Momentive RTV108 Aquarium Silicone Review
Ask any SG tank builder over forty what silicone lined their first rimless and the answer comes back the same: RTV108. Momentive RTV108 aquarium silicone has carried the structural bonds in regional tank factories for decades, and this review from Gensou Aquascaping at 5 Everton Park is based on two dozen DIY builds and seam repairs we have done with cartridges sourced locally. Expect specifics on cure behaviour under Singapore humidity, bead geometry for glass-to-glass joints, and how the product stacks against the current Dow and Wacker options stocked in SG Hardware City.
Product Background
RTV108 is a one-part, acetoxy-cure silicone originally developed by General Electric and now sold under the Momentive Performance Materials brand after the 2007 spin-off. It is a translucent, medium-modulus sealant rated for continuous service between -60 and 200 °C. The chemistry releases acetic acid during cure, which is why every fresh cartridge smells like vinegar. Crucially, RTV108 is aquarium-safe once fully cured; the cured silicone is inert and has been used in laboratory aquaria, pharmaceutical glassware, and tank manufacture since the 1970s.
Cure Time in Singapore Humidity
Acetoxy silicones cure faster in humid air because moisture drives the crosslinking reaction. At Singapore’s typical 75 to 85 percent relative humidity, RTV108 skins over in 8 to 12 minutes and reaches tack-free surface in 30 to 45 minutes. Full structural cure for a 3 mm bead takes 24 to 48 hours; thicker beads over 6 mm need 72 hours minimum before water testing. Compare this with drier climates where full cure stretches to 5 days. The humidity is a genuine advantage for SG tank builders.
Bond Strength on Float Glass
We have pull-tested RTV108 joints on cleaned 10 mm float glass and the cured silicone fails cohesively rather than adhesively, meaning the silicone tears before the glass bond releases. Tensile strength sits around 2.4 MPa with elongation at break above 500 percent, figures that match the datasheet. For context, that is comparable with Dow 732 and slightly softer than Dow 795. The elasticity matters; a stiffer silicone transfers stress to the glass edge and causes chipping at seam corners over years.
Bead Geometry for Tank Seams
Inside seams on a standard rimless build want a 6 to 8 mm triangular bead pressed into the corner after the glass is racked square and clamped. Smooth with a wet finger or a plastic spatula dipped in soapy water; too much pressure forces silicone out of the joint and creates a weaker bond line. The exterior of the joint should show an even 3 mm fillet on the outside. Internal application is structural; external application is cosmetic and hydraulic seal. Our aquarium silicone application guide covers the full technique.
Food-Safe Cure and Fish Safety
Cured RTV108 is food-safe and FDA-listed under 21 CFR 177.2600 for repeated food contact. Uncured silicone and curing fumes contain acetic acid; vent the room and wait the full 48 to 72 hours before filling. We have seen impatient builders fill tanks at 12 hours and lose fish to low-level acetate leaching. Patience costs nothing; the tank will stand for decades, what is another day?
RTV108 vs Mould-Growth Variants
General-purpose bathroom silicones contain fungicides to prevent mould growth and are toxic to fish. RTV108 does not include these additives and carries no anti-fungal, which is why it works for aquaria. Read the label carefully; Selleys Ezy Mould, Dow 781, and most bathroom-grade products in SG Hardware City are unsafe. Only pure neutral-cure or acetoxy-cure silicones without biocide additives belong anywhere near a tank. The aquarium safe silicone guide runs through the label red flags.
Where to Buy in Singapore
Cartridges of RTV108 are harder to find than they were a decade ago. SG Hardware City stalls along Rowell Road still carry stock at $18 to $24 per 300 ml cartridge, usually black or clear. Industrial supply houses along Defu Lane stock it for glaziers and laboratory builders. Shopee listings run $22 to $30 but check cartridge date codes; silicone past 18 months from manufacture will show slow cure and weak final bond. Avoid anything with a chalky film on the nozzle tip.
Shelf Life and Storage
Unopened cartridges keep 12 to 18 months in cool storage. Once the foil seal is punctured, plan to use the cartridge within 30 days; moisture enters the nozzle and cures the silicone from the tip inward. Store partial cartridges nozzle-up in a ziplock bag with silica gel. A dried-out tip can be cut back 10 mm to reach fresh silicone underneath but once the cartridge solidifies internally, it is landfill.
Common Application Mistakes
The most common failure is applying silicone to glass with residual glass cleaner or oil on the surface. Clean edges with acetone or isopropyl alcohol immediately before bonding; do not use Windex. Second most common is tooling the bead too wet with soap; a little is fine, too much weakens surface adhesion. Third is disturbing the bead after skinning starts; once the surface films over at 10 minutes, stop touching it.
Repair vs New Build Use
RTV108 performs equally well for new tank construction and for repair of small leaks up to about 30 cm bead length. Full tank rebuilds on old silicone are a different matter; removing ancient silicone, cleaning glass to bond-ready condition, and re-bonding is often more effort than buying a new tank. For small interior fillet repairs on tanks under 200 litres, RTV108 is the first tool we reach for.
Verdict
For Singapore DIY tank builders, RTV108 remains the standard against which other silicones are judged. Its humidity-accelerated cure, elongation, and long safety track record justify the slight premium over bargain bathroom silicone. For tanks above 600 litres or unusual geometry, move up to Dow 795; for everything else RTV108 is still the sensible choice.
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emilynakatani
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5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
