Whilst browsing in Wickes, it occurred to me that the rough sawn
timber sizes were 22mm, 47mm, etc. I can understand that planing will
shave a few millimetres off the wood but why is rough sawn sold in
these strange sizes? Why isn't it 25mm or 50mm, multiples of inches
rather than just under? (I suppose I should say before someone else
does, that I do realise an inch is not exactly 25mm)
Another timber question: the treated timber had that characteristic
green tint to it, yet it was covered in patches of grey mould. Surely
that's exactly what the treatment is supposed to prevent? What's going
If it's construction grade material it doesn't get planed, but is sawn
to a good enough finish for carcassing etc. Spruce blunts planers like
Softwood can suffer from blue stain, which goes right through the
timber, and is a fungal infection
On Wed, 01 Feb 2012 19:23:34 +0000, The Natural Philosopher
This wasn't a grey tint, it was circular patches of grey that looked
like mould on old bread and which wiped away. It wasn't all over, just
discrete patches and it was only on some, not all of the timber. I
could be wrong, perhaps it was a salt, but I took great care to pick
the ones without it, just in case. It just seemed strange this was on
I think it is just the saw blade width. Assuming a 3mm saw blade,
cutting 50mm of material from a larger piece gives you a 47mm finished
size. The advantage of doing it that way rather than having the
finished sizes as multiples of an inch is that for instance a 12 inch
piece of timber can be cut into 6 x 2 inch pieces, 4 x 3inch pieces, 2
x 6 inch pieces etc. To work to finished sizes of inch multiples, 6 x
2inch (50mm) pieces would need 315mm of timber, whereas 2 x 6inch
(150mm) would need 303mm.
Thanks. I did wonder if it was the width of the blade (kerf?) but I
couldn't see why they didn't compensate for a 3mm loss by cutting,
say, 53mm wide. However your answer explains that: money! By cutting
47mm, they get more from the original piece of wood. I suppose that
3mm is neither here nor there when constructing say a stud wall.
Although I have seen near rotten and well mildewed tiling battens on
sale at B&Q where they had been stored in an exposed location. Possibly
the worst supplier of treated timber on a planetary scale and of course
the didn't give a f'ck.
If the stuff at Wickes is actually wet I would pass it by just in case.
OK a number of points here ..
On softwood the so called standard 4 x 2 sizes etc., these refer to
sawn timber size at a stated moisture content.
These were metricated ( as UK has to do what France tells it ) and the
standard sizes for thickness are
16, 19, 22, 25, 32, 38, 47, 50, 63, 75, 100, 150, 250 and 300mm
The standard widths are:
75, 100, 115, 125, 138, 150, 175, 200, 225, 250, 275, 300mm
Not all thickness are in all widths ... but that is the standard range.
The BS standard for this requires these sizes to met -1mm to +3mm up
to 100mm size -2mm to +4mm above 100mm
So for a 4" x 2" your timber can be in range 99-103 x 49-53 mm
However it could be sold outside of these sizes as long as it does not
claim it meets BS EN 1313-1
If you buy is PSE (planed on 2 face) there is further loss in size ...
the example of 4" x 2" now becomes 47 x 97 and with allowable
deviation can be 96-100 x 46-50
Most wood shops would be aiming for the minimum end of finished sizes to
maximize their output. (there is also Class 2 which has tighter tolerance)
PAR would lose even more as it is planed all all 4 faces.
There other type of timber (I built my house out of it) you may come
across ... certainly becoming popular in the sheds,
CLS (Canadian Lumbar Standard)
This has rounded arrises (long edges) and is much easier to handle than
rough sawn ... having all 4 faces machined.
It is typically much consistent in size.
Typical sizes found in UK are
38 x 63 and 38 x 89
Notionally the 3x2 and 4x2 formats, and used where those would have
Extensively used in Timber frame construction as it is all much more
consistent in size.
As to the part of your question relating to Green tint ..........
This will only be there if the timber is pressure treated .. typically
BTW - once you cut it, any exposed timber has to be treated to maintain
It is difficult to comment on the grey mould you mention without seeing
it, this could be standard oxidising of softwood, which turns surface
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