You can prevent gaps between old oak planks by allowing the wood to properly acclimatize to the correct moisture content before installation, and by accounting for expected shrinkage during the laying process. Antique oak has been moving for decades, but it still responds to changes in humidity. The questions below give you a clear answer at every step.
Why do old oak planks shrink after installation?
Old oak planks shrink after installation because wood is naturally hygroscopic: it absorbs and releases moisture depending on its environment. When the moisture content of the plank is higher than the ambient humidity in the room, the wood contracts. This applies to antique oak as well, regardless of its age.
Reclaimed oak often has greater dimensional stability than new wood due to its age, but it still moves. Shrinkage occurs almost entirely across the width of the plank, not along its length. Wider planks therefore show more visible shrinkage than narrower ones. This is not a defect — it is a characteristic of the material.
The most common cause of gaps after installation is too large a difference between the moisture content of the wood at the time of laying and the equilibrium moisture content of the room. That difference always has an effect, even in wood that is already decades old.
What is the ideal moisture content for old oak planks before installation?
The ideal moisture content for old oak planks before installation is between 8 and 12 percent, depending on the conditions in the room. In a well-heated home with central heating, a moisture content of 8 to 10 percent is realistic. In a less heated or more humid space, it will be somewhat higher.
Always measure the moisture content of the wood with a reliable moisture meter before you begin. But also measure the room itself: the humidity level in the space ultimately determines the equilibrium the wood will move toward. The smaller the difference between those two values at the time of installation, the less shrinkage will occur afterward.
When in doubt, allow the wood to acclimatize for longer. Two to four weeks in the room itself, laid flat and stacked with gaps for air circulation, is sufficient in most cases. With large differences in temperature or humidity, this may take longer.
How do you install old oak planks to prevent gaps?
To minimize gaps in an antique oak floor, follow a number of steps in the correct order. Preparation is more decisive here than the installation itself.
- Allow the wood to acclimatize in the final room for at least two to four weeks, with adequate air circulation around the planks.
- Measure the moisture content of both the wood and the subfloor before you begin. The subfloor must not be more humid than the wood.
- Maintain a stable indoor climate during and after installation. Avoid extreme temperature fluctuations or construction moisture in the room.
- Fasten the planks sufficiently to limit movement, but always leave a small expansion gap along the edges.
- Use a vapor-open construction where the situation allows, so that moisture differences can equalize gradually rather than build up.
With old oak planks, it is also worth noting that they are more often hand-sawn and can therefore vary in width and thickness. Take this into account when sorting and laying the planks.
What size gaps are normal in an antique oak floor?
A small gap of one to two millimeters per plank is normal and to be expected in an antique oak floor. Seasonal variation — where gaps are slightly wider in winter than in summer — is part of the character of solid wood. This is not a sign of an installation error.
Gaps become problematic when they exceed three to four millimeters, are visibly uneven, or when planks begin to gap in places where they previously fit together well. This generally points to too great a difference in humidity during or after installation.
An antique oak floor is not a polished, lifeless end product. Small irregularities, variation in color, and modest seasonal gaps are all part of what this material is. Understanding that changes how you look at what is normal.
How do you fix existing gaps in an old oak floor?
To fix existing gaps in an old oak floor, start by identifying the cause. If the gaps are the result of low humidity in the room, increasing the relative humidity will help. If they are structural, more targeted intervention is needed.
- Increase humidity: a relative humidity of 45 to 60 percent in the room helps the wood swell and closes the gaps. This works best for gaps that are seasonal in nature.
- Wooden filler strips: for wide, permanent gaps, thin wooden strips can be cut to size and fitted in place. This is a traditional and durable solution that suits the character of the wood.
- Cork or flexible sealant: for smaller gaps, a flexible filler can be applied. Always use a product that moves with the wood — otherwise the filler will crack again.
Avoid filling gaps completely with rigid materials if the wood is still actively moving. This almost always leads to new damage. View our completed projects to get an impression of what antique oak floors look like after installation.
Does the origin of the wood affect the likelihood of gaps?
The origin of the wood makes a noticeable difference to the likelihood of gaps, but how the wood was dried and stored is at least equally important. Wood that has been stored outdoors for years and dried naturally is generally more stable than wood that has been kiln-dried quickly.
Oak that has been drying on an open timber yard for more than five years has already released much of its internal tension. It has moved, settled, and stabilized. This makes it less susceptible to sudden changes in moisture after installation. Wood from maritime applications or old structural timbers has also proven its ability to remain stable under demanding conditions.
Wood that was rapidly dried shortly before sale, or that comes from humid storage, behaves differently. It has not yet found its equilibrium and will move more after installation. Always ask about the drying history and storage conditions when purchasing. Feel free to visit the timber yard in Doorwerth to assess the wood for yourself.
How Frank Pouwer helps prevent gaps
Gaps can be prevented in most cases, but the wood must already be in the right condition before installation begins. That starts with the choice of material and the information you receive along with it.
- Our oak has a natural drying time of more than five years, resulting in a stable and well-conditioned material.
- We measure and label our planks individually, so you know exactly what you are buying: dimensions, origin, and condition are all clearly documented.
- We think along with you about the application, the expected conditions in the room, and the installation method that best suits them.
- Planks can be cut to size, brushed, or weathered, so they meet the specific requirements of your project.
- For questions about moisture content, acclimatization, or installation, we provide concrete advice — not generalizations.
Want to know which wood suits your project and how to prevent gaps? Request a quote and we will work together to find the best approach.
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