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Is Your Sanding Up To Scratch?

Floor preparation: Top tips on the selection of abrasives
Geoff Hewett, of Bona technical sales, on some guiding principles about wood flooring preparation and the choice of abrasives: 
A GOOD finish is all about the preparation! Before you start to sand a wood floor careful consideration should be given to the type of wood you are working on, the suitability of the machine you are proposing to use and the quality of the abrasives.
Poor quality abrasives will leave irregular scratch patterns, black dots in the floor and chatter marks from poor fitting belts or bad joints – and these will often go unnoticed until after the floor has been coated. We often see these problems when someone has invested in a good sanding machine but then compromised on quality by using cheap abrasives.
Let’s look at why the quality of abrasives is so important and why the type you use can make such a difference to the finished job.
Abrasive are made up of three component parts – the backing, the adhesive and the grain – often referred to as the grit.
Paper backed abrasives are the lightest and cheapest type but it’s important to realise when choosing this type, typically discs, that the higher quality brands will combine a more durable reinforced backing with a better quality resin which will provide greater durability.
When purchasing fabric backed abrasives (the usual backing for belts) I would recommend the type backed with the more durable polyester cotton mix known as ‘Y’cloth. These stand up to the heat generated by sanding more effectively than the cheaper ‘X’ cloth type and are also less prone to stretching which can result in a poor fit.
Better quality abrasives use a high performance heat resistant resin to fix the grain particles to the backing which withstands heat generated by the sanding process. A poor quality resin will become soft when hot and shed the grain more quickly and subsequently reduce the life of the abrasive.
The same principle applies to the ‘fill coat’ which comes part way up the grain to hold it in place. Therefore a ‘resin/resin’ bond type should be selected.
When choosing an anti-static paper I would recommend one which has the anti-static coating added to either the base resin coat (as our abrasives do) rather than to the fill coat which wears faster and allows the abrasive to lose its anti-static properties and clog more quickly.
Open or closed grain?: Distribution of the grain particles on the backing also influences performance. For the purposes of wood floor sanding it is advisable to choose an open grain type which will prevent early clogging of the abrasive by wood dust.
Some sanding belts although promoted for floor sanding are in fact ‘semi open’ or close grain and more suited for metal working – consequently they will clog more easily.
Abrasive grain types: Aluminium Oxide: This is a standard material that wears down evenly. A cheaper option but ideal for working with softer wood such as Pine.
Silicon Carbide: This is harder and sharper than Aluminium Oxide and so cuts better and retains its abrasive effect until the grains are fully worn down – ideal for use with high speed edge sanders.
Zirconia: Originally used in the metal working industry on metals such as stainless steel, titanium etc. In its 100% form it is far too aggressive for wood and would leave an irregular scratch pattern.
We therefore uses a Zirconia ‘mix’ to give a high quality controlled scratch pattern allowing for faster abrading without compromising the quality of the scratch pattern. The benefits it provides in terms of speed and long life outweigh its higher purchase price. Our Zirconia Mix belts can also be run in both directions to extend the wear and therefore the value even further.
Ceramic: We introduced this type relatively recently. They are designed for the removal of very hard, scratch resistant and Urea Formaldehyde factory applied UV coatings. 36 and 50 grit ceramic abrasives are a very cost effective and fast method of working with these difficult to abrade surfaces.
Diamond: Until recently it was almost impossible to abrade ceramic based factory finishes and our standard advice was always to sand off and recoat. Now patented industrial diamond abrasives are available, it is possible to cut back and overcoat these notoriously difficult finishes.
Only available in a P240 grit, it is important to follow the manufacturer’s advice when using these and to remember that previously waxed or polished floors cannot be overcoated and will need sanding back to bare wood. Always undertake a test area when overcoating an unknown existing finish!

This article has been reproduced from the Contract Flooring Journal website. You can find them at