I have to pressure wash my deck to prep for staining. In the past I just used the 40 degree nozzle and it took forever. I bought a 15 inch disc attachment for the concrete patio and wondering if I can speed the process up and use the attachment on the deck without damaging it.
Equipment- Simpson 3000psi pressure washer, 15 inch EZ clean gas surface cleaner.
Deck- About 800 square feet.

Yep those things (surface cleaner attachment) work great.

Nooooooooo......more is not better when PWing wood decking.

I cant speak for Trex or the other non-wood decking......but DO NOT use greater than 1200-1500psi on wood species.
You will blow the wood fiber to hell and be left with a poor surface.

^^ Good point ^^ when using on a deck directly.
The surface cleaner is really only for concrete.

DO NOT pressure wash a deck!!!!

1- rinses pulp wood away causing ridges and splinters

2- forces water into the wood so when sun hits it will crack and split

3- forces mildew spores into the wood causing years of issues including discoloration when a sealer is applied

4- causes the weathered wood fibers to “fuzz” so when a sealer is applied it will adhere to the “fuzz” which leads to premature failure of the coating since you’ve created an unstable substrate

I could go on....

There is not a deck board manufacturer that recommends using a pressure washer (except for low pressure rinse). All say to use an oxalyic acid based deck wash

Here’s a test... take a piece of duct tape. Place it in a deck board and remove. It will show all the “fuzz” that’s been created. When that’s no longer present you now have a properly prepared surface

(I have 18 years and counting in the archetectual coatings industry, due to my companies internet media policy I am unable to disclose which)

Power washing is fine, just don't use a great deal of pressure. If you are only needing to remove the grayed wood fibers and maybe remove some mildew or dirt, mix this up:

3 ounces of Dawn (Palmolive or Joy is OK)
1 ounce of bleach
Mix into 1 gallon of warm water

Spray this mix liberally across your wetted wood surface (your going to need more than one gallon of this mix). Scrub the deck paying attention to the trouble areas where there is foot traffic, and potential areas where mildew either has been, or could grow.

Let it sit for 20 minutes so the bleach can kill any mold or mildew spores, then either wash off with a hose or do a light power wash.

Be sure the you let your wood dry out for 2 good dry days before staining.

Oxalic acid will clean and bleach a wood deck.

https://www.amazon.com/OXALIC-...JJ2WZMZ1KFBAVW1BY9QT