Lauridsen Consultancy Group

Lauridsen Consultancy Group Consulting, Inspection, & Training for the flooring industry

08/06/2026

In the past I’ve taught about flatness when it comes to subfloors and its importance. But another area of flatness happens to involve flatness of flooring material. In this case I’ll limit my comments to flatness in engineered wood floor boards and its installation in glue down applications.

According to the ANSI/HPVA EF national voluntary standards for engineered wood floors, boards that are less than 3/4” in thickness have a flatness tolerance of 1.5% of the length of the individual board. Where the thickness is 3/4” and thicker the tolerance is reduced to 0.75% of the length. So a board length of 48” with a plank measuring 1/2” thick, the allowable amount of bow would be .72” or close to 3/4”. I know, I know that’s quite a bit but that’s also over 48”. If we reduce the length to 24” the calculation is .36” or about 3/8” as opposed to 3/4”. But even with a reduction to half as much allowed, it is more challenging to install a board with a 3/8” bow with only a 24” span, versus correcting a 3/4” bow over 48”. It even becomes more challenging when we change the installation method from nail down to glue down or floating.

While the standards tend to be universal regardless of the species, moisture content, product width, even the standards don’t address bow versus end lift which can be more challenging to install. There is even no difference with respect to thickness 1/4”, 3/8” and 1/2”, all fall under the same standard, yet 1/2” would be more challenging than a 1/4” product. But do we understand bow? I’m not talking bow and skew as sometimes seen in carpet but bow that occurs where you place a board face up on a flat surface and it lifts off the surface in the center of the board. The bottom of the board is not touching the surface, generally at the center but the ends of the board are touching the surface. If neither touched, the center and ends lifted off the surface at the same time it would be a neat Houdini trick. And so then what is end lift.

As the term suggests it’s the opposite of bow where the center is touching the surface but the ends are lifted away from the surface. So with a flatness standard which seeks a single number (ie 3/4” in 6’) how do we then measure for end lift and compare it to the HPVA standard? Turn it over. Measure the distance between lamella face and flat surface and compare it to the standard.

If you’re an installer, you’ve probably seen it. You open a carton of wood and what do you see? Boards. Often flat looking boards because if they were all bowed how would they get the carton sealed? So it’s not that every board coming out of the carton is bowed or at least not yet! So you take boards out of the carton and now you see it. Some boards appear flat with no issues and then there are boards that all of a sudden decide to lift. How did that happen? Well when you saw the material in the carton what did you see? Layers of flooring and each layer interconnected at the tongue and groove. It would then stand to reason that when disconnected and looking at Individual boards there is nothing guiding the board. But once placed into the rack of the floor it stands to reason that surrounding boards that are flat would pull down that which is bowed. The weight of the floor is what helps to pull down the floor. But all things being equal it does depend on the circumstances.

In a glue down installation it’s a little more challenging as with a nail down floor a nail, a cleat or a staple help to flatten to board. With a gluedown you are dependent on the glue not only transferring adhesive from the subfloor to the back of the wood but maintaining that bond. If a bowed board is installed in a gluedown installation but lifts out of the adhesive before the glue has the ability to cure or develop enough strength to hold it, what you wind up with is a lot of hollow areas under the floor. There is glue on the subfloor and back of the wood, but it didn’t maintain its position. So this is where tolerances come into play because if it’s in tolerance it should be installable. Right? Should be. An experienced installer recognizes the challenge and will often place weights on the floor to hold down that which is bowed. Or often seen he will use his rubber mallet to essentially beat the floor down and into the adhesive. If working on top of the floor it’s important to use a knelling board so as not to displace the adhesive underneath which can lead to a lack of glue and hollow spots. Also scooting a board over wet adhesive isn’t a good idea as the adhesive could develop memory and cause gaps in a floor. Keep in mind glue can dry unequally out on a jobsite and so areas exposed to direct sun and air vents will dry faster than unexposed areas when dealing with acrylic adhesives. Same can be said for urethane which is dependent on moisture from subfloors and air to dry. This again can have an impact on bowed boards installed in a floor during its installation. In any event the installers should follow the manufacturer installation instructions which may vary between manufacturers. Some want the floor to be rolled others do not specify. Rolling a wood floor with a 75 or 100 pound 3 section roller will aid in gaining transfer to the back of the wood and thus obtain bond. If the subfloor will accept the adhesive application. A burnished concrete slab may be challenging to bond to if it is not first profiled to make it more porous especially with urethane adhesives.

Have a question, post it here. Evan

04/25/2026

Setting and Managing Real Expectations

One way for retailers and flooring contractors to set and manage real expectations with buyers is with an addendum to a sales contract.

Typically the addendum should be introduced after the close of the sale where a commitment has been received from the buyer and the addendum made as a part of the sales contract prior to the sale being concluded. An addendum of this sort would be an advisory document as to what to do or not do and what to expect and when.

A couple of examples as to what you might include in your addendum would be a notice about product care and specific areas to be addressed such as natural characteristics found in wood flooring. This is especially important where a manufacturer may not provide complete care and maintenance instructions for a finished product or one where you finished the wood onsite. Typically care and maintenance instructions must be provided to a homeowner at the time of sale. It eliminates the potential for a buyer to later claim “the installer told me to use vinegar and water on the hardwood floor and now it’s ruined”. Believe me once you experience one lawsuit and how much it costs you in time and money just defending yourself, you’ll never want to go back to doing it the way you were.

With respect to informing the buyer as to proper expectations this is another area you can excel at and appear fully transparent. Remember how McDonalds got sued for hot coffee being spilled on a patrons lap? It wasn’t just the temperature of the coffee that got spilled and caused alleged injury but the fact that the coffee cup did not contain the warning “Caution Hot Coffee!” that got them into some hot water.

So if you’re selling a character grade floor, they get a character grade but the sample does not have the literally hundreds of characters in that one 2 x 2 sample on your display you may want to add to your addendum an explanation for character and what to expect.

Again it’s one thing to say it another to put into writing to protect your business as the mind gets fuzzy after a while. This is especially important for those in certain regions of the United States where a particular floor or species may be impacted greatly because of local climate conditions and your customer’s failure to maintain the climate control as recommended.

At Lauridsen Consultancy Group we offer retailer/floor contractor specific customized text for your needs to be added to your addendums to take to your attorney for review as part of our consultancy service. Call us at 972-689-5190 for a quote today.

04/09/2026

Explaining flatness and its accuracy

Q. I keep hearing about flatness but isn’t that the same as level?
A. No it’s not. Level is the same as slope. So if you were to place a level on a floor and the bubble doesn’t remain in the center, there is a slope in the floor. Flatness on the other hand is a measurement of two points. So if using a 10’ screed point A would start with the screed touching the surface and point b, which would be at 120” would touch the surface as well. Anything under that screed not touching the surface would then be the flatness measurement. That’s in a perfect world. Often along the way of that 10’ the screed may touch the surface which if it does the span has just been decreased and can no longer be reported as x” in 10’ but rather where it touches. So if it touches in the middle and the gap between screed and floor is 1/8” then it’s reported as 1/8” in 5’. When measuring all of the humps, valleys and crowns in a floor count and any coming into contact reduces the span.

Q. If span is reduced by crowns in a floor, can’t we just measure the crown?
A. Absolutely but then you are no longer measuring flatness but for a crown. To be fairly accurate you need to place a level, preferably a digital 4’ or 6’ level centered on the crown so that the gap at the ends of the level are equal in distance from the floor. If there is only one gap at the end where the level is hanging in mid air while the other end is touching the level you are then technically measuring slope in the area.

Q. Is using a screed or straightedge on top of a concrete slab an accurate way of determining flatness?
A. According to the concrete industry it’s an approximation, but normally all that’s required of installers and inspectors as it’s still recognized by the industry. But the most accurate way of determining flatness is the F number system and using a device called a dipstick which is very expensive equipment. It’s found under ASTM test method E1155. In my personal experience it has its applicability 48/72 hours after placement on the slab but I would argue it’s practicality in the flooring business especially after the concrete has cured for personal reasons I won’t get into here. It essentially uses a grid system of measurement in which it takes measurements every 2’ at which the center point 1’ a measurement is obtained and converted into an Ff number. There is a chart that is produced by the concrete industry that provides an approximate conversion into a fraction of an inch in 10’. So an Ff 50 corresponds approximately to a flatness of 1/8” in 10’ which would be a very flat floor. Most specs for flooring call for a Ff of 35. There is another method using an F meter but I won’t get into that here. Just know there are many options for determining flatness of a slab.

Q. Can an inspector use a laser level to test for flatness?
A. An inspector can do just about whatever he wants on a jobsite but the question is not what he uses but how he interprets the results. If I take a laser which I’ve done and point it at an object, and at the end of the object I produce a result, what is the result? If done correctly I obtained a slope measurement. A slope measurement is the same as level according to the concrete industry. With only some minor exceptions that’s not what the flooring industry cares about they want to know the flatness of the surface. Now I’m not saying an inspector cannot obtain flatness with laser but two things would be in question, one the accuracy of the laser as most have a tolerance listed in their technical data such as 1/16” or 1/8” and the second is determining two points which are exactly at 0”. There must be a point A and a point B within a span that both are exactly at 0” or no deviation. And somewhere would be a deviation between the laser and floor in which to capture a measurement between said two points to create a span. Sounds challenging, it is. I would put my string against any laser any time.

Q. Can an inspector measure for flatness on top of an existing floor covering?
A. Many inspectors do this including me. It’s not so much about obtaining the measurement as it is about interpretation of the results. I one time received a call from a sales rep asking me to come to a jobsite as his customer was tearing up and replacing a floor because the inspector wrote in his conclusion that flatness was off by 7/16” in 6’ and the claims department denied the claim and blamed the installers. I went there and did all my normal tests then let the installers take up the floor. What did I find? A rigid core floor that was floated over a concrete slab that was floated with patch/leveling compound. Not one area was 7/16” in 6’, in fact the vast majority was 1/16” in 6’ with the exception of one area was 1/8” in 6’. So how did the inspector get 7/16” in 6’ then? I cannot say for sure as I wasn’t there. I only know that no flooring was taken up during his inspection so he had to be measuring on top of the floor. A cupped floor (we refer to as curling). Surely the inspector would have surmised a measurement on top of a cupped floor would produce a measurement at the center of each plank and that would essentially create a “cupping measurement” but he didn’t write that in his report. He wrote that the subfloor was out of flat and he was disproven. The floor was torn up for the wrong reason as they had a subfloor moisture issue causing the curl.

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