Myself and my assistant Fanny would beg to differ. As long as you use the correct mix and endeavour to rid the shutter box of air (hammer drill etc) then a domestic padstone is simple to make. Not so easy to manoeuvre and patience (curing time) is essential.
How does the hammer drill trick work? I understand it would vibrate out the air bubbles, but how do you get it in suitable contact with the shuttering?