ᐅ Sealing Exterior Area Joint in Concrete Base

Hello everyone,

We are renovating our home. We want to do as much as possible ourselves. I installed all the windows, including a sliding window front, together with a colleague who is a professional carpenter.
To align the new sliding window front with the interior floor level, we had to cut a groove into the floor base.
Now there is a groove outside that is about 4cm (1.5 inches) deep.
My question is: which material should I use to fill this groove to make it watertight?
It must be waterproof because otherwise water will seep through the upper concrete layer and then into the basement brick wall. A roofer suggested sealing it with epoxy resin, but that does not look very nice. Ideally, it should be a material that can be painted so we can paint the entire base and hide the different materials in the groove.

Would it be sufficient to fill it with cement or concrete instead?

I am attaching a picture of the groove.

Thank you very much for your help and best regards.

Hello Beathomen

Concrete will start to crumble again after some time. Use repair mortar instead. It lasts longer and you can paint over it.

Steven