Blackbutt and Tallowwood are two of the most commonly sanded hardwood species in NSW — and two of the most likely to cause problems if you prime them wrong. Tannin bleed is the culprit: a dark, streaky discolouration that appears through light-coloured waterborne finishes when soluble tannins in the timber migrate upward through the coating system.
If you've ever applied a waterborne finish to Blackbutt and had the result come up patchy, dark at the edges, or with a greenish-grey tint — that's tannin. And once it's happened, your options are limited. Prevention is everything.
Why High-Tannin Timbers Need a Different Primer
Tannins are naturally occurring polyphenolic compounds in timber. In species like Blackbutt, Tallowwood, Spotted Gum and some Ironbarks, tannin concentrations are high enough to cause real problems when you apply a water-based coating system. Water activates the tannins, pulling them toward the surface. If your primer isn't specifically designed to block this migration, they bleed through into your finish coats — and they don't sand back cleanly.
The problem is more pronounced:
- In highly porous or freshly sanded surfaces where absorption is uneven
- On end grain and at board edges where timber is most open
- In humid conditions where moisture drives faster tannin migration
- When using primers that produce a light, natural colour (which shows discolouration more easily)
The Wrong Primer for High-Tannin Timbers
Bona Prime Classic UX is an excellent primer for standard-tannin species. It produces a light, natural colouration and is the recommended primer for the Bona Traffic HD RAW system. But Bona explicitly states that Classic UX is not recommended for high tannin species including Blackbutt and Tallowwood. Using it on these timbers is one of the most common causes of tannin bleed issues in the field.
The Right Primer: Bona Prime Intense
Bona Prime Intense is specifically designed for high tannin species. It produces a medium, rich colouration — enhancing the natural warmth of the timber rather than lightening it — and it's formulated to lock tannins in rather than let them migrate. The long open time and excellent flow characteristics also help achieve even, consistent coverage without lap marks.
For Blackbutt and Tallowwood, the recommended system is:
- Sand to a clean, uniform scratch profile — consistent grit sequence through to your final pass
- Apply 1 coat Bona Prime Intense — full coverage, allow to dry fully (1–2 hours at 20°C)
- Inter-coat abrasion (light screen or equivalent)
- Apply 2 coats of your chosen Bona topcoat — Traffic HD, Wave 2K, or Mega
Other Tannin-Heavy Species to Watch
Blackbutt and Tallowwood get the most attention, but they're not alone. Watch for tannin bleed on:
- Spotted Gum — variable tannin levels, test before committing to a system
- Ironbark — high tannin, high density, requires careful prep and primer selection
- Merbau — very high tannin, red extractives are notoriously difficult to seal
- Brush Box — moderate tannin, can be variable site to site
If you're unsure, do a test coat on a concealed section first. Apply your primer and one topcoat, let it cure, and check for any discolouration before committing to the whole floor.
Field Notes
A few things worth knowing from experience:
- Sanding dust affects absorption. Make sure the floor is thoroughly vacuumed and tack-cloth cleaned before priming. Fine dust left in the grain can affect how primer penetrates and bonds.
- Don't rush the dry time. In humid conditions or on a large floor, prime in sections and allow adequate dry time before screening. Rushing leads to uneven tannin lockdown.
- Temperature and humidity matter. In coastal NSW summer conditions, surface temperatures can be high and humidity elevated — both affect how quickly tannins activate. Early morning application on hot days is often the safer call.
- More coats don't fix a bad first coat. If your primer coat wasn't uniform or didn't penetrate properly, additional finish coats won't mask the problem. Get the primer right first.
If you're stocking up on primers or have questions about which system suits your current job, get in touch with Sand-Aid — we're in Toronto NSW and stock the full Bona primer range with trade pricing.