Dow Corning 795 vs RTV108 Comparison: Aquarium Silicone
The two silicones that turn up most often in Singapore DIY tank threads are Dow Corning 795 and Momentive RTV108, and picking between them is less about marketing and more about cure chemistry. This dow corning 795 vs rtv108 comparison from Gensou Aquascaping at 5 Everton Park draws on real builds where we have used both products, sometimes on the same tank for different joints. Expect straight answers on which product suits rimless nanos, which handles large cube builds, and why the cure time difference matters more in humid SG than in temperate climates.
Cure Chemistry: Neutral vs Acetoxy
Dow 795 is a neutral-cure silicone releasing alkoxy byproducts as it sets, while RTV108 is acetoxy-cure releasing acetic acid. The practical difference is that 795 does not smell and does not corrode metal fasteners or etch painted surfaces nearby. RTV108 reeks of vinegar during cure and will tarnish copper, brass, and some zinc-plated hardware if applied too close. For tanks with stainless lid hinges or aluminium bracing, 795 is the safer choice.
Cure Speed in Singapore Conditions
In SG humidity RTV108 skins in 8 to 12 minutes and tooling window closes fast; 795 gives you 20 to 30 minutes of working time before skin forms. For a first-time builder assembling a large cube with multiple corners to seam at once, the extended 795 window is a genuine advantage. Experienced builders often prefer RTV108 because the faster cure means earlier unclamping and water testing. Full structural cure for 795 takes 5 to 7 days versus 2 to 3 for RTV108.
Mechanical Properties Compared
RTV108 cures to a medium-modulus silicone with tensile strength around 2.4 MPa and 500 percent elongation at break. Dow 795 is higher-modulus at 3.1 MPa tensile with 400 percent elongation, making it stiffer and stronger per cross-section. For glass tanks over 600 litres or unusual geometries like peninsula or zero-edge rimless, 795’s higher strength margin is the sensible pick. For nano and small-medium tanks under 400 litres, RTV108’s elasticity handles thermal cycling without stress transfer to the glass edge.
Bond to Glass
Both silicones bond cohesively to clean float glass, meaning the silicone tears before the bond releases. In pull tests, 795 shows slightly higher peel resistance on 19 mm glass but the difference is academic at the bond thicknesses used in aquaria. Surface prep matters far more than product choice; acetone-wiped edges, dry glass, and no oil contamination are the variables that actually determine whether a seam lasts 20 years or fails in two.
Structural Glazing Use Case
Dow 795 was originally designed for structural glazing in commercial architecture, bonding glass panels to steel curtain walls exposed to wind load and UV. That pedigree transfers usefully to large aquariums with long unsupported panels. RTV108 evolved from general-purpose RTV silicones and suits smaller glass-on-glass applications. For a rimless 120 cm cube at 10 mm glass, 795 is the cleaner engineering call; for a 45 cm nano, RTV108 finishes faster with equal safety.
Fish Safety After Cure
Both products are fish-safe once fully cured. Dow 795 carries no fungicide or plasticiser; RTV108 is the aquarium-industry workhorse without biocide additives. Wait the full cure time before filling; for 795 that is 5 to 7 days at SG humidity, for RTV108 48 to 72 hours. Curing fumes on both products should be vented; do not cure a tank in a sealed HDB kitchen. Our aquarium safe silicone guide covers fish-safety verification steps before fill.
Availability and Pricing in Singapore
Dow 795 is stocked by Sealants Asia, Dow distributors along Joo Koon, and some specialty hardware in Rowell Road, typically $28 to $38 per 300 ml cartridge in clear or black. RTV108 runs $18 to $24 at the same outlets. Online via Shopee, both products are available but check manufacturer codes and expiry; ancient 795 cartridges with chalky nozzle tips are worthless. For small repair jobs the cost gap is trivial; for a large cube build, the total silicone bill might differ by $40 to $60.
Which to Choose for Common Builds
For a rimless nano under 200 litres, RTV108 is our default. For a mixed reef cube between 200 and 500 litres, either product works; pick on working-time preference. For a large peninsula or zero-edge build over 500 litres, or any tank with glass thicker than 15 mm, choose Dow 795 for the mechanical margin. For repair work on existing tanks, match the original product type; modern tanks are usually RTV108 or equivalent acetoxy silicone.
Handling the Unused Cartridge
Both silicones are hygroscopic once opened. Dow 795 actually stores slightly longer after partial use because neutral-cure chemistry is less moisture-reactive; a partially used 795 cartridge stays workable for 6 to 8 weeks in a sealed bag, while RTV108 dries out in 3 to 4 weeks. For occasional DIY use, 795 wastes less product across multiple small jobs. Our best aquarium silicone sealant guide covers storage and cartridge reuse.
The SG Hardware Reality
Hardware City staff will sometimes offer “aquarium silicone” that is neither 795 nor RTV108 but an unknown acetoxy bathroom-grade product. Always read labels for “no fungicide” or “neutral cure without biocide” and verify against manufacturer datasheets. If the cartridge lacks clear brand identification, walk away. The $5 saved on mystery silicone rarely survives a contact with the first stocked reef tank.
Final Recommendation
Both silicones deserve their reputations; the choice is about build scale and working time. For most Singapore hobbyists building tanks under 400 litres, RTV108 is the sensible default. For large custom builds or anyone who values the longer tooling window, Dow 795 is worth the premium. Either way, clean your glass, respect the cure time, and expect the joint to outlast the fish you put inside it.
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