This page summarizes Gilsonite’s applications in the bituminous paint, coatings and wood stain industries. It contains an outline which highlights Gilsonite’s advantages in these markets, plus sample formulations, mixing instructions, and product performance data, etc.
In the paint applications, Gilsonite is usually used in combination with bitumen (asphalt). In most cases, if Gilsonite is used alone, the final paint will be very hard and brittle after drying. If normal straight-run bitumen is used alone, the finished paint is too soft and tacky . Therefore, a combination of Gilsonite and bitumen is used to achieve the desired hardness (penetration) and drying time of the finished paint.
In addition to imparting hardness to the paint, Gilsonite is also increasing the paint’s: (1) adhesion; (2) gloss; (3) chemical resistance; (4) water resistance; and (5) body.
For hardness, Gilsonite has a zero (0) penetration (at 25°C; 100 gm, 5 sec.) compared to the 60-70 pen, 80-100 pen or softer bitumens commonly available from petroleum companies or asphalt manufacturers. Approximately 90% of all bitumen is used for road construction and these hardness grades are acceptable for that purpose. However, they are too soft by themselves for the manufacture of paint and surface coatings which require hardness values around 5 penetration for acceptable paint drying. Paint films composed of bitumen alone are tacky if the penetration is more than 10, and are brittle if less than 4.
Air-blowing soft, road paving bitumens down to 5 pen is a common practice but this is an advanced aging process which damages the bitumen. Air-blowing upsets the colloidal balance of the bitumen which can lead to films of oil or wax exuding from the bitumen. If these films exude to the surface of the paint, the result is a loss of gloss. If these films migrate to the interface of the substrate, the result is a loss of adhesion which causes the paint to peel. Other disadvantages of using air-blown bitumen in paint formulations include gelling with certain solvents and large viscosity increases during the mixing of the paints or during their storage.
Therefore, rather than air-blowing a soft bitumen down to 5 penetration, that same soft bitumen may be transformed into a hard bitumen by modifying it with Gilsonite, avoiding the disadvantages of oil/wax migration and gelation. For example, adding about 35 to 50% Gilsonite to an 80-100 penetration bitumen will transform it to 5-10 penetration, suitable for paint making.
Table I illustrates some base-case sample formulations using straight-run bitumen (A), air-blown bitumen (B), and Gilsonite addition (C and D).
Illustrative Paint Formulations
Bitumen (80-100 pen)
does not dry
The preferred formula, (C), shows that a combination of 25 parts each of 80-100 bitumen and Gilsonite in 50 parts mineral spirits yields a paint with the same penetration as using air-blown bitumen. It dries in 10-15 minutes and has greatly improved gloss and viscosity stability. Alternate formula (D) uses some air-blown bitumen and less Gilsonite, to reduce raw materials costs, giving a higher softening point but gloss and viscosity stability are reduced.
The adhesion of a bitumen-based paint may be increased with Gilsonite addition because of Gilsonite’s relatively high nitrogen content, about 3.0% for Gilsonite versus 0.3% for bitumen. The addition of nitrogen to the paint formula results in a high percentage of polar compounds which improve the adhesion of the paint to the substrate. Because Gilsonite is hydrophobic and nearly chemically inert, both the water resistance and chemical resistance of paints are increased with Gilsonite addition.
Gilsonite-based paints and coatings are generally used to protect metal surfaces. They are very popular as paints for automobile chassis, auto radiators, steel drums, ocean-going containers, steel structures, roof coatings, etc. Below are some typical starting formulations. More or less solvent may be used in each formula to achieve the desired viscosity and more or less Gilsonite may be used to achieve the desired hardness. The drying rate may be varied by choosing solvents with different evaporation rates.
Please Note: In any of the following formulas, American Gilsonite Company’s products Selects 300, Selects 325 or Selects 350 Grades may be used, depending on the softening point, viscosity and hardness desired.
General Purpose Paint
80-100 penetration Bitumen (asphalt)
This general purpose product is used for exterior use, acid resistance, chassis paints, structural metal, drum paint. Application: Brush, spray, dip, flow coat.
Please Note: Better opacity and deeper black color may be obtained with the inclusion of between 2 to 12 % carbon black (pigment grade), although gloss is adversely affected at higher levels.
This product has better outdoor weathering, solvent release, and chemical resistance than the General Purpose formulation. Other drying oils may be used depending upon requirements and cost limitations. The oil and Gilsonite are cooked together applying approximately the same procedures and temperatures as normally used for the individual oil in other similar formulations. Manufacturers in some cases merely blend Gilsonite solution with the oil without going through the cooking process. Pigmented asphaltic varnishes can be made by grinding carbon black into the vehicle in a ball mill. Application: Brush, spray.
Colored Asphalt Paints
80-100 penetration Bitumen
The pigment is incorporated in ball mills or other dispersing equipment. The intensity depends upon the amount of pigment used. Percentages as low as 15% by weight give an appreciable color, but ordinarily approximately 25% is required. Application: Brush, spray.
Asphalt Aluminum Paint
80-100 penetration Bitumen
Gilsonite is an excellent “leafing” medium for aluminum paste. In all cases, the leafing tendency is improved by the use of an aromatic solvent in the ratio of 10 to 20% of the total solvent. 25% aluminum paste is roughly equivalent to 2 pounds of paste per gallon of paint. This amount may be varied from as low as 1 pound per gallon to 3 pounds per gallon depending upon the brilliance desired and the cost permitted. Application: Brush, spray.
Gilsonite-based wood stains make use of Gilsonite’s attractive, natural brown color and also its resistance to water. They may be used for either interior or exterior uses, for wood surfaces ranging from furniture and flooring to fences, siding and decking.