Prime (Small Pin Knot Allowed, No Sapwood)
Typically, prime grade has few, if any knots, and these will be of minimal size. There will be a relatively small amount of colour variation in the timber itself.
1Bis or Select (Knots Max. 18mm, No Sapwood)
Typically, this grade will have a mix of almost prime boards with other planks which have more knots of a limited size. There will be some filled elements, such as broken knots, which will complement the natural character of the timber and may vary from batch to batch.
Rustic A or Classic (Knots Max. 35mm, No Sapwood)
Rustic/Classic Grade floors show the natural variation of timber without allowing some of the more characterful features in more rustic grades. Planks with very few knots will be mixed with some planks containing larger knots or checks (cracks across the growth ring) which may be filled. Filler colour is selected to complement the natural character of the timber and may vary from batch to batch.
Rustic A/B or Character (Knots Max. 70mm, Small trace of Sapwood)
Typically, character grade will include both heartwood and sapwood and allows a wider range of colour variation. Knots are larger and you should expect cracks. Filler will be used, the colour of which is carefully selected to complement the wood rather than to match it exactly, and it may vary from batch to batch.
Mixed Grade or Natural (Knots Allowed, Sapwood Allowed)
Known as either natural or rustic grade this allows a virtually limitless size and number of knots. Heartwood will be used, there will be colour variation, sapwood and filler; you should also expect checks (cracks across the growth ring) and possibly some end shake (cracks between the rings). The colour of the filler is carefully selected to complement the wood rather than to match it exactly and it may vary from batch to batch.