Last summer I put in a small patio, using 16" pre-cast blocks. I put
sand under the blocks, and it's remained pretty level. But due to it's
location, I have had muddy water run across it after heavy rain. I'm
presently working on installing some drainage pipes for rain water.

But the reason for posting this is because there is grass and weeds
growing between the blocks, and before I got down on my knees and
starting pulling them, it was starting to look like a lawn, not a patio.
I'm guessing the mud added some soil to the cracks, which stimulated
growth of vegetation.

Is there some chemical made to stop this?

I did try pouring some gasoline in the cracks, because I had some gas
that got water in it, but that was just a quart or so. I have not
noticed any new growth in those cracks (with the gas), but thats
probably not the safest method, and I doubt it will last long.

Any tips????

Thanks