Thank you for your review. Brazilian Teak is on the top of my list. We have concrete sub floors, so I need engineered and floating. Any thoughts on this? I also need to educate myself on humidity - I'll have to Google "hygrometer".

Laurarenos, I searched Google images for merbau floors and what a gorgeous wood! (Not very grainy, and what grain is there I'd call pretty.) A little rambling follow-up: We hope to schedule our project to start in the next month or two. I will probably look a little more into merbau but so far my husband and I have settled on one photo that we're showing to our wood-floors guy (in the biz >20 years etc.), and it's attached (Armstrong sapele in roasted bean, engineered). He's making up a sample for us of that look but without so much beveling, and one other, likely in American walnut but handscraped boards and then stained (would be on-site). After seeing the sample we'll work on what we can do about pricing and options to get as close to that look as possible for our budget. (We want a great floor are willing to pay some premium for it, but within reason.) One thing our guy was talking about was selecting boards for the most consistent color throughout the house ... they can do some things with the stain itself to encourage not a ton of variation between boards, but he mentioned sometimes ordering a bit more wood than usual can be a good idea as you get to pick and choose the boards you want to lay down with more discretion. (He's been very much more of the 'you don't need to overspend' type with his suggestions, so I'm inclined to buy his rationale here. The exotics aren't entirely out of the picture. While looking at woods I got curious about what it feels like to walk on the different hardnesses of woods. I think we had something like 5/8" oak, which upon looking at the torn-out boards looks softer and more flexible - by miles - than the samples I've seen of teak! So those of you with 3/4" tropical woods, are the floors harder than conventional-wood floors? Does a cork underlayment even do much for tropical woods for the feel of walking on them, or entirely superfluous? The other thing I got curious about was whether the handscraping I've seen on tropicals has tended to be different from the handscraping I've seen on softer woods for a reason... because of the hardness of the wood and the difficulty (historically speaking) of scraping. That is ... the tropicals that I've seen handscraped have long, shallow, flowing scrapes but the softer woods I've seen handscraped have tended to have more grooves and a more dramatic texture of handscraping. (To me it separates the tropical-floor or Asian-floor look from the Americana look ... however unauthentic that view may be.) I saw when looking at hardwood samples how the difference in the wood itself between something like birch, or even oak, and teak or other hard tropical woods, is night and day. On the edge and underside, the former looks like cheap plywood vs. an incredibly solid, dense and beautiful wood. (Certainly the former have their applications and fans, and arguably may be a lot easier to work with where nailing and sawing is concerned!) Here is a link that might be useful: Armstrong sapele in roasted bean

I'm going to disagree with the other opinions in that this could certainly be caused by humidity and acclimation. Every wood pro knows that solid wood will absorb moisture and expand. It's rather unlikely that the boards would be milled to different widths and especially that it would vary in width along a particular board. In general, 4/4 lumber is cut to uniform widths then sent through a machine that mills and kerfs the bottom, mills the top flat and cuts the tongue and groove on opposite sides, all in one machine. Another machine generally adds the end matching. Unless something in the milling machine is moving, or the unmilled boards were too narrow, all pieces will be the same width as they exit the molder. Look at this video at about 1:30 to see the molder in action. https://www.youtube.com/watch?v=wc0N6m4RNdY What you're experiencing is probably the effect of moisture soaking in to parts of boards that were more exposed to humid air. Exposed ends will grow more than centers that are less exposed. Look at the your first full row from the top. On the middle board, the end is wider than the one to the left. In the next row down the opposite is true. It's likely that those ends were exposed to more humid air. The problem is exacerbated when the installer doesn't compensate, since the wide ends can kick the next row out of line, leading to more gaps on the edges and ends. The same thing could happen in very dry air with ends shrinking. Exactly how was the wood acclimated? Was it removed from cartons and wrapping? Was it stacked so air could circulate around all sides of every board? What was the temperature and relative humidity in the space during the acclimation period? What is the current indoor temperature and relative humidity? Is the floor nailed down? I had this happen with a very high quality Canadian solid wood floor. Fortunately mine was dark stained Walnut so once the floor was aligned properly and larger gaps were distributed to make two smaller gaps on each edge, the issue didn't show and once the whole floor acclimated in place there was no issue.

Painted PT wood(as long as it is completely dry before painting and primed with an oil based primer) is safe from the chemicals and the paint helps prevent splinters. The new chemical recipe now used for the treatments are much safer than the old. The tradeoff is the newer treatments are not ground contact usable unless specifically treated for ground contact. Meaning the stand off metal bases are necessary. It is fairly easy to cover the metal with trim. You might look at composite deck flooring to get the planks you are referencing---the trade term is 5/4 decking. You would need to make floor joists at 12" on center rather than 16"OC if composite is used(in many cases). And regular framing lumber is fine for the rest---just prime and paint with a good paint. Be aware that most exterior paints are designed to chalk, which will stick to hands/clothes. You might think about a solid deck coating.