Your problem could be solved by simply adding the missing stool inside the window or by adding a piece of window stop to the inside to act as a dam. You might try to reslope the outside as well to help flow the water away from the sash. The sash also appears to be lacking any weather stripping along the bottom.

 

Tough to tell from the picture but you could always make a sill out of Azek and caulk it up right. Would definitely with stand the weather and can be painted.

 

I would cut out the defective repair and reform it with a smooth slope away from the window. Also put some sealant under the frame.
Ideally the cill should overhang the wall with a drip on the bottom as shown here.

 

Great reply's thanks

What do you think I should use to cut off the defective cement repair and what product should i use to recreate the outer cill ?


Thanks again

 

Use a hammer and chisel to cut the render away. To form a new slope use 2 coats of washed plastering sand and portland cement.
Take the slope under the frame and then use a flexible sealer. If you take the sand/cement against the frame a small crack could form between the frame and render. allowing water in.
When actually forming a proper cill insitu we make up some formwork and use concrete with re bar, or a purpose made stone one.

 

WOW! "stuart45" is in England, "markee" is in Florida, and "stuart45" give the answer I would give and use. Yes, "markee" I agree that the existing, actually non-existing, window sill should be removed and completely reshaped. I also agree that you should remove enough old material so that when you start "coming back up" you should be forming under the existing window so as to prevent any cracks and likely future leaks. When you do form the new sill, add the overhand as suggested also. IF this is not within your DIY capabilites, please call in someone who knows how to do this. After all, it's only your new home and you would want it to last a long time without any future leaks. Good Luck, David

 

I am going to venture a guess that the window is not flashed on the bottom, or for that matter on the sides. As long as you are going to remove the sill, you should install proper flashing, ideally on all sides of the window, assuming there is none. Note the flashing detail on some of the previously posted drawings. In my experience, improper or non-existent window flashing is common, and over time leads to leaks and damage to the window framing.

 

You can get "composite" (plastic) sill, nosing, and brick mold at HD or Lowes around here. That's what I would use once you get the old mess prepped. It won't rot and has the appropriate slope to channel the water away from the window.

 

That's possibly the best solution, depending on what look you want to achieve, and whether you need to match in with the rest of the house.
Other methods include a brick or tiled cill as shown below.

 

sill details

I would cut out the defective repair and reform it with a smooth slope away from the window. Also put some sealant under the frame.
Ideally the cill should overhang the wall with a drip on the bottom as shown here.

Stuart 45, There is something I don't understand about the detail you posted. Where does the flashing go? Does it turn up behind the sill? if so, does the anchor pierce it? if not, what is the purpose of the flashing?