Injecting waterproof resin glue and using clamps can help fix up cracks in your deck. Deck builders may also recommend applying a sealer once a year to protect all the surfaces of your deck better. And while most builders don't advise using caulk to fill in gaps on your decking board, some may be fine with applying coloured caulk. To better weigh the options when it comes to repairing a cracked deck, consult a decking specialist near you.