Spotted Gum Flooring

The complete sanding and finishing guide for spotted gum (Corymbia maculata) -- a beautiful, popular, and technically demanding species.

Species characteristics

• Janka hardness: 11.0 kN -- one of the harder species commonly used in flooring. Expect slower sanding and faster abrasive wear.
• Grain: Interlocked and wavy. This is what gives spotted gum its distinctive "fiddleback" figure, but it also means the grain direction reverses every few centimetres. Aggressive sanding tears the fibres instead of cutting them.
• Colour: Varies dramatically -- from pale grey-brown to deep chocolate, often with multiple tones in the same board. The colour variation is part of the appeal.
• Tannin level: Moderate to high. Not as consistently high as blackbutt, but enough to cause tannin bleed on some boards, especially darker ones. Prime Intense is the safe call.
• Natural oils: Spotted gum contains natural oils that can interfere with coating adhesion, particularly in freshly milled boards. A thorough final sand and proper primer application address this.

Recommended grit sequence

Spotted gum requires patience. The interlocked grain punishes shortcuts.

• Belt sander: P40 → P60 → P80 → P100 (SIA belts). On very hard, figured boards, some contractors add a P36 initial cut.
• Edger: P40 → P60 → P80 → P100. Keep the edger flat -- tilting on spotted gum leaves deep circular gouges that show through the finish.
• Buffer/screen: P120 screen or mesh. Spotted gum benefits from a thorough screening to knock down any raised fibres from the interlocked grain.

Do not skip grits. The interlocked grain holds deeper scratches from coarser grits that only become visible after coating. Use the Grit Sequence Picker to get a sequence tuned to the floor's condition.

Recommended primer

Bona Prime Intense is the recommended primer for spotted gum under water-based topcoats. While spotted gum's tannin level varies board to board, using Prime Intense on the entire floor eliminates the risk of patchy tannin bleed appearing only on the darker, higher-tannin boards.

Prime Intense also enhances the natural colour depth of spotted gum, bringing out the brown and amber tones rather than flattening them the way a neutral primer might.

For a deeper look at finishing spotted gum, including the oil path, see the spotted gum finishing guide.

Recommended topcoats

• Bona Traffic HD: The best option for commercial and high-traffic residential spotted gum floors. Maximum abrasion resistance on a very hard timber.
• Bona Wave 2K: Heavy residential at a lower price than Traffic HD. Excellent for open-plan spotted gum living areas.
• Bona Mega: Standard residential. Reliable, easy to apply, and durable enough for most residential spotted gum floors.
• Bona Traffic GO: Fast-cure 2K when the timeline is tight.
• Handley Urethane: Solvent option for an amber, traditional look. The warmer tone complements spotted gum's natural colour variation.

Common mistakes on spotted gum

• Sanding too aggressively. Heavy pressure on the belt sander tears the interlocked grain. Let the machine weight do the work. If the fibres are tearing, reduce pressure or move to the next grit.
• Skipping grits. The interlocked grain holds deep scratches from coarser grits. These scratches only become visible after the primer or topcoat goes on. Sand every grit.
• Using a neutral primer on high-tannin boards. Spotted gum boards vary in tannin content. Using Classic UX instead of Prime Intense risks patchy tannin bleed on the darker boards while the lighter boards look fine. Prime Intense across the whole floor is the safe approach.
• Insufficient dry time. Spotted gum's natural oils slow coating penetration. Allow the full recommended dry time between Prime Intense and the first topcoat -- do not rush it based on the surface feel.

FAQs: spotted gum flooring

Can spotted gum be oiled instead of polyurethaned?

Yes. Bona Craft Oil works well on spotted gum and gives a low-sheen, natural finish. The oil path requires different preparation -- see the spotted gum finishing guide for the full oil vs poly comparison.

Why does spotted gum look different board to board?

Spotted gum is a naturally variable species. Colour ranges from pale grey to deep chocolate depending on the tree, the position in the log, and the drying method. This variation is considered a feature, not a defect. A clear finish (Prime Intense + water-based topcoat) preserves the natural variation without adding amber.

Is spotted gum harder to sand than blackbutt?

Yes. Spotted gum is harder (11.0 kN vs 9.1 kN) and the interlocked grain makes it more demanding. Expect to use more abrasives per square metre and to spend more time on the grit sequence. Budget accordingly.

Tools

• Grit Sequence Picker -- pre-set for spotted gum
• Primer Picker -- confirms Prime Intense for spotted gum
• Coverage Calculator -- litres of primer and topcoat for the job