Hi you can buy a self adhesive tape from Builders Merchants and DIY stores, Look in the plastering dept or ask. It's made of nylon and comes in rolls a bit like the plasters scrim and then can be filled out and will prevent cracks re-appearing.
What i normally do is use skrim tape (as above said) down the join and then mix a little dry line adhesive and push it in to the gap over the skrim getting in as much as possible so there are no gaps. Let it go off for about 20-30 minutes then get a wet brush and brush off any excess leaving you with a gapless joint with the added protection of the skrim tape
DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!