Prevention of Wet Rot at Whitburn Windmill using ProBor Boron-Based Wood Preservatives

Whitburn Windmill dates back to the 1790s and was built using stone from the local magnesian limestone quarries. It had fallen into disuse by the late 1870s, but was used during the World War II when an observatory post was built beside it to give warning of approaching enemy aircraft.

Major reconstruction was carried out by South Tyneside Council in the early 1990s, and this reconstruction won a Civic Award in 1994.

In 2001 the sail arms of the windmill broke during heavy gales. The fractures revealed wet rot travelling through shakes in the large section timber of the arms of the sail and within the tenon joints.

Work Carried Out

Because of the extent of the structural damage caused by the wet rot, it was decided that the existing sails would have to be replaced with new sails manufactured from douglas fir.

It proved impossible to source pre-treated douglas fir of the large dimensions required, so the new sails were constructed from untreated timber, and treated with ProBor wood preservatives at the joinery shop. This treatment was carried out by MGM Preservation of Newcastle.

ProBor products were selected because of their ability to penetrate right into the timber, offering maximum protection against wet rot. 10 mm diameter holes were drilled in each sail arm in a double row at 150 mm centres. These holes were then injected with ProBor 50 paste. Douglas fir dowel pellets were then used to cap off each hole. The completed sails were then sprayed with diluted ProBor DB and then painted to seal in the preservative and give the required finish. The sail cap roof and floors were also treated with ProBor DB. ProBor DB is now a discontinued product which has been superseded by the ready-for-use version of the product, ProBor 10.