Why should you take moisture reading of a wooden floor before restoring
The question I get asked time and time again in training, or when I’m troubleshooting issues on site, is simple: “What was the moisture reading?” More often than not, the response is either “I didn’t take one” or “I’m not sure.” And that’s where the conversation starts to change. Because while moisture readings aren’t needed in every single case, they do have a big impact on the quality, performance, and durability of a floor finish. And in my experience, it’s still something around 70% of contractors in the UK either skip or don’t fully see the value in. So let me shed some light on why moisture readings matter — and what’s actually going on when things go wrong.
Usually, when a contractor calls me about a problem with a finish — whether it’s discolouration, bleed-back, extended drying time, premature wear, or a soft surface — the product gets blamed first. That’s fair enough; if it’s not working as expected, the finish is the most visible culprit. But the moment I ask about moisture readings, the energy shifts. Often there are none taken, or the contractor gets defensive. And I get it — we’ve all been there. But understanding what’s really happening in the timber, the air, and the room is often the key to understanding why the finish is underperforming. Moisture plays a crucial role in how wood behaves and how a finish bonds, cures, and protects. So when it’s not measured, we’re working blind — and the risk of failure climbs.
Let’s break down what we’re actually measuring when we talk about “moisture readings.” There are four key elements: the moisture content (MC) of the timber itself, the relative humidity (RH) of the room, the surface temperature of the floor, and the air temperature. Each one of these has a different impact on the behaviour of the finish. Relative humidity is how “full” the air is with water vapour — shown as a percentage. At 100% RH, the air is completely saturated and can’t hold any more moisture, so condensation begins. But RH also shifts with temperature. Warm air can hold more moisture than cold air, so even if the amount of water stays the same, RH increases when temperature drops. That’s why a room at 60% RH and 22°C might feel fine, but drop the temperature to 15°C and you could be suddenly dealing with condensation risks.
This is where things get subtle — and risky. Wood is a hygroscopic material, which just means it absorbs and releases moisture based on the RH in its environment. When you’re applying a waterborne finish, that product is introducing additional moisture into the air during the drying process. The water in the finish evaporates, leaving the polyurethane or oil behind to form a protective layer. But if the air is already holding a lot of moisture (high RH), there’s nowhere for that water to go. The result? Slower drying times, trapped moisture, or even a soft, cloudy surface that won’t cure properly. On the flip side, if RH is too low, the finish may flash off too fast, causing lap marks, poor levelling, or even cracking.
Now, surface temperature is another piece that often gets overlooked — especially in buildings with underfloor heating. A floor might feel warm to the touch, but the air in the room could still be cold. That gap between surface and air temperature brings us into the territory of dew point — the temperature at which air becomes saturated and condensation forms. If the floor temperature is at or below the dew point, you can get invisible moisture forming on the surface, even if everything seems fine to the eye. Apply a finish under those conditions, and you’re asking for trouble: peeling, bubbling, poor adhesion, and complete system failure.
Then there’s the wood itself. Moisture content — the actual percentage of water inside the timber — should always be checked before sanding or sealing. If the wood is holding too much moisture (above 12%), it will almost certainly release it later, pushing it up through the finish and causing delamination or bubbling. It might also shrink as it dries, creating gaps or stress fractures in what looked like a perfect floor just days earlier. On the other hand, if the wood is too dry (below 7%), it may absorb moisture from the air later, swell, and push against the hardened finish — leading to cupping or cracking.
Most professional systems, like Pallmann or Bona, are designed to perform best when the timber is within a safe moisture window — typically 8% to 11% — and when the ambient RH sits between 40% and 60%. These aren’t just theoretical numbers. They’re based on decades of lab and site testing. Step outside those parameters, and you're running the job on risk.
Keeping a record of these readings is more than just good practice — it’s your best defence if things go wrong. Most manufacturers offer strong technical support with their finishes. But when you call them about a floor issue, the first thing they’ll ask is: “What were the site conditions?” If you can provide the MC, RH, surface temp, and air temp from the day of application, the tech team can immediately identify whether it's a moisture-related issue or something else entirely. Without that data, you're stuck guessing — or worse, footing the bill for a problem that could have been avoided with a £150 moisture meter.
I’m not saying you need to treat every room like a laboratory. But understanding how these four factors interact — and taking five minutes to measure them — gives you real control over the job. It means you can adapt your process, delay a coat if needed, adjust air movement, or check if heating needs tweaking. It puts you back in charge of the finish, rather than hoping the conditions are good enough.
There’s also a business side to this. Being the contractor who can confidently say, “Here are my readings from the job,” builds trust. It shows professionalism, care, and pride in the work. It helps protect your name when problems arise, and it gives you the confidence to back your process. More importantly, it helps prevent callbacks, disputes, and finish failures — all things that cost time, money, and reputation.
So the next time you’re setting up for a floor restoration or finish job, grab the meter. Check the timber. Log the room temp, RH, and floor surface temperature. You’re not just ticking a box — you’re stacking the odds in your favour. In a trade where results are everything and the finish is the face of your work, those moisture readings might be the difference between a smooth handover and a sticky callback. And once you start building it into your process, you’ll wonder how you ever worked without it.
