Why does my hardwood floor have gaps in it?

You are probably wondering, “why are these gaps appearing in my wood floor?” if you live in a home with a wood floor in it.

The short answer is, wood shrinks and expands depending on how much moisture it is exposed to. If the floor is gapping, then the humidity in your home is low and the wood is decreasing in size because of it.

The science behind gaps in your hardwood floor

Wood is like a sponge. If you were to take a magnifying glass and look at (specifically the end grain) your floor, you will see that there are thousands of little holes in it. These little holes get larger as the wood dries out and smaller as it fills with moisture. This is why a dried-out piece of firewood is much lighter than a green piece of firewood. The water makes up a large amount of the weight. So, when the water leaves the wood, it becomes much lighter. If you have ever heard of the phrase “water logged,” this refers to a piece of wood, whose pores have filled all the way up with water. So, what does this have to do with gaps in your wood floor?

Wood Acclimation Period

When a wood floor is installed in your home, it should sit and acclimate to the environment of your home until the moisture level of the wood matches the moisture level of the subfloor you are going to place it over. (A high-quality moisture meter is used to determine this. Not one from Lowes or Home Depot) Many hardwood companies do not allow enough time to pass for this process to take place. This results in a floor being installed with too much or not enough moisture. This imbalance of moisture between the sub-floor and the new hardwood floor, causes the wood to be installed at a size different from its final form.

acclimating your hardwood flooring before installation
Oak wood floors acclimating prior to being installed

4 Inch oak Acclimating to the home prior to install

High Quality Moisture Meter for hardwood flooring
Ligno SD Moisture Meter

Whose Fault, Is It?

In order for your floor to gap-out, it means one of two things. First, the moisture content in your wood floor was too high when it was installed. Second, you do not keep the temperature and humidity levels of your home consistent throughout the year.

If you fall into the category of those who do not keep their home at the same temperature and humidity, the following is very likely to happen. If your floor was installed in the winter, it will likely buckle slightly when the summer comes and the humidity rises. If your floor was installed in the summer, it will gap out during the winter.

Gaps in Old Hardwood Flooring

If you have an old floor, I can guarantee you it will be gapped out. The reason for this is fairly simple. Many years ago, when wood was about the only option of floor you had, the technology did not exist to match and measure wood humidity levels. Humidifiers and dehumidifiers were not a common thing. This resulted in the wood shrinking and expanding throughout the seasons for years. This will always result in a gapped-out floor.

My hardwood floor is gapping! How do I stop it?

If you live in a place with drastic differences in temperature and humidity throughout the four seasons, your floor probably closes up during the summer and gaps out during the winter. We know the gaps are ugly and you want them to quit opening up. So how do you pull this off? As we mentioned earlier, if you have an old home with original floors, you can forget about this section. If you have relatively new floors, that you can tell are gapping, (or you have seen them do this seasonally) you can stop the process dead in its tracks.

You must determine at what point in the year did the floors look nice and tight. For most people having this problem, that time of year is in the summer months. Then as winter comes along the floor gaps out again. In my old home, the floor would gap out enough to put quarters in the gaps. (I did not make any effort to prevent this)

hardwood floor with large gaps
Gapped out pine hardwood floor

Large gaps in an old pine floor

As winter comes along, you must make sure the environment in your house, matches the environment of the summer when the floor was still tight. This translates into keeping the heat up and as well as running humidifiers. This constant environment will keep the wood floor from changing in size.

How to fix the gaps in your wood floor

So obviously, the gaps are ugly! I want them to go away and so do you. Let’s explore the options you have to fix the gaps in your wood floor.

Fix #1: Head to your local Lowes, Home Depot or hardware store and pick up some brown wood filler. It does not really matter which brand you get. Don’t get one that seems really pasty. You want it to be fairly creamy and workable. Most stores will have a filler that will match your current hardwood fairly well. For traditional old floors, a golden-brown filler is typically one of the better options. It is similar to the natural color of most woods and a fairly safe option. Grab some paper towels and a bucket of water.

You are now going to take the filler and put some on the tip of your finger. Smear it down into the crack and try to keep as much in the crack (and not on the surface) as possible. Do a handful of boards. Then, take a wet paper towel and wipe the excess off the surface before it dries. This is a tedious and time consuming process.

Check out this video to see more about fix 1.

Fix #2: This is a much more expensive option. Truth be told though; it is a much nicer finish product as well. You are going to need to sand the entire floor to do it. You will sand all the finish off the floor and get it perfectly flat. Then you take several gallons of trowel-able wood filler. You will then take a flooring trowel and then spread it as thinly as possible across the entire floor. From here, you let the filler dry. Finally, finish sanding the floor down. This allows the filler to fill all of the imperfections in the floor. The sander then does all the work of removing the extra filler off the surface.

There are several things to keep in mind when filling the gaps in your floor. Wood moves with changes in humidity and heat. If you do not keep your house at the same humidity level and temperature year around, you will have problems still. The wood filler will not flex and move with the wood. Instead it will crack and pop out over time. If you don’t plan to keep your house at a consistent humidity level and temperature year around, don’t bother fixing the cracks.

How to fill all the cracks while sanding hardwood
Trowel filling hardwood flooring during sanding

Picture: This a newly installed floor that is being trowel filled.

get rid of gaps in your hardwood floor
Trowel filling is the best fix for gaps in hardwood flooring

I recommend going for the complete refinish and troweling your floor if you want a nicer finish product. You can always hire a pro and ask him to handle these problems for you. Keep in mind refinishing a floor is a lot of work.

How to prevent gaps in your wood floor

If you have a nice and tight wood floor already, you down want to do anything to compromise that. Thankfully, its fairly simple to prevent your hardwood floor from gapping out. Throughout this article, we have talked a lot about how much wood likes to move. The key to preventing your hardwood floor from gapping, is to prevent it from moving. We prevent wood from moving by controlling the environment in your home.

Controlling Temperature

The first thing you need to control is the temperature. This is much easier for people who live in a place like Arizona. If you live in a less friendly area like I do, this can be a bit more expensive. Here in Southwest Michigan, we have drastic changes in weather year around. It’s incredibly hot and humid in the summer and cold and dry in the winter.

Figure out what temperature is best for you and stick with it. I like to keep my place around 72 degrees’ year around. My electric bill can be a bit brutal to deal with but, it’s worth it to keep my hardwood looking nice.

Controlling Humidity

The last thing you need to do is get a humidity meter for inside your home. This is a bit more tedious at first. But after you figure it out, it is a fairly simple process. You need to keep the humidity level in your home within 5% at all times. Average humidity in most homes is about 40%. That means yours should stay between 35-45% year around. You may need to run dehumidifiers in the summer and humidifiers in the winter to make this happen. You may also be able to accomplish this through your HVAC system if you have a highly advanced system.

Thanks for Reading!

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