Filling Gaps in Floorboards to Eliminate Draughts and Restore Your Floor

Gaps between floorboards are a common problem in older homes and even in newer properties with solid timber flooring. These openings develop as wood shrinks and expands with changes in temperature and humidity, particularly during the heating season. Beyond being unsightly, gaps create draughts, allow dust and debris to fall through to the subfloor, and compromise energy efficiency. Several effective methods exist for filling these gaps, from simple DIY solutions to professional-grade products. This guide covers the causes of floorboard gaps and the best techniques for sealing them, whether you plan to sand and varnish your floor or cover it with carpet.

Understanding Why Gaps Appear Between Floorboards

Before choosing a filling method, it is helpful to understand why gaps develop. Solid timber flooring reacts to its environment. When the air in a room is warm and dry, moisture leaves the wood, causing it to shrink. When humidity rises, the wood absorbs moisture and expands. This constant cycle of movement means that gaps open and close over the course of a year, especially in rooms with central heating or underfloor heating systems that dry out the air during winter months.

The severity of the gaps depends on several factors:

• Age of the property: Older homes often have wider floorboards that have undergone many years of seasonal movement, resulting in more pronounced gaps.
• Type of timber: Softwoods such as pine shrink and expand more than hardwoods like oak, so gaps tend to be wider in softwood floors.
• Moisture content at installation: Boards laid when the timber had a high moisture content will shrink more as they dry out, leaving larger gaps.
• Tongue and groove versus square edge: Tongue and groove boards interlock, limiting the visible gap at the surface. Square edge boards leave a direct opening all the way through.

Filling Gaps with PVA Glue and Sawdust

One of the simplest methods for filling narrow gaps is to mix PVA adhesive with sawdust collected from sanding the floor. This works best on tongue and groove flooring where the tongue provides a shelf for the mixture to sit on. Collect the sawdust during the initial sanding pass before applying stain or varnish.

Follow these steps for best results:

1. Clean the gaps thoroughly using a vacuum cleaner with a thin nozzle to remove all dust and debris.
2. Apply a thin layer of PVA adhesive into each gap using a small brush or a squeezy bottle with a narrow tip.
3. Sprinkle the collected sawdust over the wet PVA and press it down firmly with the handle of a screwdriver or a scraper blade.
4. Allow the PVA to dry completely, which typically takes two to four hours depending on room temperature.
5. Sand the filled area gently with a small electric sander or sanding block to level the surface flush with the surrounding boards.

The sawdust and PVA mixture sands down to a finish that closely matches the surrounding timber. However, because of the PVA content, the filled area will not accept stain like natural wood. This method is best suited to floors finished with clear varnish. For deeper or wider gaps, the wooden strip method is a better choice.

Using Wooden Strips for a Professional and Lasting Finish

For homeowners who want the best possible result, cutting thin wooden strips and tapping them into the gaps is the superior method. This creates a solid, permanent seal that moves with the floor and looks seamless. It requires more time and care than other options, but the outcome is worth the effort for a sanded and varnished floor.

The process works as follows:

1. Select timber strips that are slightly thicker than the width of each gap and the same depth as the floorboards. The wood species should match or complement the existing boards.
2. Apply wood glue or PVA to both sides of each strip and to the inside edges of the gap.
3. Using a soft mallet, gently tap each strip down into the gap until it sits just below the surface of the floorboards.
4. Allow the glue to dry for at least one hour before proceeding.
5. Sand the entire floor to level the strips flush with the board surface, removing any high spots.

One important consideration is the colour of the wood you choose for the strips. Light timber inserted into dark floorboards will stand out even after staining. Select strips that closely match the shade of your existing floor for a uniform look. Alternatively, using a contrasting timber can create an attractive feature if done deliberately. For a deeper understanding of how wood behaves, it is worth reading about common timber defects that affect how boards move and age over time. The wooden strip method works best when carried out before sanding, as the sanding step takes care of minor height differences.

Applying Flooring Fillers and Decorators Caulk for Quick Repairs

If you are looking for a faster solution that still gives a neat finish, flooring filler and decorators caulk are convenient options. Flooring filler comes in a light tan colour that blends reasonably well with light stains and clear varnishes. Decorators caulk has the advantage of accepting stain, so it darkens down when you apply your chosen finish. Both products remain flexible after curing, which allows them to move slightly with the expansion and contraction of the timber.

These fillers can be applied to square edge boards that lack tongues and grooves. Simply run a bead of filler or caulk along the edge of the gap and build it up in layers until the gap is full. Use a sealant tool to smooth the filler flush with the board surface.

The main drawback is durability. Over time, the filler can separate from the edges of the boards as the timber moves, and pieces may fall through the gap. This is more likely in rooms with large temperature swings or heavy foot traffic. For rooms where the floor will be covered with carpet, these fillers work well as a temporary measure. If you are considering a different floor covering, you may want to look at vinyl sheet flooring installations as an alternative to maintaining exposed timber.

Listed below are the main pros and cons of using filler or caulk compared to other methods:

• Pros: Quick to apply, inexpensive, flexible when cured, accepts stain, suitable for square edge boards.
• Cons: May separate from boards over time, less durable than wooden strips, requires reapplying in high-traffic areas, limited gap width capacity.

Using Draughtex and Stopgap for Superior Draft Exclusion

For floors where the main concern is eliminating draughts rather than achieving a perfectly filled surface, purpose-made products such as Draughtex and Stopgap offer excellent results. They are designed to seal gaps while accommodating the natural movement of timber, making them more reliable than makeshift solutions.

Draughtex is a soft, flexible strip material that comes in a roll, available in several thicknesses to suit different gap sizes. The product is coloured in a shade called Shadow, which mimics the natural dark line between floorboards. To install it, select the right thickness, push the strip into the gap using a credit card or blunt knife, and trim any excess at the ends. Draughtex is fitted after the floor has been sanded and finished with varnish. Allow the finish to cure for about 48 hours before installing the strips.

Stopgap works on a similar principle but uses a thin V-shaped plastic strip that springs outward when pressed into the gap. This spring action holds it securely in place across the full width of the opening. Stopgap comes in a single size that fits most common gap widths, which simplifies selection. Once fitted, the natural shadow of the gap makes the strip almost invisible, preserving the appearance of the floor. For those who prefer a modern floor covering, laminate flooring for budget-conscious renovators is an option that avoids gap problems altogether.

Both products move with the timber as it expands and contracts, so they remain effective over many years. They are particularly suitable for floors that have already been finished and where you do not want to undertake sanding or re-finishing work.

Low-Cost Options for Rooms That Will Be Carpeted

For rooms where the floor will be carpeted, the aesthetic quality of the gap filling is less important and cheap methods become viable. One such approach is papier mache made from old newspapers and wallpaper adhesive. While this is a very time-consuming process, the materials cost almost nothing. The pulp is pushed into the gaps and left to dry, after which the surface can be levelled roughly before the underlay and carpet go down.

This method has several limitations:

• The finish is rough and unsuitable for exposed timber floors.
• It takes a very long time to complete a whole room, as each strip of paper must be coated and pressed in individually.
• The material is not durable and may crumble over time if disturbed.
• It offers minimal insulation value compared to purpose-made products.

Despite these drawbacks, papier mache can be an effective way to stop draughts in a spare room or bedroom that will be carpeted, especially on a tight budget. Other low-cost options include forcing rope or twisted fabric strips into the gaps using a blunt chisel. These materials are quick to install and provide reasonable draft exclusion, though they offer no protection against dust migration.

To help you decide on the best approach, the table below compares the main methods covered in this guide.

If you plan to sand and varnish your floor, the wooden strip method or the PVA and sawdust approach will give the best visual result. For draught exclusion without refinishing, Draughtex or Stopgap are excellent choices. For carpeted rooms, filler, caulk, or papier mache will do the job. For a detailed look at different wooden flooring options and their benefits, the professionals at DIY Doctor provide extensive guidance on choosing the right approach for your home. You can also watch practical video demonstrations from DIY Doctor to see these techniques in action before starting your own project.