moss in paver joints

I have a paver patio with moss in almost all of the joints. I have sprayed the moss with moss killer and Roundup and it is now dead but not gone. I could power wash the moss out of the joints and reinstall polymeric sand. In fact, I did that last year (twice), but the moss came back this year. My question is: Is there an additive I can add to the polymeric sand to keep the moss from coming back?

Moss will always return again and again IF you don't alter the site where is growing..
Moss requires either damp / wet or dull light areas, and unless you can fix that then you will have to treat the mossy area each time it becomes either unsightly or dangerous under foot, it becomes slippery and can cause accidents when someone slips.

IF I were you I would lift the pavers and have them re-set giving more slope where any excess water can run off the pavers, I don't know how many pavers you have or how big a job this is, BUT the moss only grows where it's growing in the right conditions for it survival so, you need to remove these conditions.

Maybe resetting the pavers will also give the opportunity to put some form of drainage either under or into the pavers. there are several options regarding draining water away from one area but you must remember to make sure the flow or run off does NOT run into someone else's property.

Meantime, best thing I know for removing weeds / moss ect between pavers is the good old fashioned way, screwdriver / knife, run screwdriver between the / into the crack between pavers and use a lifting action, you feel it's quite laborious but, half an hour later all of a sudden you see just how much your cleared, very satisfying and rewarding, well I find that anyway.

Hope this gives you ideas and you get the problem fixed soon.
Best regards.
WeeNel.

Wow, you cant imagine how many of us
would love to have moss !

You are absolutely right, I have no idea how many people would love to have MOSS growing in there garden, the type of MOSS that grows in the lawn is NOT the same type that is ornamental like you see in Japanese gardens.

The Lawn moss can encroach onto pathways, steps and other places that when wet, become a hazard when walked on or should I say skate on, it's like ICE, once you start to slip on the MOSS, you just either fall injuring back, arm / leg bones or even head injuries. That type of MOSS likes damp, dull, shaded, an area with the right conditions to get hold and it spreads over a few years. Some people think it's attractive until it takes over and their kids cant play out, they cant use footpaths or worse, the moss hold moisture by the gallon and this IF left untamed, can cause damage to property especially wood, brickwork and the wet hidden by the lush green moss can also penetrate into the walls / foundations indoors.

I love moss myself but be assured, there's MOSS and there's other types of MOSS so make sure you do some research before you introduce some things, MOSS also has spores that CAN cause untold illnesses with breathing or lungs.

Don't let me put you off but just be careful what you wish for.
Best regards.
WeeNel.

There are probably spores left there after you excavate the visible moss. If the patio is not too huge, boiling water could help kill the spores, but on a flat, mostly un-porous surface, be very careful to make sure you don't burn your feet, or pour fast enough that still-hot runoff kills desirable plants at the perimeter.