There’s a lot of ways to screw up tile installation. You can have not enough mortar underneath the tile and it won’t stick. You can have too much and it comes up through the grout joints and makes a big mess! The tiles usually don’t tell you which trowel to use. So what’s the secret? Can you just buy one size of trowel and use it for everything?
Why all the different trowel sizes?
All a notch trowel does is provide a way to gauge how much thinset mortar you put down. You use the notch trowel and you can put down the same amount of mortar every time. What you want to do is put down enough mortar to get complete coverage underneath your tile. Different tiles require different amounts of thinset. Also different underlayments require different amounts of mortar.
How are notch trowels measured?
Trowels are measured by the length, depth, and spacing of the notches, or teeth.
U-notch vs Square notch
I’ll be honest with you. I don’t really know the difference between the U notch and square notch trowels. It’s my understanding that there is a slight advantage to the U notch but I couldn’t tell you what it is. For the purposes of this post I consider square notch trowels and U notch trowels to be the same thing. If I list a 1/4″ x 1/4″ square notch and you purchase that size in a U notch then you’ll be ok.
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What is the best trowel size to use?
This depends on a lot of factors. What are you installing? Membranes, cement board, tile, or ? What size tile? Which membrane? Below I have some general guidelines on which trowel size to use for different situations. This is just a guideline and you’ll have to try it out for yourself. What you want to achieve is the best possible coverage without getting too much mortar down.
Some of the factors involved in this are: The size of the tile, the thickness of the tile, how big and deep the depressions on the back of the tile are, the consistency and type of thinset being used, and the surface that you are installing over.
So start with this list below and you may have to fine tune things from here.
1/8″ x 1/8″ notch trowel : Primarily a trowel to use for installing thinner membranes. After all, the Kerdi trowel is simply a 1/8×1/8″ notch trowel. Use it for installing kerdi, Valueseal, Hydroban sheet membrane, USG Durock shower membrane, etc. I can’t think of any tiles that you would want to use this trowel for.
1/4″ x 1/4 ” (3/16) V-notch: I use this trowel and the Ditra trowel interchangeably. So this is a great trowel size for uncoupling membranes. Also I use this trowel for small thin glass tile mosaics. This may also be a nice trowel size for thin mosaics up to say 2×2 inches.
Which Thinset to use: Infographic
1/4″ x 1/4″ square notch: The most common trowel size in the tile industry. Use this trowel to install cement board on floors. Yes, you need thinset under your cement board and, no, construction adhesive isn’t the same thing. Also, use this trowel for installing Ditra Heat and Prodeso Heat membranes. A great trowel for installing small ceramic tile such as 4.25 x4.25, 6×6, and 3×6 subway tile. This may also be a good trowel size for thicker (5/16+) mosaics.
1/4″ x 3/8″ square notch: Use this for 8×8’s and some of the 5/16″ thick 12×12 builder grade tile. Even some of the 4×12+ bigger subway-type tiles. Daltile Modern Dimensions and such.
1/4″ x 1/2″ square notch: The 1/4″ x 1/2″ x 1/4″ square notch trowel is good for 12×12’s and 13×13’s maybe even up to 16×16’s no more than 3/8″ thick.
1/2″ x 1/2″ square notch: I use this trowel size for any large format tiles. 15 inches and larger. Including 12×24’s, 16×16’s, 18×18’s, 12×12 marble and granite, and the popular 6×24 porcelain plank tiles.
3/4″ x 3/4″ square notch: Anything bigger than what’s listed. 24×24’s maybe. Larger 24 inch natural stone. It’s rare that I use this trowel size.
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Smaller than 1/8 notch: A trowel size smaller than a 1/8″ square notch trowel is usually for glues. While I occasionally use glues with some of my installations (Noblebond EXT for example) it’s not very common. The manufacturer of the glue will usually have a trowel recommendation for their product.
Euro notch and slant notch: The Euro notch and slant notch trowels are supposed to be trowels to give more complete coverage. The idea is that they form notches in the mortar that are easier to collapse and leave less air pockets. I have yet to use one of these types of trowels but they are supposed to do what they advertise. However they really aren’t necessary to achieve proper coverage underneath your tiles. You can use them if you like and the Euro notch is always listed with a cross reference to which size trowel it compares to. For instance, it will say “use instead of a 1/4″ square notch trowel”.
The proper notch trowel size is important to a successful tile installation. This guide should get you started in the right direction. If there’s something that hasn’t been covered please let me know in the comments.
Evelyn says
Hi Jim!
I was wondering if a 1/4 x 1/4 square notch trowel would be suitable for 7×20 tiles that I am laying down in my kitchen? I went to a tile shop and they told me it’d be okay. I am seeing many posts on 1/4 x 3/8 but no one really mentions the 7×20 tile I will be using. Appreciate the help!
DIYTileGuy says
My post is simply a guideline. It’s up to the installer to determine the Trowel size that will give the best coverage.
However for most tiles that size I would probably use a 1/4×1/2 of even a 1/2×1/2. You could probably use a 1/4×1/4 and use the notched side on both the floor and the back of the tile. This would kind of like be using a 1/4×1/2.
Evelyn says
I appreciate the input, I will take that into consideration as well. Great site, it has definitely helped me with my kitchen project. Keep up the great work, Thank you!
William says
Is it ok to use a 1/2 x1/2 trowel for a 8×48 tile. That’s what I read before.
DIYTileGuy says
I hate to say it but- it depends. The key is to get enough mortar under the tile. Will a 1/2 x 1/2 inch trowel do that? Possibly. But this is where floor flatness, mortar consistency, and tile warpage come into play.
So I think the question to ask is: Am I getting enough mortar under my tile?
I would check this frequently by picking up the tile and looking underneath it. You may find, for example, that the center’s aren’t getting enough mortar. You may find that you have to notch both the floor and the back of the tile. This may require two different size notch trowels. You may find that you have to notch the center of the tile and back butter (flat trowel) the ends. The trowel is just a tool to gauge the mortar.
But I typically start with a 1/2 x 1/2 notch trowel and adjust from there.
art geis says
Hello, putting down large profile trav in a french pattern. I need very exact measurement at transition to the
new hardwood floor…..
I have to build up the subfloor of this tile entryway 2 1/4″. I will use a combo of plywood and hardie board. 1/2″ trowel thinset……should I estimate the thinset at 1/2″ or 1/4″.
So in your estimation how much is the thinset compressed?
Appr your thoughts
DIYTileGuy says
I just ran into this situation and chose to bring the floor up with mud (drypack) rather than plywood/hardi. However, to answer the question I would say that a 1/2″x1/2″ notch trowel would leave less than 1/4 inch of adhesive. Probably more like 1/8-3/16. But you can always bring things up rather take away material. Your probably best leaving yourself about 1/4 inch and adding a bit more adhesive at the entry if necessary.
Brian says
People often forget to calculate based on the angle of the trowel. For example, a 1/2″ square notch is usually said to leave a 1/4″ bed once the half inch notches are all flattened out. However, since you comb the trowel at a 45 degree angle, you are effectively reducing the height of the notches to SIN(45)=.707, or 71% of their actual height. The 1/2″ square notch then leaves a .25*.707=.176″ bed; or just under 3/16″.
DIYTileGuy says
Correct! Also, the metal teeth wear down in a non-uniform way. It’s basically impossible to come up with an exact measurement for mortar thickness for several reasons. But your measurements are probably the best answer so far.
Gary L says
Hi, and thanks for your service to us all!…..installing 48″x8″ planks……slab on grade floor, i tore out previous 12″x12″ ceramic..of course, previous thinset still VERY firmly on floor…but pretty darn level!…..do you reccomend a leveler type product to cover previous trowel lines?, or as long as its flat, im ok to go over?….. ive done tons of ceramic, but these are my 1st planks…(using in my kitchen)
DIYTileGuy says
The proper way to do it would be to grind down the old thinset. Probably using dust-free grinding equipment (shop vac, dust shroud, etc). But if the thinset is down good then you can probably go right over it and have the tile bond to it. Obviously your floor height will be higher than before.
Jay Son says
Nice article. I’m getting ready to start my first tile job in my small shower. Using 10×13 tiles. I plan to use a 1/4 x 3/8 trowel, or would a 1/4 x 1/2 work better? Also, what trowel can I use to apply thinset in the niche? Would it be ok to back butter the tiles instead of spreading it on the back/sides in the niche?
Thank you for the help and great site!
DIYTileGuy says
I would start with the 3/8 trowel and see how that works. I would think that would be the one to use. And it’s OK to back trowel the tile. A best practice would be to flat trowel the surface also. In this case that would be the niche.
william hunter says
Great article, I cant find a good answer to this though. I am about to start 3 tile projects all of which are on a slab. The first is Wood look tile (LFT) in my kitchen so i plan to use LFT Thinset and a 1/2 x 1/2 trowel. The Second and third are just a little out of my “norm” meaning i just have never laid Mosaic tiles on a floor application. My master bath we have 12×12 sheets of white marble mosiac tile each tile on the sheet is roughly 2″x2″, I was planning to use white thinset and a 1/4 x 1/4 Square notch. I am not sure that it will make a huge difference, but i was thinking to maybe use the 1/4 x 3/16 V notch instead? These tiles are roughly 1/4″ thick if that matters, Any input?
Also, my quest bath we are using a 12×12 ceramic tile mosaic (the small circles that are about 3/4 to 1” each). these tiles are thinner, like 1/8” thickness. Originally i was going to go with the 1/4 x 1/4 square notch but there are too many options. Do you think ones better than another for these tiles on a floor application?
DIYTileGuy says
The 1/4 inch square notch might work for the 2×2’s or it may be too much. If so, I would step down to the 1/4 inch V-notch. The same V-notch will probably work for the smaller round tiles.
But you always have to make your own assessment.
peter sooklal says
thanks for all the info very informative and to the point
vince says
installing 6 by 6 cheap Home Depot tile on shower wall, what size grout lines do you recommend? also, what size trowel would you use?
DIYTileGuy says
The 6×6 tile have built in spacing lugs on the sides. So you can set them tightly together if you like but you’ll need to use an unsanded grout. You can space them further apart if you like also.
A 1/4 x 1/4 square notch trowel would be the best for those.
Kristin says
When it comes to level systems using straps, caps and a plier, what is the best way to determine how many of each are needed with 6×48 tile? It’s a large job- 2400sqft
The manufacturer didn’t list this size in the formula.
DIYTileGuy says
I just looked at the download page for MLT systems and it looks like they figure 5/per tile (1 side only) for 16cm x 120cm plank tiles (6×48). That’s if I’m reading and converting things correctly. It’s Italian and in metric. Here’s a link to their download page and I downloaded the layout chart.
The only wedges (or caps) that you will need are enough to keep busy for a day. They can be reused the next day after removal.
mlt system layout calculator
Kristin says
Thank you very much for your quick response. This is helpful.
Vladi says
I have 24″x24″ tiles and what better trowel size for my tile work?
DIYTileGuy says
1/2 x 1/2 or 3/4 x 3/4
Brooke says
I am applying a custom mosaic floor tile in my 1920’s home. The individual tiles are 3/8″ square and I am also using 1″ hexagon mosaic. What trowel notch size would you recommend for such a small tile size?
DIYTileGuy says
It’s hard to give a definitive size but a 1/4 x 5/16 V notch towel would be a good one to try. Also a 1/8 x 1/8 square notch may work for the smaller tile.
You want as much thinset as possible under the tiles without the mortar coming up through the grout joints.
Will Marzolf says
I will be installing 7″ x 71″ ceramic plank tile on walls and a ceiling in a commercial setting. Trowel size is detrimental to the safety and quality of the finished product. I do not want too much thinset as it could keep the product from firmly staying in place while curing. Would love your recommendation for an appropriate trowel for this task.
Thank you
DIYTileGuy says
I understand what you are asking but understand that trowel size isn’t a detriment- the trowel is simply a gauge of how much mortar goes underneath the tile. The bottom line is that you want to achieve is 80% minimum mortar coverage underneath your tiles. How you get there is open for debate. I would be absolutely shocked if a 1/2″ x 1/2″ trowel will get you 80% coverage. I don’t think it will get close. So that means that you are going to be putting a lot of mortar under those tiles.
Too much thinset isn’t your enemy. Too little is. I’ve installed plenty of tile on ceilings before. If you want to skimp on mortar then make sure that you wear a hard hat because too little will cause them too fall off and crash. A generous amount of mortar will allow them to suction onto the ceiling. The suction is what you want.
Nate says
From what I understand the only advantage of using a U notch instead of a square notch is when you push your tile into the thinset, the U notch spreads from the bottom out and the square notch has a greater chance of folding over and trapping air. I still prefer square notch over U notch though.
Nate says
Also a U notch lays down less thinset than the same size square notch.
DIYTileGuy says
Good feedback and makes sense. Thanks!
Colleen says
Though enthusiastic, I have minimal previous tile experience, but plan to do quite a bit of it in a small house under construction right now. First up is a pad under a freestanding woodstove. It’s about 31″ x 40″. We’ve got concrete there now. The tile I’m planning to use is sandstone 12 x 12, 3/8″ thick, smooth on both sides, with a border of 1 inch mosaic tile. I watched a very credible YouTube video (he’s a pro!) that said natural stone tile should be buttered smoothly on the back, in addition to the notched application of thinset on the floor, and coverage should be at least 95%. Does that sound reasonable to you? It sounds like you would recommend a 1/2″ square notched trowel?
DIYTileGuy says
Yes. What the installer is referring to is called “back buttering” and it is a best practice.
For a trial size, a 1/4×1/2 notch trowel would probably be perfect. You’ll run into some issues with the mosaic border, though.
You might check out my post on shower accent strips for a way to install those. But do the big tiles first and save the border for last.
Brian says
It is either the best practice, or it isn’t. It can’t be “a” best practice, because that would suggest it is one of many best things. Only one thing can be best. Stop letting marketing folks mess with you.
Other than that… 🙂
Thanks for the tips on the accent strips. Good idea, there.
DIYTileGuy says
“A best practice is a method or technique that has been generally accepted as superior to any alternatives because it produces results that are superior to those achieved by other means or because it has become a standard way of doing things, e.g., a standard way of complying with legal or ethical requirements.” ~Wikipedia [emphasis mine] https://en.wikipedia.org/wiki/Best_practice
Bill D says
I’m laying down Marazzi 8×24 plank tile what size notch trowel would you suggest…
DIYTileGuy says
If it were me I’d use a ½ x ½ square notch but a ¼ x ½ notch may work ok also.
Billie Jo Boughter says
Hi, I saw a similar comment and response to a guy installing 7×71” plank tile. I will be installing something similar in size, that being 8×68”. I didn’t quite understand your answer. You didn’t think he would achieve 80% coverage with the 1/2”x1/2”. For my application on a wall, would you recommend the 3/4”x 3/4”? How do you know when you have good coverage? Your tile will stay on it’s own while drying?
DIYTileGuy says
The 80% coverage guideline is for dry areas but if it’s a wet area, like a shower wall, then the guideline moves up to 95%.
So to achieve that would require at the very least a 1/2 inch notch trowel and probably more like a 3/4 inch and you still may not get there.
You may have to notch the back of the tile in the middle in addition to the wall. The tile may not require a 1/2 inch notch- you may only need a 1/4 x 1/4 inch square notch. But the middle of the tile is where you’ll see the lightest amount of thinset.
To check for coverage, simply pull the tile back up after installing it. You’ll have to guess the amount of coverage that is there but if you see thinset notch lines then you don’t have enough mortar under the tile.
paul says
What size trowel would you recommend for a 6″x36″ plank tile? Can’t tell if this one falls under the “larger than 15” for 1/2 square trowel or the “bigger than listed” 3/4.
DIYTileGuy says
1/2 or 3/4. Probably bigger is better for those tiles.
paul says
Thank you. What are the consequences of using too much mortar because the notch size is too large other than going through the stuff faster and paying more? Is it more important to not use too much with thinset like CBP flexbond vs medium-bed mortar like the large format tile stuff like CBP ProLite?
DIYTileGuy says
Besides what you’ve mentioned, the consequences are that:
1.you can exceed the limits of the mortar by it being too thick of an application. This is more of a danger with thin bed mortars than it is with medium (LFT) mortars.
2. It makes for a messy installation as the mortar will come up through the grout joints.
To much is probably preferable to too thin assuming you’re within the thickness limits.
paul says
If I get a trowel that’s a bit too big, like 3/4×3/4 instead of 1/2×1/2, can I compensate by holding it at a flatter angle as I cut the notches? I mean something like 30 degrees or less instad of 45 degrees.
DIYTileGuy says
Yes, you can. You can also mix your mortar thinner/thicker.
paul says
Could you please explain how the mix thickness would help? Seems like if I mixed it thinner I would get the same bead and the same coverage but there would be less actual mortar material behind the tile once it dried and the bond would be weaker.
DIYTileGuy says
So one of the issues with having too much mortar is that it will come up through the grout joints and make a big mess. Also, it can work to not keep the tile high enough.
By mixing the mortar thicker you can probably negate this result.
On the other hand, if you find that your mortar thickness is plenty high you could mix the mortar thinner and maybe that helps counteract this issue. You may choose to do this if you are coming up on a higher section of a floor or if you need to meet up with a lower neighboring flooring such as hardwood.
But, for the most part, you should just keep the mix consistent. A 3/4 inch notch trowel should do just fine for 12×24’s and larger.
paul says
How do you estimate how thick a layer of mortar will be based on what trowel you’ll be using? I need to build the floor up to a specific level, the bottom of a cast iron toilet flange, and I know the thicknesses of all the materials except of course the mortar. I was thinking figure out the cross-section of the notches in the trowel per inch then multiply by sin(30 deg)=1/2 to account for the angle I’ll be holding it at. (so for a 1/4×1/4×1/4 square notch, it’s (0.25*0.25/(0.25+0.25))*1/2=1/16″) Sounds over-precise but I know it’s an estimate. Is there a better way?
DIYTileGuy says
There really isn’t a reliable way of doing it. What further complicates the issue is the flatness of the floor, what size the tile is, and what the pattern is.
For example, you may have a hump in the floor 2 feet away from the toilet flange. If you measure the area right near the flange you may calculate one thickness. However, because of the hump in the floor you may have to build the tile up higher than you anticipated.
But I think your calculations would be extremely close for an ideal installation. You can always make adjustments as you go such as double notching (the floor and the tile) or holding the trowel at an even more extreme angle.
But if it needs to be exactly precise, I think buying the trowel and field testing is going to be most accurate.
Russell Gibbs says
I am about to install ceramic wall.They are 3/8 thick subway tile 3 inches wide by 12 inches long.Would love to know which size trowel would be best. It is a kitchen backlash on drywall.Thanks
DIYTileGuy says
Probably a 1/4x 3/8 inch notch trowel will work for those.
Pam says
Hi! I have a 2.5 x 8″ tile for a backsplash. Do you think the 1/4 x 1/4 square notch will work, or should I move up to the 1/4 x 3/8″? Thank you!
DIYTileGuy says
It depends on the tile but a 1/4 x 1/4 square notch would probably work. If not, the 1/4 x 3/8 would be what I would suggest.
Randy says
We are installing 12″x12″ blocks of penny tile for our kitchen backsplash. Will a 3/16″ v notch trowel be ok or should we go with the 1/4″?
DIYTileGuy says
The V-notch will probably be ok for those. If you’re getting thinset in the joints then I would down grade to an 1/8 x 1/8. But the V-notch is what I would guess would be best.
Bill Albertsen says
I am installing 1×2 inch split face carrara tiles in 1×1 sheets on a wall.no grout. Will 1/4 square ntvh trowel work best?
DIYTileGuy says
That will probably do ok. It’s best to pull a sheet back off and see how well it’s covered. If it’s not covering well then it’s best to step up to a 1/4 x 3/8.
Paul says
I’m going to install 8″x48″ plank tile. I also want to back butter the tile. What trial size should I use for the floor and what size for the tile?
DIYTileGuy says
Well, it always depends. But if you are going to notch tried both sides then you might try a 1/4×3/8 notch tried on both and see how that works.
Jon says
For a shower wall with hardibacker covered in Kerdi, and installing 12×24 porcelain tile, would you recommend 1/2 x 1/2 trowel, or 1/4 x 3/8 trowel with back butter? I think 1/2 x 1/2 with backbutter may be overkill?
DIYTileGuy says
I would use either a 1/2×1/2 or a 1/4 x 1/2 inch notch trowel
Gary says
What size trowel should I use for installing a 6″ x 30-40″ x 5/8″ thick marble shower curb sill?
DIYTileGuy says
A 1/2 x 1/2 or 1/4 x 1/2 notch trowel should be fine. 1/4 x 3/8 trowel would probably work, as well.
No matter what trowel you use you want to make sure that the thinset coverage is good under the sill.
Cristian says
I’m about to install a mosaic marble backsplash in my kitchen. The wall is painted and the Flexbond rep told me I can just sand it to get good adhesion. So I bought flexbond, but now I am not sure what trowel size to use. In the Home Depot video using flexbond to install backsplash, they use a 1/4″ square notch for small marble mosaics. I thought it should be 3/16 V-Notch. The largest tile in the mosaic is 1.5″ by 7″.. I bought a 3/16 V notch but I can return it if it’s the wrong one.
What towel size would you recommend?
Their video also shows mixing grout powder and then it becomes a huge mess over the marble. Would the pre-mixed grout be a lot easier to apply than the mix yourself?
The video is here:
https://www.youtube.com/watch?time_continue=207&v=2lRBvYsono4
The grouting looks terrible.. and marble is easily discolored I heard. Your advise would be appreciated! My stone is similar to what they’re installing, but with wider pieces.
DIYTileGuy says
I think a 1/4 inch square notch trowel would probably be the correct size but it always depends.
White thinset mortar is what you are going to want to use. Yes, the kind that’s a powder and you add water to it. Premixed adhesives aren’t what you want for marble.
For grouting, you’ll want to read the instructions for all products involved- including the marble. But presealing might be a good idea. Either with a natural stone sealer or with a grout release.
Imran says
Sir i am installing 32″×32″ porcelain tile what is the recommended notch if i have very flat stucco and i also want to backbutter tile
DIYTileGuy says
No less than 1/2 inch notch would be my opinion
susan says
hello,
what is your trowel recommendation for an 8″x8″ ceramic floor tile?
thanks much
DIYTileGuy says
Depends on how thick and what the back of it looks like. Maybe 1/4 x 3/8?
Dan says
Installing 18”x18” x 3/8 porcelain tile on a flat smooth concreat floor . Would A 1/4” x 1/2” notch trowel , be sufishent , and would you recommend back buttering as well ?
DIYTileGuy says
That trowel would be a good one but I always recommend back buttering no matter what size trowel. 🙂
Jerry Billington says
Hi Jim ,
I have porcelain tile that is 4×24 and I was told by a tile guy a 1/4×1/4 trowel was ok . I am half way thru my house and read on another place should have been 1/2 x 1/2 trowel . This is my first time doing this so I’m confused and will what I laid so far be ok ?
DIYTileGuy says
Trowel sizes are only guidelines. The only thing that truly matters is how well the mortar is covering the back of the tile. You want to aim for 100% coverage. So I would check the coverage on the backs and let that tell you if the size of trowel is ok, or not. My guess is that you will need to step it up to the next size. You might also try back buttering the back of the tile if you aren’t already doing so.
Bob says
i’m installing 12.01 x 12.01 x 10mm mosaic stone tile on a mesh backing for a kitchen back splash. the individual stones ar 9/16″ x 1-7/8″. what size notch trowel would you advise?
DIYTileGuy says
Try a 1/4 inch square notch trowel. If you find that mortar is coming through the joints when you are installing then try a 1/4 inch V-notch.
Larry says
I bought some Purple Stained Natural Seashell Backsplash, 1″ x 1″ Square Shell Bathroom Wall Tiles (BK011) in 12 x12 sheets and am going to put a 16″ back splash around the kitchen above the counters. What size Trowel should I use?
DIYTileGuy says
Looks like I missed this one. You’ll have to experiment a bit and see which one is right for you. I would guess a 1/4×1/4 v-notch trowel but you may find otherwise once you get to installing the tile.
Rick Backous says
Hello, I am installing 3×6 subway tile as a backsplash and am wondering which trowel to use. I was told by the employee at Home depot that the 3/16 x 5/32 V trowel is what I need but since the longest dimension of the tile is 6″ the adhesive states to use a 1/4×1/4 square notch. Who is right?
DIYTileGuy says
Manufacturer’s instructions are always better than the store associate. In my personal experience, the 1/4 inch square notch is the way to go when installing the average 3×6 tile as well.
Nate says
I’m installing 12 x 24 tiles next to hardwood floors, over Detra Heat 1/4″ membrane. Would a 1/4″ trowel be okay for the tile to make sure they are flush with the hardwoods? The hardwoods measure 3/4″, but with 1/4″ membrane, plus the tile, I only have about 1/8″ to the top of the hardwoods when I dry stacked them.
DIYTileGuy says
The size of the trowel determines the amount of mortar underneath the tile to support it.
No matter how thick the hardwood is you still need proper coverage underneath the tile and I don’t think a 1/4 inch trowel will get you there.