cracked window sill causes moisture patch on wall

[gregor]

A cracked victorian concrete window sill has caused the wall right below it to develop a wet patch, with a diametre of about 1metre. The moisture already shows up in the bedroom of the floor below. How would this be best repaired, we do not want to spend much money and Builders in London tend to quote a fortune. Could the crack in the sill be sucessfully repaired with the right mix of concrete ? Or is it better to cover the whole sill with a made to measure metal sheet ? or bitumen ?
Thank you for any advice

 

[Gervase]

Getting the right mix of concrete would be tricky, as Victorian concrete is very different to today's stuff. This might be one area where an epoxy filler like Plastic Padding would work. When you mix the two ingredients together, add some ground or crushed cement matching the colour of the stuff you're filling to make a thick paste and fill the crack with that.
Before it sets hard, scrape off any excess and you should then be able to finish it with a sanding block once it's set.
It may also help to look at the junction between the bottom of the window and the sill to see if there's water penetration there, and sealing accordingly.

 

[gregor]

Thank you Gervase. I will consider this method. Have you, or do you know someone who has already successfully appplied that method ?

 

[Gervase]

Not on concrete, though I have done it with slate (where cracks in sills tend to run horizontally rather than vertically). It worked well, bonding the material, filling the crack and making it watertight.
How light in colour is your concrete? Some two-part epoxy fillers are quite dark in colour, so you may want to experiment with a lighter binder - powdered chalk perhaps - to match the colour.

 

[gregor]

The concrete sills are light grey, although this particular one has been painted white. Do you mean I should mix powdered chalk into the epoxy filler.

 

[gregor]

I had finally access to my upstairs neighbours flat. To my surprise the sill did not look that bad from the top. The real cause of the water patch on the wall is a dripping pipe under the neighbours kitchen sink.
:? Thank you for the good advice anyway and sorry about the wrong diagnose

 

[Moo]

Nothing to be sorry about. You've provided a v. useful object-lesson in not jumping to conclusions, and always searching for the actual source of the wetness.

 

[gregor]

it is also a lesson that we should not always believe to our neighbours. I initially ruled out a water leak only because my upstairs neighbour has assured me that the plumbing has just been checked by a surveyor and there is nothing wrong with it. :evil: