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Commercial Flooring News

Abrasives For Wood Floors

Alec Stacey on showing your grit

ONE of the largest abrasives markets is the automotive industry and other applications which involve the sanding of metal. When abrasives were first marketed for wood floor sanding the existing abrasive products were simply re-shaped to fit floor sanding machines and sold via flooring distributors in the grit sizes considered appropriate.
For several years now Bona has taken a different view, recognising that wood behaves differently when sanded compared to metal. Recent studies have revealed some interesting consequences of using generic abrasives, as opposed to those specifically designed with wood flooring in mind.
The composition and construction of abrasives can have a profound effect on the quality of the final sanding and therefore the appearance of the floor. If we consider how abrasives are manufactured – a suitable backing material is coated with an adhesive and grit particles are stuck to it.
Consider the two pictures below which show the impact that two different qualities of abrasive have when sanding two sections of the same floor.
In picture 1 below we can see that the timber has received aggressive sanding from a 36 grit abrasive. This abrasive (Bona 8300) is constructed from a mixture of silicone carbide and zirconium grits.
The striking difference is the scratch pattern produced when compared with picture 2 below. This relates to the size of the grit particles. In both pictures a 36 grit abrasive was used, but in the second instance the particles were not the same shape and size. These should be of a standard size; a grit 36 abrasive should have particles which are 1/36th of an inch in cross section.
When the grit particles are of a uniform size and shape there is less ‘fibre ripping’ of the timber and a more uniform surface texture results.
In picture 2, where a ‘generic’ abrasive was used (i.e one not specifically designed for wood flooring) the particles of grit varied in size and shape dramatically; some particles being considerably larger (24 & 16 grit!) and more irregular in shape, others smaller.
Other differences can result from the method used to manufacture the abrasives. A simple way of introducing the particles of grit onto the abrasive backing is to ‘mechanically spread’ the wet adhesive on the backing with particles. This is an unsophisticated process and as the particles fall under gravity and land on the backing glue any part of the grit is exposed as the cutting face.
A more elegant approach is ‘electrostatic spreading’. Here the backing with the adhesive ready has an electrical charge. This passes above the grit particles which jump up and imbed themselves into the adhesive.
One of the advantages is that the grit particles all face their pointed, sharp face outwards. The particles are also more evenly distributed on the backing resulting in a better quality cut.
Another way of assessing the quality of an abrasive is to determine how much grit is lost through use. By weighing an abrasive belt before and after sanding a specific area of wood one can see precisely how well the grit particles are attached to the backing. High quality abrasives should not shed particles.
The backing of an abrasive is important too. Not only must it be strong enough to withstand what is an aggressive task, but in order to function correctly on a belt sander, it must remain a constant size and not stretch or it will move on the drum and make contact with other parts of the machine resulting in damage.
The material must also be able to cope with the frictional heat generated during edge sanding, where the abrasive is moving at high speed. Dedicated wood flooring abrasives have the grit particles less densely packed together for this purpose producing fewer burn marks as well as less grit shedding.
For some time now there has been an emphasis on the dangers of exposure to wood dust. We have been very active in tackling this issue with the development of the Bona dust containment system. This system, which allows sanding without airborne dust, has been in use now for a number of years and was improved further with the addition of an antistatic coating onto our abrasives.
The coating is designed to allow the easier withdrawal of dust from the abrasive and reduces clogging.
Also, in subsequent tests, it was found that this property increases the life of the abrasive by between 15 and 20%.
It is easy to consider abrasives as a consumable product which ultimately ends up in the waste. However, there are significant differences which can have a profound impact on the success of a sanding operation.
During tests, one worrying find when assessing abrasives used for metal work, was the presence of compounds added to serve as coolants. These can be transferred onto the timber surface where they can impact on the success of the subsequent floor finishing treatment.
It always makes sense to use the correct tool for the job and it is now clear that this definitely applies to abrasives too.
Alec Stacey is technical manager at Bona
www.bona.com