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HOW TO AVOID GAPS, CRACKS AND SPLITS WITH HARDWOOD FLOORING

By Jeff Hosking – Hosking Hardwood Flooring Inc. All Rights Reserved

Wood, through its cell structure, is hygroscopic. This means it has the ability to absorb and release moisture depending on the relative humidity level within its environment. Freshly harvested logs can contain approx. 80% or more water within its cell structure. After the logs are cut into boards they are stacked and air dried for a period of time where they are then placed into a kiln to further dry the boards down to approx. 6-9 % Moisture Content, when this is achieved the boards are then taken out and milled into flooring. This 6-9% Moisture Content equals what is supposedly the average healthy home's Relative Humidity level should be of (between 30-50% Relative Humidity).

If the Relative Humidity in the home goes below 30% for any extended period of time which usually happens during the cold, dry heating season, it can cause the wood boards to dry out to less than the original 6-9% Moisture Content. This loss of Moisture Content will cause the boards to contract in size, leaving open gaps between the installed boards. Depending on the severity and length of time of this moisture loss, these gaps can close once the humid spring and summer months take hold and the boards absorb the moisture it has lost during the dry heating season.  Loss of moisture content can also cause the boards edges to curl upward or "Dry" cup. 

The reverse can also happen when excess humidity levels within the home exceed 50% Relative Humidity for an extended amount of time. This usually happens during the humid spring and summer months and can cause the floor boards to absorb excess moisture. This results in the edges of the boards swelling and cupping upward or, in extreme cases, it can cause the boards to swell against each other and to buckle up in areas. Relative Humidity levels higher or lower than the recommended 30-50% range can also cause face checking within the surface of engineered flooring and or checking within the wood surface. Floors that are improperly cleaned or soaked with water or other liquids can also cause these issues also.

Concrete slabs are notorious for allowing moisture to migrate up into the hardwood flooring causing the flooring to cup, buckle and even delaminate the ply layers. It is imperative that all subfloor types be tested for excess moisture before any type of flooring is installed.  Note: Due to ever constant changes in water table levels within the ground proper moisture retarders are always recommended to try and mitigate any future changes in excess moisture within the slab.  We recommend using Bostik Best MVP self leveling membrane which helps seal out any potential moisture migration through concrete slabs. 

Radiant heat system surface temperatures should not exceed 80 degrees along with keeping the homes relative humidity levels 30-50 RH will go  along way to keeping the wood flooring stable.  

PRIOR TO THE FLOORING BEING INSTALLED it is recommended to bring the flooring into the home as soon as it is delivered and to allow the wood flooring to acclimate to its new environment for at least 3-7 days prior to it being installed.  Manufacturers warranties require compatibility moisture readings recorded for both your flooring and your subfloor prior to it being installed. Do not store wood flooring in garages or sheds or where temperatures or moisture levels can vary greatly from where the flooring will be installed. Doing this may cause the 6-9% moisture levels within the flooring at time of milling to change causing excessive twists and bowing within the boards.

To reduce the effects of contraction and expansion within wood flooring we recommend:

  1. To purchase a small digital Hygrometer ($25.00) that can give you a daily digital read out of what the Relative Humidity level is within the home. This Relative Humidity should be maintained between 30-50%.
  2. When you purchase any wood flooring you need to acclimate the wood to its new environment for 3-10 days or more before it is installed. For nail/staple down floors we also recommend using 15 lb. black hardwood flooring underlayment paper, which slows down possible moisture migration up through the subfloor from damp basements. During installation of the 15 lb. black felt paper, overlap the seams by 4-6 inches.  For floating engineered floors or even Laminate flooring an underlayment pad with a  moisture retarder film attached is recommended. 
  3. To help maintain this 30-50% Relative Humidity during the hot humid spring and summer months, you may need to run air conditioning or de-humidifiers.
  4. To help maintain this 30-50% Relative Humidity during the cold, dry heating season, you may need to run humidifiers. Homes that have forced hot air heating systems can cause severe dryness within the home and should have a humidification system built into the furnace system. Additional Humidification may still be needed to maintain a healthy Relative Humidity levels.

Because it is out of their control, manufacturers' warranties do not cover environmental and/or jobsite issues regarding relative humidity levels within the home where the flooring is stored or installed. The responsibility lies with the home owner / installer to ensure that the particular flooring manufacturers installation and maintenance instructions were followed. To reduce possible issues most all flooring needs to be acclimated to its new environment, installed and maintained properly. Proper expansion gaps left at all fixed objects such as walls during the installation greatly reduces the chances of the flooring buckling. Wood flooring is a product of nature and not perfect. No two boards will look like or react the same to the same environmental stimuli. Some gapping and checking is considered normal and is to be expected during seasonal change. These gaps between the boards will normally close during the higher relative humidity seasons like spring and summer. Any open seams are also noticed more if a white or very dark colored wood floor is chosen, medium colored hardwood floors hide seams better.

Using a higher quality engineered wood construction will help to minimize gaps, cracks and splits within the wood and they can withstand a slightly wider range of Relative Humidity level changes before showing problems. It is sometimes difficult to be able to always maintain 30 – 50% relative humidity levels, but if you make a valid effort then you can virtually eliminate or at least minimize potential problems later.   The information contained within this article is only meant to be general information, and not a substitute for any particular flooring manufacturers specifications you have purchased. 

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Overall Rating: 4.9 stars - 8 reviews

By:
Date: April 8, 2017
Page Rating: (5.0/5)
Comments:
Thank you for the important information you provide on this website.
By:
Date: October 17, 2016
Page Rating: (4.5/5)
Comments:
This article has helped me immensely in trying to sort the wheat from the chaffe [so to speak] in understanding what makes up engineered flooring and the pitfalls to be aware of. I also agree that "you get what you pay for" Thank you.
By:
Date: July 23, 2016
Page Rating: (5.0/5)
Comments:
We installed narrow hardwood flooring in the 2nd floor and now have extensive cupping/unevenness.
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Date: May 27, 2016
Page Rating: (5.0/5)
Comments:
Your articles are fantastic! I have learned so much from your website. Thank you for going to the effort to create these informative pages.
By:
Date: April 17, 2015
Page Rating: (5.0/5)
Comments:
In addition as Jeff Hosking’s states above it is expected to see some minor movement within the wood boards in any environment but, you probably should have a certified wood flooring inspector come in to evaluate the floor to see if it can be corrected to need to be replaced. You can go to woodfloors.org to find an independent inspection company local to you.
By:
Date: April 17, 2015
Page Rating: (5.0/5)
Comments:
Michelle, I am a wood floor manufacturer and to minimize movement in wood flooring, Wood flooring is purposely manufactured to contain a 6-9 % moisture content which equals in range of what the standard normal recommended 30 – 50 % Relative Humidity level should be in healthy homes. From what you’re describing below it sounds like the homes environment should have been brought to the recommended 30-50% Relative Humidity level “prior” to the flooring being brought in, allowed to be properly acclimated and installed. From what your describing below it sounds like the wood flooring absorbed excess high humidity levels that were in the home at that time either while the flooring was originally being acclimated to be installed or after it was installed, expanded in size and is now drying out (contracting in size) to the current homes RH level leaving you with open gaps between boards and damage to the face of the of the boards. As Jeff Hosking’s article above states it is expected to s
By:
Date: April 17, 2015
Page Rating: (5.0/5)
Comments:
When our new home was built, then installed the hardwood floor PRIOR to the HVAC unit. It was installed in July/Aug in Kansas City (high temps & high humidity) again with NO temp / humidity control at all. Now there are gaps, cracks (face checking) and uneven-ness between boards. New cracks keep showing up. Question -- should the floor be replaced? Will it ever be right?
By:
Date: April 13, 2015
Page Rating: (5.0/5)
Comments:
Very Very important information in the above article. I thank you a lot! The flooring stores that I have gone to never mentioned any of this to me.

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