Internal Wet-Area Waterproofing: A Best-Practice Installation Guide

Will your wet-area waterproofing pass the test?

Liquid-applied waterproofing should be straightforward, but in reality, it’s one of the most common sources of callbacks, delays, and compliance issues on site. The good news? When the right system is used and the process is followed properly, liquid membranes deliver reliable, long-lasting protection.

This guide sets out what to check, what to remember, and the step-by-step process to ensure liquid-applied waterproofing is done right, every time.

Scope

The guidance applies to internal wet areas using Technokolla liquid-applied membranes:

• Rasogum+ (Class III)

• Rasolastik Advance (Class II)

• Rasolastik Evo (cementitious)

All installations must follow Technokolla product instructions as supplied by Surtec, comply with the NZ Building Code (NZBC), and reference IWAM and TANZ where applicable.

WHAT TO REMEMBER (AT A GLANCE)

1. Use a complete Technokolla system, including primers, bandages, accessories and membrane.
2. Hold a pre-installation meeting and confirm consent documents, sequencing, site conditions and storage. Accredited installers only.
3. Form the falls before you waterproof. Typical targets: 1:50 in shower bases, 1:60 for full wet rooms, with a positive fall to the waste or channel.
4. Install an appropriate doorway water-stop at the wet-room threshold.
5. Choose the right primer for the substrate. Porous substrates use penetrating Techno Primer T; non-porous substrates use Techno Primer 101.
6. Reinforce all junctions, changes of plane, drains and penetrations with approved bond-breakers and bandages before or while coating. Seal every penetration.
7. Apply to the specified wet-film/dry-film thickness (WFT/DFT), record it with a wet-film gauge and follow re-coat and cure times.
8. Protect fresh membrane from other trades and document the work with photos, including bond-breakers and flood testing.
9. Flood test for a minimum of 12 hours (IWAM) or 24 hours, as specified, using water from an external source. Photograph and sign off on the result.
10. Tile directly over the membrane with full adhesive coverage in wet areas, then grout and silicone movement joints.
11. Maintain the installation. Check and renew sealants regularly, clean appropriately and inspect wastes and penetrations. NZBC durability expectation is typically 15 years for wet-area waterproofing with normal maintenance.

STEP-BY-STEP – LIQUID MEMBRANES

1. Substrate check and prep. Confirm substrate suitability, structure, moisture content, falls, and drainage. Clean, dry, sound, free of contaminants.
2. Priming. Apply the membrane supplier’s nominated primer for the specific substrate type. Do not prime over bond-breakers.
3. Bond-breakers and bandaging. Install RL80 bond-breaker tape, bandage mesh and pre-formed gaskets at internal corners, changes of plane and around wastes and penetrations.
4. First coat. Apply evenly to the specified WFT. Extend to required extents on floors and walls per IWAM/TANZ. Protect from trades.
5. Second coat. Apply at 90 degrees to the first, meeting minimum DFT. Respect re-coat and cure times.
6. Key for tile if required. Broadcast clean sand into the wet topcoat where the system calls for it.
7. Flood test. Bung wastes form temporary dams, and flood with external water. Check after at least 12 hours and record. Many jobs will specify 24 hours. Rectify and re-test if needed.
8. Tile and finish. Achieve full adhesive coverage in wet areas, then grout and silicone per movement-joint layout.
9. Handover. Photograph completed works, protect surfaces, complete PS3 and any warranty pack, and brief the client on maintenance.

CHOOSING BETWEEN RASOGUM+, RASOLASTIK ADVANCE, RASOLASTIK EVO

Rasogum+. Ready-to-use Class III liquid for internal wet areas only. Fast drying, elongation around 400 per cent, tile directly over it. Pack 25 kg pail, typical coverage about 8.93 SQM per pail at 1.0 mm DFT with two coats. Not for immersion or exterior.

Rasolastik Advance. Two-part flexible cementitious, Class II, AS4858 compliant. Suitable for internal and external use, including immersed areas such as pools and balconies. Kit 21 kg powder + 7.45 L liquid, typical coverage about 8.89 SQM at 1.0 mm DFT with two coats.

Rasolastik Evo. Single-component fibre-reinforced cementitious waterproofing for concrete, positive and negative pressure, potable water-capable, internal and external, including immersed use where detailed. Pack 20 kg, typical coverage about 8.33 SQM at 1.0 mm DFT with two coats.

WHERE THE PROCESS DIFFERS

Primers. Porous substrates typically use Primer-T; non-porous substrates use Primer-101. For cementitious systems (Advance, Evo), the primer may differ from Rasogum+. Always follow the product data sheet.

Reinforcement. Bandage types and the areas to reinforce are consistent; however, some cementitious systems call for mesh embedment across wider areas. Follow the specific system drawings.

Cure and flood-test times. Rasogum+ can reach re-coat and flood-test readiness faster than cementitious systems in cool or damp conditions. IWAM sets a 12-hour minimum; some systems and councils require 24 hours.

Scope of use. Use Rasogum+ only for internal wet areas. Use Advance or Evo where exterior or immersed service is required.

COMMON DETAIL REMINDERS

• Showers and open wet areas must be fully waterproofed to the extent required and fall back to waste, with walls to 1800 mm in shower zones.
• Rebate and seal waste with wide-flange membranes. Keep the strip drain rebates falling to the outlet.
• Movement joints must be planned and honoured at perimeters, changes of plane and as designed. Use compatible silicone at these joints.
• Grout is not waterproof. In showers and high-traffic areas, consider epoxy grout for improved cleanability and water resistance.

MAINTENANCE AND DURABILITY

Maintenance is required to meet durability expectations. Provide the owner with a maintenance list as part of consent documentation. Typical expectation is 15 years for wet-area waterproofing with normal maintenance.

Inspect sealants annually and replace at the first signs of breakdown, typically after about 2 years in service. Keep wastes clear and watch for staining in adjacent spaces.

For project-specific advice, atypical substrates, under-tile heating, fast-track programmes, exterior or immersed work, or council documentation such as PS3, please get in touch with Surtec Technical Support technokolla@surtec.co.nz.