Advice needed for new project

Hello everyone!

A customer recently requested a quote on my pressure washing her back deck, the surface is not wood however, its the type of surface that looks like multiple flat stones joined together by concrete.

I added a picture. My question is, is it ok for me to use my 18" Surface Cleaner?

Im running a Honda General 4GPM 3600PSI Machine

Ive done two of them. I didnt use the SC. The ones I did would have lost material using the SC. I applied a pre soak slightly stronger than house wash and then rinsed with low pressure.

This stuff is a pain! Yours doesn’t look nearly as bad as this one we did at the start of last summer. I went in hot with 50/50 mix in a pump up, no surfactant. On the horizontal surface the black algae or whatever looked like a gel coating when wet.

We had to go white tip on it and at 2800 psi on this one we still lost some chunks. Homeowner was just happy it looked clean.


I do quite a few of these.

I would advise against using a surface cleaner, although you can use it on some with very 'light" pressure.

The best way its to xjet or direct apply a strong mix, let dwell, use a push broom and brush in (this is optional, but helps), then use under 1k psi to rinse.

With flagstone some of the top surface material will/may chip and flake off, its not a big deal, but the less that flys off the better. So the light the pressure the better.


I had this one earlier this year. I used a strong House wash mix straight (pump up sprayer) and rinsed with my 25 degree J-rod. It came out great.

I have read to NOT use a surface cleaner on flagstone, it will etch it.

I have also read to not let your mix dwell too long.

(Sorry I don’t have an after pic, I suck at pics. I either take a before or after, rarely both)

Good Luck!


Here’s one I just did today. As you can see mortar was already broken out in a few places. Just hit with a 4% mix, let dwell while I was finishing front of house and then hit again with 4% mix and rinsed with fan spray on my m5ds nozzle, probably no more than 200 psi. Cleaned up great.


Ah ok! Great Idea!

I need to get a good pump sprayer I love this idea.

Thank you so much to everyone that offered their advice and wisdom, I now know NOT to use a SC and I will be applying the aforementioned suggestions!!! :smiley: