In reply to rockjedi12345:
Hi, I've been making holds for a while and can fill you in as I spent a lot of time researching. Firstly I would definitely recommend using polyurethane (I get mine off ebay) which is much safer to work with than the toxic polyester I was going to use (albeit a little more expensive)!
I read that you shouldn't use filler (like sand or granit dust from a tomb stone maker) with polyurethane holds so I don't.
Method 1. You can shape your holds out of desert foam (also called oasis foam or florist foam) which you can get from most good craft shops. You then need to make a mould. I use clear silicon caulk from Wix (£2 a tube). This won't set by itself so I mix it in a tub with a few drops of glycerin (you can get this from a cake shop, boots or ebay) and a few drops of acrylic paint to help me see when I've mixed it fully. Spread this over your hold being careful to push it into the foam texture all over. You should make this about 1/2 inch thick. Depending how much glycerine you have used your mould should have dried in a few hours. You can then pop out the foam blank, pour in your polyurethane and 30 mins later you'll have your hold! This method can be great if you want to make the same hold a number of times but the silicon caulk is really nasty smelly, and the foam gets everywhere so watch out!
Method 2. Buy some kids plasticine and shape the negative of a hold. i.e. the hollowed out shape that your hold will fit into. Press sand paper into the plasticine to create a rock like texture (I like 60 grit best). Pour in the polyurethane and wait 30 mins to have a hold! Unless you want to make lots of the same hold this second method is quicker, cheaper, less smelly and is the one I would recommend. You can also collect real rocks at the crag and press them into the plasticine to get real rock texture.
Cheers,
Colin
