PEPermatex
Permatex
Permatex 81781 Black Silicone Sealant
- RTV silicone
- Aquarium safe formulations available
- Waterproof
- Flexible
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On this page
Is the Permatex 81781 Black Silicone Sealant worth it?
Yes, for the right buyer. The Permatex 81781 Black Silicone Sealant ranks #5 in our Best Glue for Glass to Glass 2026 list (best aquarium seal). Its biggest strength: rTV silicone is the standard material for aquarium seams - used by all aquarium manufacturers. The main caveat: not clear - black or white only.
Overview
What the Permatex 81781 Black Silicone Sealant does well
Required for aquarium and water-containment glass bonding. Its case rests on rTV silicone is the standard material for aquarium seams - used by all aquarium manufacturers and flexible cure prevents joint failure from water pressure changes. Keep in mind that not clear - black or white only.
Specs that matter
Key features
- RTV silicone
- Aquarium safe formulations available
- Waterproof
- Flexible
The trade-offs
Pros & cons
Pros
- RTV silicone is the standard material for aquarium seams - used by all aquarium manufacturers
- Flexible cure prevents joint failure from water pressure changes
- Waterproof permanently - the only correct choice for water-containing glass structures
Cons
- Not clear - black or white only
- Requires 24-48 hour cure before water contact
Fit check
Should you buy the Permatex 81781 Black Silicone Sealant?
Buy it if you're…
- Shopping for glass to glass 2026
Think twice if this matters to you
- Not clear - black or white only
- Requires 24-48 hour cure before water contact
Where it ranks
Featured in 1 best-of list
| List | Rank |
|---|---|
| Best Glue for Glass to Glass 2026· Best Aquarium Seal | #5 / 10 |
Cross-shop
Alternatives to the Permatex 81781 Black Silicone Sealant
Products ranked near it in our research, each better for a slightly different buyer.
- Best Uv CureBONDIC
BONDIC UV Resin Liquid Plastic Welder
- UV cure - hardens in 4 seconds under UV light
- No cure until UV exposure
Buying advice: adhesives
- Porous materials like wood, paper and fabric bond well with water-based glues. Non-porous ones like metal, glass and most plastics need epoxy, cyanoacrylate or a polyurethane adhesive. Polyethylene and polypropylene resist almost everything, so check the label lists them.
- Thin glues need parts that meet closely. If the joint is loose or the surfaces are uneven, epoxy or polyurethane glue fills the gap and still holds.
- Fast-setting glue is convenient for small fixes but leaves no time to adjust a big assembly. For furniture and glue-ups, a longer open time is worth more than speed.
- Standard PVA softens with moisture. For outdoor projects, cutting boards or anything washed often, look for a water-resistant (Type II) or waterproof (Type I) rating, or use epoxy.
- Once opened, super glue and some epoxies thicken within months. Smaller bottles that you finish quickly often work out cheaper than a big one that goes off.
Answers
Permatex 81781 Black Silicone Sealant: common questions
Is the Permatex 81781 Black Silicone Sealant worth buying?
Yes, for the right buyer. The Permatex 81781 Black Silicone Sealant ranks #5 in our Best Glue for Glass to Glass 2026 list (best aquarium seal). Its biggest strength: rTV silicone is the standard material for aquarium seams - used by all aquarium manufacturers. The main caveat: not clear - black or white only.
Who is the Permatex 81781 Black Silicone Sealant best for?
Based on our research it suits glass to glass 2026. It's ranked #5 of 10 in our Best Glue for Glass to Glass 2026 list.
What are the downsides of the Permatex 81781 Black Silicone Sealant?
The main trade-offs owners and reviewers point to: not clear - black or white only; requires 24-48 hour cure before water contact.
What are the key features of the Permatex 81781 Black Silicone Sealant?
RTV silicone, Aquarium safe formulations available, Waterproof and Flexible.
What are the best alternatives to the Permatex 81781 Black Silicone Sealant?
Worth comparing: Gorilla 2-Part Epoxy, E6000 Craft Adhesive and BONDIC UV Resin Liquid Plastic Welder. Each ranks near it in our research for a slightly different buyer.
Where can I buy the Permatex 81781 Black Silicone Sealant?
It's sold on Amazon. Prices and stock change often, so check the current listing before you buy, our link takes you straight to it.