Getting a floor sanding quote is exciting — you can already picture those gleaming timber boards. But it's not unusual for the final invoice to come in higher than expected. Understanding why costs can blow out helps you plan your budget realistically and have informed conversations with your tradesperson before work starts.
The Quote Is Only as Good as the Information Available
Most floor sanders provide a quote based on a visual inspection, often before furniture is moved and without pulling up floor coverings. A site assessment quote is essentially an educated estimate. Once the sander gets into the job, hidden conditions can change the scope of work significantly. This is normal in the trade — it's not necessarily a sign of dodgy quoting.
Common Reasons Costs Increase
1. Hidden Damage Beneath the Surface
Old carpet, vinyl, or cork tiles can conceal a multitude of sins. Once lifted, your tradesperson might find:
- Deep gouges, burns, or staining that require extra sanding passes or filler
- Cupping or crowning (boards warped due to moisture) that need more aggressive cutting
- Springy or squeaky boards caused by failed fixings, requiring re-nailing or screwing before sanding can begin
- Rot or structural damage that may need a builder's attention first
Any of these adds labour time and sometimes materials.
2. Previous Coatings That Are Hard to Remove
Old paint, wax, or thick polyurethane can clog sanding belts and discs at a much faster rate than a lightly coated floor. Belt and disc consumption is a real cost — professional-grade abrasives aren't cheap, and a heavily coated floor can chew through two or three times the expected number. If your floor has multiple layers of old finish, expect this to be flagged as a potential variation.
3. Nail Heads and Fixings
Every exposed nail head must be punched below the surface before sanding begins. On older NZ homes — especially villas and bungalows with native timber floors like rimu, matai, or kauri — there can be hundreds of nails across a large floor. Punching and filling all of them takes time that may not have been fully accounted for in the original quote.
4. Floor Layout and Accessibility
A straightforward rectangular room is quick to sand. Costs can rise when there are:
- Lots of edges, corners, and alcoves requiring slow hand or edge-sander work
- Stairs (often quoted separately per tread and riser)
- Furniture that wasn't moved before the tradesperson arrived
- Multiple small rooms rather than one open plan area
5. Timber Species and Condition
Different timbers sand at different rates. Dense hardwoods like kwila or spotted gum take longer than softer species. Older native timbers can also be unpredictably hard or have silica deposits that dull blades quickly. If the species wasn't confirmed at quoting stage, this can be a source of variation.
6. Finish Upgrades or Additional Coats
You may decide mid-job to upgrade from a standard two-coat finish to a three-coat system, switch from a water-based to an oil-based finish, or add a hard-wax oil treatment. These are legitimate upgrades but they cost more in both product and labour. Discuss your finish preferences clearly before work begins — BRANZ has useful guidance on timber floor finish performance if you want to research options.
7. Moisture and Subfloor Issues
If moisture readings are high, a professional sander may need to pause work, recommend a moisture barrier, or advise you to address the source before proceeding. Sanding a wet or damp floor produces a poor result and can cause the new finish to fail. Subfloor ventilation issues are common in older NZ homes, particularly in wetter regions. MBIE Building Performance outlines requirements around subfloor moisture under the NZ Building Code.
8. Lead Paint or Hazardous Materials
Homes built before the 1980s may have lead-based paint on floors or skirting boards. If lead paint is identified, WorkSafe NZ requirements mean the tradesperson must use additional PPE, containment, and disposal procedures — all of which add cost. This is non-negotiable for health and safety reasons.
How to Reduce the Risk of Blowouts
| Action | Why It Helps |
|---|---|
| Clear the room before the quote | Lets the sander inspect the full floor area |
| Lift a corner of carpet yourself | Reveals the timber condition underneath |
| Ask for a variation clause in writing | Sets clear expectations on how extras are handled |
| Discuss your preferred finish upfront | Avoids mid-job upgrades |
| Ask about abrasive allowances | Understand what's included in the quote |
A good tradesperson will walk you through potential variations before starting and get your sign-off before proceeding with any extra work. If you're comparing quotes, make sure each one covers the same scope — a low quote that excludes nail punching, filling, or extra coats isn't a fair comparison.
When to Call a Professional
Floor sanding is a skilled trade. Hiring an experienced professional from tradedirectory.co.nz means you get someone who can identify problems early, advise on the right finish for your timber species and lifestyle, and deliver a result that lasts. DIY hire machines are available from Bunnings or Mitre 10, but they are harder to control and can cause irreversible damage — particularly on thinner boards that have been sanded before. For heritage timbers like kauri or rimu, a professional is strongly recommended.
If your floor has structural concerns, springy boards, or signs of rot, you may also need a Licensed Building Practitioner (LBP) involved. Check LBP to find one in your area.
