Wood hole filling

In the UK's damp climate, leaving holes in exterior woodwork can quickly lead to wet rot, which is far more expensive to rectify than a simple fill-and-finish job. High-quality repairs use specialist resins that expand and contract with the wood, ensuring a seamless finish that lasts for years.

What Does the Work Involve?

• Inspection: The specialist checks the surrounding timber for signs of "sponginess," wet rot, or woodworm infestation.
• Preparation: Loose wood fibres, dust, and old paint are removed to create a clean, dry surface for the filler to bond with.
• Stabilisation: If the wood is slightly soft, a liquid wood hardener is applied to consolidate the remaining fibres.
• Filling: For large voids, a "backing" material may be used before applying a two-part chemical resin or epoxy filler in layers.
• Profiling: The filler is shaped while malleable to match the original contours of the timber, such as decorative mouldings or beadings.
• Sanding: Once fully cured, the area is sanded through various grits until it is perfectly flush with the surrounding wood.
• Finishing: The repair is primed and then painted, stained, or lacquered to match the existing finish.

Typical Costs

The following table outlines the expected costs for wood hole filling in the UK for 2025/26. Prices include VAT and are based on professional carpenter or surface repair specialist rates.

Costs are primarily driven by the type of filler required and the complexity of the finish. Matching a specific wood grain on a natural oak floor is significantly more time-consuming than filling a hole in a painted white skirting board.

How Long Does It Take?

• Minor cosmetic holes: 1–2 hours for prep and filling, though paint may require a return visit or homeowner completion.
• Large exterior voids: 3–5 hours, often spread over two days to allow for deep-fill resins to cure and harden completely.
• Multiple window sills: 1–2 days depending on the extent of the rot and the number of layers required.
• Grain-matched floor repairs: 2–4 hours per section due to the artistic nature of mimicking natural wood patterns.

DIY or Professional?

Small nail holes or minor scuffs on painted indoor surfaces are well within the reach of a confident DIYer using a standard "one-strike" filler. However, for structural timber, exterior joinery, or high-end hardwood flooring, a professional is recommended.

Professional surface repairers use two-part chemical resins that are much stronger than DIY wood doughs. These resins bond chemically to the wood, ensuring the patch won't pop out when the temperature changes.

If the wood is structural (such as a floor joist or roof rafter), you should consult a carpenter to ensure the integrity of the timber isn't compromised. For exterior work, professionals ensure the repair is "weather-tight," preventing future rot.

Choosing the Right Tradesperson

• Check Specialisms: For flooring, hire a floor restoration specialist; for windows, look for a joiner or sash window expert.
• Ask about Materials: Ensure they use high-quality two-part fillers (like wood-specific epoxies) rather than cheap multi-purpose wall filler.
• Portfolio: Ask to see "before and after" photos of previous repairs, specifically looking for how well they matched the grain or colour.
• Questions to ask:
  • "Will the filler be flexible enough for exterior use?"
  • "How do you ensure the rot won't return behind the filler?"
  • "Is the cost of paint/stain matching included in your quote?"

UK Regulations

• Listed Building Consent: If your home is Grade I or II listed, you may need permission to use modern resin fillers on original timber features.
• Building Regulations (Part L): If the repair involves replacing significant sections of window frames, you must ensure the thermal performance is maintained.
• Waste Disposal: Professional trades must have a waste carrier licence if they are removing large amounts of rotten timber from your site.

Common Problems

• Filler Shrinkage: Cheap, water-based fillers shrink as they dry, leaving a visible "ring" around the repair; professionals use non-shrink resins.
• Moisture Trapping: Filling over damp wood or active wet rot will cause the timber to decay faster behind the repair.
• Colour Mismatch: Wood filler often absorbs stain differently than natural timber; a pro will "over-stain" or use artist pigments to blend the patch.
• Cracking: Using a rigid filler on an exterior joint that needs to move with the seasons will result in the repair cracking within one year.

Frequently Asked Questions

Can you fill a hole in a wood floor so it’s invisible?

Yes, but it requires a specialist surface repairer. They use various shades of resin and "grain pens" to manually draw the wood patterns across the filler, making it virtually impossible to spot from a standing height.

How long does wood filler take to dry?

Standard two-part chemical fillers are usually sandable within 30 to 60 minutes. Deep-fill epoxy resins used for structural repairs may take 12 to 24 hours to cure fully before they can be finished.

Should I use caulk or wood filler for gaps?

Never use caulk for holes in the middle of wood; it cannot be sanded and will remain rubbery. Caulk is only for "perimeters" where wood meets a wall. Wood filler is designed for the timber surface itself.

Can I fill wood that has rot?

Only if the rot is minor and has been treated. All soft, decayed wood must be cut out back to "sound" timber, and the remaining area treated with a wood preserver and hardener before filling.

Will wood filler fall out of exterior holes?

Only if the wrong product is used or the preparation was poor. High-quality exterior resins are designed to bond with the fibres and move with the timber, preventing them from popping out during frost or heatwaves.