The Association has been the official benchmark for grading of solid hardwood floors since 1909 and since 1999 has also included engineered floors in their wood floor grading rules. The following is an explanation of grading of hardwood flooring, covering the four basic quality standards of grade, configuration, moisture content and average length.
Unfinished Hardwood Flooring Grades
Wood floor grading is primarily concerned with the surface finish of the product. It is this that will determine how the finished article will look, after sanding and installation. Things like knots, mineral streaks and manufacturing marks are covered and timbers are categorized into four grades; NOFMA Clear, NOFMA Select, NOFMA No.1 Common and NOFMA No.2 Common. In order from best quality:
Comprizing mainly of Heartwood, this grade has a minimum amount of discoloration and other marks and has a uniform surface finish, natural color variations excepted. Typical features are:
Showing a greater degree of coloration variation than Clear Grade, but with minimal knots and streaks.
NOFMA No.1 Common
Showing prominent color variations and various knots, streaks and other characters.
NOFMA No.2 Common
Showing prominent natural variation in color, with various manufacturing imperfections and obvious character marks.
Covering timber plank width, thickness, tongue and groove fit and location and end plank squareness, these rules insure that your timber will fit together in a predictable manner and will not require excessive sanding or other work before final finishing.
Insuring that timber is of a consistent moisture content, similar to that of installation site conditions, these standards aim to alleviate excessive movement of the timber after installation, by either contraction or expansion due to large differences in the natural state of the timber and natural site conditions.
Standards to insure that there is adequate coverage, frequency of end joints, and therefore insure predictable installation of the product.
There are also wood floor grading standards that cover the cut of the timber. This is how the grain of the wood lies as the saw cuts through the log. There are three main cuts you should be aware of; plain, quartered or riftsawn. the idea of the different cuts is to minimize expansion and contraction of the timber.
Plain sawn is where the timber is cut with the grain going across the width of the plank. This type will expand more across the width of the plank than quarter sawn. This method produces little waste and is therefore the most popular used today. Possibly as much as 80% of timber is cut using this method.
Quarter Sawn is cut with the grain going through the thickness of the plank. In theory, this cut should prevent the timber from expanding too much across the width of the plank and instead the plank will get thicker. This helps the floor by not bulging upwards as is possible with plain sawn. There is a greater yield from this cut than for riftsawn timber, but still it is a fairly uncommon type of cut. Probably 20% of timer is cut in this way.
Riftsawn timber should have all the same grain pattern through each plank, as they are cut in a radial pattern going around the log. This cutting method produces a lot of waste - riftsawn timber is rare these days.