D.I.Y. : Sanding, sandpaper: How to use sandpaper and sand wood and painted materials.
How to use sandpaper.
Sandpaper and sanding wood can be a surprisingly rich topic of conversation. In this article I will discuss several tips for the D.I.Y. Enthusiast.
The original sandpaper might have come from China in the 13th Century. Craftsmen bonded abrasive materials like crushed shells, sand, and seeds to parchment.
Sharkskin is naturally abrasive and has also been used as a sanding tool.
See also - this excellent painting article - roll and tip method.
I will talk mostly about sanding bare wood. Wood dust can be dangerous. Some resulting fine particulates when air born are toxic. By breathing the dust you can get a massive headache or worse. Therefore, always use a dust mask.
Some people are allergic to various species. In particular, oily wood can produce a contact reaction in some people. Western Red Cedar has an extremely small dust particle size. It can penetrate deep into the lungs and cause severe reactions in asthma-prone people. Manufactured laminated timber and wood that has preservatives could use nasty chemicals like formaldehyde, arsenic and chromium. Take special safety precautions at all times. Sensitivity can build with exposure, so don't get complacent. Even some sweet-smelling woods can be highly toxic.
A commercial sanding block.
Types of sanding tools:
- Wire wool,
- paper backed products
- cloth backed products
- wet-strength papers
- Disk sander
- Random orbital sander
- Belt sander
- Electric file
- Corner sander
- Finishing sander
- Plasterer's vacuum sander
- Floor sander
- Buffing tools
What to buy
This depends on what you want to do; but there is one golden rule. Don't buy cheap rubbish. It is false economy to purchase very cheap and poorly made sandpaper. It won't last, the bonding is weak, the backing breaks down quickly and the abrasive particles are not uniform, and it will clog very quickly. Sandpaper is a high-technology product, and you should purchase the best available. The best sandpaper lasts a long time. It will not clog so easily, it cuts faster and leaves a better finish. In the long run, the more expensive papers work out cheaper.
Choose the right product for the task:
Mostly, I will talk about sanding wood and paint.
Aluminium oxide is often used by car
repairers but is also used on wood. These papers are wet-strength
which makes them useful for finishing painted wood – I will discuss
that more later. Silicon oxide is another wet-strength product.
Emery cloth is marketed to people who
work with metal. It has a tough flexible backing and cuts metal
Wire wool is naturally non-clogging. It wears away quite quickly, but the results are fabulous. Since it is not a paper or cloth backed product, you can use it on unusual shapes. It cuts quickly and can produce a silky-smooth finish on bare wood or painted surfaces.
Grades of sandpaper
Different countries have various standards for quantifying the roughness of an abrasive product. For the D.I.Y. tasks, it is sufficient to know only that there are several grades.
“Macro” means big. There are four main groups:
- Very course
- Very fine
- Very fine
- Extra fine
- Super fine
- Ultra fine
Here, we explore these and their uses in more detail:
This is for very rapid removal of stock. When used in a power-tool, it is very aggressive and can remove wood as fast or faster than a hand-plane. You can use it for shaping and sometime removal of paint.
Use a course grade on surfaces that have significant scratches, rough patches and marks. Each time you use a finer grade of paper, the finish becomes smoother and shinier. Keep sanding until the surface has a uniform feel to it. With a course paper, the surface will not be particularly shiny or smooth.
Use of a fine paper on a surface that has been prepared by a course paper will give a smooth finish but it will not be shiny.
This grade of paper will make wood feel silky and it will start to develop a sheen.
Very fine, Extra fine, Super fine
These grades, when used in succession will give the wood a very soft silky feel and a decent sheen.
The ultra fine grade will polish the surface.
Do I have to use so many grades?
It seems like a lot of work to move through the grades from course to ultra fine, but by doing this, you minimise the work required. This is because each stage cuts tiny scratches into the wood, and it is much easier to eliminate the course scratches with a paper that is only slightly smoother. Each stage does not take long when done this way.
Which way do I sand?
Especially in the final stages, try to sand with the grain. If you move across the grain even once, it can take a very long time to remove the resulting scratch. It would be quicker to move back a grade or two if this happens. There are exceptions. A bur, knotted area, end grain or round piece may need cross-grain sanding just because of the nature of the wood. If you have a particularly random-grained piece of wood then consider using a random scratch pattern or abandon the sandpaper and use a cabinet scraper. In the early stages with course paper, you may be trying to make a board flat. In that case, run the sandpaper across the grain because it removes stock quicker, and will flatten the work surface better than with the grain. Finish off finer grades with the grain as normal.
Do I have to use a sanding block?
No. But if you are looking to make a flat surface or take out bumps and lumps or sand away filler, then a sanding block will make the task quicker. Sanding blocks promote a flat surfaced result, while hand sanding with no block will follow imperfections in level. The former is essential for a fine table top, and the latter works well on a curved surface or one that is meant to be a little rustic.
How hard should I press?
If you press hard, it seems like the job gets done quicker. But pressure causes heat, ruins the sandpaper and causes clogging and wear. Sandpaper is a precision tool and should be used as such. Use just enough pressure to remove stock and allow the dust to escape without clogging or heat build up. The sandpaper will last longer, and the job will be quicker.
How do I hold the paper?
It's easy to hold with a block, and not a relevant question for machine assisted sanding. Hand sanding with the paper only can be done in three ways.
Fold it in half. The roughness stops your hand slipping about. But this will not work well for paper with thin or very flexible backing.
Rip it in half and glue the two back to back. PVA glue works fine. This works quite well, but not necessarily on a tightly curved surface unless the backing is flexible even when two sheets are glued together. The trick stops the sandpaper sliding in your hand or against itself.
If you are right-handed, curl over the top left corner, slide the middle finger underneath, and the index finger on top. Then you can apply some pressure to most of the paper with the palm of your hand. This technique works well when preparing a sound painted surface.
Another useful thing to do is to glue some high-quality sandpaper to a smooth bench-top. Now you can use this for small pieces. If you have a small item to sand, then it can be very difficult to get it square if the work is fixed and the sanding tool hand-held. By flipping this about, you can hand-hold the work, and rub it against the fixed sandpaper. You get a better result.
Soft surfaces, ones with glue, sap, resin, paint and other contaminants tend to clog the paper quickly. Once it is clogged, it no longer works. Sometimes on a very course paper, you can use a sharp metal point to pull off some of the clogged lumps but this is only a limited solution. As already mentioned, use only light pressure, and don't produce a heat build up. Clear away the dust often as you work. Buy special non-clogging paper. There are two main types. One has a sparse grit distribution which allows the dust to escape between the grit, and another is manufactured with a dry lubricant which helps to prevent sticking. If you are sanding paint, and there are no bare patches of wood, then the surface is waterproof, and you can use a wet-and dry technique. Wet-strength papers can be washed, and used while the surface is wet. The water suspends the dust and you can periodically wipe it away with a damp cloth. This is a very effective method of sanding a painted surface.
What tools will help me?
The sanding block is very useful. You can make your own by gluing some cork or similar textured material to a handy sized block of wood. You can also buy or make a tool that grips the sandpaper at either end (illustrated). This means that you can use a greater area, and have the luxury of a quick-change.
Wire wool is available in various grades too. The main advantage is that is does not clog. It works well on wood, paint, and metal, and awkward shapes. The downside is it leaves steel hairs in your work. Here is a tip: Find a very strong magnet and put it inside a plastic bag. Then wave the magnet over your work and collect the steel hairs. It is very important to do this because otherwise the y will rust and mark your work. It is worse with water based paint. If you cannot guarantee to get all the hairs collected, then consider priming the wood with an oil-based primer and undercoat. You will find very strong magnets in old, large disk drives.
These are particularly useful because you can sand while the work is wet – providing of course that your stock is already waterproof. Either it is a non-oxidising metal like aluminium or it is a painted product. When you wet bare wood, it raises the grain. While on that topic, if you dampen the stock first, and let it dry, then dry sand it, you might get a better finish because the soft parts of the grain swell. It's something to experiment with for various types of wood. Wet-sanding eliminates dust which is an advantage, and it almost totally eliminates clogging. Do not use wire wool when wet. It will rust very quickly.
An electric file is like a mini
belt-sander on a stick. Obviously, being small, it fits into slots
and awkward places that would be difficult to sand any other way.
The corner sander has a triangular shaped random orbital action. It's a gentle tool, and I find that it takes a long time to remove stock. For this reason it makes a good finishing tool. Removal of stock in a corner is best done with a scraping tool.
A disk sander is hard to use. It rotates like a drill and takes a lot of experience and control to use because it tends to run along the work. It's very easy to gouge your stock badly. It is also very difficult or impossible to keep the abrasive action lines up with the grain in the wood. On the positive side, you can get a rubber sanding disk that will fit in a standard electric drill, and these are quite cheap. However, a much better tool is the random orbital sander.
Random orbital sander
The random orbital sander does a tiny figure of 8 action. It will not wander uncontrollably over your stock, and as you move it, the figure of 8 action produces tiny random scratches. This means that it can be used with and against the grain, and over knots and burrs. The downside is they are difficult to get into a corner because they are circular. But there is a similar tool called a corner sander which does a good job.
A hand-held belt sander.
A belt sander looks a little like a power planer. But instead of a small rotating blade, it has a big abrasive loop. There are three of four main grades from very course to fine, but I've not seen any super fine grades. It's a pretty aggressive tool, but very useful for shaping, sanding end-grain, flattening boards and so on. It's noisy. Some models are heavy, but the weight contributes to the pressure required to cut the surface.
Both the belt sander, and the orbital sanders have dust collection bags. These reduce the dust a little but they don't work perfectly, so you still need to wear a mask.
An abrasive sponge has one to two grades of abrasive particles bonded to it. You can use it wet or dry, in a similar way to wet-strength papers.
A finishing sander has a vibrating
rectangular pad. It's a bit like a sanding block with a motor on top.
These are gentle tools and very well suited for polishing fine pieces
using super fine sandpaper.
Plasterer's vacuum sander
One of the messiest jobs in DIY is sanding the joints between plasterer-board – also called Gyprock. To help cut down the dust, you can get a tool that sort of looks like a vacuum cleaner but at the sucker-end is a rotating abrasive pad. The dust is drawn into a bag.
To sand a floor, there are two tools that are essential. These include the large belt sander that looks a little like a mower in some ways, and a rotating hand-held edging tool. The technique on how to use these would fill a separate article, so I will reserve that for another time.
A buffing tool is very much like one of the rotating sanding tools, but a lambskin or soft cloth is used in place of abrasive. These are used in the final stages of repairing the panel of a car, but are also useful for buffing a waxed surface.
Grain fillers, putty and bog
Before sanding, fill the holes, knots and imperfections. Sometimes it's best to apply a diluted sealer before filling to avoid staining around the filled site. There are a few different kinds of filler. Some are water based, and some are oil based. The oil based fillers take longer to dry. These fillers also come in various colours, and you can tint some of them with a small amount of powder paint, or mix in some of the fine sanding dust. Putty is usually linseed-oil based and is a good choice for an outdoor situation, but linseed oil can take months to dry hard. An alternate to putty is a two-part polyester filler, sometimes called “Builder's bog”. It dries quickly because the setting process is a chemical reaction, and may be sanded, drilled, filed, planed and painted. It's a good idea to coat the imperfection first with a thinned solution of PVA glue, and make sure that it is dry and dust free before filling. This is more important in outdoor settings where temperature can cause movement in the stock.
On some timbers, the filler looks out of place even if it is a good colour match. In this case, you can mix one colour, set it to one side, mix a slightly different shade, and then incompletely twist the two together. This will create a more textured / patterned filler that blends in with the grain better.
Hopefully, I've been able to describe some of the tools, techniques and tips for sanding and surface preparation. This is an important stage before painting and polishing. Many times you will have heard, “Preparation is the key to a good finish”, and it's true!
Would you like to know how to make your own wood glule from milk? Click HERE.