DIY - Root Tabs

Anyone have confirmation that the clay breaks down and is used, that it does not build up under substrate?
 
i havent noticed anything like that. i'll start experimenting with some to see what i can come up with for you
 
The only clay i can find says it is modeling clay is a pigmented oil base modeling clay. That doesn't sound like the right clay to me. this isn't the right clay is it?
 
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