Astroflame Passive Fire Protection Products

Trade Name: Astro LST Mastic

Low Smoke & Toxicity Intumescent Mastic Sealant


Designed for use within enclosed areas such as tunnels and underground systems.

Tested for passenger carrying train systems to BS6853:1999.

Low smoke and toxicity levels.

Tested in accordance with EN 1366-3 : 2009.

Tested BS 6853:1999 D8.3: Smoke Ao (max) and tested BS 6853:1999 B.1: Toxicity R value.

Fire Classification to EN 13501-2.

Tested in accordance with EN 10140-2 : 2010.

Air Permeability testing to EN 1026.

Mechanical Adhesion and Tensile testing to EN ISO 8039 & EN ISO 9046.

Intumescent Mastic Sealant - Low Smoke & Toxicity at Astroflame.

View a range of styles

>> See more : Additional product images

>> Call us to order: 01329 844 500

>> Email us to order:


A one water based acrylic sealant designed to resist the passage of fire, by forming a char that prevents the passage of fire and smoke, while maintaining excellent low smoke and toxicity levels.

Astro LST Mastic is halogen free and does not emit halogenated by-products under fire conditions.

High performance fire resistance rating with joint movement capabilities.

Highly flexible and it has good unprimed adhesion to a wide variety of common building substrates.

Tested in Block Wall, Concrete, Masonry and Plasterboard Partition. Tested in Concrete Floors.

Tested in gaps up to 60mm wide.

In normal use it maintains the sound reduction index of a structure.

Mould Resistant.

This sealant contains no raw materials known to have an estrogenic effect in the environment.


General Characteristics

Inspection Method


Product Data (uncured)

Density (S.G)

ASTM D792:13



Paste, matt finish

Resistance to flow

ISO 7390 : 2003


Product Data (after curing)

Hardness Shore A

ISO 7619-1 : 2010


Operating Temperature °C

-5 to 40

Loss Mass of Mass on Heating

ISO 3451-1 (Method A)


Flexibility - Bend Test

ISO 1519


Longevity of Firestop Materials

ASTM E2923 : 14

30 Years



Type X

Astro LST Mastic is not affected by an outdoor environment. However, for long term storage and ease of installation, it is recommended that it should be stored indoors ideally in dry frost free conditions above 0°C and below +30°C.

Product Availability

The Astro LST Mastic Comes Only in White.

Product Code

Product Description



Astro LST Mastic White


To Order & Specify

Please contact us and quote the following information - Quantity / Product Code / Product Description / sizes
Typical wording- 10 / AFIMLST / Astro LST Mastic / 310ml

>> Tel: 01329 844 500 or >> Email:


For further information on installation requirements please review the installation video or contact the technical team on: tel 01329 844 500 or email

Health and Safety

The product does not present any known health hazards during or after installation. Normal good industrial and personal hygiene practices should be observed. For further information on health and safety requirements please contact the technical team on: tel 01329 844 500 or email

Web Page

Astroflame (Fire Seals) Ltd. Intumescent House
Unit 8, The I.O Centre, Stephenson Road, Segensworth
Fareham, England PO15 5RU



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