Womersleys Burnt Sand Mastic

Womersley's Burnt Sand Mastic is ideal for pointing around windows and doors (timber or metal). Burnt sand mastic adheres tenaciously to most surfaces and has been used for over 200 years in building construction and renovation. At Womersley’s we follow the traditional method of preparation by roasting fine silver sand and supplying with a linseed oil which has been double boiled with rosin driers added.

Preparation:

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 circumstance inert filler boards or suitable packing can be used. Keep the joints slightly recessed 4-5mm. Mastic should not be used to make up damaged or defective stone or render. These should be repaired before with natural stone repair and / or lime render products. If the masonry has a high surface absorbency use tape to protect and mask the masonry to prevent undue surface spread.

Timber frames should have loose flaking paint removed and be fully primed and undercoated before applying the finished mastic, ideally wood work is best fully finished, although a final finishing coat may be left until the mastic has properly set.

Application:

Burnt sand mastic is a two-part product. For each litre of burnt sand add approximately 200ml of the double boiled linseed oil hardener. Add only a little at a time and mix until the mastic forms a thick putty like consistency, which comes cleanly off the mixing trowel. Let the mix stand on a board for 15 minutes and use any excess oil which runs off plus any remaining oil as a primer, applied with a brush to the frame and adjoining masonry. Check the absorbency of the masonry, repair or render with water as the mastic is oil bound and high absorbency may occasionally result in bleeding from the mastic into the surrounding masonry.  If the masonry has a high surface absorbency, use tape to protect and mask the masonry to prevent undue surface spread

If the mastic mix is over wet, let it stand for longer to allow it to stiffen up and the remix vigorously. Apply the mastic whilst the primer still feels oily or tacky to touch. 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 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

Womersley’s Burnt Sand Mastic is available in Buff, Red, Yellow and Umber

Coverage = Approx' 1Kg at 10m to a 5mm joint