Loctite SI 5331

Overview

Loctite® SI 5331 is a low-strength, medium-viscosity, acetoxy silicone-based liquid thread sealant. It is specifically designed for locking and sealing plastic and metal threaded fittings carrying hot or cold water, such as industrial and agricultural plastic water pipe systems and drainage systems.

The product cures at ambient temperature by reacting with atmospheric moisture, forming a flexible, leak-tight seal that resists vibration and thermal cycling.

Why choose Loctite SI 5331?

1) Designed for plastic and mixed-material fittings
Unlike many traditional thread sealants aimed only at metal, SI 5331 is formulated for plastic threads and plastic/metal combinations, making it ideal for modern water systems using PVC, ABS, PP and similar materials alongside brass or steel fittings.

2) Reliable sealing for hot and cold water
It’s a general-purpose water system sealant, suitable for fittings carrying hot or cold water in domestic, commercial and industrial installations – from irrigation lines and process water to drainage systems.

3) Approvals for potable water and food-related environments
Loctite SI 5331 is WRC-listed and meets BS 6920 for potable water, has DVGW approval tested in accordance with EN 751-1, and is NSF P1 registered, making it suitable for use in and around food processing areas (not for direct food contact surfaces).

4) Instant low-pressure sealing, full seal after cure
According to the Technical Data Sheet, SI 5331 provides instant sealing capability up to about 0.05 MPa water pressure and develops full sealing capability (approx. 0.3 MPa) within about 12 hours at ≥40% relative humidity.

5) Low strength – easy service and disassembly
The product is classified as low strength, so connections remain removable for maintenance, modification or repair without excessive force or risk of damaging plastic threads.

Applications

Plumbing, water supply & building services

• Hot and cold potable water pipe systems

• Plastic manifolds and distribution blocks

• Mixing valves, water meters, filter housings and service connections

Industrial & agricultural water systems

• Process water lines in light industrial plants

• Agricultural irrigation systems and sprinkler lines

• Fertigation and wash-down systems (where compatible with media)

Drainage & utility pipework

• Plastic or plastic/metal threaded drainage fittings

• Grey water and non-pressure drainage connections

• Ancillary threaded components around tanks and sumps

Marine, leisure & on-board water systems

• Yacht and boat fresh water systems and service lines

• On-board hot/cold water fittings in caravans and RVs

How to Use (Thread Sealing)

Step 1: Preparation

• Ensure threads are clean, dry and free of oil, dust and loose particles.

• Remove old sealant, tape or contamination with a suitable cleaner if necessary.

Step 2: Application

• Cut the nozzle to the desired bead size and pierce the tube seal.

• Apply a continuous bead of Loctite SI 5331 around the male thread, covering the full engagement length.

• For larger fittings, ensure complete coverage of the sealing area without large excess lumps.

Step 3: Assembly

• Assemble the joint in the normal manner.

• Position correctly within the workable time; avoid over-tightening plastic threads.

Step 4: Initial Pressure & Cure

• SI 5331 provides instant low-pressure sealing (up to about 0.05 MPa) once the joint is assembled, depending on fit and surface condition.

• For higher pressures, allow adequate cure time (typically up to 12 hours at ≥40% RH) before full service.

Step 5: Inspection & Rework

• Inspect for leaks under test pressure.

• If disassembly is required, loosen the joint by conventional mechanical means; re-clean threads and reapply fresh product.

FAQs

Q1: What is Loctite SI 5331 mainly used for?
Loctite SI 5331 is mainly used as a silicone-based thread sealant for plastic and metal fittings in hot or cold water systems, including potable water lines, industrial/agricultural plastic pipe systems and drainage fittings.

Q2: Can it be used on potable (drinking) water systems?
Yes. SI 5331 is WRC listed and meets BS 6920 for potable water, has DVGW approval (EN 751-1) and is NSF P1 registered, making it suitable for use in potable water installations when applied as directed and in accordance with local regulations.

Q3: Is it suitable for plastic threads?
Yes. The product is explicitly designed for plastic pipe threaded fittings and plastic/metal combinations carrying hot or cold water. It forms a flexible seal that accommodates the different expansion and creep behaviours of plastics.

Q4: Can I remove the fittings again after using SI 5331?
Yes. SI 5331 is a low-strength thread sealant. Joints can typically be disassembled using standard tools without excessive force, making it suitable where future servicing or reconfiguration is expected.

Q5: How long before I can pressurise the system?
The product can provide instant low-pressure sealing (around 0.05 MPa) immediately after assembly. For higher pressures (up to approximately 0.3 MPa) and maximum reliability, allow up to 12 hours of cure at ≥40% relative humidity before placing the joint into full service.

Q6: Can it be used in food or beverage plants?
Loctite SI 5331 is NSF P1 registered, which means it is acceptable for use in and around food processing areas as a maintenance chemical used in accordance with NSF guidelines (not for direct food contact surfaces). Always confirm that your specific application meets local regulatory requirements.

Q7: How should I store Loctite SI 5331?
Store the tubes in a cool, dry place, ideally between about 8 °C and 28 °C. Storage outside this range (colder than 8 °C or hotter than 28 °C) may adversely affect product properties and shelf life.