What is a subfloor?
Question:I moved into a new home a few years ago and want to put marble flooring down instead of the linoleum that is there now in the upstairs bathroom...I was told I need to put in a subfloor? what is this and how difficult is it...
Answers:
A subfloor is a layer below your finished floor. Usually a subfloor in a typical house will be plywood, but the subfloor they're referring to for a marble floor is going to be a concrete backer board or Hardiboard. This is what you thinset the marble tile too. You will attach the concrete backerboard directly to the plywood floor with the appropriate fastners / thinset. You will then set your marble on top of this backing board.
A sub-floor is the underlay for the marble. It supports the marble.
a subfloor is a floor that is perfectly level and smooth that you apply the regular floor on. Its not hard but if its not done right the new tiles will not stay down they could buckle and crack if the subfloor is not flat and smooth
A subfloor is a sheathing that goes down onto your floor joists and under your regular floor panels. Usually, subfloor is made of 11/16" OSB board or 3/4" plywood (both construction grade) in 4X8' sheets, and then covered with the primary flooring, which could be hardwood, OSB, plywood, or marble. The subflooring provides a strong substrate onto which you lay your primary flooring.
The point is, you never put down your primary flooring directly onto your joists. You lay it onto a subfloor.
I hate to say this, but if you have to ask, you need to hire a professional. Especially when dealing with Marble. Not only will a professional do it right, but he will be insured in case something goes wrong.
Marble is a pricey way to go, so spend the extra $, and you will not have to worry.
If you were just laying regular tile, that is a different story. Tile is cheap (compared to marble)
Actually the terminology is subfloor directly over floor joists, underlayment over subfloor, and finish floor over underlayment. However, in this case, whoever said subfloor clearly meant underlayment. You need an adequate underlayment for marble, as you do with any tile, whether it is stone, ceramic, or porcelain. With the thickness of the subfloor, you need 1-1/8", to prevent deflection. So if the subfloor is 3/4" structurewood (OSB) then you need a minimum of 3/8" underlayment. You have several options. Hardibacker or Fiberock (USG product) Easy to work with, but not the best bond, but adequate. Concrete backerboard, harder to work with, but much better bond. Or Ditra-Mat or Map-Lath. Best bond, hands down, but expensive. For your purposes, concrete board is good choice. An option you have is, if the old floor, I assume you mean sheet vinyl, is to use 1/4" concrete backerboard over the old floor if it in good shape. However, it will raise the floor up higher than the adjoining floor. So you will need to put a threshold reducer strip down at the door(s) If you don't like the reducer strip, then you need to rip out the old floor down to the subfloor, and start fresh.
Zeebay gave you good info on a definition of sub-floors. But you already had a sub-floor in when you purchased the home. Maybe what the builder was referring too was a substrate under the marble, such as a cement backer board. Sub-floors are made out of wood and absorb moisture, while cement based backer boards do not. Since the adhesive used to install marble contains moisture, the existing sub-floor draws out the moisture in the adhesive too quickly and lessens its bonding capacity. That is why we install cement board OVER the sub-floor to install marble, unless it is installed over concrete.
Lynnt; they're probably talking about the backer board.
I suggest you go to this tilesetter forum. They have loads of good info on stone and tile flooring. http://www.johnbridge.com/vbulletin/foru...
Before you think about marble flooring your floor system [floor joist, subfloor, etc] needs to be strong enought for marble. The deflection [along the length of joist AND the floor material between the joist] needs a deflection of L/720. http://www.johnbridge.com/vbulletin/defl...
If in doubt you can always pose a question to the resident engineer there. just ask if "bbcamp" can answer your questions.
The sub floor is the sheeting.usually a 3/4" plywood.that is attached directly to the floor joists. Floor joists are the beams that span from one side of the house to the other and are usually 24 inches apart on center. Putting in a sub-floor is simple. The hard part is taking the old one out. I would recommend from experience screwing the new sub floor down to the floor joists with 2" screws rather than nails. The screws will prevent future squeaks that can happen when nails come loose. Good luck!
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