Arbomast GP

An oil-based mastic, suitable for perimeter sealing of timber frames and sealing of preformed concrete panels, e.g. for garages.

Not recommended for high movement joints or expansion joints.

Resistant to dilute alkalis and acids. Should not cause staining on many common building materials, but may stain porous materials such as marble, slate and other natural and reconstituted stones.

Flash point: 65°C.

Good UV resistance but may undergo slight yellowing.

Can be painted, but excessive movement will cause the paint to crack. Bituminous paints should not be used.

Correctly applied, the sealant should not require maintenance, and has an anticipated life in excess of 10 years.

Health and safety:

Avoid prolonged skin contact. Use of this product should be recorded in the project Health and Safety Plan.

Application temperature:

+5°C to +50°C.

Curing time:

Skins after approximately 14 days depending on atmospheric conditions.

Joint dimensions:

- Width:

  • Minimum 6 mm; maximum 18 mm (single application).

- Depth:

  • Porous substrates: Minimum 10 mm; maximum 20 mm.
  • Non-porous substrates: Minimum 6 mm; maximum 10 mm.

Joint backing:

A combined joint filler/ bond breaker, such as closed cell foam polyethylene rod, should always be used to ensure that the sealant adheres only to the joint faces and not to the back. Bond breaker tape should be used where the joint has been packed out with fibre-board.


Friable or brittle surfaces will need priming with Arbo Primer 925.

General information

Uniclass 2015

Pr_30_31_76_58 Oil-based mastic joint sealantsPrimary


H42/661 Sealant joints

L10/75 Sealant joints

L10/810 Sealant joints

L20/80 Sealant joints

L20/820 Sealant joints

Specification data - Oil-based mastic joint sealants

Product Reference

Arbomast GP








Filler: Closed cell foam polyethylene rod

Filler: Fibre-board with bond breaker tape

Primer: Arbo Primer 925

Product Options


Available in five standard colours.

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