High performance, high modulus, one component, acetoxy cure silicone sealant.
SIR-O-SIL 25™ is an easy to apply, one component sealant that cures to a durable, flexible, silicone rubber upon exposure to atmospheric moisture.

SIR-O-SIL 25™ has been specifically designed for fast curing and excellent adhesion to non-porous surfaces such as glass, metals and ceramics. SIR-O-SIL 25™ is a highly flexible silicone sealant which accommodates joint movement of +/-25 percent.

Basic Uses

SIR-O-SIL 25™ has been developed for building construction and industrial sealing applications. SIR-O-SIL 25™ is particularly effective for glazing joints and sealing curtain wall applications. SIR-O-SIL 25™ applications include:
  • Weather sealing.
  • Top sealing in glazing applications.
  • Waterproofing between glass and aluminum.
  • Sealing around worktops.
  • General industrial uses.
  • Hygiene seals in refrigeration and food preparation areas.


  • Excellent gunnability throughout a wide temperature range.
  • Excellent unprimed adhesion to most common non-porous substrates.
  • Long product life expectancy.
  • Highly resistant to ultraviolet light, ozone, moisture and extreme temperature variations.
  • Dry tools easily to a smooth, attractive finish.
  • Good tear resistance.
  • Excellent movement capabilities (+/- 25%).
  • Rubberlike properties are maintained throughout product life.
  • Service temperature range -65ºF to 400ºF (-54ºC to 204ºC).
  • Skins quickly.
  • No special cold storage requirements are necessary.


  • Glazing of insulated glass units sealed with two-part silicone secondary seals.
  • Exterior below grade use.
  • Continuous water immersion.
  • Applications over tars, asphalt or materials that bleed oils, plasticizers or solvents.
  • Porous substrates.
  • Applications in airtight enclosures as the sealant requires atmospheric moisture to cure.
  • Horizontal traffic joints.


SIR-O-SIL 25™ is available in 10.1 fl. oz. (299 ml) cartridges, 12 cartridges per case/140 per skid. Bulk packaging (5, and 55 gallon containers) is available by special request.


Clear, White, Almond, Bronze, Black, Aluminum and Tan .

Typical Properties

As Supplied
Flow, Sag or Slump
Tack-Free Time at 77ºF (25ºC) 50 RH minutes
Tooling Time, minutes 
As Cured - After 7 days 77ºF (25ºC) and 50% RH
Durometer Hardness, Shore A, points
Ultimate Tensile Strength, PSI (MPa)
245 (1.58)
Tear Strength, PPI (kN/m)
25 (4.4)
Peel Strength, PPI (kN/m)
20 (3.5)
Movement Capability, percent
Weathering (6,000 hours in Atlas Weatherometer)
No change in hardness or color
Shelf life, Months
Extrusion Rate, g/sec
Please contact Siroflex® Inc. Greenville, SC prior to writing specifications on this product.

Application Standards

SIR-O-SIL 25™ Silicone Sealant meets or exceeds the test requirements of:
  • Federal Specification TT-S-0001543A (COM-NBS) Class A.
  • Federal Specification TT-S-00230C (COM-NBS) Type 11, Class A.
  • ASTM Specification: C-920 Type S, Grade NS, Class 25, Use T, NT, M, G, A: and GSA (C.I.D.) No. AA-1556 Type S, Grade NS, Class 25, Use T, NT, M, G, A.
  • FDA-USDA Approved under food additive regulation 121.2514.

Storage Life

Product Shelf life is 12 months under normal storage conditions of 80ºF (27ºC) or less. No special cold temperature storage provisions are required.


Immediately available from both Siroflex® Inc. distributors and distribution centers strategically located throughout the U.S. For more information contact Siroflex® Inc. customer service department 1.800.359.6398.

Bead Configuration for General Purpose Sealing

SIR-0-SIL 25™ silicone sealant should have a ratio of approximately twice the joint width to sealant depth. The sealant depth should be not less than 3/16" (4.8mm, minimum) and not greater than 1/2" (12.7 mm, minimum). See the table below.
 Joint Width-to-Depth Recommendations for General Purpose Sealing
B. Depth
C. Lineal ft./gal

Joint Backing - Bond Breaker

Joint backing should be used to control the recommended joint depth and prevent 3-sided adhesion. Joint backing may be open cell polyurethane foam or closed cell polyethylene. Joint backing must be thoroughly dry. Where joint design or depth will prevent the use of joint backing, an approved adhesive backed polyethylene bond breaker tape must be installed to prevent 3-sided adhesion. Do not install more joint backing or bond breaker tape than can be caulked in one day.


SIR-O-SIL 25™ can easily be applied with conventional hand or air-powered caulking equipment. The sealant should be applied in a continuous operation with adequate pressure to fill the joint to the proper width and depth. (Do not overfill the joint.)


Dry tool the sealant with light pressure immediately after application to ensure positive and complete contact of the sealant to the joint interfaces.


Should masking be required, it is recommended the masking tape be removed immediately after tooling, before sealant skins. If necessary, the sealant can be installed below freezing provided the surfaces are clean, dry and frost-free. We recommend, however, for best conditions and performance, that the sealant be applied above 40ºF (4ºC).

Cure Rate

7-14 days


Cleaning of equipment and tools can be accomplished with solvents such as xylol, toluol or methyl ethyl ketone (MEK) while sealant is uncured.

Notice to Purchaser

Siroflex® Inc. warrants its products to conform to Siroflex®  Inc. published specifications. The user shall determine the suitability of the product to their particular application. the foregoing warranty is in lieu of all other warranties expressed or implied, including those of the merchantability or fitness for any purpose not expressly set forth herein. Manufacturer’s and seller’s liability for damage hereunder shall not exceed the purchase value of the goods used. IN NO EVENT SHALL MANUFACTURER OR SELLER BE RESPONSIBLE FOR INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF OR IN CONNECTION WITH THE USE OF THIS PRODUCT BY BUYER, BUYER’S USER, OR ANY OTHER PERSON. Notification of claim must be sent in writing to Siroflex® Inc. The notice should contain a statement as to how the product failed to meet our warranty, the proof of purchase and the amount of refund claimed.


For more information, refer to the SIR-O-SIL 25 TM SDS.