Subfloor preparation is the most commonly underestimated cost in any flooring project. Homeowners budget for the floor product and the installation rate and forget that the floor cannot be installed until the surface beneath it is suitable. In new builds with flat slabs, preparation is minimal. In pre-1980 homes with decades of layers and imperfections, preparation can cost more than the floor itself. Here's what to expect.
Why subfloor preparation matters
The installation requirements for hybrid SPC specify that the subfloor must be flat within 3mm over any 1.8m measurement. This is a tighter tolerance than most existing residential floors achieve. Variations beyond this tolerance create stress points in the click system, causing boards to separate, flex or creak over time. A floor installed over an inadequately prepared subfloor will develop problems regardless of product quality.
What preparation involves — by existing floor type
Carpet over concrete slab — carpet, underlay and tack strips are removed. The slab is inspected for levelness and moisture. Typically the least complex preparation scenario. Cost: $4–$8/m² for removal, plus any levelling required.
Tiles over concrete — tile removal is the most labour-intensive preparation scenario. Tiles are lifted, adhesive is ground or scraped off, and the slab is levelled. Old adhesive on the slab can be extremely hard to remove completely. The slab may be damaged during tile removal, requiring patching. Cost: $15–$35/m² for removal and initial prep, plus levelling compound if required.
Vinyl or linoleum over concrete — the sheet is removed and adhesive residue addressed. Pre-1980 vinyl adhesive may require assessment before removal. Cost: $6–$14/m², plus adhesive treatment if required.
Timber subfloor (floating installation) — the subfloor is inspected for moisture content, structural integrity and flatness. Loose boards are fixed, high points are ground, low points are filled. Cost: $8–$20/m² depending on condition.
The levelling compound question
If the slab has significant dips or undulations beyond the 3mm tolerance, self-levelling compound is poured to create a flat surface. This is a common requirement in older homes and post-renovation slabs that have been patched multiple times. Self-levelling compound costs $15–$40/m² for the affected area depending on depth required. A 100m² home that needs levelling compound over 30m² of affected area could add $450–$1,200 to the project before any floor is laid.
Moisture testing
All slabs should be moisture tested before installation of moisture-sensitive products. The test involves drilling a small hole and installing a probe to measure moisture vapour emission from the slab. Elevated moisture requires a moisture barrier — typically an epoxy primer — before the floor is laid. Cost: $5–$12/m² for epoxy moisture barrier treatment.
A professional retailer will include moisture testing in their site inspection. A quote that doesn't mention moisture testing has either assumed acceptable moisture levels or hasn't thought about it. Ask specifically.
How to budget for preparation
If you are in a new build or recently renovated home with a known-good slab: budget $5–$10/m² for standard preparation.
If you are in a pre-1980 home with unknown subfloor condition: budget $15–$30/m² for preparation and have reserves for surprises.
If you are removing existing tiles: budget $20–$45/m² for tile removal and preparation.
Our Floor Finder asks about your existing floor type and builds preparation costs into its project estimate. Always get a detailed written quote that itemises preparation before signing.