Sealing natural stone stairs

Hello,
I am new to the forum, as I have so far managed all our building matters with the help of experienced friends.

For 2017, I have planned to seal our natural stone staircase.

To begin with: We bought a house in 2015. The previous owner built the house himself.
The terrace was added later.
He faced the entire terrace and the staircase with hewn tombstones that he got from the rubble stone "scrap" and hewn himself.

The stair steps consist of large massive stones.
Unfortunately, the joints are not sealed and water runs into the space under the stairs.
The joints have already been re-grouted many times.

A paving company said that nothing will help, all the steps have to be completely dismantled, a separation layer installed, and then everything rebuilt again.

That is way too much effort for us.
The surface of the steps is not so important to us - the main thing is that the staircase is sealed.

I have thought about different things - but I would like to ask what ideas experienced homeowners have:

Idea 1 - but probably not an option: Cut aluminum checker plate step by step and weld them together
Idea 2: Lay a roofing membrane over the entire staircase and cover it with tread plates.
Idea 3 - and for this I ask for professional assessment: Pour concrete onto the steps - that is, apply a layer - maybe about 5 cm thick?
I thought, there are also swimming pools with concrete walls - so it must be possible to produce watertight concrete.
Can I provide formwork step by step and pour concrete into it?
I mean the horizontal and vertical edges - so that in the end I walk on concrete, but sideways have only about 5 cm of concrete on the original step?
Does this approximately 5 cm layer need to be reinforced with rebar?
Do I need special concrete?
In the end, I can cover this concrete surface with tiles if I don't like the concrete.

Or do you have other ideas?

Many thanks,

Felix

Idea 4: maybe the edges can be glued with window sealant. So this black stuff used to install car windows.

What do you mean by space under the stairs? According to the picture, there can't be much space underneath, or is there still a basement?

There is not much space, that's true. But you can get from the basement under the stairs, that is open, i.e. the room in the basement includes the cellar stairs. Since water is entering there, mold has already appeared.

Hello "FelixPrüfer". If the water – as you write – can already penetrate into a room below, then by now it should be clear to everyone that the matter must be approached with expertise. Window putty and other "sealing materials" may be suitable reading material for April 1st. They are unsuitable for construction work. Since water finds its way, exact conclusions about the location where the water actually penetrates the component can rarely be drawn. This ultimately means: dismantling and rebuilding down to the load-bearing substrate, leveling it, sealing it properly depending on the situation, and then rebuilding the steps. Everything else is less time-consuming and cheaper, but it cannot be crowned with success. The do-it-yourself craftsmen are usually certainly overwhelmed by a professional execution! ------------------------ Regards: KlaRa

Hello KlaRa,

so scraping out any kit or silicone or joints - I definitely will not do that, it is not successful.

I can only imagine the concrete option, which then changes the appearance