Sealants are one of those everyday materials that plumbers reach for without much thought; until something leaks, cracks, or discolours. Using the wrong type can cause callbacks, wasted time, and damage that shows up weeks later. With so many products on the shelf, it’s worth matching the sealant precisely to the job. Here’s a quick guide to choosing the right one, every time.

Silicone Sealants for Bathrooms and Kitchens

Silicone is the most familiar type, used for sealing around baths, sinks, showers, and worktops. The key differences are between acetoxy-cure and neutral-cure silicones. Acetoxy types cure quickly and bond well to ceramics and glass but can corrode metals and certain plastics. Neutral-cure silicones are safer for mixed materials, including aluminium and natural stone, and tend to resist mould better.

Always check for a sanitary grade label; that means it includes fungicide to resist mildew. For wet areas, a flexible finish is essential so the seal can move with slight expansion and contraction without cracking.

Plumber’s Mait and Non-Setting Compounds

Non-setting compounds such as Plumber’s Mait are designed for bedding waste fittings, taps, and flanges. They never harden fully, which allows for easy adjustment and future maintenance. They’re ideal where a watertight but flexible joint is needed, especially on basins and bath wastes.

However, they’re not suitable for pressurised joints or modern plastic compression fittings; use them only on low-pressure, static seals. Always clean away excess neatly, as residue can attract dirt and discolour quickly.

Thread Seal Tapes and Jointing Compounds

For threaded metal fittings, the classic choices are PTFE tape or a pipe jointing compound. PTFE is fast, clean, and widely accepted for gas and water systems. The secret is using the right grade; gas-rated tape for gas work, water-rated tape for general plumbing, and wrapping it in the correct direction so it tightens with the thread.

Jointing compounds like Boss White or Hawk White remain popular for high-pressure or awkward joints. Many plumbers use a light coating of compound with hemp or fibre reinforcement to ensure a robust seal on older systems, though modern regulations now prefer PTFE or approved alternatives for potable water.

Specialist Sealants and Adhesives

Sometimes the job calls for something more specific:

• High-temperature sealants for boilers and flue joints.
• Threadlockers for securing small metal fixings that might vibrate loose.
• MS polymer or hybrid sealants that combine adhesive and sealing properties; ideal for external pipe runs or fixing trims where both strength and flexibility are needed.
• Wet-fix or underwater sealants for emergency repairs without draining down; useful on site but should be treated as temporary solutions.

Preparation and Application

Even the best sealant fails if the surface isn’t clean. Always remove old product completely, dry the area, and wipe with an alcohol-based cleaner. For visible joints, mask the edges neatly and smooth the bead in one pass before it skins. On heating systems, allow full curing time before pressurising; rushing this step is a common cause of call-backs.

Keep tubes sealed tightly after use. Air exposure shortens shelf life, and expired sealants lose adhesion and flexibility long before they look “off.”

Environmental and Safety Points

Many modern sealants are low in VOCs (volatile organic compounds) and suitable for indoor use, but always check the safety data if you’re working in confined spaces. Dispose of used tubes responsibly; hardened silicone can’t be recycled, so bag it with general waste rather than washing it down drains.

Summary

Choosing the right sealant isn’t about brand loyalty; it’s about compatibility and reliability. Match the product to the surface, temperature, and pressure involved. Use neutral-cure silicone for mixed materials, non-setting compounds for wastes, PTFE or jointing compound for threads, and specialist sealants when conditions demand it. A few extra seconds of thought before squeezing the tube can save a return visit, a complaint, and a lot of wasted time later.