One-part intumescent acrylic rubber


DOWSIL™ FIRESTOP 400 Sealant is a one-part, fire rated intumescent acrylic sealant designed for internal perimeter pointing of fire rated door and window frames, where the integrity of fire walls or partitions need to be maintained. It has good adhesion to a wide variety of substrates without the use of primer. It has intumescent qualities which enable the material to swell under heat conditions producing a fire and smoke resistant seal. DOWSIL FIRESTOP 400 Sealant does not emit halogenated byproducts under fire conditions.

  • A fire rating of up to 2 hours can be achieved
  • Class 2 surface spread of flame classification
  • Mean toxicity index 2.0
  • Good unprimed adhesion to most common construction substrates
  • Easy to use, one-component sealant

For internal perimeter pointing around door and window frames, where the integrity of fire walls need to be maintained, and in the small joints formed where fire rated partition sections meet.

Typical Properties

Specification Writers: These values are not intended for use in preparing specifications.

Property Unit Result
Physical form Non-slumping paste
Slump mm 0.5
Tack-free time minutes 45-60
UV resistance Good
Joint movement capability % ±7.5


Technical Specifications & Standards

DOWSIL FIRESTOP 400 Sealant has been tested to BS 476 Part 22/1987 in joint configurations SGS (UK) Ltd. Test report No. J89325/1.

DOWSIL FIRESTOP 400 Sealant meets Class 2 of BS 476 Part 7/1987 for surface spread of flame, SGS (UK) Ltd. Test report No. J90327/2.

DOWSIL FIRESTOP 400 Sealant has a mean toxicity index of 2.0 when tested according to NES713, SGS (UK) Ltd. Test report No. J90726/2.

Fire Ratings

Fire test data is available showing that DOWSIL FIRESTOP 400 Sealant, can achieve up to a 2 hour fire rating at specified joint configurations. The fire ratings achieved have been tested according to BS 476 Part 22/1987 and are specific to the conditions of testing. They do, however, provide a good indication of the expected performance of the sealant in fire situations. DOWSIL FIRESTOP 400 Sealant has been tested to BS 476 Part 7/1987 in accordance with the flame spread classification given in this standard. Results show the material has a Class 2 surface.
Users should satisfy themselves that DOWSIL FIRESTOP 400 Sealant is suitable for their specific application. Testing of a particular system may be required. To achieve a specific fire rating, all substrates being used in the system must have an equivalent fire rating.

Handling Precautions

Product safety information required for safe use is not included in this document. Before handling, read product and safety data sheets and container labels for safe use, physical and health hazard information. The material safety data sheet is available on the DOWSIL website at You can also obtain a copy from your local DOWSIL sales representative or Distributor or by calling your local DOWSIL Global Connection.

Joint Design

 Figure 1

Ensure that all surfaces are clean, dry, sound and free from frost. Clean all joints of loose dust, dirt, laitance, old sealants and other contaminants which could impair adhesion.
Surfaces should be cleaned and degreased by wiping with a solvent, such as DOWSIL™ R-40 Universal Cleaner, using a lint- and oil-free cloth.
Note: When using any cleaning solvent, always provide adequate ventilation. Avoid heat, sparks and open flames. Observe and follow all precautions listed on solvent container label or product safety data sheet.
It is recommended that DOWSIL FIRESTOP 400 Sealant is not applied to surfaces that are below 5°C (41°F) as it is impossible to guarantee a frost-free surface at these temperatures.
DOWSIL FIRESTOP 400 Sealant has excellent adhesion to most common construction substrates. If in doubt, or if unusual substrates are involved, please contact your local technical services department.
Back-up materials
Closed-cell polyethylene foam backer rod or mineral wool should be used as specified in the fire test data.
Areas adjacent to the joints should be masked with tape to prevent contamination of the substrates and to ensure a neat sealant line. Masking tape should be removed immediately after tooling.
The joint should be tooled within 5 minutes of application to ensure good contact between the sealant and the substrate. Tooling of the sealant also gives a smooth, professional finish.
Uncured material can be removed by wiping with a dampened cloth. Cured material can be carefully removed by abrasion or other mechanical means.

Usable Life & Storage

When stored in cool, dry conditions below 5°C (41°F) and 23°C (73.4°F) in the original unopened containers, DOWSIL FIRESTOP 400 Sealant has a usable life of 12 months from the date of production.


DOWSILTM 400 Sealant is available in 380 ml cartridge, (packed in boxes of 20) in white and grey.


DOWSILTM 400 Sealant is not recommended forSealant is not recommended for external applications and has not been tested for use as a penetration seal.
It should not be applied to building materials that bleed oils, plasticisers or solvents. It is recommended to consult your local technical services department for further advice in specific applications.
All acrylic based sealants are susceptible to a degree of shrinkage. This should be taken into account when applying the material.

Health & Environmental Information

To support Customers in their product safety needs, DOWSIL has an extensive Product Stewardship organization and a team of Product Safety and Regulatory Compliance (PS&RC) specialists available in each area.

For further information, please see our website, or consult your local DOWSIL representative.

Limited Warranty Information – Please Read Carefully

The information contained herein is offered in good faith and is believed to be accurate. However, because conditions and methods of use of our products are beyond our control, this information should not be used in substitution for customer’s tests to ensure that DOWSIL’s products are safe, effective, and fully satisfactory for the intended end use. Suggestions of use shall not be taken as inducements to infringe any patent.

DOWSIL’s sole warranty is that the product will meet the Dow Corning sales specifications in effect at the time of shipment.

Your exclusive remedy for breach of such warranty is limited to refund of purchase price or replacement of any product shown to be other than as warranted.


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Joint Design