Hi All,

Thanks for such a great site - have learned a lot just by reading old threads, and am about to embark on my first-ever hardwood floor installation, in the house I'm building in rural Brazil. [The climate where I'm building is very much like Southern Florida, minus the sea-breeze, since we are 500 miles inland.]

Following what I believe to be the consensus best practice, atop a well-cured concrete slab, I plan to lay down the following:

10mil plastic sheeting (as a vapor barrier), then

A floating sub-floor composed of two layers of 15mm plywood, screwed together with 1/4" spacing between each sheet, and 3/4" of gap around the walls

Aquabar B

20mm hardwood T/G planks [Cumaru wood], nailed with 2" flooring cleats

Though I'm basically comfortable with the above, this isn't really a common installation method here. And since the normal local practice of laying sleepers on the concrete to which each floorboard is face-screwed (and then plugged) seems to me insane, I'm a bit on my own in making this work.

However, I have two questions, both of which relate to the local availability of materials:

1) Since it seems termites are a bit of a problem in these parts, I want to be careful in my choice of plywood. [I'm not so worried about them attaching the hardwood floor itself - which I hope expect to last for at least 70 years - but it would be incredibly inconvenient if the subfloor needed replacement before the surface has exhausted its useful life]. Most of what's easily available is made from pine (both marine and commercial plywood). Should I think twice about using this? At significantly greater cost, I can special order plywood made exclusively from Eucalyptus of Virola. Aside from making my project more expensive, should I expect such plywood make much of a difference in the longevity of the subfloor?

2) The mill that will cut the Cumaru flooring for me is really pushing boards that are 15cm or 20cm wide. However, I'd always understood that to avoid cupping/crowning, the ratio of width to thickness shouldn't exceed 5:1 or at most, 6:1. Which in this case, would mean maximum board width of 10cm or 12cm. Especially because they don't seem to have heard of quarter-sawing - I'm even more concerned about this than I'd ordinarily be. Am I crazy to insist on 10cm boards? Would 15cm be riskier in terms of cupping/crowing potential? And is there anything I can do during the installation to minimize this risk?

Thanks so much for any thoughts you can share on the above - or if anything else in my plan seems like it's less than best practice.

Best Regards,

Glen

You can treat plywood with a safe insecticide called BORA-CARE on all sides before you install the plywood. As long as the plywood doesn't get wet it will last.
Sleepers help to make the floor even, is your slab flat?
Have you checked it using a 2 meter straight-edge? It should be within 6 mm.
If not you should shim it before the ply. Then re-check after the ply is down.
Grind high spots and build up low areas with asphalt roofing.
Wide planks can be more of a problem if your humidity changes from season to season. If you acclimate the wide planks you will have a better chance of a flat
floor all year. You nail the edges, but you can also blind nail the ends through the tongue if it is end matched.

Thanks... was just the stuff I was looking for. I'll look for a local distributor - hope it can be had here. If so, I suppose pine plywood will be OK to use then. But if I can't find BORA-CARE (or a local equivilant), would the pine plywood subfloor be foolhardy?



Luckily, the slab is totally flat (to within 3mm).



Unfortunately, humidity here swings quite wildly from season to season. And what's more - the mill normally doesn't machine board ends with T/G, just the long edges. (Is this what you mean by "end-matched"?)

The sleepers that are used locally should be treated for direct contact with the concrete floor. What treatment do locals use? I would use the same treatment that the sleepers use. Untreated plywood will be open to attack by insects or fungus if the wood gets above 19% moisture content. It may last along time, but the treatment is good insurance.
You can still fasten one end of all the planks with the cleats you use for the tongue side of the planks, even if the ends are only cut square, sometimes on a wide plank I will use more than one fastener on the butt-joints. The mate can be glued down if you cut a small part of the aqua bar moisture barrier away to expose some of the plywood. A small area shouldn't bother, any moisture that comes through the plywood from the concrete will be negligible, there.

Well - construction has gone much more slowly than anticipated, and now, a full year after my initial message, our project has finally advanced enough that I'm ready to acquire materials and finally install my floor.

One good thing about the delay is that the concrete slabs - both upstairs and downstairs - are totally cured, so residual moisture from that source, at least, should be minimal.

As for my floating subfloor: I still intend to lay 10mil plastic as a vapor barrier directly on the concrete, and then use 2 layers of 15mm plywood. However, rather than normal plywood, there's a similar product I've encountered here - they call it Maderite - which I'm thinking of using instead. It's most often used for concrete forms, and has an identical construction to phenolic glue plywood. The only apparent difference from normal plywood seems to be a thin plastic membrane laminated to both faces of each sheet. It costs about 30% the price of commercial or marine plywood - presumably because of its poor aesthetic value. But for purposes of a subfloor - I can't actually think of any disadvantage. Before I take the plunge - does the collective wisdom here see any reasons for concern?

Also: is it essential to screw the floating floor together? Or can I staple it (or even use a mix of staples & screws?) Total job is about 1100 sqft. - and staples would go much faster.

In any case, after the floating subfloor, I'll lay down Aquabar B, then the solid hardwood, 20mm thick (a touch over 3/4"). Despite a lengthy research, the narrowest Cumaru T/G flooring I've found on the local market is 15cm (about 6"), about 50% wider than I was hoping for. In light of this reality, aside from nailing the end-joints (and possibly gluing them down, as was suggested earlier), are there any other measures I can/should take to reduce the risk of cupping on those relatively wide boards?

Thanks much, and again, for sharing your tips, experience, and wisdom. I'll be sure to post a photo once the flooring is finally in...

Cheers,

Glen

You can use inch and a quarter staples to fasten the sub-floor pieces of plywood together by removing the base plate of a floor stapler. As long as you use a sub-floor adhesive to glue the sheets together you will be fine. The flooring can then be fastened with 2 inch flooring staples.
It may not be possible to have no seasonal cupping depending on the climate, but after the flooring is laid, presuming that it reached the average moisture content of the area, you can spritz the flooring with water, which will evaporate to leave only the moisture which is required to remain in the wood depending on the humidity of the air, before sanding.
Cumaru is very dense, so it will take longer to acclimate than a softer wood like balsa.

Well - I've learned that construction here in Brazil can really take much longer than planned...

Despite my strong preference for 10cm wide Cumaru flooring (20mm thick, random lengths) - all the local suppliers remain unwilling to produce it for me in that width. They either offer me the standard 15cm wide boards they keep in stock, or offer to cut those down to 10cm at my expense - which is more wasteful than either my heart or my wallet could bear.

Resigned to the wider boards, in advance of finalizing the purchase, I did take a sample board home (just 1m long), and left it flat on the subfloor for about six weeks. The board was flat when it arrived, with about 12% humidity. But much to my consternation, during this period of acclimation, the board cupped by approximately 1mm. (As measured by my digital meter, board has dried to just 9% humidity). To prevent this sort of thing is exactly why I wanted narrower boards, and am now faced with a dilema.

If the boards are doomed to cup while acclimating, I'm not sure how I could flatten them again afterwards to ensure proper installation. Installing them while they are flat (before they acclimate) is one option, but I somehow doubt that cleats will be sufficient to prevent the cupping from happening anyway.

The local flooring guys normally just screw each board down through its face, and then plug all the screw-holes... (And they think I'm crazy for wanting to let the boards acclimate). This brute-force approach does avoid the cupping, but it's a labor-intensive process that gives what I view as an ugly result.

Does anyone here have any advice for how I can best proceed?

Get a humidifier to keep the ambient rh up.

Seasonal shifts here are quite dramatic, with a very humid/rainy summer, alternating with very dry winters. During the summers, it's also crazy hot, so we have air-conditioning to keep temperature and relative humidity at reasonable levels. [On hot winter days, however, we're also prone to use them, but in those cases, they'll only make the dry air drier].

At the moment, we're in a rather pleasant shoulder season... rains have mostly stopped, but the land is still quite moist and lush, so it's not lip-chapping dry.

For the humidifier: I suppose you weren't suggesting I use it just for the acclimation period or installation, since acclimating to an artificially humid environment wouldn't make much sense. But rather, I understood you meant I should look into some kind of permanent humidity regulation set-up. Unfortunately, I've never encountered such a system around here, and to be honest, I'm reluctant to go down the rabit-hole of trying to fight the local climate on multiple fronts. (The air-conditioners will do part of this job, but only de-humidification, and not in a way that's easy to regulate.)

I'm hopeful that something can be done - either with the flooring, or to my expectations - that can help mitigate the shock of seeing new floor-boards cupping before they are even installed.

Does the above info about our climate help diagnose what might be going on? What can I do to make the best of the hand my location (and local sawmill) have dealt me?

Acclimating to your environment will be the best you can do to prevent severe movement after the floor has be fastened down. You should sticker stack the planks so air can circulate around each plank. The should be no cupping since each plank is going to have any effect over all surfaces. Weight on top of the stack will keep the shape best. If others have successfully installed flooring there, you should follow the local protocol.
Have you seen any flooring that has been finished how you like it and has been through a year's seasons?

Unfortunately, all the nice flooring I've seen around here is in old farmhouses - 50 years or older. It's all ipe - totally clear, with quite narrow boards (8-9cm). Newer floors (especially in the city), if made of wood at all, are mainly glue-down hardwood parquet (10cm x 40cm).

So - I returned yesterday to the wood-merchant, and again explained my hesitation about using 15cm wide boards. Not only was it a matter of theoretical prudence, but also a matter of empirical reality: the sample board I'd stored on site did exactly what theory said it would, which is cup while acclimating. He replied with the following remarks [I paraphrase/translate]:

1) That [cupping] isn't supposed to happen to boards. Something must be wrong.
2) Mostly, clients today only want wide boards... 15cm, or even 20cm.
3) Normally, clients install boards just as soon as they are delivered. Nobody really lets the acclimate, since they are already kiln-dried.
4) Even if the wood is cupped, once installed, it will settle down.
5) In my [the word merchant's] own house, the floor is made of 15cm wide Ipe. This is screwed from the top and plugged, and gives no problems.
6) In a friend's house, the boards are simply glued down - with no mechanical fasteners at all. Again, no problem with cupping.
7) I think you are worrying for nothing. 15cm boards don't give problems. Just install it as soon as it comes, and it will be fine. But I don't guarantee anything.

Needless to say, this wasn't a super-reassuring set of responses - about several of which I'm quite skeptical. In the end, he wants me to buy - and seems slightly more keen on the sale than the final result.

As for alternatives, there are really just three materials that could possibly work:

a) The previously considered 15cm wide x 20mm thick, kiln-dried Cumaru T/G flooring
b) A newly arrived batch of 10cm wide x 20mm thick, kiln-dried Garapa T/G flooring
c) A lot of 10cm wide x 20mm thick Cumaru decking material, into which I could machine T/G, for a finished board dimension of 9cm wide x 20mm thick. But this stuff is rather green, and will take forever to air-dry.

The Garapa is narrow, but it's also softer, and frankly, a bit too light for our tastes. This said, a washboard floor isn't really to our taste either - so we might be open to the trade-off.

I've for the moment taken a few more sample boards of both options, and have left them again in the jobsite, to see if maybe the cupping wasn't just bad luck with one boards.

It's really hard to do this in a place with such different woodwork habits as those I'd grown up with... Glad to have this board for other opinions.

Exactly why you should have a humidification system in place for the dry periods. Amazon sells them, attachable to an HVAC system or a stand alone whole house humidifier.

When you say "humidity" I take it you mean moisture content of the wood. What is your average rh during the seasons?

Is this wood kiln dried? And if so can they kiln dry it to the average rh of the year?

Well, I may have spoken too soon about the 10cm Garapa not being to our taste... As soon as my wife saw the sample pieces of Garapa side-by-side the 15cm Cumaru, she immediately wanted to know what it was and if we could do the whole house in it!

Since it's the width I was looking for anyway, and a happy wife is a happy life, I'm totally willing to consider this. However, my doubts persist about the relative hardness and stability of Garapa vs. Cumaru. I've started asking around locally to see if anyone knows of an old-ish installation with Garapa flooring, but in the mean time, I also thought I should ask here what's wisest in the long run.

Thanks for any and all opinions from anyone who can help me compare the two options before me.

I've never seen or heard of that species used for flooring. Although it appears it is used for decking. Also called Brazilian Ash.

Specs - http://www.wood-database.com/garapa/

Further update: It seems my stubbornness about 10cm boards has finally paid off. I met today a fantastic wood-merchant, who happened to have two lots of kiln-dried Cumaru T/G boards, in just this elusive width, sticker-stacked in the back of his shop.

The first lot only includes totally clear boards - enough for about 3/4 of my job. Moisture content averages about 8%... it's beautiful stuff, and I bought it all on the spot.

The second lot has roughly the same moisture content, but some of the boards have some local areas of lighter grain pattern (almost like bleached areas), making for less homogeneous looking boards. Luckily, I can select whichever boards I want from the lot, so can minimize how much of this I'll receive, and can organize to put all such boards into one of two smaller rooms, so the effect will appear interesting and intentional.

So I can know more about what it is I'll be getting - does anyone here have any idea what these white grained areas could be? Should I be wary at all?

To give more choice when racking the floor, I've elected to buy a bit more than I'll need, with the intention of making the remainder into baseboards by cutting-off the tongue side after the floor itself is totally laid. [That's not crazy, is it?]

Also: this same wood-merchant has all but talked me out of the floating plywood subfloor I'd been planning. Instead, he suggested the following:

1) Atop the flat & level concrete slab, lay 10mil plastic sheet as a vapor barrier.
2) Then, on 40cm (16 inch) centers, lay 3cm thick (4cm wide) sleepers [also made of kiln-dried Cumaru], perpindicular to the direction of the final flooring, fixed in place [through the plastic] with steel anchors.
3) Alternate the above with 36cm wide x 3cm thick styrofoam planks, to fill the voids between sleepers (for sound abatement).
4) Skip the Aquabar B; just install the acclimated T/G Cumaru boards with cleats, not only nailing directly into each sleeper, but also gluing the boards to each sleeper as I go.

What do you think of the above? It will cost (and weigh) much less than the floating plywood subfloor, and is in accordance with local practice. Though, I'd have thought fasteners would need to be closer together than every 16-inches, maybe by gluing the boards to the sleepers, it'll be fine.

To be honest, I'm still just over the moon that I've found the narrower boards I was looking for. I'll be giving rapid thought to the proposed change to installation method; any reactions from the board would be most welcome. [As is no doubt obvious - you all have way more experience with this than I do!]

Thanks in advance for your thoughts.