I want to pour concrete over the particle board subfloor in my living room. I like the look of stained concrete. We have a crawl space underneath. What product do I use? How thick so it won't crack? Rebar, framing (or whatever that mesh is called) or no? Any info you got would be appreciated.
Frankly, Stacey, the thought of a concrete-over-wood floor frightens me badly. IF you can determine that your existing framing can carry that much additional "dead load", then definitely rebar and remesh (the mesh) well or it'll crack. You should know that the floor will want at LEAST 2" of thickness, which means each square foot of flooring will weigh at least 25 pounds, so the floor for a 12'x12' room would weigh a total of 3600 pounds (nearly two tons).
Talk with your local concrete companies - they may be able to mix a batch of lightweight concrete for your purposes - if you're dead-set on this. It WOULDN'T hurt to employ an engineer to verify that your structure will tolerate that much extra loading, though.
You do know that the concrete floor will be very cold underfoot, right?
EDIT: ...and that it'll always generate "concrete dust"?
An epoxy floor coating might provide a similar aesthetic to stained concrete due to diversity of finishes available. As a bonus:
it is likely to be easier to create consistency of appearance.
it is unlikely to require the substantial structural retro-fitting that is probable when pouring concrete over the crawlspace of a typical wood frame residence.
it will not create several inches of differential height between adjacent floor surfaces.
it will provide a more flexible finish and thus be less likely to crack as the wood structure expands and contracts with changes in temperature and humidity.
I hope t is obvious, but don't pour directly on the wood, The concrete wont cure right and the wood will fall apart. Heavy plastic or backer board would have to go down first. I doubt even a lathe and bar reinforced layer will avoid cracking. Joists bounce under load, bow when the temperature or humidity changes, and houses settle. Anything thick enough to support it's own weight over the span of a room would need special structural reinforcement on the wood support structure to hold it up. You might try backer board with a polymer-concrete overlay. It might be flexible enough not to crack. You'll want to do some research though. I suspect you'll want the backer board to "float" and you'll want to tape the backerboard seams with something pretty stout. Good luck and report back in the comments.
Such an old question... Well, I'm not satisfied with all these answers, so I put mine. I'll try to wrap most of them together.
General answer is: YES, You can.
But, as with everything on this world, come pros and cons of such operation.
- pouring concrete on particle board isn't a good idea without any isolation (like a foil); concrete is wet (when poured, by default) and any water will do no good here, even for a short time
- pouring concrete like 1/4" (self-levelling) will be ok and will look good... for some time; after that it must crack, as wooden structures are working more elastically, while concrete is solid, that means wood structures aren't best suited to coop with concrete elements
- concrete will have to be reinforced to avoid cracks (as mentioned above), even with greater thickness; it can be done either with rebars or with micro fibers (or both?) first ones will help this slab to work 'globally', second ones are to avoid local and surface damage; not a cheap solution...
- concrete floor will be (most likely) colder than wooden one, especially with a crawlspace; filling crawlspace with a concrete is also a bad idea (as Steve pointed out already); one can choose other material to choose from to fill the crawlspace
- concrete IS heavy, You can use 'lightweight' versions, but they may have worse parameters than regular one; once again - concrete is not ideally fit to wooden structures as it is very heavy, comparing to standard wooden elements
If You want to push, I would second TDHoffstetter's advise of getting some engineer to work to compute load bearings. Use foil, consider (at least) fibers reinforcement, consider thermal isolation (additional one).
I also like this 'Look' however having always though out of the box. I ripped up my carpet in my creative office space. I found the contractors sprayed the trim (a dark walnut) while still on the wall. They wrote measure ya and numbers etc in the floor- Very common practice. They left an ombré of stain around the room. I loved it! I wrote 'Beauty in everything' on my floor where my chair sits. I used a leveling product to fill in any gaps- I wouldn't do that again. It chipped hear and there. The I paint over the entire room (don't use latex paint). And rescanned it giving a white wash look. I covered it with several coats of very shiny gloss. And I was very happy with my finished product. I do touch it up where the leveling agent chips away. As I mentioned I would skip that part hind site. I plan on painting the subfloor in another room and using the high gloss again took me 4 days. To do all the extra steps. But I love my floor! And when we decide to change it-we can just cover it up. As a photographer I love the light that is increased using the high gloss. Btw my neighbors also did something similar. Using just stain on plywood( subfloors). Total cost for my office 11x 12' was -$60.
Pouring a concrete floor over particle board can be quite easy and rewarding. I have done this many times.
First, there is no need for 2" of concrete. I use only 3/4" thickness of "off-the shelf" concrete mix with aggregate no larger than pea-gravel. A sheet of water resistant plastic can be stapled down if there is living space below in case water from the concrete seeps through the cracks. Next, buy some truss plate connectors from a Lowe's and pointy side up, screw these down to the subfloor at about over 16 o.c. over the black plastic.
Now, you're ready to pour concrete. If you're not good at this, hire a stamping crew for a professional job. No need for expansion or control joints as you are tying the concrete to the subfloor rather than rebar. If done right, you'll have no cracks and the floor will only need a sealer every five years. Good Luck.
In my current house the front rooms have a crawl space (about 3' deep) under the original victorian flooerboards. There is laminate on top of the floorboards and a very thick rug. When it is cold outside, the floor is also quite cold, even if you are on the rug.
In the back rooms the previous owners filled the crawl space and poored concrete floors (not polished or stained or anything) and there is carpet over the concrete. These floors are much warmer.
So you might want to consider filling the crawl space. It will eliminate the risk of your floor collapsing under its own weight. I don't think having concrete over particle boards is an option. Even for ceramic tiles it is not advisible to put them on a particle boards subfloor, let alone concrete.