Weeds growing and repointing paving slabs

I have many weeds growing between paving slabs. I have put weed killer down and waiting for the results. Between the slabs have been left un pointed so are full of soil now. I intend to scrape the soil out and repoint the slabs. What is the best mixture to use to repoint to stop and more weeds growing.

Also does anyone have any knowledge of geofix from screwfix and is it worth it?
http://www.screwfix.com/app/sfd/cat/pro.jsp?id=31817&ts=25428

Thanks in advance

hello jackpot

I pointed mine with a mix of 3 parts builders/washed sand to 1 part cement ,DRYMIX and after 6 years now not a crack ,

I did dig /scrape out the old as much as I could then with a soft brush brushed it in on hands an knees , I then brushed off excess an then went back an pointed/troweled it tightly in ....a light brush off again an job was a good one

agree with moz. I always use 3:1 cement and sand to pint with. Should last years without weeds coming through