Steps with reclaimed yorkstone - Varying stone thickness

[doitourselves]

I have about 40m2 of yorkstone (probably laid when the house was built - early 1900s) in an existing patio. Some slabs have become loose and exposed over the years and I can see that they vary markedly in thickness (50-100mm), although I won't know for sure until they're up.
I want to reuse them to create a smaller paved area with steps coming down from this onto an asphalt drive. The steps need to drop 350-400mm over a length of 2300mm. I was originally going to have 5 x 575mm treads with a 70mm rise - would this be more of a trip than a step? Would I be better with a 175mm-200mm rise with two landings.
The biggset problem I have is with the thicknesses. I had anticipated making formwork in concrete & bedding the slabs on top, but I'm struggling to see how I could get this to work.
Would the best bet be to start at the top, bed the slabs in a lean mix on a compacted aggregate then I thought I could cut some strips out of spare slabs and lay these (flat, not on edge) under the front edges of the treads to form a riser. I would then butt the back edge of the next step up to the riser of the previous step. Does this sound practical? Is it ok not to have the tread overhanging the riser?

[Tony McC]

How can you build steps from the top down?? What do they rest on??

70mm for a riser is a trip. Go for something in between 100-175mm - 3 @ 120mm gives you 360mm of rise, and then each tread could be 765mm, or 780-800mm allowing for a nosing.

I can't see why you can't use reclaimed bricks as risers, and then bed the selected flags on top of them with a overhang to keep water off the riser face. I've never known anyone build steps from the top down!

[doitourselves]

Now I feel really stupid!! But, what about the variation in thickness? If I build brick risers and lay with an overhang what about the slab thicknesses. The uppermost surface obviously has to be flat, with adjacent stones flush, but this may mean big differences in the bed. This doesn't matter on a patio, or edged surface, but won't this look odd when looking at the overhang of the steps as you walk up.
They will widen as they fall (to over 3000mm at the bottom) and I won't know, until they're all ripped up, if I will be able to sort the slabs to get even thicknesses for the treads that overhang the risers - so if the slabs are 50-100mm thick, then the 100mm slabs will be on say 10-15mm of mortar on the riser, the next slab, if it's 50mm thick will be on 60-65mm in order for the top surfaces to be level. This is an extreme comparison, but what would you normally do, or is this just something you live with if using reclaimed stone?
The alternative is to sell the old yorkstone and use the money to buy slabs with uniform thickness like an Indian stone....but, I'd prefer to keep what I've got as it is very nicely weathered.

[Tony McC]

The thickness of the flagstones doesn't matter - you can adjust the height of the riser to ensure that you get a standard 'lift' with each step, as shown here....



...so, if each step need two of three pieces of flagstone to give you sufficient width, as long as each individual step uses flagstones of the same depth, it doesn't matter is the first step has 100mm thick flags, the second 70mm thick, the third 40mm thick and so on and so forth.

[doitourselves]

Thanks Tony...I never thought of it like that!