DIY question.

[longers]

What to use please? It's a lumpy lump of stone with tatty paint on at the minute.

 

[Night Train]

There probably isn't a lot you can do with the lumps in the stone but a scraper will knock off the loose paint. mayeb a wire brush will shift the rest. Any remaining stubbon paint could then be sanded to smooth edges of the paint enough to paint over.

Best not to use a chemical stripper as the stone may be porous.

The costler option would be to sand blast it.

 

[Brains]

What to use please? It's a lumpy lump of stone with tatty paint on at the minute.

I'd assume like most window sills it's got 100 years of paint on it
With a paint scraper scape off all the loose paint.
Then using a sander with fairly course sandpaper rub down the rest, you are trying to give it a smoothish surface
Then using something like polyfiller (not flexible one, the hard one) fill all the divots and ensure the places where the paint has come off down to the stone are filled and given smooth edges
If there are major chips put of the sill edges these can be filled with polyfiller as well.
The professionals often use offcuts of (very expensive) Amtico lino flooring to give a sill a perfect edge and then fill all the lines so that it looks perfect
Then paint. It will be several coats of a good quality exterior masonry paint.
The perfect time to do this job is mid summer, but hey ho.

 

[longers]

The perfect time to do this job is mid summer, but hey ho.

Yep, maybe it'd be best to get rid of the loose stuff and give it a quick couple of coats for over winter?
Very good advice for when I do get to do a proper job, thankyou.

 

[Aperitif]

Hello Mark,
When I used to be 'in the trade' and repairing windowsills, stucco, and wanting something good and easy to 'finish', I used Toupret products. Expensive, but easy to use and prepare for finishing.
Touprelith is the stone filler which gets you a result - in my experience. Powder which can be mixed as required, and 'prefers' being applied in the Autumn - not mid-Summer - or I should say, not in blasting heat.
Tack a batten on the leading edge if you have a lot of 'dinks' to make up - float the product on. It sands to a finish if you're not fussed about plumb edges etc - you know that bit though, I reckon!

 

[longers]

Thanks Martin, a kilo and a half bag isn't too dear if it's that good, it's the one in the yard so is seen most and if it ends up looking ok then I'd be happy to try and find some.

Does it have to be applied to totally bare stone or will a bit of persistent paint not be a problem?

 

[longers]

Also what'll be best to use as a window sealant once I've made a mess of that too? I've got a tube of bog standard silicon sealant but did see some fancier ones.

 

[Aperitif]

Scratchy sandpaper to give a 'key' will be fine - they must have a web presence with data sheets etc - they are a good co.
Do you mean sealing wood - concrete joint prior to painting? If so, I would use a decent decorators filler (which is acrylic based) - not silicone. If it was after painting, and the window was 'gappy' then maybe a low-modulus silicone over the top of everything painted - ie: if it was all white! And it would all be masked to give neat detailing - not a smudgy, smeary mess. Gentle remove masking tape just as the silicone begins to skin...
So, in short, decorators filler - let it harden and then 'cut in' a careful edge - less aggro

 

[longers]

Sorry, they're PVC. Different approach?

 

[Aperitif]

Sorry, meant to add the PVC addendum in there! If you still have detail to seal after prep and painting to finished, a low modulus neutral cure silicone will be your best bet. It takes a bit longer to skin over but will be nice and stretchy and last a long time. Don't use the 'sanitary' silicone (with the acetic acidy lovely taste) as it will not accomodate the varying coefficients of expansion so well and peel itself away from the joined surfaces eventually.
If I wanted a clean-cut line then 25mm masking tape would be my friend too. Painfully slow but pride in the job etc...