what size pw do you guys use to wash decks?

More gpm always is more speed. Psi and proper chemicals is the secret for doing wood professionally. You need to use a nozzle orifice that is about 2.5 times your gpm rating to drop the pressure correctly and always use a 45 degree fan pattern. For my 8 gpm machine I use a 20 orifice with a 45 fan pattern . (2045 nozzle). Using this oversize orifice drops my pressure to around 1200 psi iirc and you don't have to fool with the unloader or cut your gpm flow.
 
1000psi is great for wood but remember that if you have a 1000psi machine you will not have that at the end of the gun. couple that with low gpm and this where people "mess up" and overcompensate for the machine and get too close. Getting too close with these machines will still scar the wood, specifically cedar. Best is to take Pat's advice and get a higher gpm machine that way you have the volume you need. Remember you are only rinsing, the machine should not be doing the work. For this you want volume so you can rinse and get on to the next job. We also lower our psi the same way by changing tips with larger orifice sizes. I do not recommend anything except the 40 degree or white tip for wood surfaces. For most cases being approximately 6-12 inches away from the wood reduces actual psi hitting the wood surface and will prevent scarring as well.
 
That's a gold nugget right there, thanks Pat."For my 8 gpm machine I use a 20 orifice with a 45 fan pattern . (2045 nozzle)."
 
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