I don't get any build up on my iron using homemade starch.
Cooking the starch cause build up. I tried the cooking method which
didn't work for me so I went back to my old method. Dilute with a little
cold water then add boiling water. Of course you have to take a few
precautions like letting it soak then dry until slightly damp. I use
a silicone mat between the iron and the fabric to prevent scorching.
Once the fabric is pressed and cut I can use the dry iron.