Woodworm treatment of Japanese Mynkah House at The Royal Botanical Gardens, Kew, UK

Oak-framed building specialists, McCurdy & Co had been asked to import and reconstruct a traditional Japanese “Mynkah” house to form the centrepiece of the Japan 2001 Bamboo Garden at Kew Gardens. The Mynkah house is constructed from a timber frame (Japanese Cedar, Scots Pine, and Elm) with lashed bamboo poles supporting the roof. The roof is a thatched construction. Gaps are left at the gables to allow smoke to escape. In Japan, the roof-void has many uses, such as smoking fish and raising silkworm. The timber frame is in-filled with oak lathes to form panels and then rendered with a mud-straw mix. Before leaving Japan, the entire construction had been fumigated by heating over cedar-wood smoke. This should have raised the temperature of the timber to over 90°C and killed off any insect infestation.

The Problem

While the building was being reconstructed at Kew, beetles were noticed emerging from holes in the wood. Inspection revealed two distinct types of wood-boring insect infestation. The first was a classic House Longhorn pattern with large oval tunnels confined to the sapwood of the softwood. The other insect involved was widespread and much less easy to identify. Emergence holes were 3 – 4 mm wide with the pattern of damage being similar to Deathwatch beetle (albeit in softwood) and Jewel Beetle.

Work Carried Out

Because of the uniqueness of the building in question, and due to the risk of introducing a foreign species of insect, it was decided to treat the timber frame with ProBor DB. This borate-based product is supplied as a concentrate, but dilutes on site with water. When applied to the surface of the timber, it delivers a 10% borate solution. As the moisture content of the timber was only 10% WME, the active ingredient will not diffuse into the timber at any appreciable rate, but will remain in a concentrated band in the outer 10 – 15 mm of the timber, like a conventional insecticide. This protective “envelope” will kill any insects, as they try to emerge from the timber.