Poor Layup Results In Lumps & Bumps
Jim Coulson on the surface appearance of plywood
LAST month I discussed the importance of the ‘layup’ of plywood – that is, the way it’s put together. If manufactured properly, that should ensure that when you use it, the sheet of plywood gives you a good, flat panel which is completely even in its dimensions all across the whole sheet.
Poor layup – including things like core gaps and overlaps, as I described last time – will result in ‘lumps and bumps’ which may well show through to your final floorcovering, with resultant complaints from your customers.
But there is another factor in the manufacture of plywood, which can show itself through to the final floorcovering, even if the veneers have all been laid together exactly as they should have been.
And that is the appearance quality of the top surface – the ‘face veneer’ of the plywood: so even if the entire sheet of plywood is perfectly flat and level, with a completely even thickness throughout, there may be some defects in the face veneer itself that can still ‘telegraph’ through your vinyl floorcovering (or whatever it is that you’re putting on top of your
The good news is that there is a European Standard for the face appearance of plywood, EN 635-2: plywood: classification by surface appearance. Part 2 of this standard deals with hardwood plywood: but of course, that essentially means hardwood plywood made in Europe; and that in turn means Birch plywood – which hardly anyone in the flooring industry uses (mostly because it costs quite a lot).
So the bad news is that almost none of the hardwood plywood that is used in the UK obeys that European Standard! Instead, the hardwood plywood that comes into this country, and which is 99% tropical in origin, tends to follow some very vague requirements that are seldom if ever kept to; except by a handful of very good manufacturers, mainly in Malaysia and Indonesia – but you have to search very hard to find them (it can be done: so ask us at TFT Woodexperts for help).
So what sorts of defects can upset the face of plywood and then transfer that poor appearance through to your floorcovering? The obvious one is splits in the face veneer; but you can also find knots and knot holes (these don’t happen so often in hardwood plywood as in softwood plywood, it’s true: but they do occur now and again); bark pockets and resin/gum pockets – which not only look bad, but can also be quite sticky and may upset the bonding of some flooring adhesives.
But the main defects that can occur – and perhaps surprisingly, they are often not even regarded as ‘defects’ by the manufacturers – are veneer patches. These are places where repairs have been made to the face veneer, in order to ‘upgrade’ it: often cutting out some of the things I’ve just mentioned, such as knots and resin pockets.
And these patches, if not very carefully done – and if necessary, also filled at their edges – can easily telegraph through a sensitive floorcovering such as a high gloss vinyl.
So you need to be on your guard against any plywood that has its face appearance described as ‘improved’ or ‘C plus’, and so on. (That is, if there is any description given of it at all, which is often not the case!)
All too often, buyers of tropical hardwood plywoods just react to those magic letters ‘WBP’ – as though they can sort out everything. But as I told you in the first article of this series (CFJ, December 2012) , there is no such thing as WBP plywood. But even if there were, that would be only a tiny part of what you really need to know about specifying and buying ‘good’ plywood.
Next time I will explain the concept of marine plywood.
Jim Coulson is a director of TFT Woodexperts
T: 01765 601010
This article has been reproduced from the Contract Flooring Journal website. You can find them at www.contractflooringjournal.co.uk.