Repair Window Sill

I have a large Picture Window that was installed in my Walk-Out basement Block Wall 29 years ago. It is the typical 3 pane double glass windows with 3 slider type windows at the the bottom. The overall width of the window is approximately 9 1/2'.
The window is in good shape except for the bottom sill which
rests on the 10" block wall. I removed the slider windows and the bottom and side vinyl pieces to inspect the sill.
It appears that water leaked in between the outside part of the sill and the cement slope to outside of block wall.
The actual window sill is about 5" deep and has a brick mould trim attached to the outside giving an overall depth of approx. 7" leaving about 3" of block on outside where a cement slope was installed.
The damaged wood sill extends only about 2 1/2" back from outside. I am planning to cut out the rotted area with my Dremel tool and chisel and replace this cut out area to the end of the cement block wall with a cement mixture. I would then replace vinyl pieces and reinstall the slider windows.
My question is what kind of cement product or mixture should I use? The depth of the cement would be about 1" at
the cut out part of sill and would taper down to 0" at the outside block wall. Having the proper cement mixture or product that will adhere and not crack is crucial.
Would like some experienced input and suggestions.

Thanks

Art Docherty



Art Docherty
365 Cedar Ave. RR 1
Meaford, Ontario Canada N4L 1W5
amdocherty@bmts.com