Resin bleed is one of the most common headaches when sanding native or radiata pine floorboards in New Zealand homes. The good news is that with the right preparation and products, you can manage it effectively and still achieve a beautiful, long-lasting finish.
What Is Resin Bleed and Why Does It Happen?
Pine timber — including the widely used radiata pine found in many NZ homes built from the mid-20th century onwards — contains natural resin (also called pitch) stored in pockets within the wood grain. When you sand the floor, you generate heat and friction that can liquefy this resin, causing it to ooze out onto the surface. This is called resin bleed.
Resin bleed is more likely to occur:
- In older floors that haven't been sanded before
- In boards with visible knots, which are high-resin areas
- During warmer weather or in sun-exposed rooms
- When using coarser sandpaper grits that generate more heat
If resin is left untreated, it will contaminate your finish coat, causing fisheye, poor adhesion, soft spots, and a patchy appearance.
Step 1 — Identify Problem Areas Before You Start
Before you even switch on the drum sander, walk the floor and mark any knots or areas with visible resin staining using chalk or a pencil. These spots will need extra attention.
On older floors, you may also notice dark amber or brown staining around knots — a telltale sign that resin has already bled in the past.
Step 2 — Heat and Scrape Existing Resin
For heavy resin deposits, use a heat gun on a low-to-medium setting to gently warm the resin until it becomes fluid, then scrape it away cleanly with a sharp paint scraper. Work quickly and carefully — you don't want to scorch the timber.
Always wear appropriate PPE including safety glasses and gloves. Check WorkSafe NZ for general guidance on safe use of heat tools.
Step 3 — Treat with a Shellac-Based Sealer or Knotting Solution
This is the most important step. After scraping, apply a shellac-based knotting solution or shellac sealer directly to the resin-affected areas — particularly over knots. Shellac acts as a barrier that locks in the resin and prevents further bleed from contaminating your topcoat.
- Apply with a small brush directly onto knots and stained areas
- Allow to dry fully (usually 30–60 minutes, check the product label)
- Lightly sand the treated areas by hand before proceeding with machine sanding
Products like Zinsser BIN (a shellac-based primer-sealer) are well regarded for this purpose and are available from Bunnings and Mitre 10.
Note: Always check product compatibility with your intended floor finish (oil, polyurethane, etc.) before applying any sealer.
Step 4 — Sand Carefully to Minimise Heat Build-Up
When machine sanding, a few techniques help reduce resin bleed during the process itself:
- Keep the sander moving — never let a drum sander sit still on the floor while running
- Use sharp abrasives — blunt sandpaper generates more heat and friction
- Work progressively through grits (e.g. 40 → 60 → 80 → 100) rather than jumping straight to a fine grit
- Sand in cooler parts of the day if the room gets a lot of direct sun
If fresh resin bleeds during sanding, stop, allow it to cool and harden slightly, then scrape and re-treat with shellac before continuing.
Step 5 — Clean the Surface Thoroughly Before Coating
Once sanding is complete, vacuum the floor thoroughly, then wipe down with a tack cloth or a cloth lightly dampened with mineral turpentine to remove all dust and any remaining resin residue. Allow the floor to dry completely before applying your chosen finish.
Choosing the Right Finish for Pine Floors
Some finishes are more forgiving over resin-prone timber than others:
| Finish Type | Resin Tolerance | Notes |
|---|---|---|
| Solvent-based polyurethane | Good | Penetrates well; check compatibility with shellac sealer |
| Water-based polyurethane | Moderate | Can be affected by resin; shellac barrier coat is important |
| Penetrating oil | Moderate | Soaks in well but resin spots may show through |
| Hardwax oil | Moderate | Similar to penetrating oil |
For colour and finish advice on NZ timber floors, Resene and Dulux both offer technical data sheets and helplines worth consulting.
Ongoing Resin Bleed After Finishing
In some cases — particularly in very resinous boards or during hot NZ summers — resin can continue to bleed up through a finished floor over time. If this happens:
- Lightly sand the affected spot back
- Re-apply shellac sealer
- Re-coat with your finish
This is more common in floors that weren't fully treated before the initial coat was applied.
When to Call a Professional
If your floor has widespread resin bleed across many boards, or if previous finish coats have already been contaminated, the remediation process can become complex and time-consuming. A professional floor sander will have industrial equipment, the right abrasives, and experience dealing with resinous NZ pine. They can assess whether the floor needs a full re-sand or targeted spot treatment.
You can find qualified local floor sanding professionals on tradedirectory.co.nz. Always ask whether they have experience with pine floors and resin management before booking.
For any questions about whether your flooring work requires a building consent, check with your local council or visit MBIE Building Performance — most floor sanding work falls outside consent requirements, but it's always worth confirming.
