Carpet floor coverings hide a multitude of sub-floor sins and so when buying new carpet you mostly don't incur extra costs due to sub-floor leveling. However, in the world of hardwood flooring things are very different.
In our experience, roughly 6 out of 10 sub-floors will need a small to moderate amount of leveling, 3 out of 10 will need a significant amount and one will be so bad that it is cost prohibitive to fix the sub-floor and so the choice to go back to carpet is made.
Leveling adds time and money to the whole project. Ignoring the need for sub-floor leveling to save money is not a good idea because once the hardwood is installed the sub-floor cannot be corrected.
The result of installing hardwood flooring over an uneven sub-floor can be:
The problems that come with an uneven sub-floor become evident once the floor is installed. If you install a floating floor over an uneven surface then you will notice soft spots where the floor dips when walked on.
Note that a small amount of movement is normal and to be expected with a floating floor because the underlay beneath the hardwood is supposed to compress. The problem of movement arises when the hardwood flooring is allowed to bridge two high spots in the sub-floor, say 5' apart, leaving a low spot in between. The flooring is not designed to span high spots and cannot support weight in this way. Subsequently the floor deflects down into the low spot when walked on. If the floor deflects more than 1/8" (3mm) in 10' then the industry standard has not been met.
In our experience, roughly 6 out of 10 sub-floors will need a small to moderate amount of leveling, 3 out of 10 will need a significant amount and one will be so bad that it is cost prohibitive to fix the sub-floor and so the choice to go back to carpet is made.
Leveling adds time and money to the whole project. Ignoring the need for sub-floor leveling to save money is not a good idea because once the hardwood is installed the sub-floor cannot be corrected.
The result of installing hardwood flooring over an uneven sub-floor can be:
- Excessive movement which will lead to premature failure of the flooring product
- Squeaks and creaks
- Gaps and separation
- Veneer delamination (for engineered flooring)
- Voided manufacturers warranty
The problems that come with an uneven sub-floor become evident once the floor is installed. If you install a floating floor over an uneven surface then you will notice soft spots where the floor dips when walked on.
Note that a small amount of movement is normal and to be expected with a floating floor because the underlay beneath the hardwood is supposed to compress. The problem of movement arises when the hardwood flooring is allowed to bridge two high spots in the sub-floor, say 5' apart, leaving a low spot in between. The flooring is not designed to span high spots and cannot support weight in this way. Subsequently the floor deflects down into the low spot when walked on. If the floor deflects more than 1/8" (3mm) in 10' then the industry standard has not been met.
Cosmetic cracks in concrete slabs (as shown in this image) usually represent high spots in the concrete. These are not unusual to see. This picture shows about a 1/8" width crack that is about 6' long. Such cracks don't pose a structural threat unless something is obviously wrong such as a difference in height between one side of the crack and the other, if there is movement in the concrete or significant width to the crack such 1/4" or more.
High spots in the concrete will need to be ground down using a grinder with a diamond tip blade. Lots of dust is generated so a vacuum attachment should be used with this tool.
Larger areas should not be hand ground as an uneven surface may be left behind effecting the floor covering. Consult a concrete grinding specialist and use a bigger machine (as seen in this image).
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