Damp/Timber Decay

Question 1

What causes damp?

Answer 1

Rising groundwater

Penetrating rainwater

Leaking plumbing/mechanical services

Condensation

Question 2

What methods can be used to test for damp?

Answer 2

Carbide Meter

Thermography Imaging

Electrical Resistance Meter

Capacitance Meter

Question 3

What is rising damp?

Answer 3

Water ingress that travels up walls through capillary action where there is no, or a failed, DPC.

Question 4

What are the signs of rising damp?

Answer 4

Tide marks stopping at around 1.5m (due to evaporation).

Finishes peeling off.

Mould can have a musty smell.

Question 5

What are the remedies for rising damp?

Answer 5

Stop the water if possible.

Physical insertion of DPC, requiring access to both sides. This might interrupt services and is very costly.

Chemical injection - holes drilled at 120mm centres, low pressure chemical cream injected, external holes plugged.

Question 6

How can the source for penetrating damp be found?

Answer 6

Die testing.

Question 7

What is interstitial condensation?

Answer 7

When warm, moist air penetrates inside a wall, roof or floor structure, reaches its dew point and condenses into water.

Question 8

How can you diagnose interstitial condensation?

Answer 8

Due to its concealed nature within building elements, interstitial condensation is difficult to visually identify.

Question 9

What are the remedies for interstitial condensation?

Answer 9

Ventilate the area to prevent the build up of warm, moist air. A vapour barrier can be installed to prevent warm, moist air travelling into the building element. However, this may lead to surface condensation.

Question 10

What is the the most common form of wet rot?

Answer 10

There are six common wet rot fungi, the most common being Conrophora Puteana.

Question 11

How can you identify wet rot?

Answer 11

Most wet rots are brown in colour and can be identified with cuboidal cracking and cracking running longitudinally with the grain.

White rots turn the affected timber fibrous and pale in colour.

Question 12

What tool should be used to identify wet rot?

Answer 12

A moisture meter should be used to identify the full extent of the area of the rot.

Question 13

What causes wet rot?

Answer 13

Continuous damp conditions.

Question 14

What is considered ‘damp conditions’ to facilitate the growth of wet rot?

Answer 14

A moisture content of over 25%

Question 15

What is the name of the fungus otherwise known as dry rot?

Answer 15

serpula lacrymans

Question 16

How can you identify dry rot?

Answer 16

A surface veneer of sound wood is retained over the decay, making the visual identification more difficult.

Other signs included fungal growth (large brown mushroom-like fruiting bodies with a white margin), a strong musty smell, cotton wool-like vegetative strands (mycelium) that are grey and brittle when dry, red/brown spore dust and crumbling of dry timber (cuboidal cracking tends to be larger that that of wet rot).

Question 17

What are the causes of dry rot?

Answer 17

Timber coming into direct contact with water where the fungus can grow in a cool (0-25C) and moist (20-40% humidity) conditions.

Question 18

What is the difference between the fungus causing wet and causing dry rot?

Answer 18

The fungus causing dry rot has spores which can survive interruptions to its living conditions and its mycelium can spread across masonry to attack other areas of timber.

Its spores can remain dormant for several years waiting for water to be reactivated by the return of the damp conditions.

Question 19

What are the remedies for dry rot?

Answer 19

A detailed survey should be undertaken to identify the full extent of the area of rot to timber and masonry.

Remove the source of the water and heat/ventilate the area.

Follow the guidlines in BRE 299.

Remove the affected materials (450mm either side) and burn.

Remove mycelium and chemically treat the exposed masonry.

Replace structurally weakened elements with pre-treated timber and clean clean existing timber with organic preservative.

Question 20

Which insects cause infestation issues most commonly in the UK and how do you diagnose their presence?

Answer 20

Furniture Beetle (woodworm) - attack both hardwood and softwood. Leaves small flight (exit) holes that will only structurally compromise the timber in large numbers and over a longer period (years).

Deathwatch Beetle - attacks both hard and softwood. Leaves a thin shell of sound timber that can conceal the decay. Can be heard when in mating season. Egg and frass (digestible waste) can be visible.

Longhorn Beetle - mainly attacks softwood. Leaves a thin shell of sound timber that can conceal the decay. Can be heard gnawing during warm weather. Egg and frass (digestible waste) can be visible.

Question 21

What causes the insect infestation?

Answer 21

Insect eggs are laid in the timber grains and larvae feed on the wood before leaving as adults.

Question 22

What is the remedy for insect infestation?

Answer 22

Specialist timber treatments such as pressure impregnation, liquid/paste treatment, gas fumigation/smoke treatment and heat sterilisation can prevent new infestation. In severe cases, pre-treated timber replacement is required.