Sunday, January 5, 2014


Causes -
* Defective construction, e.g. broken roof tiles; no damp-proof course.
* Installation of wet timber during construction, e.g. framing sealed behind plasterboard linings; wet joists under floor decking.
* Lack of ventilation, e.g. blocked air bricks to suspended timber ground floor; condensation in unventilated roof spaces.
* Defective water services, e.g. undetected leaks on internal pipework; blocked or broken rainwater pipes and guttering.

General treatment -
* Remove source of dampness.
* Allow affected area to dry.
* Remove and burn all affected timber and sound timber within 500mm of fungal attack.
* Remove contaminated plaster and rake out adjacent mortar joints to masonry.

Note: This is normally sufficient treatment where wet rot is identified. However, where dry rot is apparent the following additional treatment is necessary:

* Sterilise surface of concrete and masonry.
Heat with a blow torch until the surface is too hot to touch.
Apply a proprietary fungicide† generously to warm surface.
Irrigate badly affected masonry and floors, i.e. provide 12mm
diameter bore holes at about 500mm spacing and flood or
pressure inject with fungicide.

- 20:1 dilution of water and sodium pentachlorophenate, sodium orthophenylphate or mercuric chloride. Product manufacturers' safety in handling and use measures must be observed when applying these chemicals.

Replacement work should ensure that new timbers are pressure impregnated with a preservative. Cement and sand mixes for rendering, plastering and screeds should contain a zinc oxychloride fungicide.

Further reading -
BRE: Timber pack (ref. AP 265) † various Digests, Information
Papers, Good Repair Guides and Good Building Guides.
In-situ timber treatment using timber preservatives † HSE Books.

Ref: Bldg. Regs. Approved Document C, Site preparation and resistance to contaminants and moisture.

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