Concrete Windowsill question

Possom1

If having small concrete windowsills replaced (not an unusual shape) I know there is the option of either buying ready-made sills or alternatively having a joiner build wooden boxes and the concrete poured in.

With the second option, the finish is not as smooth and also it's more expensive as the joiner has to be paid.

Is there any advantage in using this method as opposed to simply having ready-made sills fitted?

bonzodog2

Pretty easy to make DIY with planed timber, no need to employ a joiner, IMHO. Add a v-shaped strip for a drip groove. Fit together with screws or nails not fully driven home. Oil the inside, plaster side faces with 4:1 mix then add concrete to inside. Ensure adequate support while drying. Knock off timber carefully after a couple of days.

Possom1

Thanks. Even if the DIY method is used, without a joiner, is there any advantage to doing this as opposed to purchasing ready-made concrete sills?

Robbie.G

Possom1 wrote: »

Thanks. Even if the DIY method is used, without a joiner, is there any advantage to doing this as opposed to purchasing ready-made concrete sills?

It depends on the house would precast ones look ok or does it have to be cast in-situ sills.
The cheapest option is precast.
You have to remove window remove old sill fit new sill refit window and plaster up everything so there's a fair bit of work in it.

Possom1

Robbie.G wrote: »

It depends on the house would precast ones look ok or does it have to be cast in-situ sills.

The sills are certainly decades old, and are somewhat 'stoney' within the concrete. Certainly not a smooth finish like new sills. I don't know if originally they would have been pre-cast or cast in-situ.

I suppose all new pre-cast sills nowadays will be quite smooth.

Robbie.G

Possom1 wrote: »

The sills are certainly decades old, and are somewhat 'stoney' within the concrete. Certainly not a smooth finish like new sills. I don't know if originally they would have been pre-cast or cast in-situ.

I suppose all new pre-cast sills nowadays will be quite smooth.

They will also be quite shallow in dept around 50mm.
You can get precast that look like old style sills which are fairly deep around 75-100mm
If it's a old house with deep sills change with like for like

Possom1

Robbie.G wrote: »

You can get precast that look like old style sills which are fairly deep around 75-100mm

Is it particularly that they are deep 75-100mm which makes them look like old sills?

Or is anything additional done, such as adding in more stones to make them look more stoney, or are these deep sills generally also smooth like modern sills?

Robbie.G

Possom1 wrote: »

Is it particularly that they are deep 75-100mm which makes them look like old sills?

Or is anything additional done, such as adding in more stones to make them look more stoney, or are these deep sills generally also smooth like modern sills?

They wouldn't have the smooth finish modern ones would they have a more rougher finish

Possom1

Robbie.G wrote: »

They wouldn't have the smooth finish modern ones would they have a more rougher finish

That's great, thanks!

Calahonda52

Op, if EWI is anywhere on ur radar maybe you should consider EWI "friendly"windowsillls now

Possom1

Calahonda52 wrote: »

Op, if EWI is anywhere on ur radar maybe you should consider EWI "friendly"windowsillls now

What's EWI?

Calahonda52

External wall insulation.
I see u are doing new windows as well.
Spreading the different questions around in different posts may be sub optimal from the perspective of getting the best from here.
U have separate ones on sills, on glass, on frames.
Handles?

Possom1

Calahonda52 wrote: »

External wall insulation.

No, I'm not considering external wall insulation.

jack of all

If a precast sill profile is available I would say that this would be a better option as the concrete will be denser and have a better surface finish. These sills will have been made in steel or GRP moulds and the concrete is vibrated so there will be less chance of air entrapment (bubbles) in the the concrete which weakens the finished product and leads to a poor finish. Making formwork and casting sills requires some level of skill, if poorly done they can fail after a few years of exposure to the elements (especially frost). If you do decide to go down the formwork route ensure to include a good drip on the underside and make sure a good concrete mix is used and well tamped in place.