How to Sand and Varnish Wooden Floors
Reveal beautiful natural wood hidden under years of grime, paint and old varnish. A sanded and varnished floor transforms a room.
Difficulty
Hard
Time
2-3 days
Cost
150-350
Safety First
Always wear a proper dust mask (P3 rated minimum) and ear defenders when using a drum sander. The noise is extreme and the dust is harmful. Seal the room with dust sheets taped over doorways. Open windows for ventilation. Check for and punch down any protruding nail heads before sanding as they will rip the sandpaper and can damage the drum. If your floorboards were laid before 1960, test for lead paint before sanding.
Sanding wooden floors is hard work but the results are stunning. Hiring a drum sander and edge sander for a weekend typically costs 60-100 per day. You work through three grits from coarse to fine, then apply stain if desired and two or three coats of varnish. A typical room takes a full day to sand and then two more days for finishing coats with drying time between them. The key to a good result is thorough preparation and patience with the sanding.
What You Will Need
Tools
- - Drum sander (hire from HSS, Jewson or local hire shop)
- - Edge sander (hire at the same time)
- - Detail sander or scraper (for corners)
- - Hammer and nail punch
- - Vacuum cleaner
- - Tack cloth
- - Paint roller and tray (for varnish)
- - Dust mask (P3 rated)
- - Ear defenders
- - Knee pads
Materials
- - Sandpaper sheets for drum sander (40, 80, 120 grit)
- - Sandpaper discs for edge sander (matching grits)
- - Wood filler (for gaps between boards)
- - Wood stain (optional)
- - Floor varnish (water-based or oil-based, 2-3 coats)
- - White spirit (for oil-based products)
- - Dust sheets and masking tape
Step-by-Step Instructions
Prepare the room
Remove all furniture. Pull up any carpet, underlay and gripper rods. Check every board for protruding nails and punch them all down at least 3mm below the surface using a nail punch and hammer. Fill any large gaps between boards with flexible wood filler and let it dry. Seal doorways with dust sheets and tape. Open windows.
First pass with coarse grit (40)
Load 40-grit paper onto the drum sander. Start at one side of the room and work along the length of the boards. Keep the sander moving at all times. If you stop in one place it will gouge the floor. Work in overlapping strips. Tilt the drum up to start and lower it gently. Do the main floor area first.
Edge sand the perimeter
The drum sander cannot reach the edges. Use the edge sander with matching 40-grit to sand around the perimeter and in front of fireplaces. For tight corners the edge sander cannot reach, use a detail sander or scraper.
Second pass with medium grit (80)
Vacuum thoroughly between grits. Load 80-grit paper and repeat the entire process. Drum sand the main area, then edge sand the perimeter. This pass removes the scratches from the coarse grit and starts to smooth the surface.
Final pass with fine grit (120)
Vacuum again. Load 120-grit and do the final sanding pass. This gives you the smooth finish that the varnish will sit on. After this pass, vacuum the entire room meticulously, including skirting boards and window sills where dust settles. Wipe the floor with a tack cloth to pick up the last particles.
Apply stain (optional)
If you want to change the colour of the wood, apply stain with a cloth or brush, working along the grain. Apply evenly and wipe off excess. Let it dry completely before varnishing. Test the stain on an offcut or hidden area first as the colour varies hugely depending on the wood type.
Apply varnish coats
Apply the first coat of floor varnish with a roller, working along the grain. Start at the far corner and work towards the door so you do not paint yourself in. Water-based varnish dries in 2-4 hours. Oil-based takes 8-12 hours. Lightly sand between coats with 240-grit and vacuum. Apply two or three coats for a durable finish. Do not walk on the floor for at least 24 hours after the final coat.
Cost Estimate
Hiring a drum sander and edge sander for a weekend costs around 80-120. Sandpaper sheets cost another 30-50 (buy extra as they wear fast, especially the coarse grit). Varnish for a medium room costs 40-60. Total for a room is typically 150-250 for DIY versus 400-800 for a professional.
Sanding Direction
Always sand along the grain of the boards, never across. If your boards run diagonally you will need to sand diagonally too. For parquet or herringbone floors, sand at 45 degrees to the pattern on the first pass, then along each direction.
Water-Based vs Oil-Based Varnish
Water-based varnish dries faster, has less smell and does not yellow over time. Oil-based varnish is more durable, gives a warmer tone and is slightly cheaper. For living rooms and bedrooms, water-based is usually fine. For hallways and kitchens with heavy traffic, oil-based lasts longer.
Common Mistakes to Avoid
- - Not punching down nail heads (damages the sander drum and rips sandpaper)
- - Stopping the drum sander in one spot (creates deep gouges that are hard to remove)
- - Skipping grits (going from 40 straight to 120 leaves visible scratches)
- - Not vacuuming thoroughly between coats (dust particles trapped in varnish)
- - Applying varnish too thickly (causes bubbles and takes forever to dry)
- - Walking on the floor too soon (leaves footprints in the finish)
When to Call a Professional
Call a professional if you have parquet, herringbone or engineered wood floors as these need specialist equipment and technique. Also consider a professional for very large areas or if the boards have deep damage, woodworm or significant gaps that need professional filling. If your pre-1960s floorboards test positive for lead paint, a professional with the right extraction equipment is essential.