Window Sills

  • Nation wide deliveryNation wide delivery
  • Quality SlateQuality Slate
  • Made to MeasureMade to Measure

Slate Window Sills

Grey Slate and Stone Ltd manufacture made-to-measure slate window sills in  a variety of thicknesses and finishes.

Slate’s characteristics make it the ideal natural choice to protect your home. Our slate window sills are durable, with high resistance to acid and alkali. The surface is impervious, meaning water will not penetrate, ensuring the material is protected from frost damage, giving you and your home the protection it needs against the harsh British weather.

Please fill out the Enquiry form below with your requirements and one of our sales team will get back to you with a quotation.

If you would prefer to discuss your options with a member of our sales team first, please call us on 01766 514700, or use our contact form.

Window Sills Enquiry

Stage 1

Your Window Sills requirements

length x width

Please include includes a minimum 10mm overhang on each edge due to the fluted drip constructed in to the underside of the slate

20mm available in Cleft Black & Welsh Slate
Choose your sill detail
Your Project

Your Details

Please provide us with your necessary details.

you can upload a list of your required window size

Specifications & Options

joggles or horns


Slate window sills manufactured to your specific size and shape. We precision cut our slate to suit your window opening with an optional wrap around joggle to each reveal. Horns are cut in to each slate end so that it sits nicely in to each opening, and rendered. We do not recommend joggles for a stone clad build as the slate will sit inbetween each reveal.

profiled weathered slate sills

Profiled slate sills

Manufactured to your specific sizes, we precision cut and profile our slate to suit your project. Our profiled slate sills are all bespoke made with a seat or flat top for your window to sit on and a machined slope so the weather will not penetrate your home, with a fluted drip groove as standard. In order to produce this product we do recommend a minimum of 50mm thickness.

Plain Straight Slate Window Sills

Standard Sizes

Regarded as the most cost effective solution to your build, our plain straight slate window sills are available in most widths and lengths; rectangular in shape with a good choice of thicknesses. There are two types of finishes, a riven/cleft finish, or a smooth fine rubbed surface; all precision cut to your bespoke window or opening sizes.

Useful Information

What's available

Our custom made window sills come in two types: plain straight finish or a profiled option. Each product is available in various thickness from 30mm, 40mm, 50mm and 60mm with other thicknesses on request.

We recommend adding an overhang on the front edge of 50mm. This will allow enough overhang to accommodate a 6mm drip groove to the front long edge. This will prevent water from returning to your wall and staining over time. Joggles or horns can be cut into each slate end so that the slate wraps around each reveal.



Our slate should be fixed with a traditional sand and cement mortar bed. We recommend that a slurry mix should be painted on the back prior to fixing; this will allow the slate to bond to your wall safely and securely (see Slurry Mix method).

It is also recommend that each joint should be fixed with premium silicone mastic like our OTTO Seal S70 in either a anthracite or black color. It is a natural stone silicone guaranteed not to cause any migratory staining on natural stone, with excellent weathering and ageing resistance. Suitable for use outdoors and UV resistant.

If you have an queries about fitting please call our office on 01766 514700 and ask to speak with one of our team, who will be happy to answer any questions, and give advice on all aspects of fitting and aftercare of your slate products.

New 2 Otto Seal Logo