Dowsil 795 Silicone Sealant

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Description

[Dow Corporation] A one-part, neutral-cure Silicone material used as an adhesive/sealant. DOWSIL™ 795 cures to medium modulus silicone rubber upon exposure to atmospheric moisture. This room temperature vulcanizing (RTV) silicone was introduced in 1960. It has typically been used for case manufacturing in case construction and sometimes mount fabrication. Designed for setting glass in mounting systems while allowing for some movement of the glass within the structure.

Synonyms and Related Terms

Silicone elastomer adhesive; silicone elastomer; room temperature vulcanizing (RTV) silicone

Applications

  • Building sealant/adhesive
  • Metal-to-metal bonding
  • Glass-to-metal bonding
  • Glass-to-wood bonding
  • Metal-to-wood bonding

Personal Risks

Wear eye, hands, and respiratory protection.

SDS: sheets

Collection Risks

Literature indicates the sealant has no significant volatile components. Some silicones have curing byproducts of ethanol, peroxides or ketones. Risk to museum collections could occur if an object comes in contact with the sealant causing possible staining or adhesion (if not fully cured).

Physical and Chemical Properties

Excellent weatherability virtually unaffected by sunlight, rain, snow, ozone and temperature extremes of -40°F (-40°C) to 300°F (149°C). After curing 21 days:

  • Hardness (Shore A) = 35
  • Peel strength = 32 lb/in (5.7 kg/cm)
  • Tension adhesion strength (at 25% extension) = 45 psi (0.310 mPa)
  • Joint movement capacity = +/- 50%

Working Properties

Curing time depends upon humidity and it will initially cure quickly, but the full cure can take a long time. In 50% relative humidity:

  • Working time = 20-30 minutes
  • Tack-free to touch = 3 hours
  • Curing for handling = 7-14 days
  • Full adhesion = 14-21 days

The high flexibility of the cured sealant (+/- 50% joint movement) limits its ability to produce a sealed case with a low air exchange rate. The sealant can be difficult to work with and keep everything clean. Shelf life is listed as 360 days.

Forms and Sizes

  • Colors: 15 standard colors including: Black, white, gray, dusty rose, charcoal, spruce, etc. Can be ordered to match any substrate.
  • Supplied as:
  1. 10.3 fl oz. (305 mL) disposable plastic cartridges that fit ordinary caulking guns
  2. 20 fl oz. (590 mL) sausages
  3. 2 and 4.5-gal (7.5 and 17 L) bulk containers

Resources and Citations

  • Dow Corporation: technical data sheet
  • Dow Corporation: product sheet
  • Skeist, Irving, Handbook of adhesives, second edition.Van Nostrand Reinhold Company, New York, 1977
  • Comyn, John, Adhesion Science, The Royal Society of Chemistry, Cambridge, 1997
  • Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002