City and Guilds PowerPoint Unit 210 Defects

Level 2 Diploma in Site Carpentry

© 2013 City and Guilds of London Institute. All rights reserved. 1 of 23

PowerPoint presentation

Defects

Unit 210: Carry out carpentry maintenance



Defects

Defects can be caused by:

• Insects

• Fungi

• Conversion

• Seasoning



Fungal defects

Blue stain Dry rotWet rot



Dry rot

• Dry rot is serious and is more difficult to eradicate.

• Caused by timber having a moisture content above 20% and bad or no ventilation

• Timber loses its strength & becomes dry & powdery



Fungi

Fungi spread through & over the surface of the timber forming a mat of cotton wool like threads



Fungi

Spores will even spread through and over brickwork causing structural damage if left untreated.



Fungi

When the fruiting body is fully ripe it starts to discharge millions of spores that attack more vulnerable timber.



Control Measures

• Locate and rectify the source of dampness.

• Cut out and remove all decayed timbers with a minimum margin of 600 mm beyond last evidence of fungal decay.

• Replace timbers according to building regulations.

• Thoroughly clean down all exposed areas.

• Treat all timbers with a preservative.

• Treat all other surrounding areas with a suitable fungicide.



Wet rot

Typical tell tale signs that wet rot problem include the following:

• Look for very dark, damp wood/timber. Prod it with a sharp implement such as a screwdriver. If the wood is very soft and pulpy, this is typically wet rot in progress.

• Often wet rot fungus is largely black and typically localised

• Look out for dry timber that is easily cracked and crumbles into fine particles



Wet rot

Thank fully, wet rot rarely gets to the stage of structural defects and typically it can be treated by repairing the source of the moisture ingress and drying out the affected timbers.

However, where any affected timber has lost its strength, it is best to remove he timber and replace it with new timber treated against the potential germination of wet rot spores.

The critical element however is making sure that all the affected areas are treated or wet rot problem will return.



Insect attack

Most of the damage done to timber in the UK is caused by 5 species of insect or woodworm.

• Furniture beetle

• Death watch beetle

• Powder post beetle

• House longhorn beetle

• Weevil



Types of insect

WeevilFurniture beetle

Death watch beetle

Long horn beetle

All these beetles invade and consume wood and then leave when they have reached maturity.



Woodworm

Woodworm refers to the larvae of all wood boring beetles.

Within the woodworm lifecycle, there are 4 main stages :

1. Woodworm begins breeding 2. Woodworm larvae hatch 3. Woodworm larvae start to eat 4. Larvae turn into woodworm beetle



The woodworm lifecycle



Timber preservation

All timber contains food on which fungi & insects live.

The idea behind timber preservation is to poison the food by applying a toxic liquid to the timber.

There are 3 main types of timber preservative.



Coal tar oils

• Derived from coal and are dark brown in colour.

• It should only be used externally.

• It is not available for general public use & strict controls of its use are in place because of

• Its carcinogenic properties.

• Substitutes are available.



Water – soluble preservatives

• Are toxic chemicals

• mixed with water.

• They are suitable for both internal & external use

• are odourless.

• They are prone to leaching out of the timber in wet conditions.



Solvent preservatives

• Toxic chemicals mixed with solvent spirits.

• The spirits evaporate after application.

• They are flammable.

• Some have a strong odour.

• They are more expensive but have durable preservation properties.



Methods of applying preservatives

Brush application.

Only a surface coating is achieved.




Spraying.

A better & quicker method of application but again only surface coating is achieved.




Dipping or immersing the timber in a tank of preservative.

The depth of penetration into the timber depends on how long the timber is immersed.




Pressure treatment is the most effective form of timber preservation as all the timber is coated.

The timber is placed in a sealed cylinder were the preservative is forced into the cells of the timber under pressure.



Any questions?

Education

City and Guilds PowerPoint Unit 210 Defects