Difficult something very hard to stop but can reduce it.
First you don't have a tumble dryer in their if so these don't help. Johnstones do a condensation paint but you'll have to shop around for it. Try the big DIY stores and or your local paint shop. It comes under 'specialist paints' catagory.
Venting the garage can considerable reduce it. Most people make the mistake of sealing off all draughts when using it as a workshop this introduces condensation warm air and cold surface means condensation.
Bob
Bob, December 2005