Pencil hardness test

You will need a dry, clean, well-sanded piece of wood to do your own pencil hardness test

Type of coatings	Pencil Hardness
Catalyzed polyester	9H
Catalyzed polyurethane	9H
Catalyzed Modified Acrylic polyurethane	4H
Catalyzed Acrylic polyurethane	2H
Water-based polyurethane	3H
Water-based urethane/ Isocyanate Catalyst	2H
Conversion varnish	4H
Low VOC Catalyzed laquer [24 hrs]	2H
Low VOC laquer	3H
Urethane/Nitrocellulose laquer [24 hrs}	F
Water reducible laquer	2H
Tung oil/polyurethane wipe-on finish	2H
Water-based polyurethane wipe-on finish	HB-F
Aerosol precat	3B
Aerosol water clear acrylic	3B
Aerosol clear shellac	3B
Aerosol nitrocellulose/ polyurethane	HB
Aerosol nitrocellulose	3B
Amber (orange) Shellac 1 lb. cut	3B

Usually the coating thickness being tested is 1.0-1.5 mils (a mil is one millionth of an inch) and has been allowed to dry for 7 days. In some cases, a different drying schedule is used, and the chart indicates those in brackets. The ambient temperature during the test can also be a factor in the drying times and can have an effect on the coating’s hardness.

Select a pencil from your set and make a line about 1/2-inch long. If the pencil you start with scratches the surface of the coating, then go down the pencil grades until you come to the first pencil that doesn’t scratch the coating. Redo the test, and if you get the same results, you have determined the ‘Pencil Hardness’ of the coating you are testing. It’s that simple. There are some coatings so hard that the 9H pencil won’t scratch them-all of these coatings get a 9H rating to designate their hardness.

Use this chart only as a guide. It is also important to understand that the degree of hardness of any generic coating may not always be the same; in other words, if one company has a polyurethane with a 3H hardness, do not assume that every other polyurethance will have a 3H hardness. They won’t; they will vary from manufacturer to manufacturer, and from product to product.

As I mentioned previously, the pencil hardness test is only one of many tests that are done to evaluate a coating’s performance. Other tests are abrasion, reverse impact resistance, direct impact resistance, cross-hatch adhesion, oxidation, gloss retention, UV resistance, yellowing, blistering, drying times, chemical/solvent resistance (using both the rubbing and spot/time tests), salt spray resistance, humidity resistance, acid and caustic resistance, the VOC and HAP contents, and so on.

All this information is helpful in choosing or evaluating a finish. But regardless of a finish’s rating, the best advice is always: ‘handle with care’.

http://www.pencilpages.com/articles/simmons.htm

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