Best Wood Filler for Staircase Gaps: 2025 Expert Review
DR Joinery
Expert Joiner & Staircase Specialist
Nothing spoils the look of a staircase quite like unsightly black gaps between the treads and risers, or cracked filler along the stringers. In York particularly, where many of our homes settle and shift over decades, keeping a staircase looking pristine can be a battle against movement.
The mistake most homeowners make is assuming one tub of filler does it all. However, staircases are dynamic structures; they flex when you walk on them. A hard, brittle filler in a joint that moves will inevitably crack and fall out, often within weeks of decoration.
In this review, I'm sharing the products I keep in the van. We will look at a budget option for static repairs, a high-quality flexible sealant crucial for moving joints, and a quick-drying specialist filler for surface repairs.
Live in York?
Struggling with a squeaky or damaged staircase?
Get a free quote from our local team.
Specs vs. The Real World
The Spec: "Stainable Wood Filler"
"Manufacturers claim filler accepts wood stain exactly like the surrounding timber."
Filler lacks grain and porosity. It will almost always stain a slightly different shade (usually darker or flatter) than the real Oak or Pine. Always test a small patch first.
The Spec: "Hard vs Flexible"
"Hard fillers are stronger and better for all gaps."
On a staircase, 'strong' often means 'brittle'. For the gap between the tread (where you step) and the riser (the vertical board), you absolutely need a flexible sealant, not a hard filler, or the vibration will crack it.
My Top 3 Recommendations
Three options to cover different needs and budgets
Bartoline Ready Mixed Wood Filler White 500g
Bartoline
This is a staple in any decorator's bag. It is exceptionally cheap and easy to use, making it perfect for filling nail holes, static gaps in skirting, or the side strings of the staircase before painting. It sands down very smoothly.
The Good
- Excellent value for money
- Very easy to sand smooth
- Perfect for surfaces that will be painted white
The Bad
- Not flexible enough for tread-to-riser gaps
- Will crack if used in large, deep holes without layering
Installer Tip:
Use this for the 'stringer' (the side structural board) and pin holes. Overfill slightly as it shrinks back when drying, then sand flush with 120-grit paper before painting.
Priced at £2.99 at the time of writing
Check Price on AmazonLami Mate Flexible Sealant | Floorboard Gap Filler | Pine | Pack of 2
ABL Supplies
For the actual steps of a staircase, hard filler is useless. You need something that moves with the timber. Lami Mate is a flexible sealant ideal for the junction where the tread meets the riser. It stops draughts, flexes under footfall, and prevents that annoying dust trap.
The Good
- Highly flexible – won't crack when stairs are walked on
- Stops draughts coming through old staircases
- Pine colour blends well with natural timber finish
The Bad
- Cannot be sanded like a hard filler
- Requires a steady hand or masking tape for a neat finish
Installer Tip:
Clean the gap thoroughly with a vacuum and a scraper before applying. This sealant relies on good adhesion to the timber. Run a bead along the back of the tread, smooth it with the tool, and leave it to cure fully before walking on the stairs.
Priced at £12.99 at the time of writing
Check Price on AmazonRustins AWOON250 Acrylic Wood Filler, Natural, 400g
RUSTINS
When you have gouges on the nosing (the front edge) of the stair or surface damage that needs a tough, quick repair, Rustins is the go-to. It is acrylic-based, so it dries faster than traditional solvent fillers and has a 'natural' tone that is a good base for staining.
The Good
- Fast drying allows for same-day sanding and finishing
- Low odour compared to solvent fillers
- Suitable for interior and exterior use
The Bad
- Can sink slightly in deep holes (apply in layers)
- Natural colour is quite light – may need staining to match aged pine
Installer Tip:
This is excellent for repairing 'dog damage' or scuffs on the stair nosing. Apply it proud of the surface, let it dry, and then sand it back to recreate the rounded profile of the stair nose.
Priced at £7.65 at the time of writing
Check Price on AmazonFrequently Asked Questions
Why does the filler in my stairs keep cracking?
Should I stain the wood before or after filling?
Can I use decorators caulk for staircase gaps?
How do I fix squeaky stairs before filling?
Do I need a professional joiner to refurbish my stairs?
Need Professional Bespoke Staircases?
Our team at DR Joinery specialises in Bespoke Staircases across York.
Get a free quote for professional installation.
View Our Bespoke Staircases Service