Burnt Sand Mastic

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Cornerstone Burnt Sand Mastic is a traditional jointing compound for forming joints between timber window and door frames, render or masonry.

Designed to harden slowly but remain flexible, Burnt Sand Mastic efficiently reduces the risk of cracking when forming joints.


SKU: N/A Category: Tag: Brand: Cornerstone


Supplied in two parts, burnt sand and oil driers, 16kg of sand and 2.5L of oil blend, this provides a volumetric mix of 4 parts powder to 1 part oil, the standard mix ratio. Burnt Sand Mastic adheres tenaciously to most surfaces. Please note that colours represented online are indicative.

Cornerstone Burnt Sand Mastic is available in 12 colours, with the ‘Standard’ colour held in stock and ready to order.


The extended Burnt Sand Mastic colour range is made-to-order, with an estimated lead time of up to five working days.

Please note that colours represented online are indicative. Images may vary slightly from actual products due to these natural variations and screen resolution.

For use where timber joins render or masonry.

The Burnt sand mastic is combined with a mixture of oils and driers (supplied with the sand mastic) on a clean surface, mix thoroughly using the minimum amount of oil. (If the mix is over wet, let it stand in a warm place for a few hours to stiffen up then remix vigorously before use).

Once mixed with oil driers, mastic will harden. Mix only that which can be used in a few hours.

Before pointing ensure that all wide gaps between the frames and the masonry are tightly packed with well haired lime mortar that has been allowed to cure and harden. (This was the original material used to bed window frames). In some circumstances inert filler boards of suitable packing can be used. Keep the joints slightly recessed 4-5mm. Take a small painters fitch brush and apply a light primer coat of the supplied oil dryers to the frame and the adjoining masonry surface, making sure that the line of the proposed mastic joint is maintained. Do not over oil surfaces.

Working with a mastic box or a small hawk and a proprietary mastic trowel press the mastic firmly into the angle of the frame / jamb and filling from the bottom up, forming the mastic joint to a neat 45 degree angle. Keep tools wiped with an oiled cloth during the application. After forming the angle, starting from a corner, press a clean oiled mastic trowel tightly against the face of the timber frame and masonry jamb and carefully press and draw the trowel to create a neat regular fillet. Clean away any excess mastic and wipe the finished timber edges on completion.

For mastic to sills, ensure the mastic does not bridge any drips and is left recessed behind the drip check. Mastic should not be over painted. Mastic fillets should be neat 20 – 25mm across the diagonal face, mastic should not be used to make up damaged arises or defective renders, these deficiencies should be repaired properly before mastic work commences.

See the Technical Data and Documentation section for more detailed product information, application guidance and datasheets. Always read the available datasheets and guidance before use. Each project is unique; always seek professional advice before undertaking a project.

Always read the available datasheets and documentation before use.

Pallet orders with Palletforce Economy are typically dispatched from Cornish Lime within 1-2 business days, providing your item is in stock and not made-to-order. Once dispatched, Palletforce will deliver your order within 3-5 business days, depending on your location. Please ensure that your site can accommodate articulated lorries or similar-sized vehicles.

Local Delivery
The Cornish Lime team provides local delivery with a 12-tonne vehicle with a crane to assist with unloading. You will be contacted by phone to arrange delivery and ensure your site can accommodate our vehicle.

APC Parcel Courier
Orders shipped by APC parcel courier are typically shipped the next business day and arrive within 2-3 business days, providing your item is in stock and not made-to-order. APC will contact you via email with delivery information, and orders can be tracked on the APC website.

Premium or Expedited Service
For a premium or expedited delivery service, please get in touch to discuss if this option is available for your order.

For further information, see our delivery information page.

Colour Comparison

Colours and textures can look different on a computer screen. We recommend viewing or purchasing a sample before ordering.

  • Large Images
  • Small Images
  • Standard
    £35.99 £43.19 inc VATSelect
  • WhiteBurnt Sand Mastic in colour 'White'
    £75.47 £90.56 inc VATSelect
  • ParchmentBurnt Sand Mastic in colour 'Parchment'
    £63.86 £76.63 inc VATSelect
  • PointingBurnt Sand Mastic in colour 'Pointing'
    £63.86 £76.63 inc VATSelect
  • LinenBurnt Sand Mastic in colour 'Linen'
    £63.86 £76.63 inc VATSelect
  • SawdustBurnt Sand Mastic in colour 'Sawdust'
    £63.86 £76.63 inc VATSelect
  • Burnt TanBurnt tan burnt sand mastic
    £35.99 £43.19 inc VATSelect
  • Brick BrownBurnt Sand Mastic in colour 'Brick Brown'
    £63.86 £76.63 inc VATSelect
  • Earth BrownBurnt Sand Mastic in colour 'Earth Brown'
    £63.86 £76.63 inc VATSelect
  • Saddle BrownBurnt Sand Mastic in colour 'Saddle Brown'
    £63.86 £76.63 inc VATSelect
  • Khaki GreenBurnt Sand Mastic in colour 'Khaki'.
    £63.86 £76.63 inc VATSelect
  • Smoke GreyBurnt Sand Mastic in colour 'Smoke Grey'.
    £63.86 £76.63 inc VATSelect
  • BlackBurnt Sand Mastic in colour 'Black'.
    £63.86 £76.63 inc VATSelect


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Burnt Sand Mastic is a traditional jointing compound made of burnt sand and oil for forming joints or sealing time windows or door frames with the surrounding masonry or render. We always advise using a burnt sand mastic instead of a modern non-breathable sealant when working with lime.

Burnt sand mastic takes some time to fully cure and harden, although this is temperature dependant. Generally, we recommend protection from environmental conditions, including direct sunlight, wind, and rain, stays in place for one to three weeks.

Burnt Sand Mastic typically doesn’t require painting. The Cornerstone range of Burnt Sand Mastics is designed to provide colour options that will ideally suit most structures. However, if a particular colour is required, we can colour-match the burnt sand mastic for you, as most paints will not bond to this material. Get in touch with the team if a colour match is of interest.