Draft no 2 of the Timber Basics article... I've added more sections
too. Lets see what you think.
The timber industry has long operated in imperial sizes, and imperial
terms are still in widespread use today. However legislation has
outlawed the sale of goods in inches and feet, so timber is marked as
the nearest metric size to the standard imperial sizes.
Most timber is bought in imperial sizes, with for example 2x4 meaning
2"x4", however sellers must describe it in metric and an increasing
amount of timber is bought as metric sizes.
For rough sawn wood the nominal size is usually very close to the real
size supplied. However this isn't so in all cases, especially when
dealing with used wood. Its not unusual to find historic 2x4s that are
nearer 1.5" x 3.5"
Planed wood is a little smaller than rough, usually by about ¼" or
5-7mm each way. 2x4 PSE is simply 2x4 rough sawn that has been planed
to make it smooth.
When timber is sold in metric, the stated size is the size you get.
Timber is sold in various lengths that are multiples of 30cm (a foot).
Most common are 6', 8' & 10'. Several longer sizes are also sold. Note
however that the metric equivalent lengths are very slightly shorter
than imperial, so if you need exactly 8', 2.4m is slightly short.
Most timber is sold by price per length, and some by price per cubic
foot. Some example price lists:
* http://www.tottontimber.co.uk /
These are not company recommendations
:Usually a splintery finish, but smoother sawn surfaces are seen on
:Planed All Round. There's no guarantee of accurate squareness with
PAR, a lot of PAR is true, some not. PAR has mostly been supplanted by
PSE today. Hand planing produces PAR.
:Planed Square Edge. This is planed all round with sides accurately at
:Canadian Lumber Standard. CLS is planed smooth, has rounded corners,
and is free of large knots at the edge of the wood. These features
reduce the spread of fire in [[Partition Wall|timber frame wall]]
cavities and make it safer to handle.
: American Lumber Standard, very similar to CLS
: Similar to CLS but the planed surface is not consistently smooth, it
may be rough sawn in areas.
;Kiln dried, KD
: timber dried to a specified moisture content. However poor storage
by the merchant (after drying) may result in higher moisture content.
Whitewood is spruce timber intended for [[First fix & second fix|first
fix]] use, ie domestic woodwork that will not be seen when the project
is complete. It may have some splits & stains and some warp.
[[Special:Allpages|DIY]] sheds sell a lot of whitewood.
The quality of whitewood on sale has improved over the years, and a
percentage is good enough for [[First fix & second fix|second fix]].
Spruce doesn't take dyes well, and preservatives have limited
Redwood is a grade of wood intended for [[First fix & second fix|
second fix]] use, ie domestic woodwork that will be seen when the
project is complete. Its mostly free from splits & stains, and
generally has much less warp than whitewood, though warp is still an
Redwood is generally spruce, fir or pine.
Joinery timber is clear, with a knot-free surface. Its used for
Grading is an assessment of the structural strength of the timber. Key
features assessed in grading are splits and knots, especially large
knots at the edge of the wood.
Small timber bought for [[Special:Allpages|DIY]] use is mostly
ungraded. Graded wood is stamped with the grading details.
For new floor joists and roofing one should use graded timber.
C16 is the most common grade, but C24 and some less common timber
grades are also available. The higher spec grades may be used where
dimensions need to be minimised.
Most wood used for [[Special:Allpages|DIY]] is spruce, fir or a pine.
Other species are also used, but command a higher price, limiting
Ordering wood to be delivered means you don't pick the timber. This is
ok for [[First fix & second fix|1st fix]], but with work where the
wood needs to be straight it can be a problem, timber yards are known
for sometimes using new customers to clear junk.
Bent stock is a regular problem.
Selective cutting or 'docking' deals with a lot of warp. Wood often
warps at points (knots) rather than all along, so cutting it at those
points gives shorter pieces of straight wood.
In principle warp can also be straightened by [[Adhesive|gluing]] and
[[screws|screwing]] 2 pieces of warped timber back to back. Its not
normally worth doing, but if you're stuck for one piece it might be
quicker than going out.
Warped wood is good for [[Partition Wall|framing]], where considerable
warping is tolerable. When the warp is too bad, the wood can be cut
short and used for noggings.
Twisted wood can sometimes be made good enough by cutting to short
lengths, as the amount of twist on each piece is then much smaller.
This often works for [[First fix & second fix|first fix]], but there's
always more junk wood than uses for it.
Other ways to deal with twisted wood are:
* Using it fixed firmly to something much stronger, thus forcing it to
* Use it for [[Partition Wall|framing]], which is somewhat tolerant of
* Plane it to give smaller straight timber.
* Don't buy it in the first place!
Planks are prone to cupping, whereby one side becomes convex and the
other concave. If its desired to fix it, wetting the dished side will
expand it a little, and it can then be dried while weighted flat. The
thinner the plank, the more chance of success.
Timber defects can often be worked around, but warped or twisted
timber has bent since cutting, and is thus unstable. Changes in
moisture content are prone to producing movement again. This further
restricts the uses for such wood.
===Uses for junk wood===
[[Partition Wall|Timber framing]] is the main use. All sorts of
defects can be hidden behind [[Sheet Materials|plasterboard]] once
* Wood with [[paint]], [[nails]] or damage will all be hidden
* Bent wood can be fitted bending sideways
* Even wood bent both ways will only cause gentle undulation on the
plasterboard if not too bad, and this usually isn't noticeable.
* Split wood can be used too, adding a few [[screws]] to fix it
* Almost anything can be used as noggings: undersize, odd shaped,
badly bent, even [[Adhesive|glued]] offcuts.
Mildly bent wood can also be used in timber framed [[Sheds|shed
construction]]. Its hidden by the cladding.
All timber contains some [[water]]. Where stabilty matters, which is
most applications, timber should be either purchased with water
content similar to final use, or else acclimatised before use. If
ignored, warp and twist are more likely after fitting.
Timber used in new build for structural elements is required to have a
maximum of 18% water content. (Many houses have been built with green
===Green & Seasoned===
Most wood for [[Special:Allpages|DIY work]] is seasoned. Green wood
(meaning unseasoned rather than green in colour) has high [[water]]
content, and is liable to move during drying, making it of limited use
for [[Special:Allpages|DIY]]. The main exception is green oak used for
oak frame. Timber frame [[sheds]] can also be built with green, as
some movement on drying is usually acceptable.
Most DIY timber is not durable, meaning it soon [[Wood Rot|rots]] if
used outdoors without protection from [[water]]. The options for
outdoor timber are:
* durable timber
* non-durable timber plus [[Wood Preservatives|wood preservative]] or
Well known durable species include
* oak (very durable)
* red cedar
Note that the sapwood of all species is non-durable, its heartwood
that's durable. The majority of timber is heartwood, with only the
outer layer of the tree (under the bark) being sapwood.
Timber is available ready treated against rot. Vacuum treated timber
is most effectively preserved, as the [[Wood Preservatives|chemical]]
soaks further into the wood. Cutting it exposes unpreserved ends,
which should be [[Wood Preservatives|treated]] for best life
When applying [[Wood Preservatives|preservative]], the cut ends need
the most attention, as they soak up water like a sponge. Cut ends will
usually sponge up several coats of preservative, which helps it last
Timber also comes in board form. The most common types are hardboard,
chipboard, MDF, plywood and timberboard. These are all described in
[[Sheet Materials#Hardboard|Hardboard]]: thin non-rigid brown board,
typically 3mm thick. Most used as low cost drawer bottoms.
[[Sheet Materials#Chipboard|Chipboard]]: wood chippings glued
together, and sometimes coated with white melamine, brown imitation
wood veneer etc. Most common furniture board in Britain. Usually
fairly weak and vulnerable to water.
[[Sheet Materials#MDF|MDF]]: a uniform brown material, can be machined
and worked without grain being an issue. Vulnerable to water and not
[[Sheet Materials#Plywood|Plywood]]: Available in many grades for
different purposes. Dimensionally stable, strong in both directions,
and one of the stronger wooden board types. Lower cost plywoods are
vulnerable to water and delaminate fairly easily.
[[Sheet Materials#Timberboard|Timberboard]]: Strips of wood glued side
by side to create flat board. Gives a real wood finish. Strong along
the grain, less so across. Cups badly if exposed to water on one side
for a day, but normal cup spills don't do this.
Pine is a genus of conifers covering many different varieties of tree.
Timber described as pine isn't necessarily a pine species at all, but
it will have much the same appearance and properties, making the end
result the same. Redwood has the highest odds of being real pine.
Most holes [[Drill Bits|drilled]] in wood are either pilot holes,
clearance holes or countersink holes.
'''Clearance holes''' allow the [[screws|screw]] to slide through
freely. An ideal size for this is the full width of the screw shank
plus half a millimetre. Hole size isn't critical, but if too large the
head may sink into the hole when tightened, enlarging the hole in the
'''Pilot holes''' are holes that enable [[screws|screws]] to be driven
in without difficulty or risk of splitting the wood. A good size for
pilot holes is half a milimetre slightly larger than the narrowest
width seen on the screw spiral.
'''Countersink holes''' are very shallow tapering holes for the
[[screws|screw head]] to sit in. These allow a counterunk head to sit
flush with the surface. They are generally [[Drill Bits|drilled]]
using a [[Drill Bits|countersink]], but can also be made with a large
drill bit. In most cases the size and shape of the countersinking hole
need not match the screw head well, as the head will distort the wood
under it to some extent.
____ /\/\/\/\/\/\/ |
pilot hole ____ < |
clearance hole < |
____ \/\/\/\/\/\/\ |
< | countersink
Guide to Approximate Hole Sizes
Experience will soon tell you when to use a pilot hole and when not.
Generally speaking, small screws in medium timber or bigger don't need
pilot holes, but with medium to big screws or small timber the chances
are a pilot hole would be wise. Lack of pilot hole can cause splitting
in small wood, or jamming with medium to large screws.
Again sometimes they're needed, sometimes not. [[screws|Plasterboard
screws]] have heads that penetrate less than traditional countersunk
heads, and can usually be sunk fine without [[Drilling Techniques|
Knots are made of much tougher material than the surrounding wood.
Screwing into knots with standard size pilot holes causes the wood to
split. Its generally best to avoid knots when fixing, but sometimes a
[[screws|screw]] is needed there. A simple solution is to use a
slightly larger pilot hole, then they behave fine, good grip and no
splits. Never try to screw a knot with no pilot hole.
[[Nails]] may be driven through knots if a pilot hole is [[Drill Bits|
drilled]] first - though this is rarely necessary. Don't attempt to
nail a knot without pre-drilling.
Awkward [[screws]] that are proving difficult to get in mean you need
a pilot hole, or a bigger pilot hole. If the right [[Drill Bits|drill
bit]] isn't to hand, dipping the screw in oil makes a difference and
is often enough. Dipping a screw in oil before driving reduces
friction, requiring less energy to get the job done. Various
substitutes can be used, such as margerine, chocolate, etc.
Don't labour over a tough [[screw]], if it won't go in just take it
out and fix the problem. If you keep at it you'll only end up with a
well jammed screw that requires repeated curses to get out.
There are numerous ways to get stuck screws out. See [[Screws#Removing
a Damaged Screw|Removing a Damaged Screw]]
There is a gotcha with used wood: most power [[saws]] and embedded
[[nails]] really don't mix well. If you regularly use old timber, nail-
safe circular saw blades are available. For occasional work one can
use a hand saw or jigsaw. Nails can damage the blades on these, but
not the operator.
Planes are also vulnerable, so used wood is generally better not
* [[Sheet Materials#Plywood|Plywood]]
* [[:Category:Wood|All Wood category articles]]
* [[http://188.8.131.52/search ?
+glossary&hl=en&ct=clnk&cd=1&client=opera Timber Glossary]]
* [http://books.google.com/books ?
* [[Special:Allpages|Wiki Contents]]
* [[Special:Categories|Wiki Subject Categories]]