I want to make coasters for the holidays. I was going to buy tiles at the local hardware store, but the smallest option (in a decent price range) is way too big for a coaster. While at the local craft store I found paper/cardboard coasters that will work, but I'm wondering how to completely waterproof them (heat proof would be nice too). Any ideas? Thanks in advance.
Even regular paper-based coasters are not completely water-proof. Rather, they absorb the water sweating from the glasses.
You need to polyurethane them. Paint it on and let it dry. Sand lightly, then repeat this step at least 3 times. They will come out really smooth, like glass, it is the same way you would do a piece of wood.