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I'm installing Lumber Liquidators' Morningstar XD bamboo laminate flooring in my basement. According to their tech support, they have the following flatness requirements for the underlayment:

(1) no more than 1/8" over 6', and (2) no more than 3/16" over 10'.

A contractor friend thought that sounded excessively stringent. And to meet those requirements I'd need to smooth out the existing concrete floor, so I want to be sure.

Are those tolerances overkill?

  • You've wandered into the realm of prerogative. How much clicking, squeaking, and flex are you willing to tolerate? – isherwood Mar 18 at 15:38
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    Have you looked at specifications for other brands of floors? Bamboo is popular now so you should have a lot of examples to look at. Opinion: overly strict specifications mean less warranty claims, but if they fall in line with other manufacturers, it makes that conspiracy theory moot. – JPhi1618 Mar 18 at 15:43
  • "You've wandered into the realm of prerogative. How much clicking, squeaking, and flex are you willing to tolerate?" This is my first time installing laminate flooring, so I don't really know what the tradeoff curve is like. I guess my goal is "No regular person would NOTICE any difference between the result I got vs. what I'd have gotten if I'd followed Lumber Liquidators' stated tolerances." – Christian Convey Mar 18 at 15:51
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It's really hard to provide objective advice. There are many factors, and the shape of the irregularities is critical.

  • Is it a gentle curve or a hard angle?
  • Does it curve in several directions?
  • Is there more than one such issue?
  • Do you have multiple underlayment options, whereby an upgrade could help mitigate the concerns?

It would take a booklet to lay it all out. I'd stick with mfr specs + maybe 25%.

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FWIW you will notice noise more on the floor above. Over a concrete floor your footfall noise will dominate.

I have laminate in two rooms at present. I know the floor was more irregular than that, and it has done well with very few flaws visible after 10 years. Modern stuff keeps getting better.

The choice of foam underlay also makes s difference. A thicker, higher density foam will tolerate more variance in the existing floor.


That said: I have lived in 3 houses with basements. All of them have had incidents with very wet floors, either from a cracked foundation, failed sump pumps, or washing machines that failed. Lots of problems in nearby Edmonton from storm drains backing up in heavy rain and flooding basements. I will not install a floor in a basement. Given laminates lack of tolerance for wet, this is a bad idea.

Other options:

  • Vinyl plank if you need a finished look. It's water proof, and the nature of vinyl is that it's more forgiving of irregularities.

  • Ceramic tile. This is a lot more work, but it results in a floor that is close to indestructable. If the house is several years old, and all the cracking that is likely to happen has happened already this is a good route. Tile is a reasonable DIY activity, but it is time consuming. If your floor isn't flat, go with smaller tiles

  • Another option is to paint your floor, and get arty about it. I have seen interesting concrete floor stencils.

  • Or just paint your floor, and put down area rugs.

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