Commercial Flooring Subfloor Preparation & Moisture Testing Guide Melbourne: Concrete, Screed & DPM

The single biggest cause of commercial flooring failures in Melbourne is not the product — it is the subfloor. Trapped moisture, missed deflection, high-alkalinity concrete, dusty surfaces and out-of-tolerance flatness cause debonding, bubbling, cupping and warranty claims on projects that otherwise look specified to a premium standard. This specifier’s and installer’s guide explains how A1 Flooring prepares subfloors for commercial vinyl sheet, LVT, carpet tile and resilient flooring on Melbourne projects, covering moisture testing, damp-proof membranes, levelling compounds and AS 1884 compliance.

Why Subfloor Preparation Matters

The Australian standard for the installation of resilient floors, AS 1884, is unusually blunt: the installer’s warranty is void if the subfloor is outside tolerance for moisture, flatness, strength or contamination. Manufacturers such as Polyflor, Armstrong and Forbo echo this in their own installation manuals. A floor that is laid over a non-compliant subfloor is, from the first day, a warranty write-off waiting for a failure to appear. For commercial projects where the rectification cost dwarfs the original supply, getting the subfloor right is the single most important decision on the job.

Moisture — The Number One Cause of Failure

In-Situ Relative Humidity Testing

The gold standard for concrete moisture testing is the in-situ relative humidity probe, specified by ASTM F2170 and accepted by most European manufacturers. A sealed sleeve is drilled to 40% of slab depth (or 20% for a slab drying from both sides), left to equilibrate for 72 hours, and measured with a digital RH probe. The AS 1884 pass mark for most resilient vinyl is ≤ 75% RH; some LVT and acoustic-backed products demand ≤ 80%. A1 Flooring carries calibrated Wagner, Protimeter and Rotronic probes for in-situ testing on every commercial project where the slab is younger than six months or has been subject to a wet trade.

Tramex and Surface Moisture Meters

Handheld Tramex-style non-destructive surface moisture meters are a useful triage tool but are not a substitute for in-situ RH. They read only the top 20 mm of the slab and can under-report deep moisture that will migrate up to the adhesive after the floor is laid. A1 Flooring uses Tramex readings to screen a slab and identify wet hot-spots before committing to the full in-situ probe regime.

Calcium Chloride and Anhydrous Testing

Calcium chloride (ASTM F1869) and anhydrous calcium chloride tests are still common in the Australian market but are losing ground to in-situ RH because they only measure the top of the slab and are sensitive to ambient conditions. Most current manufacturer specifications accept either ASTM F1869 or ASTM F2170; specifiers should check the product datasheet before committing to a test method.

Damp-Proof Membranes (DPMs)

When a slab tests above the resilient-flooring limit and the project programme does not permit natural drying, a liquid-applied two-part epoxy DPM is the standard remedial. Products such as F. Ball Stopgap F77, Ardex DPM 1 C and Mapei Eco Prim PU 1K are routinely applied at 250–400 g/m² to provide a vapour barrier up to 95% RH. The DPM cures in 3 to 24 hours and must be overlaid with a calcium sulphate or cement-based smoothing compound before the finished floor is laid.

Levelling and Smoothing Compounds

Commercial resilient flooring and LVT demand a Class A smoothing compound surface — no trowel marks, no laitance, and flatness within 3 mm under a 2 m straightedge. For Melbourne projects A1 Flooring routinely specifies Ardex K 15, Mapei Ultraplan Eco 20 or a similar calcium-sulphate-based self-levelling compound at 3–10 mm build, primed first with an acrylic or epoxy primer matched to the slab condition. Where the slab is badly out of tolerance or contains services, we supplement with a pumpable deep-section levelling compound — see our guide to self-levelling concrete for flooring for the detail.

Surface Preparation — Mechanical Grinding and Shot Blasting

AS 1884 requires the subfloor to be clean, sound, dry and free of contaminants. In practice that means diamond grinding or shot-blasting every commercial slab before any primer, DPM or smoothing compound is applied. Grinding removes laitance, curing compounds, paint, adhesive residues and surface hardeners. Shot-blasting delivers a more aggressive profile for thicker DPMs and resin screeds. Both generate significant dust, so A1 Flooring’s crews work with HEPA-filtered vacuum systems and silica-compliant PPE on every Melbourne commercial project.

Timber and Existing Floor Substrates

Not every Melbourne commercial project is on a green slab. Retail refits, heritage hospitality projects and first-floor office fit-outs often start with a particle-board or plywood subfloor, or with an existing tiled or vinyl finish that cannot be economically removed. In those cases the subfloor must be mechanically fixed to eliminate deflection, cleaned of wax and contamination, primed for the substrate type and overlaid with a fibre-reinforced smoothing compound at 3 mm minimum. Our commercial flooring installation methods guide covers the full decision tree.

AS 1884 Compliance and the Documentation Pack

On handover, A1 Flooring supplies a subfloor compliance pack that includes: slab moisture test results with location plans, DPM product and batch data, primer and smoothing compound data sheets, flatness survey readings, photographic records of the prepared surface, and the AS 1884 declaration signed by the installer. This pack is the evidence a commissioning engineer needs to release the manufacturer warranty and is the first thing we are asked for on any future rectification claim.

Talk to A1 Flooring About Your Melbourne Project

Subfloor preparation is where commercial flooring projects are won or lost. A1 Flooring has delivered AS 1884-compliant subfloor prep on commercial projects across Melbourne, from new-build slabs in Fishermans Bend to heritage timber floors in the CBD. We can test, remediate and document the subfloor as a standalone package or as part of a full supply-and-install commercial flooring contract — browse the full commercial flooring range and then contact our commercial team to discuss your site.