Neutral Axis

Bamboo Floor Installation in a Basement Bedroom

by on Nov.18, 2011, under Uncategorized

Last week, my girlfriend, N, and I embarked on a project to put down an engineered bamboo floor from in a basement bedroom and closet area (a total of about 300 sq.ft.) It was a lot of work, but we’re very happy with the results. [Update: Cali Bamboo has put this up for project of the month for December 2011.  You can vote for it at Project of the Month]

Being a basement, we were working with a concrete slab. The basement is dry, but contrary to conventional wisdom, concrete is porous, so there’s always potential for moisture to wick up through a concrete slab. So before any wood can go down, a vapor barrier is required. In addition to the vapor barrier, the bamboo material we chose (more on that later), requires an underlayment. We chose to do what’s called a “floating floor”, which means the flooring is not nailed, nor glued down. That makes it free to expand and contract with temperature and humidity changes without buckling. The underlayment subfloor we chose is the same.

So, we need 3 layers. A vapor barrier, subfloor, and finished surface.

I remembered seeing a product a couple of years ago at Lowes that was 24×24 OSB panels with a waffle textured plastic bottom. The idea was to create a subfloor that provided a barrier to moisture in the slab, yet unlike a simple sheet of plastic, would provide an air space so moisture could dry. That product seems to no longer be available there, but I found a product online called Delta-FL that would work for our installation, was reasonably priced, didn’t add much thickness, and was available as a special order from Lowes.

Delta-FL is a thin plastic dimpled sheet. The dimples make it about 1/4″ thick. It can be ordered in rolls or 4×8 sheets. I special ordered the sheets from Lowes at a cost of just less than $0.50 per square foot. The dimple pattern makes the material stiff enough that heavy weights from furniture and even pool tables can rest on it without crushing. It is able to act as both vapor barrier and subfloor in one. That takes care of my first two layers. (Side note: If I were installing carpeting, tile or nailed down flooring, this product would not be suitable as it is not rigid enough and wouldn’t hold a nail.)

But wait… Delta-FL has some idiosyncrasies. The type of plastic is such that if just placed on concrete, it might make tapping noises as you walk across it, so they recommend putting down a layer of geotextile (landscaping fabric), between the Delta-FL and concrete. The fabric helps to eliminate tapping noises. Between the Delta-FL and flooring, they recommend putting foam sheets so the wood floor doesn’t “tap” on the plastic.

So a total of 4 layers is needed. Fabric, Delta-FL, foam, and finished surface. The fabric and foam together only add about 1/16″ of thickness to the whole assembly, so those additions aren’t a problem and they’re cheap.

A single roll of landscape fabric big enough for the area ran me $5 at a local building supply store. Varieties carried at Lowes and Home Depot were more expensive and included weed barrier and such that wasn’t necessary. They also had thin foam underlayment that cost me less than $10.

With everything on hand it was time to start.

Step 1: Clean and vacuum the slab. If the slab isn’t flat you will need to fill in the low spots with floor leveler.
Step 2: Roll out the landscape fabric. N and her son took care of that step, using a roll of blue painter’s masking tape to help hold the strips together. It was a little difficult to get it down and keep it in place without wrinkling as it was walked on, but they managed to get it down very smoothly. We didn’t think to take a photo of the floor at that stage but you can see a little of it in the photo below.

Step 3: Lay out the Delta-FL. Pain In The Ass! The 4×8 sheets are supposed to be butted together and have the seams taped with their special waterproof tape. It’s nearly impossible to get it down and taped without buckling, but after the first night of work, it was all down and laying flat. A few days later was another story. We came back to the room and there had been some movement and several seams were lifting. N un-taped those areas, trimmed the edges so they weren’t butted right against each other and re-taped. So far, so good. We suspect the rolls might have been easier to use than the sheets because there would be fewer seams. All the problems we had with buckling were at seams.

The next problem we ran into with the Delta-FL was that instructions said to use “low expansion foam” to seal the perimeter to the studs. I got a can of “Great Stuff” gap sealer and went around the perimeter. After a couple of hours, we went back to look at it, and discovered that the foam had expanded underneath the Delta and lifted it. Apparently Great Stuff’s product expands too much for this application. We had to lift the edges of the Delta and trim the foam off the slab. Fortunately, the foam didn’t actually adhere to the plastic very well. A silicone caulk would have likely been a better product to use.

Another tip for anyone else using this stuff. Once its down and flat, DON’T WALK ON IT. Lay out some plywood sheets and walk on those. Walking on the Delta will push it and you’ll start getting buckling and lifting again.

Step 4: Roll out the foam. The foam underlayment I got had a peel-off adhesive strip, so it was very easy to roll it out, peel the strip, and stick it down. Rolls were 3′ wide, so I could put down a 3′ width and then do 7 rows of planks before doing the next pass with foam.

Step 5: Lay the bamboo. I ordered my bamboo from It’s called “fossilized strand flooring” and doesn’t have the usual bamboo look where you can see the growth rings. I think the stranded is just bamboo cut into strands and then bonded together to form an exceptionally hard product. We opted for the natural finish, and for their “click-lock” system where each 5″ wide x 6′ long plank interlocks with the previous. There is no glue required and no nailing. Again, this is a “floating” system that allows for expansion and contraction so there are no anchor points anywhere and gaps all around the perimeter. Everyone I talked with and emailed during planning of this project at Calibamboo was fantastic. They know their stuff and are very helpful. I wouldn’t hesitate ordering from them again.

Around the perimeter of the room, you are to maintain a gap of approx. 3/8″ to allow for expansion. The baseboard trim will cover that gap. I cut a bunch of shims from 3/8″ plywood to use for maintaining proper spacing from the walls.

Instructions also tell you to begin laying the planks along the length of the longest wall first. That didn’t work in my case because that wall was interrupted by a closet. I actually had to do the narrow closet first, and plan it very carefully so that by the time I emerged from the closet along the long bedroom wall, I would be at a full plank width. You can only interlock the pieces in one direction, so it wasn’t possible to start in the room and then do the closet.

Interlocking the planks in the closet couldn’t have been easier. Outside the closet was a different story. The closet was 5′ wide. Planks are 6′ long. We opted to just cut each plank down to 5′ and not have any short runs in the closet. As such, I had only to lock one piece with another piece and they fell into place easily. Once we got out into the room where seams start to get staggered, I discovered it was much more difficult to get a plank to interlock with 2 planks because of that butt joint. On occasion I had to use a rubber mallet to “persuade” planks to lock. If they don’t lock perfectly, they won’t lay flat. Even with the difficulty though, I’m glad we went with this system. I think it would have been more difficult to glue a tongue and groove system and have the seams stay closed and tight as it was being walked on.

After a 6 hour marathon session, I had about 2/3 of the bedroom finished. I’m by no means a pro at this, and was learning as I went how best to do it with the tools I had available. A chop saw would have made cutting pieces to length much easier than the way I was doing it with a table saw. And to avoid bruises on the knees the next day, do yourself a favor and get a rubber mat or knee pads before beginning.

Other tips now that I’ve got this one under my belt. If you have access to a chop saw or radial arm saw, get it. Either would have made it significantly faster and easier to make cross cuts than the way I was doing it, trying to slide a 6′ long plank crossways across a table saw. Also, find a good tool store and ask for a 80 tooth, triple-chip laminate blade. The one I got is by Freud, ran about $70 and goes through this stuff like a knife through warm butter with a very clean edge. Bamboo is very hard, but brittle, so a blade with fewer teeth is more likely to cause chips. Lowes and Home Depot employees didn’t know what a triple chip blade was.

And the finished product.


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