I'm having difficulty understanding this question. Please elaborate.
Oh, good question. Pressure washing is an easier way to get all the dirt and grime off the patio so that the mastic will stick properly. Mastic doesn't stick to dirt well and if there's the slightest bit of grease or slim from leaves or insects, it definitely won't stick to that. You an always use a stiff bristle brush and hot water with soap to clean. Just rinse well Happy DIY'ing!
The surface needs to be squeaky clean otherwise the adhesive will not stick. Just as you wash the walls for a paint project - same rules apply. Always start with a clean surface for best results.
Need to start with a clean surface so the flagstone will adhere well.
To get it clean for a good adhear