Leaking window sills

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Would once again like to ask for the wisdom of you lovely people in a minor issue we need fixing in our house.

So, here’s the issue. We have a number of “sectional”, flat cement windowsills on our property that have been badly fitted. They are flat (i.e. no slope so water just sits or runs down the joints) , no mortar between the sill blocks and apparently (do to the vast amount of rainwater water leaking into the house) no DPM beneath the sills!

Ideally I would take the sills off (at least 4 of them) and put a DPM beneath them. Unfortunately, its an issue I’m not going to be able to fix myself in the short term requiring scaffolding and more money than I have at the moment, so looking for a fix to last me a few year whilst I squirrel some pennies together.

So far my thoughts have been:

1: Take off the sills put a DPM underneath and replace, preferably for something more attractive. Fairly sure I cant afford this option at the moment as will need scaffolding at a minimum and someone else to help given the size of the sills!

2: Put some form of oversill onto the existing, but concerned a UPVC prophylactic for my sill isn’t going to look very good and probably isn’t that cheap either!

3: Flashband, some form of paintable flashband. Again not ideal but probably my preferred option at the moment given the low cost and relative ease.

Would much appreciate any other suggestions if anyone has one!?
 

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Maybe cover sills in tiles. Although I'm not sure about that.
Or
Masking either side of joints and fill with epoxy. I've used chemical fixing in the past. Pull tape as it's setting.

Don't know if I'm helping but all I can think of.
I have fixed upvc leaks by foam injection
 
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Cheap and cheerful- just buy some tubes of MS Polymer (eg CT1 or Sikaflex) and fill any possible gaps. They are almost as flexible as silicone but can be over painted and can be applied to damp surfaces. CT1 is available in a number of different colours.

It might be advisable to check the old silicone seals though. They may have failed.
 
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I would:

1) cut a small V in those joints, to create somewhere for mastic, then use a modified silicone polymer filler.

2) I would dig out that silicone at the back and redo

3) usually upvc windows without external cills have face drainage holes -do you have those and is water getting through the upvc window seals and running inside
 
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