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Few woodworking shops would getfar without sandpaper. Its used foreverything from flattening roughpanels to polishing delicate finishes. Its

versatility comes from the variety of avail-able grits, coatings, and backings. Follow-ing is a primer on the combinations that

work best for the types of sanding you arelikely to do.

Manufacturers offer a variety of sophis-ticated abrasives, backing materials, andadhesives. Sandpaper is engineered forspecific uses, depending on the materialto be abraded and whether the paper isdesigned for hand- or machine-sanding.

Some of these new high-performanceabrasives have migrated into woodwork-ing from other industries. While they make

sanding faster, they also cost more than theold standbys.

For woodworkers, striking a balance be-tween cost and performance amounts toknowing what you are buying and under-standing what the abrasive is designed todo. Manufacturers put a variety of abrasivesinto belts, disks, sheets, rolls, and sandingsponges, and these products come in sev-eral price ranges. There is a sandpaper forjust about any purpose.

Printed on the back of most sandpaperis information about abrasive type and gritsize (see Pay attention to your gradeson p. 60). You also might find the weightof the backing and the type of glue. Theinformation, however, isnt likely to be allthat helpful.

For example, unless you know there three conventions for grit size (in adtion to the generic coarse, medium, afine found on some inexpensive paper

you might not really know how coaor fine the sandpaper is. Do you need

A-weight or a C-weight paper for sand varnish between coats? Knowing the baof abrasives, backings, and coatings help you sort through the jumble of tranames and murky product codes.

Abrasives: the sand in sandpaper Although manufacturers still use a natural minerals, synthetic abrasives cmost of the sandpaper we buy. The mcommon abrasivesaluminum oxide,con carbide, and ceramicsare synthe

For power-sanding, new abrasives are worth the extra cost

Sandpaper

Beltsanding abrasives must withstanBecause theyre heavy and capable of running at high speeds, belt sandersexcel at rough sanding. The resulting heat and high pressure requires thatsanding belts be made from tough material, such as cloth backing, andtough grits like aluminum oxide or the newer synthetic abrasives .

Overlapping joint

Butt joint

Some belts should run only one wayTape-reinforced butt joints (left) allow belts to run either way, slightly extending

their life. Older-style, lap-joined belts (right) run in only one direction.

B Y S C O T T G I B S

ALUMINUM OXIDE

SYNTHETIC ABRASIVE


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F I N E W O O D W O R K I N G56

while garnet and emery (used mostly inmetal-working) are the only commonabrasives that occur naturally.

Manufacturers have concentrated theirresearch on aluminum oxide and newerceramic abrasives, designing abrasivegrains that are friable or semifriable, mean-ing they break down to expose fresh cut-ting edges as the sandpaper wears.

Friability is an excellent thing, says ChrisMinick, an advanced product developmentspecialist at 3M and a consulting editor to

Fine Woodworking . What it does is rejuve-nate the points, so it extends the life of thesandpaper. Second, it gives you a much,much more consistent scratch pattern than

youd get with a nonfriable material.Most sandpaper for woodworking has an

open coat, meaning that abrasive grainscover between 40% and 70% of the back-ing. The space between grains gives saw-

dust a place to go, so the paper doesntclog as readily. On the other hand, closed-coat sandpaper produces a more uniformscratch pattern, making it a good choicefor sanding finishes.

Coatings keep abrasives on and saw-dust out Stearates are no-load coatingsthat help to prevent clogging when sand-ing painted surfaces between finish coatsor resinous wood like pine. Stearated pa-per costs more, and its not really neces-

sary when sanding dry hardwood.Unlike some of their predecessors, mod-ern stearates are engineered not to inter-fere with water-based finishes. However,there are anecdotal reports to the contrary.

Jeff Jewitt, a frequent contributor of finish-ing articles to Fine Woodworking , claimsgood success using 3Ms 216U Frecut Goldand Mirkas Royal papers, as long as he

The minerals make the difference

Paper or cloth, glue, and abrasive particlesare combined to make durable and reliablesandpaper.

Turning abrasive gritinto sandpaper

1 Sandpaper starts as a huge roll of clothor paper backing. The thicker and stiffer thebacking, the more aggressive the sandpaper.

A L U M I N U M O X I D E : T H E S H O P WO R K H O R S E

Aluminum oxide is the most common abrasive in woodworking sandpaper. It workswell on a number of materials, including bare wood, painted surfaces, and metal.In its most basic form, this furnace-produced mineral does not fracture easily.It tends to wear down until it becomes too dull to cut efficiently. More expensiveforms are friable or semifriable. A number of companies offer more than one gradeof aluminum oxide in sandpaper. More expensive, heat-treated versions of themineral tend to go into higher-priced product lines, such as Nortons 3X or 3MsSandblaster. Generic aluminum oxide, with its familiar brown and black flecks, isused in tandem with hide-glue adhesives on less expensive sandpaper.

Abrasive performance is a balance of hardness, sharpness, durability, andfriability. Friability is the highly desirable tendency to fracture with wear andexpose new, sharp cutting edges. For general use, aluminum oxide seemsto present the best compromise, although several otherabrasives have specific uses that make them worthkeeping in the shop.

S I L I C O N C A R B I D E :F O R L E V E L I N G F I N I S H E S

Also a synthetic, silicon carbide is sharper and harder

than standard forms of aluminum oxide. It has needle-like grains that resemble shards of broken glass. Thesehard, sharp grains cut glass, plastic, and metal very wellunder light pressure, but silicon carbide is not a ver ytough mineral. Its elongated shape shears off easily,making it too friable for bare-wood sanding becausethe abrasive wears down too quickly, according tomanufacturers. Its an excellent choice for smoothingfinish between coats, and for rubbing out film finisheslike lacquer and shellac, because it cuts quickly andproduces a very uniform scratc h pattern. Waterproofversions wont degrade when used with water or oil.

Photos: An


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ABRASIVE

2 The backing passes between rollers,which apply measured amounts of hideglue, urea-formaldehyde, or phenolicresin as the first, or make, coat.

3 A static charge of about20,000 volts applied to the glued-up paper attracts a uniform coatof abrasive. A trip through anoven sets the adhesive.

4 A pass through a second rollercoats the paper with the second, orsize, coat of glue, followed by morebaking, then with the application ofany special coatings or backings.

5 In the final step beforepackaging, a large pressdie-cuts the paper to theshape youll use in yourshop.

A L U M I N A Z I R C O N I A A N DC E R A M I C S : T H E T O U G H O N E S

A tough alloy of aluminum oxide and zirconium oxide,alumina zirconia outlasts aluminum oxide but costsabout 20% more. Because its greater durability is most

evident under heavy loads, alumina zirconia is usedmainly in products for power sanding. Other high-performance abrasives include ceramicaluminum oxide from 3M (Cubitron) and a similarmineral from Norton (SG). Ceramics are extremelytough, sharp, and long-wearingand at least severaltimes as expensive as anything else. They often areblended with other abrasives on premium belts anddisks. Nortons 3X random-orbit disks, for example,combine its SG mineral and aluminum oxide. 3Mmakes disks and belts with both aluminum oxide andCubitron (theyre purple and called Regalite).

G A R N E T: T H E N AT U R A LOne of the natural minerals still on the shelves is garnet, a relatively softsubstance with a characteristic orange color and without fancy tradenames. Garnet is garnet. Although it wont last as long or cut as quicklyas aluminum oxide or the ceramics, traditionalists think garnet producesa finer and softer scratch pattern for final sanding. Youll find it in sheetsfor hand-sanding or for use on an orbital block s ander for fine finish work.Garnet is steadily being replaced by newer aluminum oxidesNorton sellsless garnet every year, and Mirka lists no garnet products.

Drawings: Brian Jensen


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wipes down the stearate-sanded wo with alcohol. Jewitt says this techni

works best on closed-grain wooOn open-grain woods such as o

stray accumulations of stearateremain in the pores.

Backings also affect pemance. Backing paper comefive common weightsA, C

E, and F. A-weight paper islightest, used for finer grits. E

F weights are found on disksheavy grinding. Cloth backings

more durable but not quite as smoothpaper. Cloth comes in J-weight, the mflexible, and X, Y, and Z.

Beltsanding: Look for cloth backingand tough abrasivesBelts for stationary sanding machcome with either a cloth or paper backiBelts for portable sanders are always clotypically X-weight. Because of their slength, belts for portable sanders run h

paper-backed belts wouldnt last lonThe standard abrasive for porta

sander belts is aluminum oxide. Mafacturers also offer belts coated walumina zirconia or ceramic aluminoxide, which stand up to heat a

pressure better than ordinary aluminoxide.Open-coat belts dont clog as read

and belts with P-graded abrasives (see sidebar on p. 60) produce a more constent finish. Butt-joined belts can runeither direction, so they are easier to pon the machine and last slightly longe

Bargain hunters should think twabout stocking up on b

for their portable sers. Accordi

Lisa Beard,ager of te

cal serat Klinthe asives

Random-orbit sanders can be fine finishing machines, or nearly as aggressive as beltsanders. Consequently, disks for these sanders are available in almost the

entire range of backing-paper weights, abrasive types, and coatings. Most areperforated for dust collection.

Holes allow dustcollection. Five- andeight-hole disks are intended for specific sanders, whilethe universal type fits anymachine of a matching diameter. A mesh alterna- tive, Mirkas Abranet,comes in grits fromP120 to P600 andis intended for

virtually dust-free sanding. Its saidto work on hook- and-loop bases,but an adapteris also available.

Sanding disks come in many fla

FIVE- AND EIGHT-HOLE DISKS

UNIVERSAL DISKS

MESH DISKS

F I N E W O O D W O R K I N G


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At the time of this printing, a major woodworking outlet sold a 3-in. by 24-in.aluminum-oxide belt on X-weight cloth for about $1.40. An alumina-zirconiabelt cost about $3.10, and a ceramic-grain belt was about $3.80. Premium

belts wear slowly and can be cleaned repeatedly to nearly new conditionwith a rubber cleaning stick. Likewise, the alumina-zirconia and

ceramic random-orbit disks Ive used seem to cut faster andwear more slowly than conventional aluminum oxide.

However, meaningful tests for abrasive lifeand efficiency require expensive test-

ing equipment that I dont have. Inwriting this article, I spent a lot of

time sanding wood, and while I maylack the scientific data, my subjective

take is that high-performance belts anddisks are worth the extra money.

High-performance abrasives reallyshine when used under high heat and pres-

sure, like machine sanding. Im less con- vinced that high-tech abrasives are worth the

money for hand sanding, considering that mostof the hand-sanding I do is limited to light fin-

ish work. I will pay extra, however, for awaxy coating called stearate. Stearatedpapers dont clog as quickly, and oftenare used for sanding out finishes.

S

to join belts last foronly about a year. Beltsthat have been sitting aroundtoo long can pop apart when theyreput on the sander. Beard suggests buyingno more than will be used in a year.

Random-orbit sanding: A variety of disks for the finishing touch

Most random-orbit disks have either five oreight holes that feed dust into the sanderscollection system. Some disks come withslots instead of holes and so can fit anybase with a matching diameter.

Disks can be had with paper, film, orcloth backings, although C-weight paperseems to be the most common. Clothbackings are more durable but not quiteas smooth as paper. The edges of a clothrandom-orbit disk dont crease or tear asreadily when sanding into a corner, but formost applications, paper works fine. Flat-

ter and more expensive than paper, filmbacking often is used in automotive finish-ing. It may be overkill for sanding wood.

Because random-orbit machines dontgenerate a lot of heat and pressure, theydont take advantage of the properties ofpremium alumina zirconia or ceramic abra-sives to the same degree as do belt sand-ers. Manufacturers offer these abrasives on

High-tech abrasives pay for them- selves in time saved. Not only dothey cut faster, but premium sandingbelts and disks last longer under theheat and pressure of power sandingthan do traditional abrasives.

Are high-performanceabrasives worth the cost?

No-load coatings work great for sandingfinishes. Uncoated garnet sandpaper (left)clogs quickly, while stearated paper (right)remains clean and ef fective longer.


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random-orbit disks nonetheless, promisinglonger disk life over standard aluminum-oxide products.

For sanding finishes, random-orbit disksare available with stearate coatings. Someeven come in extremely fine grits: Mirkas

Abralon pads, useful for polishing high-gloss surfaces such as a rubbed-out finish,are available in grits up to P4000.

Disks are available with either pressure-sensitive-adhesive (PSA) or hook-and-loopbacks. Hook-and-loop systems are worththe extra cost because they can be reused.PSA disks stick only once, so if you needto switch between different grits frequent-ly, count on wasting a lot of paper.

Hand-sanding: Rolls and sponges add versatility to the old standby, sheetsPower sanders help take the tedium out ofsanding, but its still sometimes less trouble

to pick up a sanding block or a scrap sandpaper and do the job by hand. A of sandpaper wrapped around the pad

your thumb quickly takes off milling mafrom the inside curve of cove molding, aseveral suppliers sell detail-sanding blothat match a range of profiles.

Hand-sanding offers outstanding con when sanding between coats, and a finhand-sanding with the grain can elimineven a random-orbit sanders minor crograin scratches. You can buy abrasives intended

handwork in just about any formsherolls, sponges, and even thin cord on 50spools. Rolls come in a variety of widtypically from 1 in. to 6 in., in length10 ft. and 25 ft., and they can be had weither hook-and-loop or PSA backingnew class of abrasives, nonwovens, isandpaper in the traditional sense at

Manufacturers grade the size of abra-sive particles using the CAMI standard,the FEPA standard , and micron grad-ing (identified by the Greek letter ).The first two are the most common.

CAMI is the old American standard.FEPA is the European standard, but ap-pears more and more often on productsin the United States. It is sometimesidentified with a P placed in front ofthe numbers that designate grit size. Inboth CAMI and FEPA scales, the higher

the number, the finer the grit.FEPA-graded abrasives

are more uniform in sizethan CAMI abrasives, and

thus leave a more uniform

scratch pattern, which isbetter for fine finishing. CAMI

and FEPA grits are roughly thesame until they get above

220. Above this grade,FEPA papers are sig-

nificantly more abrasivethan identically numbered

CAMI papers.The most accurate scale, mi-

cron grading, sometimes is foundon finishing films, more common in

auto-body work than in woodworking.Micron-graded papers in very fine gritsarent necessary for most woodworking.

For more on sandpaper grades, seeFWW #176, pp. 117-118.

ALUMINUM OXIFOR ROUGH SAN

Pay attention to your grades

F I N E W O O D W O R K I N G60

As of this printing, the four major man-ufacturers whose products are avail-able in the United States use the CAMIand FEPA scales as follows:3M: Both CAMI and FEPA; FEPA

papers all carry the P designation.

CAMI abrasives are silicon carbideand garnet.

Klingspor: All FEPA; some marked,some not.

Mirka: All FEPA and marked.Norton: Most FEPA, but unmarked;

silicon carbide is CAMI grade.


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Hand-sanding requires a variety of abrasives ...For hand-sanding as well as machine, aluminum oxide is the first choice for rough work. Garnet is still loved by many for the last sandingof bare wood because of its soft scratch pattern. Silicon carbide cuts quickly with light pressure and so is great for wet-sanding finishes.

GARNET FORFINE SANDING

SILICON CARBIDEFOR SANDING FIN

Nonwovens resemble nylon scrubbingpads used in the kitchen and are intendedfor contoured areas and for rubbing outfinishes. A standard sheet of sandpaper, which

measures 9 in. by 11 in., can be cut intofour equal pieces to fit a sanding block.

Sheet sandpaper also can be had with alightweight cloth backing thats more flex-ible and more durable than paper. Lookfor a no-load coating when sanding resin-ous softwoods or finishes.

Sanding sponges, which combine flex-ible foam blocks and sandpaper in one,are available in different foam densitiesand thicknesses, so they can be matchedto the application. Firm rectangular blocksget into corners more easily than a fold-ed piece of sandpaper or a conventionalsanding block.

Will you find the huge range of modernabrasives in your local hardware store? No,but you are likely to find most of what youuse from day to day. And every productmentioned in this article is easily found incatalogs or online.

Scott Gibson is a woodworker and writer in SteepFalls, Maine.

... on a variety of backingsIf you can imagine an abrasive back-ing, someones probably alreadymaking it. Abrasive cords of vary-

ing diameters get into the nooksand crannies of intricate turn-ings. Sanding sponges conformto molded surfaces toremove machine marks.Abrasive-loaded plasticwool knocks down fin-ishes. Flat paper comesin adhesive-backedrolls for quick stick-ing to sanding blocks.Despite the variety ofspecialty backings ontodays market, theold standby, 9-in. by11-in. sheets, remains

viable. Found on theshelves of every hardwarestore, sheets are effectiveabrasives, and generally theleast expensive option.

J U L Y / A U G U S T 2 0 0 5

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