There's an excellent sealing course run by resiblock but it's in Basildon so quite a trip. costs about £30 , lasts a day, they give you £200 worth of sealer and tools, you can become an acreditted installer, they will tell you about the different types of sealer, you can talk to other guys about their experience. they do of course plug their own products which are expensive but widely accepted as the best available, even by other manufacturers.
Ged