craftgrrl | Stenciling Tshirt Problems

Hey guys. I have a problem. I have a lot of tshirt orders (stenciling) and I guess I jumped on the bandwagon because the one I made for my boyfriend is starting to crack after its second wash. After its first wash it looked great, but now its starting to crack. I am using the 1/3 textile medium 2/3 acrylic paint mixture for my paints. And I dont to sell people shirts only for them to be ruined after a few wearings.

Is it because of multiple layers? Is it the paints? I know a lot of you have had great outcomes with doing stenciling, so I really need some help. I am willing to buy Jacquard or Speedball if I have to, but only if it means I will not have cracking. Its just I have to buy it online. And if thats the case, which is better? Jacquard or Speedball?

Could it possibly because of drying? Should it only be air dryed?

Note: I DID heat set! Also, I follwed the textile medium instructions and let the shirt set on its on for 3 days before I did the first wash.

Any tips/suggestions would be GREATLY appreciated! Thanks in advanced.