Flagstone step repair

[cmegeri]

Hey everyone, we moved into a new house last year and I've noticed that some of the mortar underneath our flagstone steps is coming loose. (The stones for the steps themselves are still in place, but I want to fix the mortar before anything gets shaky or the stones crack.)

Do you have any thoughts on what kind of material I should use to make the repairs?

I thought about using a basic repair mortar, but I was also considering an expansion joint sealant.

Thanks for your help.

[cx]

Welcome, Chris.

It would be helpful if you'd add a geographic location to your User Profile.

Looks more like a basic repointing application to me.

Can't tell how your steps might have been set initially, but if the stones are still solid, I'd be inclined to try to pull out all the loose mortar I could, wash the joints out well, and then re-pack the joints with a Type S or M mortar. You can find Quikrete's Mortar Mix or Mason's Mix at your local home center and either would be suitable for the application, but I forget which actually meets the Type S requirements. I think one or the other is only a Type N. Wouldn't hurt to toss in a bit more Portland cement if in doubt.

What is the reason for that black color? Were the steps painted, or is that some other sort of coloring?

My opinion; worth price charged.

[Davy]

Tap on the stone with the handle of a screwdriver and see if they are hollow sounding. Most likely some of them are. Pull those up, remove the old mortar and grout and restick them. I would add thinset to the stone and concrete using fat mud in between. The type M is 2500 PSI, Type S is 1800 PSI and type N is 750 PSI.

[cmegeri]

Thanks CX, I'm in Washington D.C. No black color, that's just the shadow where the mortar has already popped out.

Thanks Davy, looks like Type S is probably what I'll use. Would you pull up the stones with a crowbar or something like that? I wouldn't want to crack them, but I'm not sure if that's a real risk.

[cx]

I was talking about the overall dark charcoal color, Chris. Is that the color of the stone?

If you need a crowbar to remove the stones, I would leave them in place.

My opinion; worth price charged.

[cmegeri]

Gotcha. Yeah, I'm pretty sure that's just the color of the stone.

I'm inclined to leave the stones in place since none of them are loose.