I recently had an idea to build an outdoor bouldering/traversing wall for my children so looked in to the materials I would need to buy. Having looked at commercial climbing holds I was wondering how I might make some myself and if I could make a cost saving. I did quite a bit of research on the net and found quite a few different ways all with a variety of cost and quality associated with them. In the end I decided I would go down the route of making the best I could even though I think in the end I won't save much money at all.....I will have my own one-off custom climbing holds though.
The method I use is to shape a hold in florist foam (oasis foam) and to cast a negative in RTV silicone; this silicone is very flexible and strong, albeit expensive, and cures in around 12-18 hours. I then cast my holds using polyurethane resin; a two part liquid system which I believe is the same as/similar to the material commercial holds are made of. This resin turns out really strong and non-brittle so has less chance of breaking when tightening against a wall or climbed on.
Florist foam - I used a brand called Oasis. I tried the dry and wet foam and found the wet green foam gives a better texture
RTV silicone (room temperature vulcanizing silicone) - comes in two parts silicone + catalist
Polyurethane resin - comes in a two part liquid
Paper clip - optional i used it for stamping in to my hold
M10 bolt and washer - used for reference and making a hole through the hold
I got all of my materials apart from the paper clip from ebay and should be available all over the globe.
10mm drill bit
Cone nose pliers
Plastic mixing cups
Step 1: Creating the hold shape
I am no experienced climber (only been once about 8-10 years ago) so have no idea about the way holds are shaped and what sizes they might be. I just looked through images on google to get a rough idea of size and shape and just gave it a go.
All you need to do it cut a piece of the florist foam off your big block a little bigger than you want your final hold and roughly carve to the shape you want using a small knife. As you will find this foam is very delicate which makes it ideal for smoothing and final shaping with your fingers....it can get a little messy though.
Next you will need to create a hole through your hold big enough for your bolt. I use an 8mm auger bit to create my hole is it was something I already had, i then enlarged the hole with my 10mm fixing bolt. I then countersink a larger hole for my washer using a small grinding wheel on my hobby drill. Try to make the hole as perpendicular to the flat back edge as possible as this will reduce the chance of the hold spinning.