timber defects Flashcards
how does water naturally and artificially affect timber?
natural - rain, snow frost, dew, ground water, solubility, absorption
artificially - condensation, leaks, splits
how do mechanical processes affect timber naturally and artificially?
natural - applied loads, wind loads, impact, abrasion
artificial - impact, abrasion, vibration and applied loads
how do biologial and human processes affect timber?
biological - fungi, plants, insects and animals
human - abrasion, mechanical damage through fire use, fire vandalism and applied loads
What is moisture content?
The ratio of the weight of water to the weight of the moisture content.
At what percentage moisture content is timber susceptible to insect and fungi attack?
20% and above
What type of material is timber?
timber is hygroscopic
Timber is a hygroscopic material. What does hygroscopic mean?
Wood is a hygroscopic, meaning it is a material that absorbs water
What impact does excessive notching have on the strength of wood?
reduces the strength of wood causing structural issues and reducing load bearing capacity of the joists
what potential defects effect timber in house construction?
overloading natural defects within the timber itself - knots, resin pockets, weak and short grain, waney edge fungi wood boring insects water / moisture
Which organisms attack timber and why?
fungi and wood boring insects attack timber for food and moisture
what is the life cycle of fungi?
fruit body
spores
germination
mycellium
what is white rot?
wood develops fibrous consistency
tends to become lighter in colour
cracking in mainly along the grain
what is brown rot?
cuboidal cracking
wood becomes darker becomes dry and crumbly
what is the difference between wet and dry rot
all brown rots and white rots are know as wet rot
serpula lacrymans is known as dry rot
what is the life cycle of wood boring insects in timber?
larvae tunnel into wood, eating it pupa forms adult emerges through exit hole after emerging, adult mates and lays eggs larvae eggs hatch and process repeats
what is the most common insect attacking buildings? how big are adults?
how big are exit holes?
common furniture beetle
adults size 3-5mm long
exit holes about 1-2mm diameter
what are characteristics of the house longhorn beetle relating to timber
causes relatively severe damage
limited to some home counties
up to 24mm long
oval shaped exit holes 6-10mm diameter
what are characteristics of the death watch beetle relating to timber?
commonly associated with historic buildings
usually only attacks damp decayed timber
adults 6-9mm long
round exit holes 3mm diameter
What factors must be dealt concerning insect attack?
changes in environment may cause insects to die out
inertial treatments are intended to kill existing attack and leave a layer of poison against future attack
adverse effects of treatments on humans and other creatures need to taken in account
what are the size of upper floor timber joists dependant on?
expected loading
spacing between joists
required span
why is timber in houses the most suitable material?
it is readily avaialable it is relatively cheap it is easy to cut and shape fixings are easy timber is relatively easy to repair or alter
what factors affect the risk of damage by timber pests?
the natural durability of the species of timber
the food value of the timber
adverse environmental conditions - moisture content of timber
the protection afforded through any treatment by chemical preservatives
how are some timbers naturally resistant to fungi attack?
this durability is determined by the presence in the tree of naturally occurring substances which are toxic to fungi
How what are advantages and disadvantages of preservative chemicals relating to fungi attack?
can reduce the risk of fungal or insect attack
there are financial and environmental costs that come with their use
