[Histonet] Blocks cracking

[Erica Canal]

Hello all, 
We are wondering harder paraffin makes blocks more fragile.
We have been using Leica's Formula R and on a few occasions & when we have mailed blocks out, we receive them back in pieces. Could this be because of type of wax we are using? The quality of our slides is great, we just seem to be having a problem lately with our blocks breaking after they have been sent out & we want to try to prevent that.