Laying wide pine floorboards over concrete?

[Galen C]

This is a non-boat related question, but I thought I'd put it to the knowledgeable members of this forum.

My dad has an old-ish (early 50's) house, built on a concrete slab. When he first renovated the house about 20 years ago, he ripped out the old wall-to-wall carpet and painted the concrete. Since then he's either tiled or laid engineered wood flooring in most of the rest of the house, but the living room and dining room still need to be done. Coincidentally, a few years ago he had a few large longleaf and slash pine trees removed from the front yard. We borrowed a wood-mizer from a friend and milled them up with the idea of using the wood for flooring. It's mostly quartersawn, 4/4, in 4-8 inch widths. It's good and dry now, so we're trying to figure out how to actually use it. We'd like to keep the planks close to their current width and have a floor with mixed-width boards.

The challenge is this: how can we secure the new wood floor over the concrete slab while keeping the planks as wide as possible? Our current plan is to level the slab with thinset, install some battens with liquid nails & a ballistic nail gun, and then nail the wood flooring to this in the typical manner. We're not at all sure that this is a good idea, however. Most solid wood flooring is pretty narrow, about 3.5" or less from what I've seen. I assume this is to deal with wood movement and to make it possible to blind nail it. What happens if the planks are significantly wider, say 8" nominal? Is a blind nail through the tongue enough? Would a bead of some flexible adhesive like SikaFlex between the floorboard and the batten help with adhesion and wood movement? Are we on a complete fools errand? If it comes down to it, we can just rip the boards down to a reasonable width, but that would involve a lot of waste, and it wouldn't be nearly as interesting looking.

I'd appreciate your advice!

[StevenBauer]

Since there is no hurry, apparently, could you do a small area and see how it does for a year or two? Like 4’x4’?

On a big waterfront remodel I worked on a few years ago they glued down 3.5” white oak flooring directly to the concrete. Seemed crazy to me but this was a $750,000 remodel and the flooring guys said it would be ok. I’d like to go back and see for myself.

[Galen C]

We've thought about doing a test patch. We may still, but the concerns are
1) My mother, who doesn't like living in a construction site, and
2) that the behavior of the floor will change when we've covered the entire room, either because of moisture and air circulation or because the expansion of the floorboards will be constrained by the walls.

Any idea what adhesive they were using? Did they put down any sort of moisture barrier first?

[hawkeye54]

Galen, do you know what type of paint your dad used on the concrete slab ? I have no information on the process you wish to follow, having only worked the other direction - my 1903 farmhouse had wood floors the PO destroyed by using roofing nails at each joist to try to stop squeaking, so I wound up replacing the floor with 3/4 " tongue and groove plywood on sleepers (2x2) over a vapor barrier - dirt floored basement below. You may try one of the flooring company websites for 'frequently asked questions' ( such as LL flooring (no affiliation) - used to be called 'Lumber Liquidators'


Rick

[Zulu]

Your biggest potential enemy is moisture coming up through the floor. You can check for that by taping down a square foot of plastic, something thick-ish although a bread bag will do if you're confident it has no holes in it. Let it sit for a week and look for moisture collected under the plastic. This doesn't take into account seasonal changes that might see more moisture under your slab. The less moisture you have, the less worry. I rolled the dice once and glued bamboo flooring directly to my basement concrete floor with PL400. Put down two or three strips and then all my tool boxes, ammo, reloading stuff etc. Let it set overnight and repeat until the room was done. That stuff was stuck. I pity anybody who thought they might change it. We moved a couple of years later but it was sound when we left. Pine isn't going to provide you with the rot resistance that bamboo would though. I have always found that with flooring in anything other than a predictable, known situation, it's a gamble. Sounds like you're going to put a lot of effort into this and you may not want to gamble to the extent I did.

[Garret]

Not quite what you're asking about, but close. We redid all the floors in our house 6 years ago. On the plywood upstairs we went with 5" cherry. It is beautiful, but over the winter, a few joints open a little - though nothing more than about a sixteenth.

Downstairs is a slab with prefinished solid maple. While it's 3" wide & made up of short pieces, I think it's similar to what you are talking about. The guys who did the work said they'd done quite a few floors on slabs, so we went with their method. They laid down tyvek, which they then covered with 3/4" Advantech - powernailed into the slab. The maple was then installed normally on the Advantech. In the 1200 +/- sq ft floor, there is one spot where the Avantech seam matched with the maple seam & that will grow to a 1/8 gap in the winter. I seem to be the only one who notices it. OK - maybe others notice it, but no one has said anything...

The added thickness (1 1/2" Advantech + flooring vs. ~3/4" carpet & underlayment) meant I had to cut the bottoms of all the doors, but that wasn't too bad - though I had to get a bit creative with a metal clad exterior door.

Crummy pic that I just snapped (without picking up) that shows the wide gap just about dead center:

floor.jpg

[WFK]

I wouldn't glue directly to the concrete, especially with a wide pine board. On the current project we laid down 4mil vapor barrier. Over this we put down 2 layers of 1/2" ply. Using a panel saw, each sheet was kerfed on the back side in a 12" x12" grid to remove any stress and were glued and screwed with a 50 /50 mix of titebond glue/water and 1" screws. we've now created a 1" floating floor that the wide board flooring can be nailed directly to.

[hawkeye54]

^ Interesting solution, WFK.





Rick

[jpatrick]

A slab on grade will have moisture issues forever. I would use an engineered floor and use the planks for something else.

Jeff

[willin woodworks]

Slab on grade will have issues no doubt. I'd go with bituthene over the slab, Advantech and then the wide pine boards.

[L'Ankou]

There is also cork sheeting you may use, will also act as insulation.


And after groove each plank's side and insert some ply as false tongue before dropping them on the floor.
Need to provide for wood expansion on the sides.

If you want to fasten them, I would use intermediate beams, 1x2"

[Larks]

I have done a couple of hardwood floors pretty much as you described in your OP, albeit quite a few years ago. Last I heard from friends who are still living in one of those houses they were still in good shape 30 or so years later.

I have always stacked the floor boards in the house/room where they are to be laid for a few weeks to somewhat stabilise them to the conditions that they’ll be staying in, conditions change throughout the year anyway but getting them used to their new home does minimise movement - at least early on.

In both cases I fixed hardwood battens to the concrete (which had been poured with a moisture barrier under the slab in each case), glued and nailed the floorboards to the battens using liquid nails for the glue and hidden nailed (edge nailed) the floor boards. They were only 90mm floor boards so not as wide as yours may be.

If you are unsure of there is a moisture barrier under the concrete slab I’d lay one over the slab under the hardwood battens.

[Paul Schweiss]

I wanted a wood floor for my shop I built at our home property. I had Douglas Fir from the trees I needed to take down sawn to 4/4 and kiln dried. I also put a vapor barrier under the slab on grade.
After a lot of reseach and talking with concrete guys I went ahead with the visqueen test about 10 weeks after the slab was poured. Taped down a 3’ x 3’ piece overnight in a couple spots, especially the NE corner where the holes for the posts tried to fill with water. The tests came up dry after 24 hours.
Next was a layer of roofing tar paper, followed by two layers of 1/2” T&G OSB nailed as needed with a powder actuated gun. I could not physically handle the 1-1/8 OSB, so the 1/2” allowed me to lay each layer in opposite directions.
I had milled my Doug Fir into 7/8” T &G and edge nailed it to the OSB.
Two coats of Daly’s Floorfin and finished setting up shop.
Zero issues with warping after two winters, I have a Rinnai ducted propane wall heater and a 6’ ceiling fan that makes it pretty economical to heat with the R7 insulation batts.
It is a joy to walk on and makes setting up building forms and jigs a breeze.
Every shop I worked in up to 1998 had a wooden floor, it’s just the right thing to have.