Bricks and Blocks...

["Kinney, Travis" <kinney at pdtarchs_com>]

I use brick samples (1/2" thick various sizes) to weight down my riccia
growing through netting. You shouldn't have any problems with a good clean
brick. If it were to leach anything it would be Fe. What you want to avoid
is the mortar which will leach lime and screw up your Ph. The patio blocks
would be more of a concern because they are not just made up of clay like
most bricks. The patio blocks will have Portland Cement containing lime.
Still, there might not be enough leaching in any of these to make a
difference.

-Travis