All my patios are dry laid, so I can't help you with with filling in with cement (although I have heard there is a sand product which you can fill the cracks with, wet it and it will harden). In part-sun areas I use sagina subulata in the cracks and it does well. I find creeping type is not dense enough unless it gets full sun and it also has to be cut back if you don't want it to cover the stones. The sagina is more compact in part-sun and doesn't overlap the stones too much.

I have a similar issue- sort of. I have clay brick edging that I have laid. I did the same stuff you did, filled in with sand etc. I'm unhappy with the way the weeds STILL manage to get through so I am looking into applying something to halt this. I am also in a frost area so I would prefer that there still be some flex in the edging which will not happen if I use cement.

There is a product called Envirosand that looks like the perfect solution. It is organic and it is solid (like cement) when dry but will flex when wet. Pavers can be removed by wetting it which deactivates the 'glue'. It is a new product so I am trying to find some reviews on it first and I'm really hoping it is available in my area.

Yeah, woolly thyme and shade do not get along. You simply need to find a different ground cover, either one that creeps under or over the surface. I think it is in the Woodlands Forum that there is an old thread about groundcovers for shade in which literally dozens are named; you could look them up and find the smaller ones. Other sources of info: Gordon Hayward's book on Pathways has a section on good groundcovers, or just ask at your local nursery. Some suggestions I'd have would be dwarf mondo grass (Ophiopogon) or Mazus reptans. But there are tons of choices.

Has anyone ever found a dealer for Envirosand? I can't seem to locate one. I live in PA. That sounds like something I could use. Thanks.