So, here's the questions first, with explanation of my situation to follow:
Is it a good idea to install a plywood subfloor on top of the concrete so that I can put in engineered bamboo flooring?
How does that compare to using the vapor / barrier glue directly on the concrete?
What type of plywood do I need, and what vapor barrier should I use to protect the plywood, if I do install subfloor?
How do I fasten the plywood securely to the slab?
Once I have the subfloor in, should I nail or glue the bamboo to the plywood subfloor?
Is the answer different if I'm talking about a 2nd level subfloor versus a subfloor on top of the concrete?
I have an above-ground concrete slab foundation and a big stack of engineered bamboo flooring. I also have plywood subfloors on the second floor of my home. I'm trying to find out the best way to get my floors installed and have them look great and last forever. Sorry for the long explanation but I'm trying to do my homework and I'm getting conflicting theories.
The slab isn't super dry (it has failed a moisture test indicating that we need to have a vapor barrier of some kind), and as the bamboo is _not_ click/lock and is merely tongue and groove, I am under the impression we cannot float the floor.
I am aware that we can purchase a vapor barrier / glue that can be used in this situation. However I've heard that after 5 or 10 years the stuff doesn't hold up and can start to let moisture in, so I'm looking for my best alternative solution for having my floor last longer.
Recently we had a flooring contractor give us an estimate on installing the floor and he included the installation of a plywood subfloor over the concrete, to which he would nail the bamboo. Previously I was under the impression that the bamboo wouldn't hold up to the nailing, but I've seen other websites say that it can work if you use a low PSI.
Apparently people don't often put tongue-and-groove bamboo flooring on slab, so I'm having a harder time finding a reliable source of proven online information. I'm hoping that somebody here can help me out!
Thank you for your question and welcome to the community!
I personally wouldn't recommend to install plywood directly over concrete for your engineered floor. I would only opt for this if you first seal the concrete floor....if it is rated below grade. Knowing what the manufacturer of your bamboo states for install will determine if it can be glued or nailed down.
The best wood-based foundation over concrete for glue, nail, or even floating systems would be to create floor members via studs under plywood. This is really needed for below grade concrete floors. The diagram below shows more of this in further detail.
The materials in the diagram above are really the best bet if you still want to use wood as a substrate to go between the concrete and your bamboo. 4 MIL or thicker plastic works great for a vapor barrier and exterior grade plywood is really your best bet if you wish to do this type of setup.
I would strongly recommend this above for below grade concrete. If this is above level as you stated on a 2nd floor, then you can still use the system above, but you can also just install the engineered bamboo directly over the concrete using a urethane-based glue...if the manufacturer states it is a glue-down.
Since your bamboo is engineered, and if it can be glued down, you can also use a fairly new product called Elastilon. This unique system also works for engineered floors if they are rated for being glued down; but this won't work for floating systems. Click on the image below for more information.
From what you are telling us, you already have plywood subfloors but are you installing over concrete as well as the wooden subfloor...I'm not exactly sure why you were asking about in terms of exactly where to install.
So again, you can install engineered bamboo directly over concrete....but prepare the concrete first and use the right materials. Use a urethane-based glue if you decide to adhere it without using the stud members and plywood. This type of glue, when applied correctly, will give you the moisture barrier since it isn't water soluble.
However, using a stud member system for below grade concrete is really the best way to get the bamboo completely away from the concrete. Also don't forget to have the bamboo acclimate to the floor for at least 2 days before you install it in the room you want to install.
As for nailing, this can be done provided your contractor uses and knows the right nailer. Using it over a plywood/stud member flooring system with a pneumatic nailer will do this just fine.
In either install method you choose, as long as the contractor or you read the information above and use the right materials effectively, then you can get bamboo down and make it last.
Let me know if you have any further questions,
Hi Joseph, thanks for the reply.
So first off, allow me to clarify.
I have a 2-story home. The 1st floor is on a concrete slab foundation that's about 8-inches above ground level. The 2nd floor is already a standard plywood subfloor. So nothing is 'below grade'.
I intend to install the bamboo on both floors throughout and both are above grade, preferably doing the work myself (without a contractor). The concrete slab failed a moisture test which prevents me from installing the bamboo without a moisture barrier.
Second, there are portions of the ceiling that are already pretty low on the slab level. I cannot install a sleeper floor there because I just can't sacrifice the headroom. This is why I'm looking at a plywood subfloor on top of the concrete instead.
That brings me to my questions regarding the main floor:
You said I could install a plywood subfloor if I "properly sealed" the concrete. Would that mean just using a standard vapor barrier before nailing down the plywood subfloor? Or is there another type of sealant I should look into?
Alternatively, I can use a vapor barrier glue to install the bamboo directly on the concrete itself, but I have heard that solution isn't very durable for the long term. Would you recommend a plywood subfloor method over the vapor barrier direct glue method?
I appreciate you making me aware of Elastion, though it would be our most expensive solution so far.
The upper floor is a much simpler problem to solve: Should I use glue or nails for the bamboo? The manufacturer recommends glue, but I could also nail or staple. I'd like to know which is better for long run, and potentially easier / faster for installation.
You are quite welcome.
Since nothing is below grade, you are actually more flexible in your choices for your bamboo floor.
Given your situation, I still wouldn't do sheets of plywood for the 1st floor due to several reasons:
We don't carry it in our stores anymore, but we can order (or you online) one of the best all-in-one hardwood/engineered glues on the market. Most pros and floor installers choose a high quality glue shown below instead of a plywood base mentioned above.
Shown and linked below, the Bostik SuperGrip acts as a moisture barrier, sound reduction membrane AND adhesive.
If you still REALLY want to install plywood first (which really you don't have to if you use the glue above), I'd opt for a better yet easier to install system.
Shown below, you can use a DRIcore raised plywood system. I've heard nothing but great things about this material. It is plywood, but it has a very slight raised plastic bottom, allowing air flow and proper movement for your floor. Click below for more information including a video.
With either option above, you forgo the sleeper floor system.
In either case, sealing the concrete floor can be done right away once the moisture is low enough. We carry various forms of clear and opaque sealers. One that flooring carries is called RedGard and works for waterproofing as well as preventing cracks in the slab. Clear sealers by Behr, Flood or Thompson's works well too for sealing the concrete.
As for the upper floor, it really is up to you if you want to use glue, nails, or floor staples. Most people aren't aware that if you are very careful, you can glue AND use a fastener together to ensure the floor stays down. A urethane-based glue tends to work well, but it is more labor intensive due to clean-up and small work area.
Staples or nails can come up in time due to the house's wood frame settling. While this may not happen, it is a possibility and it is faster for installation up front.
In closing, you have a lot of options that will work for your bamboo floors. Go with the one that fits your budget and familiarity. Hopefully these choices I've given will assist you.
Keep us updated on your progress,
After comparing all of our cost options we are probably going to use Elastion after all on the main floor. It's only about 15 cents more expensive per square foot and we'll probably save a lot of time. My only concern is the amount of leveling we'd have to do compared to laying 4x8 plywood boards, but we'll see how it goes. Self leveler isn't super cheap and isn't a picnic on labor / time either, so the subfloor method still has some attraction for us. I think we have more homework to do before I can say for sure what our best choice is.
The top floor we'll likely tackle with a nailgun but I've had mixed recommendations between using nails or cleats, having heard that cleats can squeak more. I'll keep this thread posted on progress, but feel free to chime in.
You are correct about using self-leveling compound vs. using a subfloor to smooth out everything in terms of pricing. However, if the leveling isn't too much; doing this step isn't as time-consuming as one would think.
For the main floor, I'm glad you chose Elastilon. It will really hold up over time.
As for the top floor, I've had better luck from conversations with my customers via nails (or crown staples) versus cleats. The staples have two fasteners instead of one cleat, giving you double the strength of fastening.
Using a pneumatic nailer rather than a manually-powered one will guarantee you accurate and flush staples going into the planks/subfloor.
Continue researching, listening to the flooring pros advice and comparing prices. And as you stated, keep us updated on your progress. We would love to see before and after images of your floors!