Grout for Flagstone?

I am getting ready to start a fun DIY project for my fireplace. I'm completely refacing my red brick fireplace with Cultured Stone drystack stone veneer and using varying sized pieces of Arizona flagstone as the hearth. Yesterday I scored, then laid all of the flagstone pieces out on the hearth in a fashion that looks nice. Tonight I am going to fashion a 2x4 frame that will rest around the edge of the current hearth. This will be to form the grout against the edge so that I will have a clean finish. I will then mortar perfectly cut pieces of stone veneer up against the sides of the hearth to cover the brick edges.

My question ...since my grout lines in-between the flagstone pieces are of varying sizes and shapes, what is the best grout to use in-between these pieces? I was at Home Depot last night and most all of the sanded grout is for 1/8" to 1/2" grout lines. They had stuff for saltillo tiles ...it could handle grout lines up to 1 1/4". I thought about buying that but they only had bags of 50 lbs which is way more than I need. I will most likely go to a specialty tile shop to buy whatever I end up going with. But can I use standard tile grout that is desinged for 1/8" to 1/2" for my project or will the shrinkage after curing totally mess up my job? I had flagstone installed in my backyard and the installers used concrete for the grout lines but I don't really want to use that for this interior job. Please advise.

Thanks,
Steve

 

Type S mortar, either premixed if available, or mixed if not.

Formulas would be:

Type S masonry cement plus 2-3 parts masonry sand.

Portland cement, Type I, plus 1/2 part type S lime, plus 2-3 parts masonry sand.

All parts by volume of cementitous material.

 

Holy cow??!! All of that for the grout? Or do you mean I should use that as the mortar to secure the flagstone down to the red brick? Damn, I thought there might be something off the shelf I could buy or are you saying to buy Type S mortar and use that and the formula you provided is if I need to make it from scratch? Can I color this stuff with grout dyes? I don't want the typical dull gray cement/mortar look for in-between each stone ...I wanted more of a sand or sahara type color.

Thanks for your input.
Steve

 

Type S is usually available pre-bagged, and it can be used to set and grout, and can be colored.

 

OK ...thanks. I'll check the tile specialists shop I typically go to or RCP Block and Brick would have it for sure I bet. Is there a reason why I should use Type S over regular tile grout? And will the Type S for securing the flagstone to the brick base be a better option than using polymer enhanced thin set?

Thansk for your feedback, Tscarborough.

Steve

 

I am a fan of thinset, but the type S will be adequate.