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What filler works for gaps in floorboards?

In Cheshire, a narrow gap between sound floorboards is often a draught to seal, not a new floor. The Planning Portal describes a tube sealant for gaps at the boards and the skirting, and says under-floor airbricks must stay open.

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By the QuoteZila editorial team. Editorial policy.

What can you put in a small floorboard gap?

In Cheshire, including Crewe, Nantwich and Sandbach, a filler question usually starts in a hallway or a bedroom where a line of daylight shows between two boards, or where a curtain moves beside the skirting. The useful distinction is between a hairline draught and a board that has shrunk, split or started to rock.

The Planning Portal's floor-insulation note says you can use a regular tube sealant, such as silicon, to fill gaps between floorboards and skirting boards to stop draughts [S1]. That sentence is about the joint where the floor meets the wall, which is a common cold path on a suspended timber ground floor. A flexible sealant can also sit in a narrow joint between two boards if the boards are stable. It is the wrong material for a hole, a missing tongue, or a board that drops when you stand on it.

A tub of rigid wood filler is for a shallow dent or a nail hole, not for a joint that opens and closes as the room is heated. If the label does not say the filler stays flexible, do not assume it will move with the boards.

When is filler the wrong repair?

Stop and look under the gap before you buy a tube. Dark, soft or mushroom-smelling timber, a board that flakes, or a patch that feels damp is rot or a leak, not a cosmetic joint. Filler on top of that traps moisture against the wood. The Planning Portal warns that floorboards will rot without adequate ventilation, and tells you not to block under-floor airbricks in the outside walls [S1]. Those bricks are how a suspended ground floor breathes. Sealing the room against draughts is fine. Covering the airbricks with soil, a new path or a skirting packed with foam is not.

Also leave filler alone when:

  • the gap is wide enough to see the joist void, or a cable or pipe runs in it
  • several boards in a row have cupped or sprung
  • the floor bounces near a hearth, a doorway or a staircase trimmer
  • you are about to lay a new covering that needs a flat, fixed deck
  • the house is listed, and the boards are part of the historic fabric

A joiner or flooring fitter can splice a new piece, refix a loose board or sister a damaged section. That is a different job from a Saturday tube of sealant. Describe the room, the width of the gap and whether the boards move, and ask them to say which one they have priced.

How do you fill a draught gap without sealing the floor solid?

Vacuum a dry joint so dust does not stop the sealant gripping, and rake out only the loose old fill. Do not pour water into the gap. The airbricks are there to keep that void dry [S1].

At the skirting, run a thin bead of the tube sealant the Planning Portal describes and tool it along the timber joint [S1]. A fat bead splits. Do not push sealant into a service notch or down an air path that leads to an airbrick.

Between two stable boards, squeeze flexible filler in and strike it flush. A foam backer can support a deep joint so the sealant is not a plug hanging in the void. The backer is not ventilation. If a board is loose, do not nail at random: a pipe or cable may sit under it. Lift a loose end and look, or leave the refix to a joiner.

Paint only after the product has cured, and only with a finish the label allows. Silicon often leaves a line that stain will not cover. If the whole floor is going to be sanded, say so before you fill, because some sealants smear and clog the abrasive.

Does filling gaps count as building work?

Filling a draught gap is maintenance of the floor you already have. The Planning Portal says planning permission is not generally required to replace a floor or a ceiling [S2]. Replacing is a larger job than sealing a joint, so a bead of sealant is not the case that page is written for. The same page says that if you live in a listed building you should contact the local planning authority [S2]. In a listed house in Cheshire, even internal floor work can need listed building consent. Ask before you sand, stain or replace boards, not after.

A separate Planning Portal page covers renovation of the floor itself. Renovation of more than 25 per cent of a solid or suspended floor, where that work replaces the screed or the timber floor deck, has to meet the standards in the building regulations Approved Documents [S3]. Sealing a few gaps is not that renovation. Lifting most of the boards to insulate, or replacing the deck, can be. If the job grows from a tube of filler into a new deck, ask the building control body before the boards come up.

The installation of insulation in a floor has to meet the energy-efficiency values in the Approved Documents [S3]. No method is set out for insulating between joists. If that is the real project, read the Planning Portal note and speak to building control, and hire a fitter who will leave the airbricks working [S1].

What should you tell a fitter in Cheshire?

If the gaps are beyond a sealant, post the job with the same facts to each business. QuoteZila is free for customers and local businesses [QZ1]. Up to five matched local businesses can send a quote [QZ2].

Say which room, which floor (ground or upper), and whether the boards are painted, varnished or bare. Mention a cellar or a void, and say if airbricks sit in the outside wall. A ground floor in a terraced street and an upper floor over a living room are different jobs, because only the ground floor is using those airbricks to stay dry [S1]. Add a photo of the widest gap and a photo of any soft timber. Say whether you want the gaps sealed only, or boards replaced where they have failed.

Citizens Advice says some traders charge for a quote, so ask before anyone comes out [S4]. A quote is a fixed price for an agreed piece of work, and an estimate is a rough guess, so ask which one you have been given [S4].

Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.

Posting a job is not open yet

Anyone in the UK can post a job or register a business. The first towns on this site include Crewe, Nantwich and Sandbach. Say if the boards have to come through a narrow hall or a street with little room to park, because that is about access, not about which filler suits the gap.

Questions about floorboard gaps

Can I fill every gap in an old timber floor?

Only the gaps in boards that are firm, dry and not crumbling. A flexible sealant is for a draught path at the edge or between narrow boards. A wide, moving or rotten gap is a repair, and forcing filler into it hides the problem until the board fails. If you are unsure, ask a joiner to look before you seal anything.

Will filler stop draughts from a suspended timber floor?

The Planning Portal says a regular tube sealant, such as silicon, can fill gaps between floorboards and skirting boards to stop draughts. That is an edge seal, not insulation between the joists. It also says floorboards rot if under-floor ventilation is blocked, so leave airbricks in the outside walls clear.

Do I need permission to fill or replace floorboards?

The Planning Portal says planning permission is not generally required to replace a floor or ceiling, but a listed building is different and you should contact the local planning authority. Filling a few gaps is smaller than replacing a floor. If the work becomes a new floor deck, ask the building control body whether approval is needed.

Should I sand the filler flat on the same day?

Read the tin or tube you bought and follow that instruction for drying. No drying time is given, because products differ and a guessed time can tear the seal out of the gap. Keep off the strip until it has set, then sand only if the product says the surface can be sanded.

Does QuoteZila check the joiner who replies?

No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.

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Sources

  1. QZ1: QuoteZila product fact. QuoteZila pricing line.
  2. QZ2: QuoteZila product fact. QuoteZila terms.
  3. S1: Floor insulation, Planning Portal. Accessed 2026-10-27. https://www.planningportal.co.uk/permission/common-projects/energy-saving/floor-insulation/
  4. S2: Planning permission: ceilings and floors, Planning Portal. Accessed 2026-10-27. https://www.planningportal.co.uk/permission/common-projects/ceilings-and-floors/planning-permission/
  5. S3: Building regulations: floor insulation, Planning Portal. Accessed 2026-10-27. https://www.planningportal.co.uk/permission/common-projects/insulation/building-regulations-floor-insulation
  6. S4: Before you get building work done, Citizens Advice. Accessed 2026-10-27. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/