Sand mastic repair
Burnt sand mastic: the traditional wind- and watertight joint between stone and timber windows and doors.
Two hundred years of use
A method that has never been surpassed
This method of fitting timber frames to openings in traditional masonry buildings has never been surpassed. Burnt sand mastic was the original mastic for junctions between masonry, render and wooden windows and doors, and was also used extensively for leaded or metal-framed windows up and down the length and breadth of the United Kingdom and Ireland for at least 200 years. It fell out of favour because it required mixing on site.
The emerging DIY market developed more user-friendly but significantly less durable off-the-shelf products with a much shorter lifespan — an often-repeated short-term solution, now clearly recognised as ineffectual and not fit for purpose without constant maintenance.
How it works
A wind- and watertight flexible joint
Traditional windows set behind a masonry rebate are not fixed in any way to the outside masonry. They are wedged and held from the inside — by battens for lath and plaster, by plaster on the hard with plaster straight into the woodwork, or by window shutters. In all cases the window frames themselves are free.
They were often face-bedded around the frames with hairy lime plaster to ensure full contact with the rebated masonry detail, and then pointed up externally with burnt sand mastic to form a long-lasting, completely wind- and watertight flexible joint between the outside masonry and the timber frame. This method of fitting timber frames to openings in traditional masonry buildings has never been surpassed, and should not be altered.
Window mastic failing?
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