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Gyprock Fire Mastic is a permanently flexible, water based acrylic sealant for fire resistant caulking of penetrations and joints in plasterboard walls and ceilings

Product Overview

Gyprock Fire Mastic is an off-white, low VOC, fire and acoustic sealant manufactured to stringent product specifications, and features in many Gyprock fire and acoustic rated systems. It is a one-part water based sealant with a working life of 30 minutes and a skin time of 15mins. It provides a neutral paintable surface once cured, and is intumescent, expanding when exposed to fire or extreme heat.

Typical Applications

Gyprock Fire Mastic is designed to create a fire resistant seal around pipes, conduits, busways, cable trays and ducts which penetrate walls, floors and ceilings. It will bond to plasterboard, masonry, concrete, steel, and cable coverings.


*CSR Gyprock only support the use of Gyprock Fire Mastic sealant when used as part of specified Gyprock systems as noted in our literature.

Extensively Tested

Fire Testing

Gyprock Fire Mastic has been tested for periods of up to four hours, in systems, in accordance with AS1530.4 and achieved the following fire resistance levels (FRL):

- Plasterboard systems up to FRL 120/120/120.
- Masonry systems up to FRL 240/240/240.

Mechanical Testing

Tests to AS4072 have shown that Gyprock Fire Mastic has movement capabilities of ±20% after curing, which means that this product remains flexible and resists cracking.



Gyprock® Fire Mastic
sealants icon with caulking gun


Off-white acrylic sealant

fire rated icon with flame

Fire-rated Properties

Assists in fire-rated caulking of penetrations and junctions

acoustic performance icon with sound

Acoustic Properties

High acoustic rating when used in a system

Technical Specifications

Product Options

Gyprock Fire Mastic is available in a 600ml sausage and has a shelf life of 12 months from date of manufacture.

For product availability and to place an order, contact your nearest supplier.

Physical & Chemical Properties

Appearance Off White paste
Working time Skin time = 15mins, Working time = 30mins
Joint movement capability +/- 20%
Intumescent Yes
Specific gravity (H20=1) ~ 1.55
Acoustic rating Rw Tested to Rw + Ctr 55 as a gap sealant in a wall system.
Fire rating

For use in junctions and penetrations in CSR Gyprock wall systems rated up to 120/120/120. Refer to Gyprock The Red Book for details

Isocyanate free Yes
VOC content (as specified by GBCA) 8g/L as VOC content per material
Service temperature -20 to 80oC
Hardness (Shore A) ~ 35

Product Manufacture

FireMastic is manufactured for CSR Gyprock in Australia to stringent product specifications.


Store unopened sausages below 30°C in a cool dry place away from direct sunlight. Opened sausages may skin and form a lump near the opening. Discard any lumps or skin and remaining product can be used.

Health and Safety

Safety Data Sheets are available on the Gyprock web site. They are important documents in the construction industry and assist in the continuing focus on occupational health and safety on and off work sites.

Installation Instructions

Surface Preparation

Ensure substrate surfaces are clean, sound, dry and free of oil, grease and surface contaminants such as dust, loose particles, release agents, silicone and water repellents.
This is particularly important regarding highly porous surfaces such as aerated concrete or cut edges of plasterboard. In circumstances where it is difficult to ensure completely dust free surfaces applying by brush a 1:1 solution of Fire Mastic and water as a primer will assist to improve the integrity of the substrate. Areas adjacent to joints may be masked to provide a neat finish. Masking should be removed immediately after tooling


Apply Fire Mastic in ambient conditions between 5 and 35 degrees centigrade. Higher temperatures should be avoided to prevent the possibility of bubbling of the
sealant due to rapid moisture evaporation. Do not apply below 5 degrees centigrade.
Fill joint with trowel or caulking gun, then tool off with a spatula and clean off excess with a damp cloth.


Protect from water for at least 24 hours until a suitable skin has cured (will require significantly longer at temperatures below 15 degrees centigrade). Some shrinkage is normal during curing, and should be anticipated when measuring joints.

Firemastic is not recommended for use in external applications where 2 non-porous substrates need to be sealed. In these situations, Firemastic will be very slow curing and any water from rain, dew, fog etc may result in wash-out of Firemastic from the joint.


Clean up

After applying Fire Mastic, clean all tools and metal surfaces with warm water while the sealant is still wet. Cured sealant will need to be removed mechanically.


Firemastic sealant is suitable for painting when fully cured. To avoid paint cracking issue, Firemastic should be cured for at least 24 hours, longer under adverse drying conditions (cooler, high humidity) before painting where possible. In standard conditions (25 °C or higher) Firemastic may be painted after 6 hours, however, care should be taken to ensure a flexible acrylic coating is used and that a firm skin has developed.


  • Do not apply to wet surfaces, contaminated, dusty, loose substrate surfaces.
  • Firemastic sealant may be used both for interior and exterior sealing, but not recommended for use in water retaining structures or water may be pooling.
  • Firemastic is not recommended in exterior applications where non-porous substrates are to be sealed.
  • Firemastic sealant has good servicing characteristics when unprotected in internal applications.
  • For external use, Firemastic sealant must be protected from direct rain or water, until such time as the sealant builds up a thick skin to avoid washout. Therefore, do not apply sealant when rain exposure is likely before a thick skin has develop. This is typically 24 hours in summer (25 °C or higher), but will be significantly longer in cooler, high humidity conditions.



Gyprock makes available resources that provide comprehensive selection, design, installation and maintenance guidance. 

Commercial Installation Guide

Design considerations and installation instructions.

Manufactured For Life red logo with the shape of Australia in the centre.

Manufactured for Life

Gyprock plasterboard products are manufactured for life with all CSR products designed to achieve optimal performance when part of a CSR integrated system.