Raised grain after the first coat of finish is completely normal — and nothing to panic about. When water-based finishes or even some oil-based products hit bare timber, they cause the wood fibres to swell and stand up, creating a rough, slightly fuzzy surface. The good news is that a light sand between coats will knock it back and set you up for a beautifully smooth final result.
Why Does Grain Raise in the First Place?
Timber is a natural, porous material. When any liquid finish — especially water-based polyurethane or waterborne lacquer — soaks into the surface, it causes the tiny wood fibres to absorb moisture and lift. This is called raised grain or grain raising, and it's most pronounced after the very first coat because the timber is completely bare and thirsty. Subsequent coats raise the grain far less because the fibres have already been sealed.
In New Zealand, where we commonly work with species like rimu, kauri, heart pine, and macrocarpa, as well as imported hardwoods and radiata pine, the degree of grain raising can vary. Softer, more porous timbers tend to raise more noticeably than dense hardwoods.
What You'll Need
- Fine abrasive paper or mesh screen — typically 120 to 180 grit for between-coat sanding
- A pole sander or hand sanding block
- A vacuum cleaner with a floor attachment
- A tack cloth or slightly damp microfibre cloth
- Your chosen floor finish for the next coat
Step-by-Step: Dealing with Raised Grain
1. Make Sure the Coat Is Fully Dry
Before you touch the floor, confirm the first coat is completely dry — not just dry to the touch, but cured enough to sand. Check the manufacturer's data sheet for recoat times; these vary significantly between products and are affected by NZ humidity and temperature. In a warm, well-ventilated room this might be as little as 2–4 hours for water-based products, but in a cold or damp environment it can take much longer. Sanding a coat that isn't ready will clog your paper and drag the finish.
2. Choose the Right Grit
For between-coat sanding to remove raised grain, 120 to 180 grit is the standard range. You're not trying to remove the finish — just knock off the raised fibres. Using anything coarser risks cutting through the coat and back into bare timber, which means starting again.
3. Sand Lightly and Evenly
Using a pole sander with a 150-grit screen or abrasive sheet, work with the grain across the entire floor using long, overlapping passes. Apply only light, even pressure — let the abrasive do the work. You should see a fine white powder forming, which tells you you're cutting the raised fibres without digging into the finish itself. Pay attention to edges and corners with a hand sanding block.
4. Vacuum Thoroughly
Once you've sanded the whole floor, vacuum up every bit of dust. Dust left on the surface will be trapped under the next coat and show up as gritty bumps in the final finish. Use a good vacuum with a soft floor attachment, then follow up with a tack cloth or a microfibre cloth barely dampened with water to pick up any remaining fine particles. Allow the surface to dry completely before recoating.
5. Apply the Next Coat
With the floor clean and dust-free, apply your second coat following the manufacturer's instructions. You'll notice the surface feels much smoother after sanding, and the second coat will go on more evenly. Repeat the light sand between every coat except the final one.
Common Mistakes to Avoid
- Sanding too aggressively — you'll cut through the finish and expose bare wood again
- Skipping the vacuum step — trapped dust ruins the finish
- Recoating too soon — always follow the product's recoat window; NZ conditions (especially in winter or in humid regions like Northland and the West Coast) can slow drying significantly
- Using the wrong grit — anything below 100 grit between coats is too coarse for this job
A Note on Water-Based vs Oil-Based Products
Water-based finishes raise the grain more noticeably than traditional oil-based polyurethanes, but they dry faster and have lower VOC emissions — an important consideration for indoor air quality. BRANZ provides useful guidance on timber floor finishing and indoor air quality for NZ homes. Always work in a well-ventilated space regardless of which product you use, and check the safety data sheet. WorkSafe NZ has information on safe handling of finishing products.
For product selection, Resene and Wattyl both offer floor finishing systems with technical data sheets that specify recoat times and between-coat sanding recommendations. Always follow the specific product's instructions rather than generic advice.
When to Call a Professional
If after sanding between coats you're still getting a rough or uneven surface, or if you've accidentally sanded through the finish in patches, it's worth calling in a qualified floor sanding professional. Uneven finishes, blotchy colour, or visible lap marks can be tricky to correct without experience and the right equipment. A professional will also have access to commercial-grade machines and products that can rescue a difficult job. You can find licensed floor sanding tradespeople in your area on tradedirectory.co.nz.
For heritage or high-value timber floors — particularly native species like rimu or kauri — professional advice is especially worthwhile, as these timbers can be irreplaceable.
