How to Fill Gaps in Skirting Boards – DIY Guide
How to Fill Gaps in Skirting Boards
Seal draughty gaps around skirting boards for a clean, professional finish in hours.
Fill gaps in skirting boards using flexible decorator’s caulk for gaps between the board and wall, and wood filler for cracks or splits in the timber itself. Clean the gap, apply the filler, smooth it off, and paint once dry.
- Caulking gun
- Putty knife
- Fine-grit sanding block
- Damp cloth or sponge
- Filling knife
- Craft knife or utility knife
- Decorator’s flexible caulk (paintable)
- Interior wood filler
- Fine-grit sandpaper (120–180 grit)
- Low-tack masking tape
- Primer (if needed for bare wood)
- Gloss or satinwood paint to finish
- Damp cloth for tooling caulk
Step-by-Step Guide
Identify the Type of Gap You’re Filling
Check where the gap is before you pick a product. A gap between the skirting board and the wall needs flexible decorator’s caulk — it moves with the house and won’t crack. A split, dent, or hole in the timber itself needs wood filler, which dries hard and can be sanded smooth. Using the wrong product is the most common cause of the repair failing within months. Our Timber & Joinery Guide covers when to use each type of filler across different joinery tasks.
Clean and Prepare the Gap
Remove any old, cracked caulk or loose filler with a craft knife or the edge of a filling knife. Scrape away flaking paint from the immediate area and brush out dust and debris. Wipe the surface down with a damp cloth and allow it to dry completely — filler and caulk will not bond well to a dusty or damp surface. If the skirting board is bare timber where you’ve removed old filler, apply a thin coat of primer before filling to prevent the wood grain from absorbing your filler unevenly.
Apply Masking Tape for Clean Edges
Run low-tack masking tape along the wall just above the skirting board and along the top face of the board itself, leaving the gap exposed. This gives you a straight, clean line on both surfaces and saves time cleaning up. Press the tape edges down firmly so caulk can’t bleed underneath. This step is especially worth doing on textured or painted walls where ragged edges would be very visible once painted. Painting skirting boards is far easier when the caulk line is straight from the start.
Fill the Gap with Caulk or Wood Filler
For wall-to-board gaps: load your caulk tube into the caulking gun, cut the nozzle at a 45-degree angle to match the gap width, and run a steady bead along the full length of the gap in one continuous pass. For timber cracks or holes: press wood filler firmly into the gap with a filling knife, slightly overfilling so it sits proud of the surface. Work in sections no longer than a metre at a time to maintain control. For very wide gaps at the wall (over 5 mm), push a thin bead of filler rope into the gap first to give the caulk something to sit against — this prevents the caulk skin from sinking as it cures.
Smooth and Tool the Surface
For caulk: within a minute of application, run a damp finger or a damp cloth in one smooth stroke along the bead to press it into the gap and create a clean, slightly concave profile. Remove the masking tape immediately while the caulk is still wet, pulling it back at 45 degrees to avoid dragging the bead. For wood filler: once the filler has hardened (check the manufacturer’s guidance — usually 30–60 minutes), sand it back flush with 120–180 grit sandpaper using a sanding block. Choosing between gloss and satinwood paint for the final coat is worth deciding before you reach this stage, as the sheen level affects how visible any imperfections are.
Prime and Paint the Repaired Area
Allow caulk to cure fully before painting — most paintable decorator’s caulk is ready to paint in two to four hours, but check the product label. Spot-prime any bare timber or filled areas with a suitable primer before applying the topcoat. Apply one or two coats of gloss or satinwood paint with a small brush, feathering the edges into the existing painted surface to avoid a visible join. If your topcoat looks patchy or uneven, a light sand between coats and a second pass will resolve it.
Frequently Asked Questions
What is the best product to fill the gap between a skirting board and the wall?
Use a flexible, paintable decorator’s caulk for the gap between skirting board and wall. It accommodates the natural movement of the building without cracking, unlike rigid fillers. Choose an acrylic-based caulk for easy water clean-up and compatibility with emulsion and gloss paints.
Can I use silicone sealant instead of caulk to fill skirting board gaps?
Silicone sealant is not suitable for interior skirting board gaps — it cannot be overpainted, and standard decorator’s paints will not adhere to it. Use a paintable acrylic decorator’s caulk instead, which is specifically designed for interior joinery joints and accepts paint cleanly once cured.
How do I fill a large gap between the skirting board and the floor?
For gaps larger than about 5–6 mm between the bottom of the skirting board and the floor, pack the gap first with a thin strip of timber or compressed foam backer rod before applying caulk on top. This prevents the caulk from sinking and gives it the support it needs to form a durable, flexible seal. Filling gaps in floorboards nearby at the same time keeps the whole floor perimeter looking consistent.
How long does decorator’s caulk take to dry before painting?
Most paintable decorator’s caulk is touch dry in 30–60 minutes and ready to paint in two to four hours under normal conditions. Always check the specific product label — drying times vary and applying paint too early will cause the finish to wrinkle or crack.
Do I need to sand caulk before painting?
No — sanding caulk before painting is not necessary and can actually damage the smooth surface you’ve created. Once the caulk is fully cured, simply paint directly over it. If there are any minor ridges or finger marks, a very light pass with a fine damp cloth while the caulk is still fresh (not after curing) will smooth them out.
When running a long caulk bead along a full wall, keep a small cup of water and a damp finger close by and tool each 600–900 mm section immediately after application rather than running the whole wall and then going back — caulk that has started to skin will drag and tear when you tool it, leaving a rough finish that’s hard to correct without stripping it out.
Sources
- HSE — Decorator’s caulk and sealant use: health and safety guidance — hse.gov.uk
- Which? — How to fill gaps and cracks in walls and woodwork — which.co.uk
- Historic England — Repair of timber features in traditional buildings — historicengland.org.uk
This guide is for general information only. Always work safely and follow manufacturer instructions. DIYnut accepts no liability for injury or damage arising from DIY work.
