I have re-sanded monoblocking after cleaning it many times.
I've tried mixing something (can't remember what at the moment) in with the sand in an attempt to reduce weed/grass growth in the joints, but it wasn't very effective.
I have never used a sealant at the end of the process.
I did watch "a professional" clean a neighbour's drive a few years back. They did a decent enough job, but the sealant that they applied after re-sanding looked suspiciously like water that they lightly sprinkled on with a watering can. I wasn't convinced it did much
I was under the impression that sealant was intended to provide an anti-fungal coating on the surface of the block, but I became aware recently that some/all of them are more focussed on solidifying the sand in the joints in order to prevent it being blown/washed out, and to "inhibit organic growth". This may not be news to some of you, but to me it was an.... AH. 
So this time I tried some of this stuff this stuff. Opted to apply it with a roller. It looks quite like milk and smells a bit like PVA glue. Which makes me wonder if it is a variant of PVA glue? I'm pretty sure it's not a variant of milk. Dunno.
Unfortunately I under-estimated how much I'd need. 20 litres covered around 85% of my blocking
The good news is that - whilst I wait for more to arrive - I can confirm that the sand has indeed firmed up nicely (contrasting markedly with the loose sand in the untreated area). It claims to be a matt finish, and it is - you can see the line where I ran out, but it's not glaringly different.So lets see if it actually lasts any longer before picking up weeds/moss/ingrained dirt........
More exciting product reviews. As they happen. Here on ov9.
