Aclimatising Timber Flooring
Get a real understanding of how and when to acclimatise timber flooring
Acclimatising Timber Flooring
So here’s the scenario. You’re thinking of installing timber flooring in your home. You’ve been researching on the internet or visiting flooring showrooms, and you keep coming across or hearing about acclimatising the timber. But the information is always conflicting, unclear, or the people you speak to don’t seem to know what is the right way to handle it. Well, I have good news for you – you can stop searching because I am going to explain what acclimatisation is, when it should be done and how it should be done.
To make an informed decision about acclimatising timber flooring, the first things you need to understand is how the timber is dried, what moisture content is, what relative humidity is, and what part it plays in the stability of your floors.
Moisture content (MC) refers to the percentage of water contained within the timber.
Relative humidity (RH) is the amount of water in the air as a percentage. Relative humidity is measured using a psychrometer and by having a look at the psychrometer definition, you can find out more about how it works in order to measure humidity.
The third part of the equation is temperature. Temperature activates the moisture contained within the timber.
Timber flooring is kiln dried to specific moisture contents according to the species, and for the area it is to be installed in. The moisture content of the timber is determined by the average “relative humidity” and “temperature” of the in-service environment.
Companies that produce timber flooring use the average of these determining factors to ascertain what is the correct moisture content to dry the timber to. They also look at the region that they are selling their product. The relative humidity and average temperatures vary greatly around Australia, therefore the required moisture content in the timber will also need to vary to suit the different conditions in each area.
So what does this mean? By taking readings of the moisture content of the timber, the relative humidity and the temperature within your home, it is possible to make an educated decision about whether or not to acclimatise the timber.
Below is a table that shows the relationship between these three factors. When you line up, for instance, the columns with 21 degrees C and relative humidity of 55%, you can see the moisture content of the timber is 10.1. So if your timber is dried to somewhere between 9% and 11%, the temperature averaged 21 degrees C and the RH of the environment averaged 55%, under these circumstances your timber floor will be quite stable and not likely to move, and hence can be installed straight away. However if you change any of these numbers, the equation changes and this is when acclimatising may be needed.
For the purpose of this exercise, let’s change the relative humidity from 55% to 80%. When you look at the table, you see now that the timber now needs to have a moisture content of 16%. Assuming we have measured the moisture content of the timber and it is 10.1% for the floor to be stable long-term, something now has to change. The first step would be to find out if the RH of 80% is normal for the room, or if there are other contributing factors such as water getting under the house, causing the RH to increase. If there is water sitting under the house, the water problem should be fixed and the RH should return to what is considered normal of around 50% to 60% – in which case there would be no need for acclimatising floorboards to bring the moisture content up to 16% so they will remain stable and not grow in size, causing problems like cupping.
Similarly, if the RH were to be, say 30%, we would look for the cause first. It may be that there is a heating and cooling system in the house that is stripping the moisture from the air – it would have to be determined if this was normal for that house because the heating or cooling system is never turned off and is set to maintain a constant temperature, or if this only a short-term situation and the RH will normally be within the average of 50% to 60%.
Now this is where it gets interesting, and where most people or suppliers get confused. What do you do when a house is under construction, and you have no way of knowing what the normal living conditions are going to be once the house is finished and occupied?
Most suppliers will recommend putting the timber into the house for 2 to 4 weeks before laying – even when it’s a new house that is being built, they say this mostly because they are just sales people and don’t have the experience to know what to do or say, and are simply repeating what they have heard elsewhere. This, in my humble opinion, is completely WRONG and here’s why.
If your house is under construction, there is no way you can control the environment inside, since generally there is no heating or cooling, no window coverings, doors are left open all day with tradesmen moving in and out of the house, etc. Basically you would be acclimatising to whatever the current weather conditions were at the time. If you were to put the timber into your house during the construction phase of the building and it was the middle of summer and the house had not yet been insulated, had no window coverings, no cooling system, and you were to put the timber into this environment, you will have effectively put the timber back in a kiln for 4 weeks. Take a look at the table and assume that the temperature inside the house over that 4 weeks was 38 degrees C and the relative humidity was 48% – your floorboards would dry to 7.2 MC and the result would be every board would reduce in size.
Now let’s assume that the change in size is 1mm per board. If you were then to lay that floor, and in a few months you move into the house and now you have window coverings, air conditioning and insulation. It’s now winter and the humidity inside the home is at 60% and the temperature inside is 20 degrees C. The boards will now take back in the moisture lost while the house was being built and will return to their normal size increasing by 1mm per board. If your lounge room is 5 metres wide and you laid 85mm boards, you would have 59 pieces across the 5 metres and the floor will grow by 59mm, resulting in cupping or tenting in the floor and possibly pushing your walls out. Now you can see why I believe this is the totally wrong way to approach this installation. The way I would handle this would be to install the floor at the closest time to completion, (usually straight after plaster) so the boards have the minimum exposure to the wrong environment. You may be wondering if the house is still at 38 degrees C and 40% humidity, wouldn’t the floor still shrink? And the answer to that question is possibly yes, BUT the boards were laid at their correct size of 85mm and at the correct moisture content for normal conditions (based on average conditions in a house in Victoria) and when the environment changes they can return to there original size and be sanded and polished. Also, there are ways to compensate for the low humidity and reduce or stop the shrinking.
I recommend that floors are not polished for at least a month after installation. This way the boards have a chance to settle in their final position, and as different areas of the house have different conditions, this will always produce the best results. Boards in front of full sun windows will react differently to those that have no sun on them, as will boards around heating vents or fire places, so it is preferred if these boards are to shrink at all, that it happens before polishing rather than after.
So how do you properly acclimatise your timber floor when you have the opportunity and it is necessary? First, contrary to what you may have been told, it is not a good idea to simply place the timber in the house for 2 to 4 weeks or to stack the timber in a room. You must cut out the floor in its final resting place and lay it all out. Then every day or two, turn the boards over so the entire board is exposed to the environment. You must also take constant readings of the MC of the timber and the RH and temperature until the correct equilibrium has been achieved, then and only then can the floor be installed.
It has been my experience, that people who have experienced problems with their floors has been as the result of a couple of factors. They have purchased timber from a supplier that hasn’t handled it correctly after receiving it from the mills, or it has been incorrectly handled by an inexperienced installer or there has been a major change of the conditions in the house from the time the floor was installed.
Timber floors in the right conditions do NOT grow in size or shrink; there must be a contributing factor and it always is related to moisture, either ingress into the timber or loss. Having a complete understanding of this will help you make the right decision when it comes to having your floors correctly installed.
At Connollys we always keep the timber stored and wrapped in our warehouse where the MC of the timber will remain the same as when it was initially dried. No timber is ever stored outside. We only ever deliver the timber at the correct time for the installation of the timber and ensure it is always taken straight into the house and never left exposed to the elements.
Every pack of timber is tested for the correct MC at the time of delivery.
Following these simple steps will help ensure the very best outcome with any timber floor that Connollys either supplies or installs.
These comments and based on my over 30 years experience within the timber and flooring industry, and are my own thoughts and opinions. Any decision on whether or not to acclimatise timber, and what method to use, should be your own after careful assessment and research. Therefore, l accept no responsibility for individual outcomes if you choose to follow my advice.
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Acclimatising Timber Flooring