just starting my own buisness pressure cleaning in australia and was wondering do any of you guys use any chemicals while cleaning concrete driveways...is it necessary to use a chemical ,as i have done a few already and they seem to come up alright.also what is the best procedure to clean mould or moss of pavers. im looking at buying a whirlaway but my machine only pumps out 14 litres a minute which would be 3.696 gallons per minute.do any of you recommend a certain size whirlaway or my machine just wouldn,t run one.sorry for sounding dumb on the subject but like i said just starting out and sick of mowing lawns so im trying something new.whirlaways a really hard to get hold of in australia.i priced one the other week ,i think it was a 21" and he wanted $900 for it. im not paying that much.is there somewhere in the states that sell them cheaper.