Rustic Grade wood floors are the most natural form of wood. It is also known as a CD grade that is characterised by a large number of knots and wide colour variation in the heartwood. A virtually limitless size and number of filled knots. sapwood; you should also expect checks, splits across the growth ring and possibly some end shake splits. 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.