Hence the grey strip at the bottom here which is foamcore with the paper cover stripped off the top.
Having checked the fit of pieces I paste the back of the walls with a thin layer of water reduced pva glue (pva glue that is left open for a week or so before using to evaporate off much of the water content). The base I glue with a hot glue gun so that I can stick the walls in place and use the fixed hot glue to hold them firmly in place while the stronger pva sets. That way there is no risk of them moving and no need for weights or dowels to hold them in place.
Once dry I start to texture the wall surfaces. I do not use filler pastes or sand/grit cover as the former is way too messy and with cardboard makes everything too wet, while the latter gives a very definite texture that I don't think looks like excavated rock.
I use an old household knife with a rounded end and lightly drag it across the foam wall in 2 or 3 directions to ripple the surface (using a round end knife leaves soft crescent shaped furrows rather than angular gouges). Then using the tip of the rounded blade to dig into the foam I tear out a small chunk with my thumb. Remember to create the texture from different angles and directions for a more realistic looking mined stone surface.
What you get:
What it really looks like:
Next up: scree rubble, texturing the floor and slapping on some paint.