When I answer questions on my site I am always telling people to backbutter their tile. It has recently been brought to my attention that normal people (the ones who don’t stand in showers all day) have no idea what that means.
Backbuttering tile simply means spreading a flat layer of thinset onto the back of the tile before installing it on your wall or floor or whatever.
First you have to ‘comb’ the thinset onto the substrate – that means it is spread with the notched side of the trowel leaving little ridges. It should look like that first photo there on the right with the ridges all combed in one direction. This allows any air to escape from beneath your tile more easily.
(You can click on any of the photos for a fine example of my horrible photography skills…)
Then, before you install each tile, you need to spread thinset onto the backside of the tile with the flat edge of your trowel – the one without notches. This accomplishes a couple of things:
- It forces thinset into the body of the tile. It completely fills all the little open pores in the back of the tile. This allows the crystals of the cement portion of your thinset to grow more deeply into the body of the tile, leading to a stronger, more durable bond to your substrate.
- It gives the back of the tile a 100% bonding surface for the thinset on your substrate. Rather than having areas on the back of your tile which may remain open or unbonded because the thinset cannot fully bond to them, it covers the entire tile with a flat, bondable surface.
In my photos I am installing a travertine tile, which is a porous natural stone. This will exhibit the need for Backbuttering since you can actually see the open pores in the back of the tile. The same applies to porcelain or ceramic, or any other type of tile as well, just on a more microscopic level.
I am also using a tool called the back butter buddy. It’s that turquoise frisbee looking thing (although you may be able to get it in designer colors – I’ll have to ask Phil…). It’s simply a turntable of sorts that you stack tile onto so you can spin it around to spread the thinset. It makes things a lot easier with larger format tiles.
All you need to do is flip your tile over so the backside is up, throw a glob of thinset (that is a standard industry measurement – a glob…) onto the tile and spread it out, forcing it into the body of the tile. The purpose is to force thinset into the tile, so you want to apply a fair amount of pressure as you’re doing this.
The least messy way is to start with the glob in the center of the tile and pull it towards the outside edge. Always starting with the entire blade of the trowel on the tile. If you start with part of the trowel off the edge and pull it toward the tile you’ll end up with a nice bead of thinset along the vertical edge of your tile. It’s difficult to explain – until you do it once. Then you’ll know exactly what I’m typing about.
And it’ll piss you off. And you’ll have to flip the tile, clean it off, wipe it down, your dog may burst into flames…it’s a whole thing. So try not to do that.
Once it’s evenly coated you can be assured you have a 100% bondable surface on the back of your tile rather than randomly flush surfaces where thinset may or may not bond.
Backbuttering is necessary. With any tile 12 inches square or larger you need to backbutter your tile to ensure proper coverage. If you do not the thinset may not bond properly to your tile.
The photo to the right is a tile I removed from an installation that began having issues – not backbuttering led to a poor bond. While that was not the only issue here, it definitely contributed to the overall failure.
The bottom photo is the same issue – but these were installed ON THE CEILING! How long do you think those would have lasted before they came crashing down on someone’s head?
In both of those photos you can see that there is VERY little, if any, thinset actually bonded to the back of the tile. Backbuttering is necessary.
Backbuttering is only one step in the process of a proper tile installation. Every step that is done correctly increases the chances of a successful, long-lasting and durable installation. Every step you skip increases the chances of a failure. So take your time, utilize the proper technique and pay attention to detail. If you do that you and your dog will both live a long, flame-free existence.
Excellent site! Great details and I really like knowing why you are supposed to do it a certain way. If you know why you do it, you don’t forget and it helps when you have atypical situations. If you don’t mind a question. I am in the process of replacing just the pan of my 1950’s era tile shower. The walls are in great condition, I can live without a modern mixer. I am amazed that this shower was constructed with no waterproof membrane, no metal pan, no topical waterproofing, no drainage mat, no waterproof backer board. The walls are a layer of gypsum board, and layer of cement board, a thin layer of white masonry that looks like thinset (but I know thinset wasn’t invented yet, could it be grout?) diamond lathe, then a 3/4 inch layer of hot mud and tiles on top of that. The floor is nothing but grouted tile on mud (hot mud?) over a thin layer of what looks like tar paper (not hot mop), directly on the subfloor. Now the floor did start leaking around the perimeter after 70 years or so, and some tiny cracks are visible between the shower floor and the first row of wall tile which is why I am replacing it. Any thoughts on how we got by before PVC, hardibacker, redguard, and epoxy grout?
Most of the substrate materials used back then, such as plaster and mud, continued to absorb water after they were cured. There also should have been tar paper behind all that wire lath, which is still an acceptable moisture barrier behind cementitious substrates. Also, many of the adhesives used back then were solvent-based, which meant that they were essentially waterproof once cured, they let VERY little moisture into the substrates themselves.
Thanks for the 101 tips. Very useful tips!
I have a question. What do you use to attach “tile bookmarks”? In my shower I have 2 glass mosaic accent strips separated by 8×12 wall tile. The use of these spacers will make this work much better and easier.
I have no idea what you mean by tile bookmarks?
I think he means sorting the tile out so that the patterns or marks in the tile next to it will match like a perfect flowing stream. This is normally found in super high end homes. Not sure why someone would even bring it up here. Maybe watching too many 30 million plus home shows. Lol
Yeah, probably. I know what is meant by bookmarks, but in the context of the question (what the hell IS the question???) it makes no sense at all. What “spacers”. What do you want to bookmark with accent mosaic in between?
What the hell is the question???
Do you recommend wetting the tile backs with a damp sponge before back buttering, or is that overkill?
If it’s porcelain then yes, it’s overkill. With most modern ceramics it is not necessary, but it doesn’t hurt anything. If it’s a porous bisque tile then it definitely helps.
We are putting 12 x 24 tile on the floor and was wondering a few things:
What size trowel do we need to use?
How much thinset do we need to put on the floor surface…..
We will need to back butter with thinset the back of all tiles with the smooth side of the trowel as well?
Thanks so much for your assistance…
Read through this, it will help you with trowel size. The amount of thinset depends on the size of the trowel. Yes, with tile that size you should backbutter.
Hello dear fellow; I’ve got a possible “dah” question … but I want to be sure … so I opened my Laticrete 317 thinset mortar several months ago by cutting the bag in half … the half I didn’t use has been sitting on my bedroom floor opened to the world and air and such … that exposure doesn’t affect it in anyway, yes? I’m planning on using it this weekend to put up my shower tiles so need to be sure, as I said, it hasn’t been compromised … thanks
It can be affected, but likely isn’t. It can absorb moisture and humidity from the air, but that takes over a year of doing so to negatively affect it.
I would just like to thank you so much for indirectly helping me with waterproofing and installing tile in my bathroom (two) walls and floors. Without your insight and guidance, I do not think I would have been able to do as good of a job. It may not be 100% perfect, but my experience with installing tile has only been with these two bathrooms. I have the deepest appreciate and respect for you. Once again, thank you!
Thanks Dan! Glad I could help.
great info – how to backbutter a 6 x 36 plank?
sorry duplicate post
Hey Roger, I have the opposite issue, where the mortar stuck to the tile but not the substrate. I just pulled up a section of 12″ tile in a home from 1981 for a new closet and several tiles came up together from the foundation in a sheet, like the topping of a pizza! The grout appears to be holding the jigsaw puzzle-like tile of the entire kitchen together, floating on top of the concrete. I inspected and took pictures of the backside, and the mortar is well adhered to the tile but where the mortar should have adhered to the concrete, it is glassy-smooth. I am now planning to lay new tile and I’m concerned why the former install failed. Could the floor simply have been dirty, the concrete needed prep in some way, or possibly incorrect mortar? Any guidance appreciated. Glen
There could be several reasons it did that. As far as installing new stuff, splash some water on your concrete and see if the concrete soaks it up. It should soak it in with thirty seconds or so. If it does not then that means the concrete was sealed with something that prevented the thinset from bonding to it. If it does soak it in then it is purely incorrect installation in some manner. Either a dirty subfloor, not keying the thinset into the concrete, letting it skim over, incorrect mix, etc.
If it does not soak in water then the thinset will not bond well. You’ll need to chemically or mechanically scarify the surface of the concrete to remove that sealer.
Thanks for the quick reply Roger! I was thinking the same about prepping it, just wasn’t sure how to test/identify the former issue. I didn’t think the problem was the thinset, since it bonded very well to the tile and it would be odd to key it to the tile back and not the concrete. Any recommendation on the ‘optimum’ method of scarifying the surface, if needed? I currently have a 4″ diamond disc, and the area is perhaps 300 ft^2.
I use a 7″ scarifying disc. The 4″ will do it, but it’s a process. 7″ takes about 1/3 of the time. And make sure you have at least a shop-vac hose up to it, a cover that goes over the disk and hooks up to the vacuum is better. It makes a damn mess.
Thanks for the great information. Will be back to read / study. Any tip for applying thinset – backbuttering – 6″ x 36″ ceramic plank? glop at one end and …paint roller…?
Nope, it’ll end up all over the sides of your tile. I just start at one end and go crosswise over the tile the length of the trowel. Keep doing that until you get to the other end. You want to go the short way, your trowel is longer than your tile is wide, anything wider than what you are trying to backbutter will just make a mess.
thanks! just picked up a box and will practice on a plank. Not having done tile, will go slow and practice before going full tilt.
What do you think about just lightly skimming a Kerdi fleece wall
with thinset and back buttering the tile with normal trowel notch size thinset;
i.e., most thinset on the tile (kinda backwards, but easier to handle and cleaner)
by using the butter buddy. Thinset would still be on both surfaces.
It works fine, but takes AT LEAST twice as long.
On the thickness of the back-butter – how thin should that layer be? I’ve struggled with this from way too much to just a film of thinset. 1/8″ or less, or half the groove depth of the trowel used?
It’s just a film of thinset. It is to fill the pores of the tile, nothing more. That is not to say that you can’t add more if needed, and it likely will be, to get the installation flat in certain areas. But for the purpose of backbuttering it is only there to fill any pores or open areas in the back of the tile with thinset.
Thank you for continuing with the emails.
I don’t do any social media crap, so email is my lifeline.
Good writeup about keeping the tile off ones head.
Is the back butter buddy a product of the kitchen (lazy susan?), or can it be purchased?
It is tile specific. You can get one here. It’ll be blue instead of turquoise, ’cause I’m special like that.
I had to take down a couple of walls that had tiles like the ones you show in your photo. They had not been backbuttered and those tiles popped off with almost no effort, which was why I was redoing what had been done! Which was only a partial part of the total job, as it was failing even before it was finished.
The current shower has been up for a couple of years now, goes up 11+ feet on one side, over 9 on another, but still looks like it did when first installed, largely thanks to your advice and guidance.
The walls and floor of bathroom are plank tiles, the shower floor proper is mosaic tile. Thanks.
good post…although it would be better if you came up with a more precise volume measurement for the “industry standard glob”. is that about a golf ball size or a tennis ball size for a 12″ square tile?
It depends on the texture of the back of the tile. I just keep tossing thinset on there until I have the entire thing backbuttered.
I am in the process of laying tile now, but I have been ‘combing’ the back side of the tile along with the substrate and placing the tile down matching the lines together…..
Is this okay or overkill? It seems to be working for me and I have not had any issues…..???
Would you back butter mosaic tiles on a mesh for a ceiling ?
No, I normally only backbutter tiles larger than 12″ square. To put mosaic on a ceiling just ensure that you have them embedded well and every tile around the edge is up well. If one starts to come loose it’ll pull down the entire sheet before the thinset cures.
Thanks a lot for the reply! I am a bit unsure when you say 12 inches square. Is it anything 12 x12 or bigger?
I am using for my project 12×4 metro tiles (so they are 48 square inches), but inches square are not the same than square inches… Right?
Correct, it is different. However, you asked me about mosaics. Is each individual tile in that 12 inches square or larger? 1 inch square mosaics in a 12×12 sheet is 144 individual tiles per square foot – no, you don’t backbutter them. I backbutter when individual tiles are 12 inches square or larger.
Or are you talking about two different tiles? If so, no, don’t backbutter the mosaics – yes, backbutter the 12×4’s.
I used the term mosaic but the individual tiles are oblong ovals (I had a picture in my original post) and on the mesh it adds up to less than 1 square foot (I also have that in the pic). It is for the ceiling. The wall tiles are 4 x 12 metro tiles. With perhaps an insert of the same mosaic tiles somewhere or not….
It is clear from your reply that I do not need to backbutter the mosaic tiles for the ceiling.
Should I backbutter the metro wall tiles?
Oh, okay. Yes, you should backbutter the wall tiles.