How to sand and varnish floorboards

Inspired by a helpful YouTube guide. This guide draws on “How to sand & varnish floorboards — preparation and sanding”, a clear and practical UK tutorial that covers the process from an empty room right through to a finished surface. The video is particularly useful for understanding the order of passes with the drum sander, which is the part that most people get wrong on their first attempt.

1. Clear and inspect the room

Remove all furniture and any rugs or carpet. If there is carpet, pull it up along with the gripper rods around the edges. Check the floor carefully for movement — boards that bounce or flex will show in the finished surface, and loose boards can catch the sander disc and flip it.

This is also the moment to look for any boards that need replacing. A badly damaged board is far easier to swap now than after you have put three coats of varnish down.

2. Punch down protruding nails

Any nail head sitting proud of the surface will tear your sanding belts to shreds in seconds. Go over the entire floor with a hammer and nail punch, sinking every visible nail at least 2 mm below the surface. Take your time here — a thorough job saves a lot of frustration and money on belts later.

Run your hand along each board after checking with your eyes. You will feel nail heads that your eyes missed.

3. Fill gaps between boards

Narrow gaps between boards can be filled with a flexible wood filler or a mix of fine sawdust and PVA glue to match the floor colour. Wider gaps need a timber strip cut to fit. Gaps that let cold air up from below the floor are worth dealing with properly — flexible filler alone will compress and crack over time if the boards continue to move.

Let any filler dry fully before sanding. Follow the manufacturer’s instructions on drying time — rushing this step shows in the finish.

4. Hire a drum sander and start with a coarse belt

Hire a drum floor sander from a local tool hire shop — most offer day or weekend rates. You will also need an edge sander for the perimeter and a belt sander or orbital sander for corners. Get plenty of belts in different grades: typically 40 grit to start, 60 grit as a middle pass, and 80 grit to finish.

Start with the 40 grit belt and work diagonally across the room at 45 degrees to the boards. This removes the worst of the old finish and evens out any cupping or level differences between boards. Keep the sander moving — stopping while the drum is running will leave a visible depression in the floor.

5. Sand along the grain

Switch to the 60 grit belt and sand along the length of the boards. Overlap each pass slightly so you do not leave ridges. The floor will start to look genuinely light and fresh at this stage, which is encouraging. Two passes in opposite directions along the grain are better than one heavy pass.

Finish with the 80 grit belt for a smooth surface ready for finishing. Vacuum the drum sander bag regularly — a full bag reduces suction and lets dust build up on the floor, which affects the finish.

6. Sand the edges

The drum sander cannot reach the edges of the room. Use an edge sander (also available from tool hire) with matching grit progression to work the perimeter. Work in the direction of the boards where possible. Keep the sander moving and do not linger in one spot.

Edge sanding is noisy, creates a lot of dust, and takes longer than the middle of the floor. Patience pays off here.

7. Get into the corners

An orbital sander or hand-held belt sander handles the corners that the edge sander cannot reach. Work through the same grit progression. If you have dado rails, skirting boards, or fireplaces to work around, a sanding block wrapped in sandpaper by hand is the safest approach close to paintwork you want to keep.

8. Vacuum and apply the finish

Vacuum the entire floor thoroughly — twice. Then wipe with a tack cloth or a slightly damp cloth to pick up the last of the fine dust. Dust in the varnish will ruin the finish. It is worth sealing doorways with masking tape and plastic sheeting to stop dust drifting back in while the finish dries.

Apply your chosen finish — floor varnish, hard wax oil, or a water-based lacquer — in thin coats along the grain, working from the far corner toward the door. Follow the manufacturer’s recommended drying times between coats and lightly sand with 120 grit between each coat for adhesion. Most finishes need two or three coats. Do not be tempted to skip the middle coat — durability comes from building up the layers properly.

When to call a handyman

Call Richard if the boards are in poor condition and need replacing before sanding, if the floor is a parquet or herringbone pattern that needs specialist equipment, or if you simply want the job done without a weekend of hiring equipment and breathing dust. Sanding and finishing a floor is satisfying work, but it is properly exhausting. Nothing wrong with having someone else do it.