CT1 turns up on almost every trade job, but the name does not always come with an explanation. You have seen it on the shelf next to the silicones, you may have been told to use it on a spec, and now you want to know what it actually is, what it does that standard silicone cannot, and whether it is worth carrying on the van. This guide covers all of it: the chemistry, the substrates, what it replaces, where it earns its place on an electrical job, and where to buy it locally at trade prices.
The short answer: CT1 is a hybrid sealant and construction adhesive manufactured by C-Tec. Built on TRIBRID polymer technology, it bonds and seals in one 290ml cartridge, replacing silicone, acrylic, butyl and polyurethane products across virtually any substrate, without primers and without mechanical fixings.
Who Makes CT1?
CT1 is manufactured by C-Tec, a Northern Irish company that has built its range around a single proprietary chemistry: the TRIBRID polymer. C-Tec developed CT1 as the founding product in that range and has since extended it into specialised sister products for bathrooms, decorating and surface preparation. Every product in the full CT1 range at Harbro shares the same TRIBRID core.
The Chemistry Behind CT1
CT1 is not a silicone and it is not a polyurethane. It uses C-Tec's TRIBRID polymer technology, independently tested to BS EN ISO 8339:2005, which measures bond strength and elongation under load. The results: up to 360% greater bond strength and 250% more elongation than standard hybrid polymers.
What that means on site is straightforward. CT1 does not shrink on cure, does not crack over time, and holds its bond where a standard silicone will eventually pull away from the substrate. Because it forms a structural bond rather than a surface seal, it can replace mechanical fixings in many applications where drilling or screwing would damage the material you are working on.
Unlike acetoxy silicone, CT1 is also odourless and solvent-free. It gives off no acetic acid smell during cure, which makes it a practical option in occupied buildings and enclosed spaces.
What Does CT1 Bond To?
CT1 bonds without primer to:
- Metal, including lead and galvanised steel
- Glass and mirrors
- All timber species and MDF
- Concrete, brick, blockwork and render
- Most natural stone, without staining
- Fibreglass and GRP
- The majority of synthetic materials and plastics
The exceptions are PP, PE and PTFE, which resist adhesion across the hybrid-polymer category. That is not a CT1 limitation; it applies to all products in this class.
What Does CT1 Replace on Site?
One cartridge of CT1 Sealant and Adhesive 290ml replaces standard silicone sealant, acrylic sealant, butyl rubber, polyurethane sealant, and many wood and PU adhesives. For trade electricians that means fewer products in the van, no risk of grabbing the wrong one on the job, and one application technique to remember rather than five.
It is worth being precise about two areas where CT1 is not the first choice. For dedicated bathroom and sanitary sealing, C-Tec's BT1 bathroom sealant is the better product because of its enhanced anti-fungal protection. For pre-paint joint filling around skirting, architrave and coving, FC1 Decorator's Caulk is the correct tool. CT1 is not designed for over-painting with emulsion in those fine decorating applications. See our BT1 vs CT1 comparison for a full breakdown of when each product applies.
How Does CT1 Cure?
CT1 cures by moisture absorption from the surrounding air and the substrate. This means it does not need a dry surface to bond, and it will cure underwater, which is covered in more detail in our guide to whether CT1 is waterproof. Under normal conditions, CT1 skins over in approximately 10 to 15 minutes and cures at roughly 3mm per 24 hours. For thicker beads, allow up to seven days for full cure. The bond reaches handling strength well before that point, but joints under load or sustained water exposure should be left to cure fully.
Where CT1 Turns Up on Electrical Jobs
If you are an electrician and have not used CT1 yet, the most likely places you will reach for it are: sealing around accessory back boxes where they meet a tiled or rendered wall; fixing conduit and trunking to brickwork before mechanical fixings go in; sealing cable entry points on external enclosures against moisture ingress; bonding glass control plates or switch surrounds to surfaces that cannot be drilled; and anchoring mirror plates, escutcheons and finishing trim where no visible fastener is acceptable.
CT1 is also used by electricians for bedding consumer unit enclosures against damp external walls, sealing around cable runs in wet utility areas, and as a quick structural adhesive for fixing cable management accessories to polished or coated surfaces where screw fixings would cause damage.
The CT1 Range at Harbro Electrical
CT1 is available from Harbro in nine colours: Clear, White, Silver, Grey, Black, Anthracite, Oak, Beige and Brown. Alongside the original cartridge, we stock the full C-Tec supporting range: PeelTec paint and sealant remover for stripping cured sealant and old paint before a new application, MultiSolve for degreasing and surface preparation, BT1 bathroom sealant for sanitary work, and FC1 Decorator's Caulk for pre-paint joint filling. All are held in stock at our Peterlee trade counter and available for UK mainland delivery, with free delivery on orders over £70. Trade account customers receive invoiced pricing at checkout.
Applying CT1: Practical Notes
CT1 is applied with a standard cartridge gun. Cut the nozzle to the bead size required, apply in a continuous run, and tool immediately with a wet finger or spatula to achieve a clean finish. The product skins quickly, so tooling must be done before the surface becomes tack-free. Clean any excess from adjacent surfaces immediately using MultiSolve before the product cures; once fully cured, removal requires mechanical means or PeelTec.
CT1 is compatible with most paint systems once fully cured. If you are over-painting, allow a full cure and test on a small area first. For joints that will not be painted, such as a sealed conduit penetration or a bonded mirror, no further treatment is needed once the cure is complete.
CT1 Certifications Worth Knowing
CT1 holds EC1 Plus A+ Indoor Air Comfort Gold certification, ISEGA approval for food preparation environments, and approval by the Norwegian Asthma and Allergy Association. It is solvent-free and odourless, suitable for occupied buildings, and carries approval for marine and salt-water environments.
CT1 is in stock at Harbro Electrical in nine colours alongside BT1, PeelTec, MultiSolve and FC1 Decorator's Caulk. View trade prices on the full CT1 range.