Roskote A-51 Plus Mastic by Royston

Roskote A-51 Plus Mastic by Royston
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Royston Roskote A-51 Plus should be used as a general purpose coating for underground corrosion protection of all fabricated steel products, such as pipes, tanks, conduits, cylinder casings and structural steel.

It is particularly useful for corrosion protection of bolted couplings, valves, fittings and other objects of irregular shape. It is frequently used with Royston Glas-Wrap as a reinforcement for coating field joints of mill coated pipe or elevator hydraulic cylinder casings.

Because of its resistance to gasoline and oil, it should also be used at service stations, terminals, bulk stations, producing fields and similar locations. It is used above ground for resistance to corrosive fumes and severe atmospheric conditions.


  • High electrical resistivity designed to protect underground steel pipes, tanks and other structures against corrosion particularly in soils saturated with oil and gasoline.
  • Excellent above ground coating for protection against severely corrosive atmospheric fumes and against moisture and salt in coastal areas.
  • Bonds firmly to steel surfaces without the use of primer.
  • Forms a tough coating which becomes resistant to oxidizing, crazing, alligatoring, cracking, checking, loosening or scaling.
  • Endures over a long period of time because of its resistance to soil stress and to attack by alkalis, acids, salts, moisture, gasoline and oil.

Surface Preparation

Surfaces should be dry and cleaned of all rust, scale, soil, mud, oil, grease and other contaminants in the field by wire brushing. Sand blasting or chemical treatment may be more convenient for in-plant surface preparation. No primer is required.

Typical Properties


Heavy mastic with synthetic elastomeric additives
in a mixed solvent system.



Weight per Gallon:

9.22 lbs.

Specific Gravity:


Percent Solids:

By Volume - 51%
By Weight - 62%

Volume Resistivity:

1.4 x 1011 ohms cm3

Temperature Range:

-40oF to 150oF ambient and to 300oF transient.

Flash Point:

40oF Seta-Flash Closed Cup. ASTM D327 8-73

Shelf Life:

At Least One Year


MSDS for Roskote A-51 PLUS

Application Procedure

Royston Roskote A-51 Plus should be stirred thoroughly before using. Thinning is not required except for cold spray at temperatures below 60oF. The heavy mastic is specially formulated to obtain a thick protective coating. If excess thickening occurs because of solvent losses from opened containers, restore to original viscosity with Royston Thinner No. 70 or a mixture of equal parts of toluene and MEK.

Apply cold by brush, glove or booster-pump spray. Apply to cover 65 to 70 square feet per gallon, which will provide a dry film thickness of about 12 mils per coat. When the first coat has dried to the touch, which will usually require less than an hour, apply a second coat at the same thickness.

Brush and Glove Application

Apply liberally with a generous amount at all times. It should never be applied thin. However, a wet film thickness of .040 inches is maximum per coat to reduce the possibility of mud cracking.

Spray Application

Booster type spray equipment is required because of Royston Roskote A-51 Plus's heavy consistency. It may be sprayed with minimal thinning at temperatures above 60 F. It is usually necessary to thin with one quart of thinner to each five gallons of Royston Roskote A-51 Plus in temperatures below 60oF. Use high boiling (250oF) mineral spirits for spray thinning.

Either air type or airless spray equipment commercially available from several manufacturers may be used. The following equipment procedures have provided satisfactory results, but alternates may be equally successful.

Airless Spray

Good spray results can be obtained with an airless high volume 10:1 pump with air cap assisted atomization, e.g., Binks Model 98-792 outfit or equal.

Airless Spray with Air Cap Boost

Pump Ratio



5 GPM or better

Air Consumption (typical)

4 CFM/gal

Tip Minimum Opening
(Consult Corrosion Control Products Company)

Binks 47 x 3/8 or equal


Use high boiling (250oF) mineral spirits up to 3-1 ratio -- thinner can be adjusted for best results with specific equipment.

Using with Reinforcing Wrap

Apply one coat of Royston Roskote A-51 Plus and allow to dry to the touch. This amount of drying is necessary before proceeding further to prevent the wrap from pulling through the coating to the metal surface. From this point there are two alternate procedures in common use:

  • Apply Royston Glas-Wrap and then put on a second coat of Royston Roskote A-51 Plus.
  • Apply the second coat of Royston Roskote A-51 Plus and then wrap while the Royston Roskote A-51 Plus is still wet. Wrap tightly to embed the mesh in the coating.


Royston Roskote A-51 Plus is available from inventory in 1-Gallon cans, 5-Gallon pails and 55-Gallons drums. One-Gallon cans are packaged 4 per carton. All sizes are available from Corrosion Control Products Company.