There are a few methods to add texture to your 5 Tendons climbing holds.

Base Coat:

This is a good place to start with any texture option you choose below. First give the plastic a light sand to scuff out the shiny surface to help bonding. Mix up a small portion of resin and mix with 30% sand. You can add acrylic paint at this stage if you like. This is good for doing dual texure holds.

Paint on with a cheap paint brush.

Once final coat is dry, give a light sand with 80/120 grit to take off any sharp points. Foot holds can be left unsanded. 

Final Coat Options:

1. Course friction: Spray with clear acrylic and sprinkle with dry, seived sand or Garnet Sand Blasting Shot
2.  Fine friction: Spray with clear acrilyc and sprinkle with 80 (courser), 120 or 180 (finest) grit Aluminium Oxide Powder
3. Then finish with coloured acrylic spray paint, or leave unpainted.

Note: You can add this sort of texturing to only certain parts of the hold if you want. Use tape to mask sections for cool dual texturing.

For maximum durability, choose the first option.