Stone windowsill repair

[nero44]

Hello,
the window sill on my rear window is quite old and has been painted over many times. I can't see any hints of cracks or so, but over time with flaking paint etc. it has developed a very uneven surface, which collects spots of water when it rains. See picture below. I don't have access from the outside, but looking for some ideas to flatten/smoothen the sill on the top, so it does not collect water and develops moss, like the one in my front window (second picture).

Could I just use a good amount of toupret exterior filler to lay a flat (maybe even slightly downward sloping) new surface on top and coat this with zinsser primer followed by a coat of outdoor masonry paint? Or will I do more harm than good?

Rear

Front

 

[Ivor Windybottom]

Anything you put on top will only stick as well as the paint already isn't, so could blister or flake off.

If you're really bothered by it then it could be chemically stripped back, taking great care to cover the walls below and those solar panels.

Or just put a nice thick gobby coat of paint over. I've previously had good results using Sandtex textured paint to hide blistered old masonry paint, making it look deliberately textured rather than trying to make it smooth.

Have you put a level on the outer surface? Hopefully it slopes outwards to shed water, if not then it will always go green if water is collecting on it.

 

[Koolpc]

You could fix a upvc sill on top. Cut correctly and sealed will last a lifetime.

 

[nero44]

Or just put a nice thick gobby coat of paint over. I've previously had good results using Sandtex textured paint to hide blistered old masonry paint, making it look deliberately textured rather than trying to make it smooth.

Have you put a level on the outer surface? Hopefully it slopes outwards to shed water, if not then it will always go green if water is collecting on it.

Thanks I might try this. I actually still have half a can of sandtex masonry paint from painting another window . The sill is fairly level, so water does not run off easily, hence my idea to put a layer of exterior filler with a slight slope, but maybe a thick coat of paint will do. I will need to wait for a few dry and sunny days to make sure it has the chance to dry/cure properly...

You could fix a upvc sill on top. Cut correctly and sealed will last a lifetime.

This is also a brilliant idea. I can always put this on top of anything in case I am not happy with any paint layer. The window is south facing though, so reallly need something weather durable, including outdoor sealant.

Thanks both.