Solvent Weld Waste System
Step-by-step guide to installing solvent weld waste pipe systems for kitchens and bathrooms, covering 32mm and 40mm applications.
Safety Warning — Solvent Cement Fumes
Solvent weld cement contains volatile organic compounds (VOCs). Always work in a well-ventilated area. Avoid prolonged inhalation of fumes. Wear nitrile gloves to prevent skin contact. Keep cement away from naked flames — it is highly flammable. If working in an enclosed space, use forced ventilation. Read the solvent cement manufacturer's safety data sheet before use.
What You'll Need
Tools
- Hacksaw with fine-tooth blade
- Deburring tool or half-round file
- Tape measure
- Spirit level
- Pencil or marker pen
- Clean cloth or paper towels
- Pipe clips and drill/driver
- Nitrile gloves and safety glasses
Materials
- Solvent weld waste pipe (32mm or 40mm)
- Solvent weld fittings (elbows, tees, couplers)
- Solvent weld cement (BS 6209 compliant)
- Cleaner/degreaser (MEK or manufacturer's prep)
- Waste traps (bottle trap, P-trap, or S-trap)
- Pipe clips at appropriate centres
- Wall plugs and screws
Technical Specifications
Step-by-Step Installation
1 Plan the Waste Run
Map the route from each appliance (basin, bath, sink, shower) to the soil stack or external hopper. Use the shortest, most direct route with the fewest fittings. 32mm pipe serves basins (max 1.7m unvented run); 40mm serves baths, sinks, and showers (max 3.0m unvented). If runs exceed these limits, a separate vent pipe or air admittance valve (AAV) is needed. Plan the fall at 18–22mm per metre — this keeps the pipe self-cleansing without stripping water from the trap seal.
2 Measure and Cut Pipe
Dry-fit the entire run first — measure each section, allowing for the socket depth at each fitting (typically 20–25mm). Mark and cut pipe squarely using a hacksaw with a fine-tooth blade. A mitre box helps achieve a clean, square cut. Deburr the cut end thoroughly using a file or deburring tool — remove both the external and internal burrs. A rough cut end will prevent the joint from seating properly and can cause leaks.
3 Clean and Prepare the Joint
Using a clean cloth and manufacturer's cleaning solvent (MEK-based), wipe both the outside of the pipe spigot and the inside of the fitting socket. This removes dirt, grease, and surface oxidation. The surfaces must be completely clean and dry before applying cement. This cleaning step is not optional — cement will not bond properly to dirty or greasy surfaces. Allow the cleaner to evaporate fully (a few seconds).
4 Apply Solvent Cement
Working quickly, apply a generous, even coat of solvent cement to both surfaces — the pipe spigot and the fitting socket. Use the brush built into the cement tin lid. Apply to the spigot first (larger surface area), then the socket. The cement should be wet and glossy — if it dries or becomes tacky before assembly, clean and reapply. In cold weather (<5°C), the cement sets slower; in hot weather (>25°C), you have less working time.
5 Assemble the Joint
Immediately push the spigot fully into the socket with a slight twisting motion (quarter turn). Hold firmly for 15–30 seconds — the joint will try to push apart as the solvent softens the PVC. A small bead of excess cement should appear around the joint, confirming sufficient cement was applied. Wipe off the excess with a clean cloth. Do not disturb the joint for at least 5 minutes. The joint is not fully cured for 24 hours — do not pressure-test before then.
6 Install Pipe Clips and Support
Fix pipe clips at 500mm centres on horizontal runs and 1.2m on vertical runs. Position a clip within 150mm of every fitting. Ensure the pipe follows the correct fall — 18–22mm per metre towards the stack. On long runs, use an expansion coupler every 3 metres to accommodate thermal movement. Solvent weld joints are rigid (unlike push-fit), so the expansion coupler provides the necessary movement.
7 Connect Traps and Appliances
Fit the appropriate trap to each appliance — bottle traps for basins (32mm), P-traps or S-traps for baths and sinks (40mm), and shallow traps for showers (40mm). The trap provides the water seal that prevents drain odours entering the room. Every trap must maintain a minimum 75mm water seal depth. Connect the trap outlet to the solvent weld waste pipe run. Ensure the trap is accessible for future maintenance and cleaning.
8 Test the System
After allowing 24 hours for full cure, run water from each appliance and check every joint for leaks. Fill each basin/bath, then release the plug to create a full-bore discharge. Check that trap seals remain intact after discharge (no gurgling sounds). Verify the system drains freely with no standing water in the pipe run. Any leak at a solvent weld joint requires cutting out and replacing the joint — solvent weld cannot be re-made once cured.
Common Mistakes to Avoid
- Not deburring cut ends — Burrs prevent full socket insertion and create rough surfaces where the cement cannot bond effectively.
- Skipping the cleaning step — Cement applied to dirty, oxidised, or greasy surfaces will not bond. The joint may hold initially but fail under pressure or over time.
- Insufficient cement — If no bead of excess cement appears around the joint, not enough was applied. The joint will leak.
- Disturbing the joint too soon — The cement needs 15–30 seconds to grab and 5 minutes before any movement. Disturbing it creates a weak, leaky joint.
- Excessive fall — Too steep a gradient (>45mm/m) causes water to run off faster than solids, leaving deposits that build up and cause blockages.
- Using old or thickened cement — Solvent cement has a limited shelf life. If it's thick, stringy, or jelly-like, discard it. It will not create a reliable bond.
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