Advise for DIY outdoor stone step project I'm about to start.
June 7, 2017 6:27 AM Subscribe
This is my first time installing an outdoor flagstone steps, and I have no experience with mortar. Details and questions inside.
My DIY backyard slope project is entering the "install flagstone steps phase", I have a basic plan but am struggling to imagine how it will go and how best to plan.
Plan:
I’ve calculated a tread height (5”) and depth (approx. 18”) for the rise/run.
The treads are approximately 2” thick.
I’m using flagstone leftover from building a retaining wall to make up the rest of the height in the front, and will form a dam, which will be backfilled filled with crushed stone/stone dust, and compact. I will probably need to do this on the sides as well. I’ll check for pitch so water can tun off. Then after adding some mortar, I'll cover with my cut & shaped irregular flagstone.
Questions:
I don’t know how exactly to use the mortar. Should I mortar between the smaller flagstone dam pieces, and then slop .5” of the mortar over the packed in fill before adding the tread?
I live in PA. How deep should I dig down for the base of the first step? Will crushed stone suffice or should I air some concrete first under that first base step and then add stone?
After the first step, should my smaller flagstone dam pieces overlap onto the back of the step, or should the next dam be behind? This will affect depth calculations.
How do I deal with the sides of the step, should I add stones to the corners to block erosion from the side, leaking onto the step? Any other tips or words of wisdom?
Pictures of project site and materials are here.
My DIY backyard slope project is entering the "install flagstone steps phase", I have a basic plan but am struggling to imagine how it will go and how best to plan.
Plan:
I’ve calculated a tread height (5”) and depth (approx. 18”) for the rise/run.
The treads are approximately 2” thick.
I’m using flagstone leftover from building a retaining wall to make up the rest of the height in the front, and will form a dam, which will be backfilled filled with crushed stone/stone dust, and compact. I will probably need to do this on the sides as well. I’ll check for pitch so water can tun off. Then after adding some mortar, I'll cover with my cut & shaped irregular flagstone.
Questions:
I don’t know how exactly to use the mortar. Should I mortar between the smaller flagstone dam pieces, and then slop .5” of the mortar over the packed in fill before adding the tread?
I live in PA. How deep should I dig down for the base of the first step? Will crushed stone suffice or should I air some concrete first under that first base step and then add stone?
After the first step, should my smaller flagstone dam pieces overlap onto the back of the step, or should the next dam be behind? This will affect depth calculations.
How do I deal with the sides of the step, should I add stones to the corners to block erosion from the side, leaking onto the step? Any other tips or words of wisdom?
Pictures of project site and materials are here.
I think this is a lot to tackle for a first stone project. I'd advise reading some books, there's too much to give an overview here.
But what I really came in to say is that 5" rise and 18" run sounds super awkward to me. We are generally trained to accept a range of tread depths and heights, and this falls outside most comfort zones. You ca shorten the whole depth, reduce the number if steps etc, several steps can be taken to fix this, see here For some general guidelines and discussion of stair design.
posted by SaltySalticid at 6:39 AM on June 7, 2017 [2 favorites]
But what I really came in to say is that 5" rise and 18" run sounds super awkward to me. We are generally trained to accept a range of tread depths and heights, and this falls outside most comfort zones. You ca shorten the whole depth, reduce the number if steps etc, several steps can be taken to fix this, see here For some general guidelines and discussion of stair design.
posted by SaltySalticid at 6:39 AM on June 7, 2017 [2 favorites]
Additionally: I would fit this all dry. Lots and lots of stonework is done dry, including stairs, on purpose. I'm fairly confident your "inspiration" photos are dry laid stone. If you do it right, it can last for decades to even hundreds of years. If you inevitably mess things up, you can adjust and re-do in a few years. This is not possible with setting concrete and mortaring joints, and if you mess those up, you can't re-do it and you're basically asking for cracks after your first freeze/thaw cycle.
posted by SaltySalticid at 6:55 AM on June 7, 2017 [2 favorites]
posted by SaltySalticid at 6:55 AM on June 7, 2017 [2 favorites]
Best answer: From OP: What about the very first base step though? Do you think that will that be ok with just gravel base if I dig really deep?
Hi Mikey, glad my answer was helpful! I'll post this in the main thread in case any future readers may benefit as well :)
First: I should add the caveat that I've never designed this kind of stuff all by myself. My father was an accomplished stone mason. I learned a lot from him, but ultimately I am not an expert, and he called the shots. I helped him do everything from retaining walls to fire places to patios to etc. Lots of super rich clients getting high-class luxury work done at rather high prices.
One recurring lesson was: dry fitted stone like in patios, retaining walls, and stairs, should be solid yet float. This reduces cracking, and ultimately adds to the longevity, while increasing ability to adjust/repair. The earth will move plenty on decadal scales no matter what you do: better to have your stone shift slightly with it, than to crumble.
So yes, with 2" flag stones, I'd be confident that a nice thick layer of compacted crushed lime would hold it just fine.
If you really want to do a dry foundation right, you do it in three or more layers, tamping between each: coarse limestone, tamp, crushed lime, tamp, sand-- don't tamp or tamp very lightly, stone, tamp/settle. The idea is the last thin layer of sand will settle in as you tamp the stone. I don't think I've ever seen anyone do more than five layers of successively finer grains but even having just two will keep your bottom step more stable for longer than one layer of comparable thickness. See here for a list of do's and don'ts for gravel foundations under stone.
posted by SaltySalticid at 9:50 AM on June 7, 2017 [2 favorites]
Hi Mikey, glad my answer was helpful! I'll post this in the main thread in case any future readers may benefit as well :)
First: I should add the caveat that I've never designed this kind of stuff all by myself. My father was an accomplished stone mason. I learned a lot from him, but ultimately I am not an expert, and he called the shots. I helped him do everything from retaining walls to fire places to patios to etc. Lots of super rich clients getting high-class luxury work done at rather high prices.
One recurring lesson was: dry fitted stone like in patios, retaining walls, and stairs, should be solid yet float. This reduces cracking, and ultimately adds to the longevity, while increasing ability to adjust/repair. The earth will move plenty on decadal scales no matter what you do: better to have your stone shift slightly with it, than to crumble.
So yes, with 2" flag stones, I'd be confident that a nice thick layer of compacted crushed lime would hold it just fine.
If you really want to do a dry foundation right, you do it in three or more layers, tamping between each: coarse limestone, tamp, crushed lime, tamp, sand-- don't tamp or tamp very lightly, stone, tamp/settle. The idea is the last thin layer of sand will settle in as you tamp the stone. I don't think I've ever seen anyone do more than five layers of successively finer grains but even having just two will keep your bottom step more stable for longer than one layer of comparable thickness. See here for a list of do's and don'ts for gravel foundations under stone.
posted by SaltySalticid at 9:50 AM on June 7, 2017 [2 favorites]
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posted by koolkat at 6:37 AM on June 7, 2017 [1 favorite]