ᐅ Sealing a natural stone staircase

Hello,
I’m new to the forum because so far I have been able to handle all our building projects with the help of experienced friends.

For 2017, I plan to waterproof our natural stone staircase.

A bit of background: We bought a house in 2015. The previous owner built the house himself.
The terrace was added later.
The entire terrace and the stairs are clad with shaped gravestones, which he took from broken stone “scrap” and shaped himself.

The stair treads are made of large solid stones.
Unfortunately, the joints are leaking and water runs into the space under the stairs.
The joints have already been regrouted multiple times.

A paving company said there is no solution other than to completely remove all the steps, install a separation layer, and then rebuild everything.

That is far too much work for us.
We don’t care about the surface appearance of the steps — the main thing is that the staircase is watertight.

I have considered different options but would like to ask what ideas experienced homeowners might have:

Idea 1 – probably not feasible: Cut aluminum checker plate step by step and weld the pieces together.
Idea 2: Lay a roofing membrane over the entire staircase and cover it with tread plates.
Idea 3 – and here I would appreciate professional advice: Pour concrete over the steps — apply a layer about 5cm (2 inches) thick?
I thought about swimming pools having concrete walls, so it should be possible to make watertight concrete.
Could I install formwork for each step and then pour concrete?
I mean the horizontal and vertical edges — so that in the end I would walk on concrete but only have about 5cm (2 inches) of concrete on the original step surface on the sides?
Does this approx. 5cm (2 inches) layer need steel reinforcement?
Do I need special concrete?
In the end, I could cover this concrete surface with tiles if I don’t like the concrete finish.

Or do you have other suggestions?

Thank you very much,

Felix

Idea 4: maybe the edges can be sealed with window sealant. You know, that black stuff used when installing car windows.

What do you mean by the space under the stairs? According to the picture, there doesn't seem to be much room underneath, or is there a basement as well?

There isn’t much space, that’s true. But you can access the area under the stairs from the basement, as it is open, meaning the basement room includes the stairs that are below ground level.
Since water is entering there, mold has already appeared.

Hello "FelixPrüfer."

If water can already penetrate into the room below—as you describe—then it should be clear that the issue must be approached with professional expertise. Window putty and other sealing materials might be suitable reading material for April Fools' Day, but they are not appropriate for proper construction work.

Since water finds its own path, it is rarely possible to pinpoint exactly where it enters the building component. This ultimately means: dismantling and rebuilding down to the structural substrate, leveling it, professionally sealing it depending on the situation, and then reconstructing the layers.

Anything less may be quicker and less expensive but will not lead to a successful outcome. Do-it-yourself builders are generally overwhelmed by tasks requiring professional workmanship!

Best regards,
KlaRa

Hello KlaRa,

I definitely won’t be scraping out any sealant, silicone, or joints—that never leads to success.

The only option I can imagine is the concrete version, which would then change the appearance.