Waterproofing Under Timber Floors: Bali Screed & Membrane Specs

1) Specific Problem/Question

How do you specify and install a robust underfloor waterproofing system beneath timber floors in Bali so planks stay flat, quiet, and mold-free through monsoon humidity, salt air, and day‑to‑day spills—without compromising finishes during renovation or furniture installation? This Bali area guide explains the exact screed and membrane specs Teville applies to protect timber against rising damp, plumbing mishaps, and vapor drive from warm, wet subgrades common in Bali villa construction.

2) Technical Deep Dive: What Fails, and What Works in Bali

In Bali’s tropical climate, timber is constantly challenged by moisture. Even water‑resistant engineered timber is vulnerable to three main sources:

• Rising damp/vapor drive: Warm, humid ground pushes vapor through slabs and unvented voids, swelling boards from below.
• Liquid ingress: Plumbing leaks, AC condensate mismanagement, balcony blow‑in rain, and cleaning water find paths under skirtings and thresholds.
• Trapped moisture: Non-breathable finishes and blocked perimeter gaps prevent drying, causing cupping and mold.

The control strategy under timber floors is a coordinated system: substrate preparation, membrane selection, screed design, and integration with adhesives, skirtings, door thresholds, and villa utilities. Based on current technical bulletins (e.g., ARDEX TB119.007) and comparative studies of sheet vs liquid membranes (Surtec), two proven membrane categories are used under timber in Bali:

• Sheet membranes (TPO/EPDM or modified bitumen): Factory‑controlled thickness, welded laps, excellent as primary moisture/vapor barriers. Best where hydrostatic or high vapor pressures exist—ground‑bearing slabs, external decks leading indoors, or near planters/pools. TPO (1.2–1.5 mm) is clean and heat‑weldable; bituminous SBS (3–4 mm) is robust but may need odor‑care in occupied renovations.
• Liquid-applied membranes (cementitious flexible, polyurethane, or epoxy vapor barriers): Ideal for complex geometries and penetrations. Cementitious/polyurethane membranes provide crack‑bridging; 100% solids epoxies form high‑perm‑resistance vapor barriers to cap residual slab moisture before installing timber.

Key technical distinctions under timber flooring in Bali:

• Vapor vs liquid water: A Class III flexible membrane (high elongation) handles micro‑movement and incidental wetting. A true vapor barrier (e.g., epoxy to ASTM F3010‑type performance) resists vapor drive. In damp sites, we often specify a hybrid: epoxy vapor barrier + flexible topping membrane at edges/penetrations.
• Screed location: Under timber interiors, we typically use a polymer‑modified, fibre‑reinforced leveling screed over the primary barrier to create plane, thickness for services, and acoustic isolation. On external decks meeting timber inside, screed is laid to falls over the membrane with protected outlets; the interior receives a separate vapor barrier to avoid moisture telegraphing through thresholds.
• Dryness thresholds: Prior to timber install, in‑situ RH in screed/slab should be verified (commonly ≤75% RH per ASTM F2170 approach) or per adhesive manufacturer limits; timber moisture content should stabilize around 8–12% in Bali’s conditioned interiors. Skipping this step is the leading cause of cupping.
• Movement accommodation: Perimeter movement joints (10–12 mm concealed under skirting) and breaks at door thresholds/large bays prevent telegraphed stresses. Liquids with high elongation or uncoupling layers are used over cracks/control joints.
• Interfaces: Plumbing, AC condensate, and electrical conduits must be detailed with collars and sealants bonded to the membrane. We avoid punctures where possible and coordinate with villa utilities routing early.

Adhesive and underlay selection is equally critical. In Bali’s humidity, we prioritize:

• Adhesives: Moisture‑curing polyurethane or high‑performance MS polymer adhesive compatible with the chosen membrane; avoid water‑based PVAs over new screeds.
• Underlays: Closed‑cell acoustic underlays (3–5 mm) that do not wick; when used, they must be approved over the membrane/vapor barrier system.
• Fasteners/trim: Stainless steel (304/316) for clips and trims; back‑primed skirting; breathable detailing so the perimeter gap can vent to the wall cavity without admitting bulk water.

Finally, choose timber systems suited to the tropics. Engineered boards with stable cores or dense hardwoods (properly kiln‑dried and treated) outperform softwoods. In interior finishing Bali projects, Teville often pairs engineered timber with a verified vapor barrier and a controlled indoor climate for long‑term dimensional stability.

3) Materials & Standards We Specify in Bali

Teville’s baseline specification aligns manufacturer data sheets with recognized standards and local conditions. We do not improvise on membranes or screeds; we build subfloors as carefully as visible finishes.

• Substrate preparation: Mechanical grind/shot‑blast to ICRI CSP 2–3; remove laitance; patch with polymer‑modified repair mortars; treat active cracks with epoxy injection or elastomeric banding.
• Primary moisture control:
  • Epoxy vapor barrier: 2‑part, 100% solids, applied to achieve manufacturer‑stated perm/performance (often 0.5–1.0 mm DFT in 1–2 coats), broadcast with sand for key.
  • Sheet membrane: TPO 1.2–1.5 mm or SBS‑modified bitumen 3–4 mm, fully bonded with welded/torched laps, turned up 100–150 mm at walls; use compatible primers.
  • Liquid flexible membrane: Cementitious or polyurethane, applied to specified dry film thickness with reinforcing fabric at corners/changes of plane.
• Screed (leveling/overlay): Cement:sand 1:3–1:4.5 with polymer additive; w/c ≤0.45; polypropylene micro‑fibres 600–900 g/m³; minimum thickness 30–40 mm (bonded) or 50–60 mm (unbonded over slip sheet). Strength ~C20/25. Use rapid‑drying screeds where program demands.
• Acoustic layer (if specified): Closed‑cell, moisture‑resistant mats (ΔLw rated); ensure chemical compatibility with membranes/adhesives.
• Timber and adhesives: Engineered timber acclimatized on site; moisture‑curing PU/MS polymer adhesive approved for use over the selected barrier; stainless trims/fasteners.
• Sealants and tapes: Low‑modulus, high‑adhesion sealants for penetration collars; butyl or fleece‑backed tapes for junctions.

Standards and guidance referenced:

• Manufacturer Technical Bulletins (e.g., ARDEX TB119.007) and data sheets for compatibilities and curing/dryness limits.
• AS/NZS 4858 (wet area membranes) and AS 3740 (domestic wet areas) for membrane performance and detailing in analogous climates.
• AS 4654.2 (external above‑ground membranes) for decks/balconies adjacent to timber interiors.
• BS 8204 (screeds) and ASTM F2170 (in‑situ RH testing) for subfloor moisture verification; ASTM F3010‑type performance for epoxy vapor barriers.
• Local code compliance and SNI-aligned practice; site‑specific engineering where hydrostatic conditions exist.

We choose between sheet and liquid by risk profile: sheet/TPO where sustained moisture exposure or complex jointing exists; epoxy + flexible liquid where vapor control and crack‑bridging are both needed. As a finishing‑quality specialist, Teville validates every layer with on‑site tests before timber is laid.

4) Step‑by‑Step Process (Teville Site Method)

Step 1 — Moisture and substrate audit

• Survey for rising damp, external sources (gutters, planters), and AC/plumbing routes.
• Record slab moisture (in‑situ RH or CM method) and ambient RH/temperature. Identify cracks and hollow areas.
• Agree on target system: sheet membrane, epoxy vapor barrier, or hybrid; define interfaces with bathrooms, kitchens, and door thresholds.

Step 2 — Surface preparation

• Mechanically abrade to sound, clean concrete; vacuum dust.
• Repair defects; honor control joints; isolate live cracks for flexible banding.
• Prime per membrane manufacturer; confirm pull‑off strength where required.

Step 3 — Primary barrier installation

• Epoxy vapor barrier: Apply first coat; sand‑blind; apply second coat to required DFT; verify coverage and continuity. Maintain 100–150 mm upturns onto walls or integrate with wall damp‑proofing.
• Sheet membrane: Lay with correct laps; weld seams; perform probe/peel tests; turn up at perimeters; form collars to penetrations; protect from damage.
• Liquid flexible membrane (if used at edges/penetrations): Reinforce corners with fabric; apply multiple coats to achieve dry film spec.

Step 4 — Screed/leveling

• Place polymer‑modified, fibre‑reinforced screed to achieve levelness; in wet‑adjacent zones provide falls away from thresholds.
• For unbonded screeds, use a slip sheet over the membrane as specified; maintain minimum thicknesses.
• Cure per product data; for rapid screeds, monitor moisture daily; do not trap moisture with premature coverings.

Step 5 — Moisture verification and auxiliary layers

• Test screed moisture (RH or CM) against adhesive/timber tolerances; if marginal, add a compatible epoxy sealer per manufacturer instruction.
• Install acoustic underlay where required, ensuring compatibility with adhesive and barrier system.

Step 6 — Timber acclimatization and installation

• Acclimatize timber packs 5–10 days in conditioned interior; verify MC 8–12%.
• Full‑spread PU/MS polymer adhesive; maintain trowel notch; roll per manufacturer; respect open time.
• Keep 10–12 mm perimeter gaps; use stainless trims at thresholds; avoid blocking expansion with sealant at the visible edge—seal to the membrane behind the skirting instead.

Before finalizing your finishing works plan, check realistic cost ranges for your Bali villa project.

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