This is not a paver patio we installed. But we have a client who's home we maintain as part of our landscape maintenance service. They have a good 3000+ sq. ft. of pavers (driveway, back patios, pathways). A month or two ago they called us to help get rid of the moss that had started to grow on the pavers and the weeds that had begun to grow in the joints. It looked to me like the people who installed the pavers several years ago didn't use poly sand. So my idea was to pressure-wash the entire area (the pavers looked a little dark and dingy anyway), get all the moss off the top of the pavers in the shady areas, jet the weeds out of the joints, and then install poly sand. So we did that. But unfortunately the weeds that were in the joints were very difficult to get out with a pressure-washer alone. So 4 of my guys actually spent several hours on their hands and knees digging out weeds with screwdrivers prior to installing the poly sand. They weren't able to get 100% of the roots, but they got most of them. We installed the poly sand and all was finished. Or so we thought..... Now the weeds have started to come back through and are looking pretty bad again. At this point, I'm not about to go through that whole process again. I'm thinking we'll just spray the weeds with round-up or some other herbicide. My main concern is staining the newly cleaned pavers. I saw a property recently where the homeowner had sprayed *something* on the weeds in his paver joints and it bleached out the pavers around every weed. It looked really bad. Now, I have no idea what he used. For all I know, he used actual bleach. But I don't want to make that same mistake. Anyone know if (properly mixed) Round-up will stain pavers? I think once we get the existing weeds killed off they shouldn't return. Maybe we'll fill in a little more poly sand after they die and we remove them. But I don't anticipate them coming back so strongly now that we've filled in all of the joints that were so open before. The main thing is just killing the existing weeds and roots. I just want to make sure I don't stain the pavers in the process.