Is lauan underlay really that bad?

Lauan plywood is a controversial flooring underlay.

I went with 5.2mm lauan plywood from my local Home Depot with a recent flooring project because it seemed like the “obvious” choice. It’s recommended all over the internet on seemingly reputable sites, the University of Massachusetts recommends it,  a major tile manufacturer recommends it,  and my Home Depot Home Improvement 1-2-3 book recommends it.

However, after going through six and a half pounds of 6d 2″ ring shank nails and hours upon hours of work with my wife, I found some web sites highly critical of lauan.

Some allege that lauan board is inferior to regular plywood for various reasons, including inability to resist indentation, hygroscopic properties, oils in the wood, and so on. This is generally the opinion taken by an author for Floor Covering International.

I freaked out. We were in the middle of a major weekend project, we had no time for major problems, and going back would be a giant setback.

To add insult to injury, when we were finally ready to apply the tiles, we found instructions inside the box. The very first line of instruction read, “Do not use mahogany plywood.” AAAUUGGHH!!! (While technically incorrect, “mahogany plywood” commonly refers to lauan.)

We went ahead and finished the project as is because we had no better alternative.

Since then, I’ve calmed down. My experience working with the wood and further thinking suggests:

  1. Lauan plywood resists dings well. It took a solid, direct hammer blow to dent it, and those blows didn’t dent it too badly.
  2. Running our refrigerator over some bare lauan didn’t do a thing to it.
  3. The criticisms of lauan aren’t objective, nor are they quantitative. They appear to be both communally reinforced and based on fuzzy memories. I also suspect that confirmation bias may influence these detractors to blame lauan for bad projects that may have been affected by other factors such as bad installation practices.
  4. The only lauan in the plywood is actually an extremely thin top surface. As far as I could tell, the rest of the plywood is regular wood you might find anywhere.
  5. Lauan is used in boatmaking because of its water resistant properties.
  6. We primed the wood. While this isn’t a sealer per se, it should act as an additional barrier, reduce any moisture-related problems.

I am not flooring expert, but the evidence suggests that lauan is actually a fine underlay choice as long as you get the right quality.

The only valid criticism might be that lauan is a tropical wood and its use may contribute to tropical deforestation. However, even then, there are lauan tree farms, so this might be able to be managed?

6 thoughts on “Is lauan underlay really that bad?”

  1. Thank you for your post. I am currently at the stage of having fully prepared my own bathroom floor to ceramic tile, over Luaun that was recommended by our local lumber yard. I purchased the high grade polymer based mortar, Luaun, and ring nails from them, and they were aware of my intended use.

    Then, I read the same darn thing on the mortar mix, and on the mastix pre-mix I had around here too. Mad? That doesn’t describe it. I then jumped on the Internet to search for “luaun underlayment for tile floor”, and found the same disgusting information you found.

    My question is, after time, how did your floor hold up? Did you have tiles come loose, or crack? I’m faced with tearing it all up, and starting over with cement board, but might consider chancing it, based on your reply.

    Thank you for your time.

    1. It’s been almost 6 years now, and it has held up just fine. Not a single problem, even in areas that I know get some water spillage and the vinyl tiles aren’t against each other as they should be.

  2. It’s interesting that one of the criticisms of Luan is that it is hygroscopic. That’s actually a positive, because it means the substance will adsorb (not absorb) moisture, without becoming wet itself. (Rice is hygroscopic, which is why we put it in our salt shakers.)

  3. Luan makes a great underlayment for vinyl flooring, both sheet and tile. It is not suitable for ceramic or porcelain tile, though. Do some folks get lucky when using it? Sure, but why chance it? The main factor to consider is that the expansion coefficients, both thermal and humidity, vary significantly between tile and wood. This means that if you set tile on wood, the surface under the tile will be expanding and shrinking at a different rate than the tile on top, leading to cracked grout and popped tiles. Additionally, thin set is a cementious product meaning it cures rather than dries. If the wood underlayment sucks the moisture content out of the thin set, it won’t hydrate properly and can lead to a weakened bond.
    Both of these deficiencies can be corrected by using an underlayment intended to decouple the tile from the subfloor–cement board products like hardibacker or decoupling mats like ditra will yield much better results by providing a like material to which the tile can bond.

    1. I have good news: the kitchen has been redone completely, and the lauan is gone. The lauan was under vinyl tiling, and it worked fine for the eight years that it was installed. Perhaps the problems you mention could have happened if we kept it longer. In areas with hard tile, we now have the cement board like what you mentioned.

  4. Lauan is to make the floor flat so things don’t transition through. It is not a substitute for a solid subfloor. Put it under vinyl floors that are glued down.
    If your subfloor is screwed up, you need to fix it. Covering it with lauan isn’t fixing it. You don’t use lauan under tile. The thinset will smooth imperfections.
    Saying it has a bad rap is misleading. It has a purpose. When people use it wrong and complain, that isn’t a failing in the product, it is a failing in the person.

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