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 London Underground stations.

Tested for passenger carrying train systems to BS6853:1999 * and LUL approved

Low smoke and toxicity levels.

Tested in accordance with EN 1366-3 : 2009 and EN 1363-1 : 1999.

Tested BS 6853:1999 D8.3: Smoke Ao (max)

Fire Classification to EN 13501-2.

Tested in accordance with En 10140-2 : 2010.

Tested BS 6853:1999 B.1: Toxicity R value

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 rating. Joint movement capability of +/- 12% .

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.

Performance Table


0-5mm After 1hr in 30mm Joints


Approximately 12%

Cure Rate

3mm Per day at 50% Relative humidity 23°C

Shore A Hardness


Application Temperature

+ 5°C to + 30°C

Tack Free

15 mins at 23°C, 50 RH

Joint Movement

+ 12% of Original Size

Fire Resistance

EN 1366-3 EI120 , EN 1366-4 EI240 & BS476 300mins


EN1366-3 & EN1366-4 120mins

Smoke & Toxicity

BS 6853 , ISO 4589

Air Permeability

EN 1026 to 600Pa 100Pa 11.1/2.8m3/h/m2


EN 13501-2 , ISO 11600

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

Astroflame (Fire Seals) Ltd. Intumescent House
Unit 8, The IO Centre, Stephenson Road, Segensworth
tel 0800 023 2482
(01329 844500)
fax 0800 023 2483
(01329 844600)
tel +44 1329 844500
fax +44 1329 844600



Email Astroflame