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Allow For Movement

Jim Coulson on solid hardwood floors
UP to now (in my series for CFJ), I have stuck more or less to discussing problems that may be encountered with wood-based panels used for flooring: primarily as overlays on older floors; but also (in the case of chipboard) as the floor substrate itself. However, the recent spell of very hot weather has prompted me to consider other, solid wood flooring products, and with them, the perennial question of moisture content.
Solid hardwood floors used to be very fashionable: but they have been ‘ousted’ in recent years by the more ‘sophisticated’ laminate flooring. Although that in itself is not without its potential problems of variable quality and issues to do with its upper surface – whether or not it has a ‘real wood’ veneer and if so, how thick and how hard-wearing it is.
But that’s where solid wood floors – hardwood or softwood – have a distinct advantage over laminates: you can always re-sand them if they become too marked or worn, and you won’t risk breaking into the MDF or HDF sub-layer if you take too much off the top!
So let’s assume that you have a client who really wants – and who can afford – a solid hardwood floor. Taste and aesthetic appeal will of course come into it since not all timbers look the same, by any means. And the ‘fashion’ at present seems to be for lighter-coloured or mid-coloured timbers, such as Oak or Maple (though you people at the ‘coal-face’ will have a better idea of that than I will: being a mere technical bod!).
But my point is not so much to do with what particular colour of wood is ‘flavour of the month’, as the fact that whatever wood is chosen, you will need to understand its ‘movement’ properties and check its ‘as delivered’ moisture content.
Different species of wood have different – and sometimes wildly different – responses to moisture; and they are rated as being ‘small’, ‘medium’ or ‘large’ in their movement characteristics. For example: Oak is ‘medium’, whereas Iroko is ‘small’ and Beech is ‘large’ – and to put that into perspective, if a 100mm wide board should reduce (or indeed, increase) in moisture content by 10%, then the Oak could change dimension by a bit less than 3mm, the Iroko by something less than 2mm and the Beech by up to 4mm!
Now translate that into a ‘run’ of boards across a typical floor: which could consist of 30 or 40 boards in width – then you have the potential for your floor shrinking or growing by anything from 60mm (2½ inches) to 160mm (over 6 inches) – and that could spell disaster!
The lesson to learn with any wood floor is: first of all, check its ‘as delivered’ moisture content – on a selection of pieces, not just one – and secondly, work out what the ‘settled’ moisture content is likely to be, in the location where the floor is going to end up; and thirdly, find out the movement characteristic of the chosen hardwood so that you know whether it is likely to ‘behave’ better or worse if the in-service conditions should change.
If any or all of those paramenters do not match up well: then you need to do something about it – such as ‘conditioning the flooring’ – don’t just lay the floor and hope for the best! And please, please, do not fall for the words ‘kiln dried’ on the packaging: that does not mean that the wood is now magic and will not misbehave…
Jim Coulson is Director of TFT Woodexperts, based in North Yorkshire
T: 01765 601010
www.woodexperts.com

This article has been reproduced from the Contract Flooring Journal website. You can find them at www.contractflooringjournal.co.uk.