Draft no 2 of the Timber Basics article... I've added more sections too. Lets see what you think.
=3D=3DTimber Sizes=3D=3D 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 =BC" 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.
=3D=3D=3DLength=3D=3D=3D 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.
=3D=3DPrice=3D=3D Most timber is sold by price per length, and some by price per cubic foot. Some example price lists:
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are not company recommendations
=3D=3DTerms=3D=3D ;Rough sawn :Usually a splintery finish, but smoother sawn surfaces are seen on some goods.
;PAR :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.
;PSE :Planed Square Edge. This is planed all round with sides accurately at
90 degrees.
;PFS :
;CLS :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.
;ALS : American Lumber Standard, very similar to CLS
;Regularised : 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.
=3D=3DQualities=3D=3D =3D=3D=3DWhitewood=3D=3D=3D 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 penetration.
=3D=3D=3DRedwood=3D=3D=3D 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 issue.
Redwood is generally spruce, fir or pine.
=3D=3D=3DJoinery=3D=3D=3D Joinery timber is clear, with a knot-free surface. Its used for [[Furniture Links|furniture]].
=3D=3DGrading=3D=3D 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.
=3D=3DSpecies=3D=3D Most wood used for [[Special:Allpages|DIY]] is spruce, fir or a pine. Other species are also used, but command a higher price, limiting their use.
=3D=3DBuying Wood=3D=3D 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.
=3D=3DProblem Wood=3D=3D Bent stock is a regular problem. =3D=3D=3DWarp=3D=3D=3D 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.
=3D=3D=3DTwist=3D=3D=3D 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 untwist
- Use it for [[Partition Wall|framing]], which is somewhat tolerant of twist
- Plane it to give smaller straight timber.
- Don't buy it in the first place!
=3D=3D=3DCupping=3D=3D=3D 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.
=3D=3D=3DStability=3D=3D=3D 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.
=3D=3D=3DUses for junk wood=3D=3D=3D [[Partition Wall|Timber framing]] is the main use. All sorts of defects can be hidden behind [[Sheet Materials|plasterboard]] once finished.
- 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 together.
- 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.
=3D=3DWater Content=3D=3D 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 timber.)
=3D=3D=3DGreen & Seasoned=3D=3D=3D 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.
=3D=3DDurability=3D=3D 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:
- non-durable timber plus [[Wood Preservatives|wood preservative]] or [[paint]]
Well known durable species include
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.
=3D=3D=3DTreatment=3D=3D=3D 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 expectancy.
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 longer.
=3D=3DBoard=3D=3D Timber also comes in board form. The most common types are hardboard, chipboard, MDF, plywood and timberboard. These are all described in [[Sheet Materials]].
[[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 very strong.
[[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.
=3D=3DPine=3D=3D 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.
=3D=3DDrilling holes=3D=3D 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 process.
'''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
=3D=3D=3DPilot Holes=3D=3D=3D 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.
=3D=3D=3DCountersink holes=3D=3D=3D 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| drilling]] first.
=3D=3D=3DKnots=3D=3D=3D 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.
=3D=3DDifficult screws=3D=3D =3D=3D=3DGoing in=3D=3D=3D 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.
=3D=3D=3DComing out=3D=3D=3D There are numerous ways to get stuck screws out. See [[Screws#Removing a Damaged Screw|Removing a Damaged Screw]]
=3D=3DUsed wood=3D=3D 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 planed.
=3D=3DSee Also=3D=3D
- [[Sheet Materials#Plywood|Plywood]]
- [[:Category:Wood|All Wood category articles]]
- [[http://216.239.59.104/search?q=3Dcache:IfN6hPrQTfUJ:oak.arch.utas.edu.au/glossary/glossary.pdf+timber+glossary&hl=3Den&ct=3Dclnk&cd=3D1&client=3Dopera Timber Glossary]]
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[[Category:Wood]]