Sanding and Sandpaper
Why we sand: to transform a rough, coarse surface to a smooth surface; to smooth out the roughness and unevenness of our driftwood pieces; to show the grain and uniqueness of the piece at its best; to allow finishing oils to penetrate the wood evenly; to make good woodwork into exceptional wood work.
Let’s talk about sandpaper:
The term sandpaper is a generalization to describe a variety of abrasive particles (grits) adhered to a paper or cloth backing in differing densities. True “sandpaper” (paper with sand adhered to it) is not made. The most common abrasive particles used, are made of flint, garnet, emery, aluminum oxide and silicon carbide. In the past, the abrasive was randomly applied to the glue. Today, the abrasives can be electro statically charged so all the abrasive particles line up in the same orientation. This creates a fast cutting, long lasting, product. New technology has made it possible to create abrasives the size of smoke particles (!) used for “superfinishing.”
Types of Abrasives:
Flint: is the original form of mass produced sand paper and the least expensive. Flint is a natural, gray mineral (a form of quartz) and wears down quickly. Flint paper is coarse. Particles dislodge easily and unless the wood is cleaned, they can mar the surface of the wood upon continued sanding. This paper is no longer popular. Mostly found at dollar stores.
Garnet: Another natural material, garnet is harder and sharper than flint and is recognizable by its red color. Garnet paper is more suitable for woodworking. Garnet has paper backing and comes in a wide range of grits. Garnet papers have a shorter life than manmade types but are a good choice for final sanding.
Aluminum Oxide: A synthetic product it is probably the most popular for woodworking (it is also used in metal work). It is made from bauxite and is tan to brownish red in color. It is longer lasting, sharper and more uniform in grit size than garnet paper. When heat and pressure are applied, aluminum oxide fragments and creates new sharp edges. This self renewing property allows it to last longer than other papers. Aluminum oxide paper comes in a wide range of grits and is a good finishing paper.
Emery: This sandpaper is primarily used in metal work. It has a distinctive black color.
Silicone Carbide: Another manmade abrasive, it can be used wet or dry. It is the hardest, sharpest, sandpaper of all. It re-sharpens itself as it wears so it stays sharper longer. It is generally bluish-black in color and comes in a wide variety of grits from very coarse to micro-grits.
Other abrasive particles used in making sandpaper are: alumina-zirconia, chromium oxide, ceramic aluminum oxide.
Types of Backings:
The three most common backings are paper, water proof paper and cloth. These backing are given a letter designation to indicate their weight. Paper backing comes in 5 weights from “A” (lightest) to “F” (heaviest). Cloth backing also has 5 weight designations; “J”, “X”, “Y”, “T” and “M”. “X” is the heaviest weight and “J” is the lightest weight. Each of these backings is made in light weight to heavy duty strength depending on proposed usage. A flexible backing (light weight paper or cloth) allows sandpaper to follow irregular rounded contours of a given work piece. Inflexible backing is good for regular rounded or plane surfaces as well as use in moving sanding applications (belt or disc sanding).
Grit refers to the size of the particles of abrasive material embedded in the sandpaper. Grit is a reference to the of particles per inch the sifting screen. The lower the grit numbers the rougher the sandpaper and conversely, the higher the grit numbers the smoother the sandpaper. Each type of grit has different characteristics which make each most suitable for specific applications.
|Extra Coarse||16-24||Very fast removal of material; heavy sanding and stripping; roughing up the surface; machine sanding floors.|
|Coarse||30-50||Initial sanding when necessary; rough sanding to remove paint and finish; rough shaping.|
|Medium||60-100||Preliminary sanding on rough wood; intermediate sanding, especially soft woods; shaping; preparation for finishing.|
|Fine||120-180||Preparatory sanding of hardwood; final sanding of soft wood; finishing bare wood.|
|Very Fine||220-280||Final sanding of hardwood; sanding between finish coats; final sanding of bare wood.|
|Extra Fine||320-400||Sanding between finish coats and smoothing final coat.|
|Super Fine||500-600||Polishing metal, ceramics, stone. Not usually used for wood; sanding plastics; final sanding of finishes.|
|Ultra Fine||800-1000||Final sanding of finishes|
Open coat vs. closed coat: This refers to the density of the abrasive material on the sandpaper surface.
On open coat papers only about 50%-70% of the surface is covered with abrasive, it has gaps and open spaces between the grits, leaving space to accommodate sawdust build-up. Open coat abrasives make them better suited for machine sanding and for working resinous or gummy materials. It is best used in initial sanding.
Closed coat means that 100% of the surface is covered. This provides more cutting surface and faster cutting ability than open coat abrasives; this can lead to faster clogging of the paper as wood particles are caught and fill in the spaces between the pieces of the grit. Closed coat is better suited for hand sanding, particularly finish sanding.
Sand paper comes in many different styles and forms. The most common that are used are: sheets, belts, discs, rolls, “sponges” and specialty pre-cut shapes.
How does sandpaper work?
It works like, and should be thought of as, a cutting tool. The particles on the sandpaper are made up from a number of sharp edges which cut and remove material from what is being sanded. The type and size of grit, type of adhesive and the type of backing material all have an effect on the suitability of sandpaper for a particular job.
How to sand:
Although it seems tedious and time consuming, sanding is our most important work. Sanding is crucial to a well finished project. It is the simplest of woodworking tools to learn and the most important for achieving a quality finish.
“Without proper sanding, any imperfections will be magnified when the final finish is applied.” -Norm Abrams
Choose your sandpaper: Presumably you have done all the scraping and removal of unwanted wood on your piece. Don’t start sanding too soon. Start by choosing the grit coarse enough to quickly remove surface imperfections. Use the above chart to help you determine which grit to choose. Another method for choosing is to test the sandpaper on a hidden spot on your piece to see if it is the correct grit to use.
“Going through the grits”
This refers to the process where progressively finer grits of sand paper are used to get a smooth final finish. Example: Start with a coarse, 100 grit and progress to a fine, 180 grit then 240 grit and end with very fine 320 grit. Don’t be tempted to skip a grit. If a grit is skipped (say from 100 to 320) the finer grit will be inadequate to quickly smooth the surface. The time it takes to smooth the wood will be increased and sanding will become a tedious chore. As you progress in grits, vacuum or brush away the dust as you sand. This will keep the dust from loading the next finer grit of sand paper. Using a tack cloth or Swiffer cloth is also helpful in removing dust.
When sanding it is important to always sand with the grain of your piece. Never sand across the grain. Start at the end of the piece and using long, even strokes sand with the grain, back and forth, with an even pressure throughout the range of motion.
Sand with the same grit throughout the whole piece. It is important that the same degree of smoothness is consistent through the whole piece.
Sanding odd shaped pieces requires some ingenuity and occasionally special shaped tools. With difficult pieces, irregularly shaped pieces or difficult to reach areas of your piece, it’s tempting to stop at a coarser grit than you may have used in an easier piece or at an easier area to reach. If you do that, the finish you choose will show the imperfections of improper/incomplete sanding.
Using a sanding block or pad is helpful in evenly distributing the pressure of the sand paper.
You cannot rely on just your hand to act as even backing for your sandpaper. If you feel heat when sanding you are pressing too hard.
Let the sandpaper do the work. You may need to step back down to a coarser sandpaper to remove the wood material than bearing down harder with a finer one. This applies when using power tools as well, let the machine and the sandpaper do the work.
In the case of driftwood sculpture, don’t rely on the boning process to finish a piece. Incomplete sanding will show up as muted scratches on the surface of the wood.
To check your sanding finish look at your piece in the sunlight or under a low angled back light, the imperfections will show up and can be corrected before your finish is applied.
If the sandpaper is no longer cutting the surface effectively, discard it and get a new piece. A fresh piece of paper will allow you to work more quickly and efficiently. Sanding wood takes considerable effort, new sandpaper is inexpensive compared to your effort.
When do you stop? When the smoothness you want is achieved.
Choose your tools: When you start to sand you need to choose which method of sanding you want to start with.
Power: There is a large variety of power sanding tools available to help you. There are belt sanders, disc sanders, drum sanders, pad sanders, random orbit sanders, palm sanders, detail sanders, profile sanders, rotary tools (Dremel). All are helpful in the fast removal of wood but caution must be used. It is possible to remove too much wood or leave the surfaced marred with accidental gouging with the power sander. Choose the power sander most appropriate to your pieces and the outcome you wish to achieve. Remember, power tools are not used in final sanding. Final sanding must be done by hand. If sanding with a power tools seem to become laborious, check your sandpaper for wood build up. Clean or replace your paper and begin again.
Hand-Tools to help you sand by hand are also numerous. Hand sanding is easier with one of these tools. There are sheets, sanding sponges (angled and flat), sanding blocks (cork, wood and plastic), sanding pads, sanding sticks (for tight spots), contour sanders (tadpoles), sanding cord and the great variety of homemade tools we make for ourselves. Each of these has their own positive attributes and most times it is a matter of personal preference when choosing which on to use.
Power tool safety:
Wear safety glasses or face shield. Your prescription glasses are not enough protection.
Wear a dust mask or respirator every time. Minimum N95 NIOSH/OSHA rating.
Wear ear plugs or ear muffs.
Make sure the sander is switched to off before connecting the power supply
Inspect sanding belts and discs before using. Replace them if they are worn.
Use two hands to operate the sander.
Keep all cords clear of sanding area.
Clean dust from motor and vents at regular intervals, by brushing or vacuuming.
Always, always wear a dust mask or respirator when sanding. Often we don’t know what type of wood we’re working on, and there are many dangers in the wood we sand because of this lack of knowledge. Spalted wood, western red cedar, yew and iron wood are some of the woods that create toxic dust we encounter. There are also many molds and fungus in the woods that can be toxic and can cause adverse reactions. A dust mask is cheap and a necessary protection from these dangers. Having a dust collector or dust collection system is recommended.
Purchase good quality sandpaper it will save time by doing its job right the first time.
Refold or shift the sandpaper on the block often to expose fresh cutting surface.
Use rubbing alcohol or heat gun to remove pitch from the wood before sanding.
Use anti-vibration gloves when power sanding for more comfort.
To increase the durability of sandpaper, cover the back side with duct tape. This can be used for hand sanding and power sanding.
To remove “stuck” sanding drums place it in the freezer for several minutes. It will contract making removal easier.
Use an abrasive cleaning stick (sandpaper eraser) to clean sand paper. Especially useful in power sanding.
Attach sand paper to thin strips of wood with double back tape to get into narrow, tight spots.
Using a vise is helpful when needing to have your piece steady when sanding.
Use a pencil line, in a zigzag motion across the surface to be sanded. This allows you to see the areas you still need to sand.
Swiffer sheets are good dust removers.
When using a flap sander, use on a slow speed only. Faster speeds only burnish the wood.
Sanding is a very important part of finishing our pieces.
Remember: For the love of the wood, you need to put in the time. Bring out the beauty the wood deserves.