Removing broken cast stone window cill

[Lincolnshire Ian]

Hi folks

I need to replace a cast stone window cill following an accident with a scaffolding plank (see picture). 

As the wall is rendered I clearly need to do whatever needs doing very carefully. 

To remove the cill I am planning to protect the surrounding area with plastic sheeting to avoid getting dust on the render. Then use a combination of drill and grinder to remove the damaged unit as carefully as possible. 

Can anyone think of a way to improve upon my approach?

Many thanks 

[marshian]

4 minutes ago, Lincolnshire Ian said:

Hi folks

I need to replace a cast stone window cill following an accident with a scaffolding plank (see picture). 

As the wall is rendered I clearly need to do whatever needs doing very carefully. 

To remove the cill I am planning to protect the surrounding area with plastic sheeting to avoid getting dust on the render. Then use a combination of drill and grinder to remove the damaged unit as carefully as possible. 

Can anyone think of a way to improve upon my approach?

Many thanks 

 

Can you not glue the broken piece back on? 

[Redbeard]

38 minutes ago, marshian said:

Can you not glue the broken piece back on? 

My thoughts too, though it depends on how many pieces the 'piece' is in. Many people have a lot of success with epoxy. If you have the piece as a whole piece you could try drilling holes for, say, 3 dowels in the main cill, bed the dowels in epoxy in  those holes, and drill corresponding, perhaps slightly oversized, holes in the broken piece, clean and 'butter' the faces with epoxy, then breathe deeply and  and press together. If you are lucky the reveal could help wedge it together.

 

Optimist's view: Done!

 

Pessimist's view: (Just refuse to entertain that view!)

[Mr Punter]

Yes, just stick it back on with adhesive from a mastic gun.  I would not bother with dowels etc.

[Redbeard]

15 minutes ago, Mr Punter said:

I would not bother with dowels etc.

 

But I am a pessimist! And someone for whom wonder-glues rarely do what they say on the tin/cartridge/tiny tiny little tube...

[Russell griffiths]

I would look at a multi tool blade that is longer than standard with a tungsten edge to it 

go under the cill and plunge in for the full depth 

then cut out the mastic under the window. 
good luck. 

[crispy_wafer]

Wonder if one of those magicman outfits could effect a repair on something like this.

 

a quick google and this bod has done something with a cast stone corner block

 

https://magicman.co.uk/examples/

[Bonner]

Another vote for glue, two part epoxy and dowel (stainless or brass)

[torre]

Another vote for epoxy glue if you have the other piece intact as it'll save loads of effort. I think you may find it hard to align into position as tightly once you've put a dowel in though

[markc]

2 hours ago, Bonner said:

Another vote for glue, two part epoxy and dowel (stainless or brass)

To expand on the dowel - definitely worth doing but masonry style, not close fitting or you will never get it aligned as mentioned above. Drill a couple of holes in both sides fairly well aligned and use screws or pieces of wall tie as the dowels (loose in holes). Once happy it will push back into place, glue on the faces and in the holes and push it in place. If you must remove the Cill, a carbide reciprocating saw works well

[Lincolnshire Ian]

Thanks for the responses everyone. The break wasn't clean, lots of little bits which are dispersed in the scaffold mat. Gluing isn't an option. I have a new piece being delivered on Monday. 

[marshian]

52 minutes ago, Lincolnshire Ian said:

Thanks for the responses everyone. The break wasn't clean, lots of little bits which are dispersed in the scaffold mat. Gluing isn't an option. I have a new piece being delivered on Monday. 

 

Gutted for you - good luck with removal and replacement - hope it goes perfectly

[Nickfromwales]

On 28/01/2026 at 20:43, Russell griffiths said:

I would look at a multi tool blade that is longer than standard with a tungsten edge to it 

go under the cill and plunge in for the full depth 

then cut out the mastic under the window. 
good luck. 

Defo this. 
 

Use a battery multitool and have a hose running to manage dust. It’ll wash off the render if it’s not left to settle. Leave the section held captive by the render, and mastic the joint to recreate the weathertight seal. 
 

Be sure to multitool the full length of the underside of the bit you need to remove so you can lift it away from the render. Don't simply hope the render will be ok if you just lift the cill up and away. It needs to be disconnected by you just multitool’ing inti the render for maybe 5mm or so.

 

Steady hands and lots of time and patience invested here will make this quick and simple. Rush it and you’ll be into another few cans of real ugly worms.