Which To Use Precision Grout Or Polymodified Mortar?

I have a outside bluestone patio that has large bluestones. The existing grout lines are filled with mortar that is cracking, breaking apart and turning sandy and powdery. I plan to have all the grout joints ground out and replaced with something much more durable.

I'm talking with a couple of contractors who are suggesting to use either Precision Grout or Polymodified Mortar as a much better and longer lasting solution to the constant maintenance required when using regular mortar for filling grout lines. Some research I've done indicates using Epoxy Grout is the best solution for grouting outdoor stone but I cannot find a locate contractor willing and able to use it. So I'm looking for the next best solution.

I am hoping there is some experience with both products on this forum that can give me some guidance.

I would appreciate any input.

Thank you

 

Without more details about the actual construction it's difficult to say but assuming the bluestone is just lying loose there is nothing keeping them from moving so regardless what is used they will probalby just break up with time.

Have you considered using polymeric sand?

 

Thank you for your response Marq1.

The bluestone was set in mortar on a concrete base and does not move. I have considered and quickly dismissed using polymeric sand because of the need for continued high maintenance every few years. In addition, the bluestone pieces are very large with grout lines averaging 1/2" in width.

Given my comments above, are your thoughts about using Precision Grout or Polymodified Mortar to fill the grout lines any different?