Contractor Talk - Professional Construction and Remodeling Forum banner
1 - 18 of 18 Posts

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #1 · (Edited)
I have inherited a problem with crumbling mortar in a flagstone walkway/steps, and some stones are loose, while a few others have a hollow sound when tapped with a wooden broomstick. I would like to make these repairs myself, hence I wanted to ask the question here of what might be the cause of the crumbling mortar, as well as what would be the best fix. I suspect (due to the consistent/uniform 3/8 inch gap in many of the stair riser mortar joints, which looks as though the mortar shrunk (I do not detect any subsidence at any point of the flagstone. The stone was wet laid (assuming this is the term for installed on a concrete pad/footing). I am wondering if the wrong mortar was used that resulted in the shrinkage and the cracks in the horizontal surfaces. I know this will only get worse with freeze and thaw cycles, so I want to fix this as soon as possible.

I am thinking in terms of first cleaning the stone to remove as much of the mold spots/leaf stains/etc then onto removing as much of the mortar in the joints as I can by chiseling and grinding (or whatever else works) then blowing out the joints with compressed air then using a mortar with lime in it so it will flex more when movement happens. My question: would this be the right fix that will last? or is there a better fix or better mortar to use, or what are some suggestions on how to do this so I minimize or eliminate it from happening again?

Lastly, I personally don't think putting a sealer on natural stone is a good idea when its outdoors. But, would this be right, or would it help in giving the mortar longevity?

I will post a couple of pics.





 

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #3 ·
From what you're seeing Stuart, you suggest the entire thing was built wrong, not just the wrong mortar used? As I said in my previous post, there doesn't appear to be any subsidence anywhere. It looks like the mortar shrunk when it cured. At least this in my guess.
 

·
Registered
Joined
·
8,139 Posts
Pull up the tops, clean it up, brush weld o bond on everything you can, add a couple short scoops of portland to the mortar, keep the joints under 1/2", fill along side the sides, make sure it pitches, dont seal it.

Assuming the shell of the steps are filled and built on something correctly and its not moving.
 

·
Registered
Joined
·
8,139 Posts
Yeah if it is hot when doing flat work ill soak a canvas tarp and toss it on the bluestone or whatever it is im working on. If I can wet it again before I leave I will.
 

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #6 ·
JBM,

Thanks for the input! A couple of questions: what type of mortar would you suggest, or rather what would you typically use? Would you use something different for setting (type S maybe) than what you'd use in the joints (something added like lime or some other additive)? And what do you mean by "fill along side the sides"?
 

·
Registered
Joined
·
8,139 Posts
The way the stone are laid up dry you would want to fill alongside the edge to stop water from getting under the tops.

I would use a bag of iron clad light (N) with a couple short scoops of portland in it.

I will almost put money on it that under that flat work you will have a big fat glob of mortar. If yes and under that is sound then I would repour it with a portland and concrete sand bed. Big fat mortar beds always end up failing.

Even though the risers look like 6"'s, I doubt that 6" block was used nice and neatly on the insides. Probably filled all cockeyed.
 

·
Registered
Brickwork
Joined
·
1,126 Posts
From what you're seeing Stuart, you suggest the entire thing was built wrong, not just the wrong mortar used? As I said in my previous post, there doesn't appear to be any subsidence anywhere. It looks like the mortar shrunk when it cured. At least this in my guess.
Not the whole job Jeff, I meant taking up the flags rather than trying to cut out the joints and repoint them.
Sorry for the confusion.
 

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #11 ·
Looks lke it was patched at least once already. In a non wintery state that is a warning sign something is amiss under that.
I agree, JBM, it looks as though it was patched already, and the house is 14 years old now. I also agree with your suggestion that something is amiss; however, I was thinking along the lines that the wrong mortar was used, or perhaps some other issue with the mortar curing properly.

I really appreciate the help you guys are giving!
 

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #12 ·
http://www.pavingexpert.com/crazypav.htm
A bit of info here from a popular site, although it may not apply to your climate.
Awesome! Thanks for sharing the link!

On a side note, it seems pretty clear from what you guys are saying that I will need to get some more flagstone that fairly well matches what I got just to have them on hand when I do this just so I am able to close up the huge mortar joints by rearranging and adding stone as needed.

Thanks again, Stuart!:thumbsup:
 

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #14 ·
Not really a thing in the Carolinas as the wrong mortar on steps. I mean home depot premix mud will work if everything else is done properly.
Do you think the mortar on the flat work that failed and is crumbling (2nd pic) is due to the bed failed/big glob of mortar/etc? This area is why I was suspicious of the mortar mix/type of mortar being wrong.
 

·
Registered
Joined
·
8,133 Posts
What kind of a winter did you guys have? From what i hear the Southern US got some actual cold weather with snow and everything. Too much salt may have played a role. Too much heat when installing is another factor that causes crumbling mortar. Personally i doubt that the wrong mortar did this, in warmish climates that don't experience many freeze thaw cycles the type of mortar isn't near as important
 

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #16 ·
What kind of a winter did you guys have? From what i hear the Southern US got some actual cold weather with snow and everything. Too much salt may have played a role. Too much heat when installing is another factor that causes crumbling mortar. Personally i doubt that the wrong mortar did this, in warmish climates that don't experience many freeze thaw cycles the type of mortar isn't near as important
We do experience some rough patches of winter here, freezing rain being the worst of it, but we do get some snow/sleet too along with some winters of multiple days/weeks of temps hovering in the teens and single digits for highs. These types of days seem to come in 1-3 week spurts, then gets a bit warmer, then back to frigid cold. A lot of back and forth with temps, ergo, a lot of freeze/thaw cycles most winters since I've been here (2004), but certainly not as bad as it is further north.
 

·
Registered
Joined
·
8,133 Posts
Freeze thaws in heavy use areas like front steps are tough. I've done quite a few that have lasted 10 years plus but I always feel like it;s a crap shoot. Salting, water pooling, stone shaling and making an area for water to pool where there wasn't one when it was built.

A lot of the problem with the walkway could also be the inherent build problem. No overhang on the treads and then a "drystack" riser can allow tons of water to get behind the riser and riun down and under the treads and the rest of the flags. Personally there's not much i like about that design but not having built it i have no idea if there were any measures taken to stop the water form getting under the flags.

But i REALLY don't like the treads with no overhang. Esthetically as much as anything but it does serve a purpose as well. It creates a cover and even if there isn't a saw cut drip it most of the water will drip off rather than running the inch back to the wall. Looking back at th pics most of the problems seem to start at the leading edge of the trad and run back. That is the first place I'd start I think
 

·
Champion Thread Derailer
Joined
·
1,228 Posts
Discussion Starter · #18 · (Edited)
Yeah, everything is pitched correctly (about 1/4" per foot on steps, a little more on the walkway). I too thought about that dry stacked risers letting in water. It seems the risers were all set first, then the treads with mortar packed in where riser meets tread.

I am going to do as JBM suggested and remove all the tops, and maybe end up reworking the entire steps. I definitely do not want this to happen again in a few years, so I hopefully will get it right this time, particularly with the advise I'm getting here.:thumbsup:
 
1 - 18 of 18 Posts
Top