I haven`t used a chemical yet,not had too,practice on friends and family,charge them for the sand and petrol with a little added on,don`t get stuck into any hard jobs untill your confident,cherry pick the jobs that look easy with good drainage,don`t sand till job is totally dry,make sure your gun tips are in properly or it will fly off and will break something,lower your pressure down greatly when cleaning doors and windows,i`ve asked every question and learned loads in my first month,job is really busy so i`ve had plenty of ups and downs,i make a point not to take on a job i know i can`t do to the standard i want to keep but most ofit is common sense,you just have to get stuck in and take your time.good luck mate.