Can I Tile Over Hardwood Flooring?

We ran into this situation on a recent project and it seemed like a good time to talk about it.

Even though personally I would rather listen to Miley Cyrus talk about politics than to allow anyone tile over hardwood, the long and short of the answer is yes, you can.
The real question is; Why would you want to?
You have to remember that the same rules apply for tiling over hardwood as do for tiling over any suitable substrate.

Let me illustrate:

This is a picture from one of our jobs where ceramic tile had been installed over 2 1/4" oak flooring. We discovered it when removing the tile to install an updated tile.












 
As you can see, the tiles came up with little of the thinset mortar still attached to the floor. This is a perfect example of a poor bond. When we look at the tiles themselves, you can see that the thinset had no problem staying attached to the back of the tile.







After the tile had been completely removed from the area, this is what the floor looked like with no major scraping.

Barely any real adhesion had occurred.

So let's talk about these "rules" for tile installation. There are three very important things you always want to be aware of when you are installing a tile floor.

Rule #1: Motion is your enemy. 

Anytime you install a tile floor, you want the surface you are tiling over to have minimal motion. If a floor moves, tiles can loose their bond and/or crack along with the grout lines.

Things that may cause your wood-frame floor to move:

1. Undersized framing: Older homes may have been built smaller framing than code currently requires. It bounces and flexes more than the beefier framing of today.                                                                                           
2. Wider framing layout:  Another situation we often find in older homes is that the framing is wider than 16" on center. This forces the subfloor to span a longer distance and allows it to flex more than in a newer home.                                                                                                                                               
3. Unsuitable subfloor sheathing: In older homes you may find wide plank floor boards, newer homes usually require 3/4" plywood as their subfloor. When it comes to installing tile, the rule of thumb is to have at LEAST 1 1/4" of subfloor sheathing underneath to provide the necessary strength. That means that if you have 3/4" plywood, you need to add another 1/2" layer of substrate over it to create a thick enough subfloor (always run additional plywood layers in the opposite direction of the previous for added strength). I like to fasten additional layers with 1 1/4" galvanized screws at 6" on center, 2 1/2" screws along the framing lines. This gives the entire floor frame every opportunity to lock itself together tightly.                                                                                                 
4. Improper fastening: Sometimes the subfloor is not properly anchored to the framing and can move which can result in tile bond failure. Don't be afraid to dance around on your subfloor before you tile. Spreading your legs apart and leaning side to side like your trying to tip a boat over is an easy way to spot creaks and squeaks which can often be cured with additional fasteners.

Plank (hardwood) flooring is more susceptible to motion because there are many more individual pieces which can (and will) expand and contract at different rates. The only way to minimize this is to make sure the hardwood flooring is fastened as securely to the subfloor as possible. This means you'll need to nail through the face of the flooring to make sure it has the best chance of staying in place.

Rule #2: Surface must be clean for a strong bond.

Hardwood flooring is usually finished with some form of polyurethane. The nature of this finish will tend to reject things that are trying to bond to it (including your tile adhesive). To tile over hardwood, you'd need to clean it first, preferably with mineral spirits to remove any build up you may have on the surface. Any waxes or soap that have been used to maintain the floor over the years will leave a build-up that is awful for adhesion.
Sanding the floor with a low grit sand paper (30 grit or lower) would create a better bonding surface. Rough wood makes for a much better adhesion. Also, the less porous a substrate is, the harder it will be for thinset to bond to. Another reason a finished hardwood floor isn't the best candidate for tile installation.

The natural surface of cdx plywood provides a rougher more porous surface to allow thinset to adhere to.

Rule #3: Use a premium modified Thinset mortar 

This is extremely important.  All your other steps will be for nothing if you don't use a high grade latex/polymer modified thinset mortar. These modifier additives help improve the bonding and flex characteristics of the mortar. You can purchase liquid additives though I've found the high end, pre-mixed powders have excellent bonding strength when properly applied. Make sure you don't mix your thinset too dry. A drier mix can have poor adhesion. You're looking for a consistency somewhere between pudding and peanut butter.

In conclusion: Why we don't recommend tiling over hardwood

Having read the steps it would take to even consider hardwood flooring as a suitable surface, it's usually just easier to remove and replace it with a decent cdx plywood or cementitious backerboard substrate. The grain of cdx plywood is perfect for creating a long lasting floor tile bond. There are those that would say using a tile backer board is preferable but when it comes to floors, I still prefer to put down a material with the ability to carry more weight. Although backer board has excellent moisture resistant qualities, I can snap most backer boards without a lot of effort. Backer board is much better suited for non-traffic tile installation in moisture heavy areas such as shower stall walls or counter tops in my opinion.


So in conclusion; Follow the three steps for any tile installation, don't tile over your hardwood because it's just silly and always remember to floss! (That has nothing to do with flooring but my 8 year old son can't seem to remember to do it so, I find myself constantly saying it.)

Do you have a flooring nightmare project on your plate? Drop us a line in the comments below and we'll see if we can help! 

FLOOR TILE: Does SIZE matter?

Janice T. sent this question to Ask A Home Improvement Expert:

"We've been thinking about changing the tile in our bathroom but we aren't sure which size tile we should use. Is smaller tile better for a bathroom?"

 

That's a great question!.... and it's nice to finally have a woman ask a man if size matters.
My personal opinion is that the more grout lines you have, the busier a floor looks. A lot of people grew up looking at their parents bathrooms with tiny mosaic tiles and mauve colored fixtures.
You've seen how your parents used to dress, do you really want to use their sense of style as a point of reference?

                                                        

{{{shiver}}} Yikes......Anyway, I always start by trying to use the largest tile I can in a given room. The reason I start here as I said, is that more grout lines make a floor look busier and unfortunately
Busier = Smaller. I don't want a small room to feel even smaller, I want it to feel spacious and open. Larger tiles can make a small bathroom feel bigger. There is no rule saying you can't use 18" x 18" tiles in a 50 sq. ft. bathroom. It's all about the look you are trying to create. However! There are a few issues that can potentially sway the choice of tile size that  you should always take into account.

How level are your floors?

Run a level over your floor before you make any decisions to spot the inconsistencies in your floor and to see which way it may be pitching. Smaller tiles have the ability to conform to these inconsistencies. In a perfect world, you'd never want to have a floor with a lot of pitches and rolls but often in homes that are 150-200 years old, the best you can hope for is to minimize the motion of the floor. If you tried to get it back to perfectly level, you'd likely end up with a floor that's much higher in some areas than you want. This is especially troublesome when the doorway transition ends up being over an inch out of level (unless you enjoy watching your friends trip in and out of your bathroom). In these cases, we are try to get the floor to be as FLAT as possible... not as LEVEL.
Larger tiles such as an 18" x 18" are more difficult to lay flat due to the fact that each tile covers so much floor space. If the area you're working is a little higher in the middle of where a tile lands, you may find that corners of your tiles are left sitting up higher than you would like. Sometimes adjusting the layout of where your grout lines will land can help work around some of these problem areas.

Desired Effect

Is there any other tile in your room? If there is a specific tile pattern on your walls or shower, it may dictate how you want to approach your floor. There are common styles that people are trying to recreate or achieve that can help determine the floor tile. For example, A subway wall pattern: We often see a smaller mosaic tile pattern with subway-style tiled walls.

There are no hard and fast rules but, there are applications that you may have seen and are subconsciously trying to recreate.

If you are simply looking to update your floor, I  would suggest picking color before size. It's often more important to get the color you desire and you may find that the color you love? Isn't available in every size and shape. Your question may be answered before you ask it!

Bathroom usage

Is this a bathroom that gets a lot of family use? If it is, I would point out that for every grout line you create is also one you need to maintain. Grout needs to be cleaned and sealed according to usage, sometimes as often as once a year. A full bathroom with 5 family members and a dog that  you can't seem to keep clean no matter how many times you wrap him in plastic, will be subject to more water and soil on the floor than a half-bath connected to a guest room. (I'm kidding, don't wrap your dog in plastic.....kids are optional)
Fewer grout lines can also mean fewer possible areas for moisture to get through to the substrate if those grout lines ever open up over time. Remember: More grout lines = More maintenance.

Grout color

Grout color will affect your choice as well. There are two ways to go with grout color, one that blends or one that pops. Both have their advantages in certain situations but more often I try to find a grout color that blends with the color of the tile itself. This helps keep whatever floor tile I choose feeling like one consistent floor not like a bunch of smaller pieces. I see this mistake a lot, a bad grout color choice making a floor look too broken up. Example:

I also tend to avoid very light grout colors in favor of more neutrals because lighter grout colors are much more difficult to maintain and they discolor quickly. I only use white & off-white grout when it's specific to the effect the customer desires. Which brings me to my last point:

Personal preference

What do you like? I always ask potential customers to pick out a few pictures of bathroom floors that they think are cool. When a customer shows me three pictures of bathrooms all with larger style tiles or perhaps all with a particular pattern, it makes finding their solution simpler. Sometimes I even find they don't like the floors they've shown me at all, they actually like the color, layout or style of a room. It's important that whatever you pick works with the room itself and when in doubt? I would suggest that something simple, clean and neutral often works better than something bold and intricate. It also allows you to update other elements of the room over time without limiting your choices.

So, there are no universal answers but there are certainly considerations in making your choice. Try to ask yourself these questions before you make a decision or Ask A Home Improvement Expert!

As always, I'm Daniel and I'm a General Contractor. (<--- and that's still a link)

-Cheers!