I would like this spring to fix my driveway interlock as in between stoones I see lots of grass growing. Question I have are: 1. Do I have to use elctric/gas preassure cleaner to get rid of grass and other debris between interlock. 2. What type of sand should I use to fill up gaps in between stones. I do know that there is a special interlock sand, but there is on for 4$/20Kg band and there is another for 16$/bag. Homedepot staff was usless there explaining. I did hear that more expensive sand gets very hard, but now sure about that. Anyone had experiece in this? 3. Is it a good idea to seal interlock after fixing it? I am not sure how to do that? Just spray with some special liquid?