Abrasives - the 7 characteristics
Assess your sand paper
Sanding is an arduous task. It is often described as the job that people least favour. Not only have sanders improved to make the task easier but there’s also been significant development to abrasives to make them more efficient. Once you know which grit you’ll need, here we guide you through what to look for when selecting abrasives for your power tool.
Are more expensive abrasives worth the money?
If you plan to work on an important project all the hard work leading up to that point can be for nothing if the finish isn’t right. The precision of the abrasive is therefore key and there are seven main characteristics that need assessing to get the perfect finish.
1) Quality of the backing material
The backing material needs to be strong enough to be stable but at the same time flexible enough to move as you need it to. A good quality backing material will have the right combination of flexibility, stability and tear resistance.
- Easily to cut and fold to the required size
- Greater flexibility
- The grit and coating doesn’t crumble
With a harder backing
- Scratches to the worksurface
- More brittle and breaks more easily
2) What does the actual sanding sheet look like?
Poorer quality sanding sheets will often have a marked difference in appearance to their more expensive counterparts. Look at the quality of the edge of the disc. Is it frayed, cracked or peeling away? Bosch make a point about the precision of the holes in their sanding discs as even poorly punched holes can affect the quality of the finished product.
Precision punching advantages
- Better extraction
- Consistent quality
- Burr free holes without grit loss
Standard hole disadvantages
- Uneven edges create defects when sanding
- Extraction performance is reduced
- Loss of grit on the edges can scratch the surface
3) How good will the extraction be?
When sanding with power tools, good extraction is crucial as not only does it prevent you breathing in harmful material but it will also extend the life of the abrasive. You also gain better visibility of the work surface for a more precise finish.
Dust Free Sanding
Perforations over the whole area of the disc allow for better dust extraction as the airflow can pull material from the entire surface area. This helps to prevent build up on the disc which prolongs its working life and is safer as less dust is deposited in the air.
Hermes also produce a multi hole abrasive which allows better dust extraction and a smooth finish without swirl marks caused by build up. Another key advantage of these discs is that you can use them with different types of sander as you don’t have to match the holes to those on your machine. They’ll work with different sanders so there’s no fiddling around getting the holes to align.
Hermes Multihole Discs 150mm 120g (10 Pack)
4) Bonding Agent
The bonding agent used to bind the abrasive substances to the backing material is a key component in creating an effective abrasive. The grit needs to be held in place securely without being overly hard. There needs to be a balance between flexibility and hardness as a harder bonding agent means the abrasive will be more aggressive and able to remove more material. If it’s too hard however it will be brittle and crack more easily resulting in areas needing to be redone.
5) Abrasive Grit
Aluminium oxide is one of the most common minerals used for abrasive grain due to its versatile qualities. It’s tough and maintains its sharp edges as it fragments when heat and pressure are generated during sanding. The scientific parlance for this is the friability. When sanding this is beneficial as the fragmentation means the cutting edges renew so you’re able to use it for longer before having to replace the disc.
There are, however, many different kinds of aluminium oxide which vary in quality and therefore performance. It is difficult to determine the type on the paper alone so often it’s a question of trying different types and seeing which works best for you. In addition to aluminium oxide there are other abrasive minerals that are suited to different tasks. Silicon carbide for instance is effective on brittle surfaces such as tile and glass.
How the abrasive grit is distributed on the sheet is also important for a good finish. A quality sheet will have an even distribution which is carefully monitored during the manufacturing process. Abrasives with an uneven distribution, the material collects on the pad and this can cause it clog and even burn the surface.
Certain abrasives are also fitted with an additional coating such as stearate which is best used for sanding paint and varnish. On varnish this prevents heat build up and also works to bind varnish dust together for easier extraction and significantly prolonging the life of the abrasive.
Bosch C470 Discs Gold 125mm 8 Hole 40g (5 Pack)
Abrasives that have an electrostatic coating applied ensure that the grain is distributed evenly and the sharpest edge is facing outwards ready to sand the material.
7) Does the abrasive meet the FEPA standard?
The Federation of European Producers of Abrasive, FEPA, is dedicated to producing the highest standards in abrasives. Manufacturers such as Bosch, Festool, Hermes and Mirka all produce abrasives to the FEPA standard; another reassurance that the abrasives are of the best quality.
All excellent points but my main problem is the backing that adheres the grit sheet to the backing pad via the hook and loop principle. In most, including Bosch, the backing material wears and fails to keep the sheet on the pad and, if you have to change the pad to use a different tool on the oscillating multi tool, the backing on the sanding sheet looses all it grip once you have removed it to access the holding bolt - it is now useless even if it is not worn. Any experience on what is the best for backing grip?
I had the same problem with my Bosch GEX-125A. Bought five pads at around 16 quid each in one year (admittedly i use it often). I've now sanded off the remaining Velcro of all five. i buy adhesive Velcro from eBay (hook and loop 100mm) not as wide as ideal, so 1+a bit strips are needed to make my own. Use a craft knife/scalpel to trim off edges and holes. If it comes unstuck add super-glue. This take ages, but mine last longer than the Bosch ones!
Thanks Adrian for the tip