Acetoxy Silicone Sealant 

Acetoxy Silicone Sealant Medium/high modulus acetoxy silicone sealant.

  • High strength
  • Good elasticity
  • Conforms to ISO 11600-F&G-20LM
  • Resistant to ozone, ultra-violet radiation and temperature extremes



DowSilTM 781 Acetoxy Silicone Sealant is a one-part, silicone sealant which has good adhesion to a range of non-porous surfaces including glass, aluminum, painted surfaces and composite boards. It offers excellent resistance to aging, shrinkage, cracking and discoloring. It is also approved in certain countries for use in contact with potable water once cured.

Typical Properties

Specification Writers: These values are not intended for use in preparing specifications. Please contact your local DOWSIL sales office or your Global DOWSIL Connection before writing specifications on this product.

Test Method1





Cure system




Application temperature

°C °F

+41 +104



 Specific gravity



CTM 364C

Extrusion rate




Skin-over time (23°C or 73°F, 50% R.H.)



CTM 663A

Cure rate (23°C or 73°F, 50% R.H.)



1 day



3 days



2mm thickness S2 dumb-bells (ISO 37)

CTM 137A

E-Modulus 100%



CTM 137A

Tensile strength



CTM 137A

Elongation at break



 12x12x50mm size T.A. joint (ISO 8339/DIN2-8339)

CTM 677

E-Modulus 100%



CTM 677

E-Modulus 60%



CTM 677

Tensile strength



CTM 677

Elongation at break




Hardness (Shore A)



ISO 9047

Joint movement capability



1. CTM: Corporate Test Method, copies of CTMs are available on request. DIN: Deutsche Industrie Norm. ISO: International Standardisation Organisation.

Technical Specifications & Standards

Conforms to ISO 11600-F&G-20LM. Listed by the UK Water Fittings Byelaws Scheme for use in contact with potable water, once cured.

How to use

Surface Preparation: Ensure that surfaces to be sealed are clean, dry, sound and free from frost, release agents, old sealants and other contaminants which could impair adhesion. All surfaces should be cleaned and degreased by wiping with a suitable solvent such as DOWSILTM R40 Universal Cleaner on a clean oil- and lint-free cloth before application of sealant. 

Note: When using any solvent, always provide adequate ventilation. Avoid heat, sparks and open flames. Use solvent resistant gloves. Observe and follow all precautions listed on solvent container label. 

Masking: 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. 

Priming: All joint surfaces other than glass and glazed ceramics should be primed. For specific advice, please refer to the DOWSILTM Primers’ Guide or contact one of DOWSIL’s Regional Service Centers for technical assistance. 

Back-up materials: When back-up material is required, a closed cell polyethylene backer rod is recommended. Low tack polyethylene tape should be used in joints too shallow to allow the use of a backer rod. Back-up materials provide back pressure and prevent three sided adhesion that limits sealant movement capability. 

Finishing: 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. 

Clean-up: Excess sealant may be cleaned off tools and non-porous surfaces whilst in an uncured state using DOW CORNING® R40 Universal Cleaner. If sealant is misapplied to porous substrates, it should be left until it is just cured and then removed by peeling, cutting or other mechanical means. Care should be taken not to damage plastic or coated surfaces. 

Joint design: The sealant joint width should be designed to accommodate the movement capability of the sealant. When designing joints using DOW CORNING® 781 Silicone Sealant, the minimum width should be 6mm. For joints between 6- 12mm wide, a seal depth of 6mm is required. For joints above 12mm wide, a width to depth ratio of 2:1 should be used. In situations where fillet joints are needed, a minimum of 6mm sealant bite to each substrate is recommended. For joint dimensions greater than 25mm, please contact one of DOWSIL’s Regional Service Centers for technical assistance.

Handling Precautions

Product safety information required for safe use is not included. 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.

Usable Life & Storage

When stored in cool, dry conditions below 30°C (86°F) in the original unopened containers, DowSilTM 781 Silicone Sealant has a usable life of 27 months from the date of production.


DowSilTM 781 Silicone Sealant is supplied in 310ml cartridges packed in boxes of 12.


DowSilTM 781 Silicone Sealant is not recommended for use on porous substrates such as concrete, stone, marble or granite. DowSilTM 781 Silicone Sealant should not be used in contact with the edge seal of an insulated glazing unit. Do not use DowSilTM 781 Silicone Sealant on bituminous substrates, substrates based on natural rubber, choloroprene or EPDM, or on building materials and flexible plastics which might bleed oils, plasticizers, or solvents. Do not use DowSilTM 781 Silicone Sealant in a totally confined space because the sealant requires atmospheric moisture to cure. Because acetic acid is released during curing, it can corrode mirror silver and sensitive metals such as copper, brass and lead. DowSilTM 781 Mirror Adhesive should be used for this application. DowSilTM 781 Silicone Sealant is not recommended for use on submerged joints, or in joints where physical abuse or abrasion is likely to occur. DowSilTM 781 Silicone Sealant is not suitable for food contact applications. However, it has been listed by the UK Water Fittings Byelaws Scheme for use in contact with potable water, once cured. DowSilTM 781 Silicone Sealant has not been designed for use as an aquarium sealant. DowSilTM 781 Silicone Sealant is not recommended for structural glazing or insulated glazing applications. DowSilTM 781 Silicone Sealant is not recommended for structural glazing or insulated glazing applications. This product is neither tested nor represented as suitable for medical or pharmaceutical uses.

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. DOWSIL SPECIFICALLY DISCLAIMS ANY OTHER EXPRESS OR IMPLIED WARRANTY OF FITNESS FOR A PARTICULAR PURPOSE OR MERCHANTABILITY. DOWSIL DISCLAIMS LIABILITY FOR ANY INCIDENTAL OR CONSEQUENTIAL DAMAGES. We help you invent the future.™

Fillet Joint
Shallow Joint