Hollow spots are a common problem in hardwood floors which are a nuisance for homeowners.
They can give off hollow sounds and even cause structural weaknesses in the floors which may lead to cracks or other types of accidents.
Hence, it becomes crucial to fix these even if many homeowners think of it as a minor issue which can be ignored without any inconvenience.
However, it is important to fix these hollow spots, and the best way to do so is by using an injection kit or resurfacing.
While resurfacing becomes necessary when there are too many hollow spots or structural weaknesses due to these which cause shaking or other problems, an injection kit can be used if you have only a few small hollow spots scattered around the floors.
The method of using them is quite simple and is mentioned at the end of this article so make sure you read it completely to ensure you don’t miss out on anything.
Table of Contents
What causes hollow spots?
The most common reason behind hollow spots is improper installation of the hardwood subflooring or the boards which can leave gaps in the structure or the joists, leading to hollow spots in the flooring.
Oftentimes, homeowners take up the task of installing the hardwood floors themselves as they want to save money.
However, the installation of hardwood floors is a crucial project which can’t be executed by simply following a DIY project.
Unless you have any prior knowledge or experience of this niche, it is preferred that you contact and hire a professional for the jobs you don’t have to face such issues.
Besides, the professional you hired must have complete knowledge of the flooring material being used and the requirements of the material according to the atmospheric conditions so that adjustments can be made accordingly.
Wood needs to expand and contract, as a result, leaving too much or too few gaps can lead to hollow spots in the wooden surface.
Besides, these gaps or spots can become bigger once the wood contracts, especially in winter.
Another important factor to note here is that the subflooring should be flat and must meet the criteria given by NWFA (National Wood Floor Association).
Moreover, you can counter-check the rating with the subfloor flatness ratings given out by the manufacturer to ensure that the installation process will go smoothly.
The manufacturer will also have standards for subfloor flatness.
Below are some credible ratings you should look for to avoid hollow spots on hardwood floors after installation.
- If you have concrete slabs instead of wooden flooring, the flatness tolerance should be around 1/8″in a 6-foot radius and/or 3/16″ in a 10-foot radius.
- In the case of wooden subfloors, the process is a little sophisticated. The usual specifications for flatness are as follows:
- For mechanical fasteners which have a length of 1 and a half inches or more, the flatness rating should be within a one-quarter inch in 10 feet or 3/16” in a 6-foot radius
- If you are opting for glue-down installations or fasteners which are shorter than 1 and a half inches, a flatness within 3/16” in 10 feet or 1/8” in a 6-foot radius will be required.
Ways To Prevent Hollow Spots In Hardwood Floors
If you install hardwood floors on uneven subflooring, there can be many dangers and threats that may come from this.
The most prominent among all these are hollow spots in hardwood floors as the subflooring will not be in contact with the ground at all times.
This will be repeated for the hardwood planks which will hence, create hollow spots. These hollow spots are dangerous as they are quite weak due to a lack of support underneath.
This can increase the chances of cracks and breaks in the boards which might induce many other dangers.
However, you can make the concrete slab level to place your hardwood flooring on it. A suitable solution is to grind the high spots on the concrete slab to make it level.
For the points where there are compressions in the slab, you can use patching compounds to fill them up.
A recommended approach would be to fill the compressions first and then move on towards grinding as you will achieve a smooth and fine surface this way.
You can also make the wooden subflooring structure more stable by using leveling compounds.
Although the process is not very simple and requires a lot of other procedures such as; reinforcing a metal lap and binding it to the floor with a self-level primer, it is possible.
Another factor to keep in mind is that the thickness and the dimensions of the planks can also be major factors in the stability of the subfloor.
For instance, if you have thick and wide hardwood boards, chances are that the subflooring would need to be given a lot more attention as the smallest unevenness can result in a lack of stability in the entire structure.
Moreover, such planks would require even more attention when it comes to leveling gauges.
Any hardwood plank which is more than 5 inches wide and/or more than 1/2 inches thick needs special attention by the installer so that the hollow points can be avoided.
Another reason for hollow spots is the insufficient use of adhesive or incorrect measurements.
For glue-down installations, attention has to be given to the application of glue, installation of the planks, and drying of the adhesive.
If the glue is not sufficient, the planks can lift from the surface and create hollow spaces underneath.
Moreover, if the planks are not adjusted properly when they are being installed, they can move in any direction and create air pockets in the adhesive which can later become hollow spots.
Lastly, if pressure is not applied on the planks (weights should be placed on the floor) while the adhesive is drying, it can still cause the floors to rise a bit leading to many hollow spots under the surface of the wood.
As a result, it is crucial to comply with the NWFA guidelines for installing your hardwood floors if you do not want to get any hollow spots afterward.
Choosing the right installer is a very crucial part of this process.
As mentioned earlier, being accustomed to the wood type is necessary but the installer should also be aware of the weather conditions of the area to be able to get the right measures in place beforehand.
Moreover, make sure to use the right flooring trowel and choose a durable and lasting adhesive specifically made for wooden surfaces.
Lastly, ensure that sufficient adhesive material is used in the process to prevent any hollow spots in your hardwood floors later on.
How to Fix Hollow Spots In Hardwood Floors?
Using an injection repair kit is the most plausible way of fixing hollow spots in the hardwood floors which are not too serious.
While more dire situations may call for stripping off the entire part of the floor and reinstalling it after removing the problems, you can try an injection kit first to save you from the time and effort of the resurfacing process.
Injection repair kits are often known for their spot treatment as they can fill in the air gaps and hollow spots with the adhesive.
This can result in firmness under the planks and when the gaps are filled and the structure has become even more durable, the floors do not give off any more hollow sounds.
Hence, the gap is closed and the noise is silenced.
Also, it is crucial to keep some pressure on the areas where the adhesive has recently been injected.
These are sensitive areas that can lift if the surface is not pressed and kept tight with the subflooring until the glue has been dried completely.
This method is very easy to use and maintains the tacky surface of the floors for a lifetime which can allow the owner to stay safe from problems such as hollow spaces and noises from the hardwood floorings.
Although hollow spots are usually thought to be a minor issue that can be fixed if the owner wants to or can be ignored completely too, you must not think the same.
You must ensure that your hardwood floors and subfloors comply with the dimensions and rating given out by the NWFA as they are made for your benefit.
Not doing so can cause you penalties from the local authorities and even cause many dangers regarding the floor itself as the structure is not strong enough in many places where there are hollow spots.
Having said that, you must never ignore these and try your best to identify the exact place where you can feel or hear that the floor is hollow underneath and try to fix it as soon as possible.
If you tend to ignore it, the damage can worsen and cause some serious destruction to the planks which might raise a replacement requirement for the hardwood boards.
Hence, it is best to spend a little money to solve the problem rather than having to completely strip off an entire part of the flooring and get it replaced.
Related: How To Fix Gaps In Hardwood Floors?
Conclusion
If you also have hollow spots in your hardwood floors, you need to pay attention to them immediately.
Ignoring these can be very dangerous in the long run and can destroy the surface of the wood.
This has many reasons, a few of which are; the intensity of traffic is higher on hollow spots due to lack of support from underneath, they can get gritted easily due to the same reason, and they are more prone to cracks and splinters.
Hence, it is crucial to fix these on time. Therefore, you must use the method mentioned in the guide above to ensure that the hollow spots in your hardwood floors are fixed almost as soon as they are identified.
As a co-creator of FlooringFlow.com, Emma Sophia comes on board to answer all your questions related to any flooring problems. Together with John Henry, she’s gained extensive experience in fixing many flooring problems in their own house as well as in friends and family’s. Now, she wants to share her knowledge that she gained during floor remodeling, restoring, and DIY projects.
