Here, I am trimming some air-cure silicone material off from a previous patch attempt. The surface adhesion was very good for the silicone, but the material itself cracked in use.
2. This next step is key, and should be done outside for safety reasons. Fire up your propane torch. Run the torch flame LIGHTLY BUT THOROUGHLY over the cleaned area on your boot to be patched. DO NOT LET THE FLAME MELT, DEFORM OR CHAR THE SURFACE OF THE BOOT! That would be way overdoing it! The flame should be held a few inches from the surface of the boot, and “brushed” across the surface a few times. If the surface is was still damp, stop when the water disappears. If the surface starts to smoke, back off! The purpose of the flame is to break surface molecules and increase the surface energy (adhesion capability) of the rubber boot material, similar to the action of the solvent in tire patch kits.