I used a normal paint brush twice now with no issues. One thing I'll say, is to make sure to seal the unused can up GOOD! I put saran wrap on inside, then the lid.
they claim you can spray it too.. the friend i had helping me out when we did the manifolds couldn't get it to this properly.. the foam brush worked great. we just went over the freshly blasted metal.. i didn't use their cleaner or prep.