Caulk or Grout in Corners?

by Roger

One of the most asked questions by do-it-yourselfer’s is whether they should use caulk or grout in the corners. Industry standards state that a flexible material be used at all changes of plane. But! – if you ask a hundred different professionals you will more than likely receive fifty of each answer.  While there are pros and cons of each, I am in the camp that uses caulk. That being the case, I will discuss using grout first. I’m backwards like that.

Using Grout at Changes of Plane

While the phrase “changes of plane” may sound a bit uppity or technical – it’s not. It simply describes the corner or edge of any surface that changes direction such as a corner, a wall to a floor, or a wall to the tub edge. Many professionals simply grout that corner as they do any other space between the tiles. There are a couple of things that must be taken into consideration before choosing this method.

  1. Your walls and the framing of your shower must be absolutely rock solid. I do mean absolutely. Grout is a cement-based product and as such is not meant to flex. If your wall moves your grout will eventually crack – it’s that simple.
  2. The space between the tiles at the change of plane must be large enough (for sanded grout) or small enough (for non-sanded grout) to be able to support the grout. That simply means that if you are using sanded grout you cannot butt the tiles against each other at the corner and expect to be able to force grout into it. It will not stay if the grout has no grout line to hold onto – if it is simply attempting to grab onto the face of the tiles at a 90 degree angle. There must be a grout line at the changes of plane.
  3. You must decide you are going to use grout at the changes of plane before you install the tile. You can then make sure to leave a line for the grout as well as adding additional support for any spots that may move even the tiniest bit (which it should not do anyway).

If you have taken the above points into consideration and still decide to use grout in the corners – go ahead. The big advantages of using grout here is that it will match all the grout lines and it will never have to be replaced. So although extra care must be taken to properly use grout at your plane changes, the advantages for some people are worth the extra time.

Using Caulk at Changes of Plane

There are several advantages to using caulk in corners and any other area where there may be a plane change or where tile meets another material such as your bathtub or sink.

  1. Unlike grout you are able to use caulk in a corner where tiles are butted against each other. It will stick to the face of the tile rather than needing a space between the tiles to grab.
  2. Caulk is flexible. If there is any movement the caulk is flexible enough to move with it and remain in place. It will not crack out or fall off.
  3. Caulk is waterproof – grout is not. Water will collect in corners such as where your tile meets the tub more than it will on the face of the tile.
  4. If your caulk does crack out or need to be replaced it is easily done.

The only two disadvantages to using caulk instead of grout are that you need to periodically remove and replace the caulk and, depending on your choice of grout, you may not be able to find a caulk that matches exactly. The first reason I consider to simply be regular maintenance and the latter is less of a problem since most major grout manufacturers sell matching caulk.

When to Use Grout

The only time I will use grout for a plane change is when I am using epoxy grout. Epoxy grout is bulletproof! OK, maybe it’s not bulletproof but you can hit it with a hammer a couple of times before it chips. (Don’t do that.) If you are using epoxy go ahead and grout the corners and changes of plane as well. Although it is not flexible it will grab the tile well enough to prevent it from splitting or cracking out. Precautions must still be taken but the Epoxy is strong enough to withstand normal structural movement.

How to Decide

Given the above parameters I believe caulk to always be the best choice. What you must understand about tile installation is no matter where you are installing the tile, it is always a structure that moves, no matter how minutely. Concrete moves, (the ground beneath it) that’s why it has expansion joints – to control where the movement goes. Most shower installations are over a wood structure of some sort. Whether you have drywall, backerboard, or a membrane, if you go far enough behind the tile, you’ll find wood. Wood moves, it’s just a fact of life. Humidity, weather, even the structure’s foundation all affect how much it moves. By taking proper precautions you can minimize the movement, but it’s still gonna move. Taking structural movement into consideration caulk is, for me, the logical choice.

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Jay

I am tiling a show and have a pre-made base. I have waterproofed the walls per your guide (thanks!). When installing the first row of tile on the base (12″ porcelain) to they rest on the base or do they need to be raised a bit.

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brandon

Hey Roger! Thanks for all the great advise! Browsed thru a bunch of questions but didn’t see mine so…

1. When you do your corners in a shower stall, do you butt the corners of the tile up to each other or overlap one edge over the other? Does it matter?

2. If you can overlap the corners could you stagger the pattern side to side as you go up?

3. If You butt them how much gap do You leave? Im using 3/16 tile spacers.

Thanks Rodge!

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Roger

Hi Brandon,

1. Overlap with one (almost) butted to the other. Yes, I know that wasn’t one of the options.

2. No

3. 1/16″ – 1/8″

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Chuck Liberman

Hi. My building inspection requires insulation on the exterior walls in the shower. Inspector suggested Reflectix which is plastic honeycomb sandwiched between aluminized layers. I was going to use Redguard on the concrete board walls. Won’t this be like having 2 vapor barriers which is a no no? Which would you suggest changing? Love your books.

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Roger

Hi Chuck,

You can have Reflectix behind the substrate. It’s not ideal, but if it’s required, it’s required.

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Waaa Hoo

Sanded or unsanded grout for shower corners? Plan on using Tec Powergrout.

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Waaa Hoo

Doh. I meant to ask “sanded or unsanded CAULK for corners?”

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Waaa Hoo

Plus: Any super cool tricks like the bullseye pattern on ceiling tiles for tooling caulk neatly?

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Roger

Install it, spray it with denatured alcohol and run your finger down it. As long as the top of the bead is wet it won’t stick to your finger.

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Roger

Oh, sanded. :D

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Roger

Silicone.

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Waaa Hoo

Sanded silicone it will be.

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Larry Liddell

I would like your opinion on the Kerdi shower pans. I am on a concrete slab and would like to use the Kerdi shower kit.

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Roger

Hi Larry,

They’re a good product. I just don’t use them because they rarely fit the size of the showers I build.

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Ben

Hi Roger
You mention epoxy grout as acceptable to use at the change of plane. What’s your opinion on the urethane grout for the same application?

We’re using urethane grout on large format glass tiles in a shower remodel. The good folk at Bostik, who we purchased the grout through, are of the opinion silicon is the way to go at the change of plane but don’t have a product to match to the colors of their urethane grouts and suggested a color match with the tile instead. The tiles are a clear glass with a colored backing and we would like to avoid this approach if possible. A tad apprehensive about the appearance of the finished product Don’t want to have to scrape it out if it looks rubbish.

Can you shed some light on color matching caulk/silicon to glass tile and can you suggest a suitable product/brand you found satisfactory for the job? Are there brands who make a caulk that might match up to Bostik’s urethane grouts?

Any wisdom you can impart on this would be greatly appreciated.

Cheers
Ben

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Roger

Hi Ben,

With large format glass I would absolutely NOT use grout at your plane changes. With clear glass and a colored backing you can go with clear silicone (which WILL hide the very back corner behind the tiles that you see now) or a color that matches the color on the back of the tiles. Clear is likely a better choice. There is not going to be any company that makes a silicone to match another manufacturers grout colors. You may be able to cross-reference your color with laticrete or color-sil silicones. If you call either one of them they’ll be able to tell you which to use.

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Renee parks

Should I use caulk in the corner joint of my green board, which is in the “dry” area of my bathroom, and the tape and thinset since it’s getting tiled? Also, can you tile over green board Ina dry area? I know it’s a no-no in showers, but what about the rest of the bathroom? And can I use a liquid membrane on the green board in this area, or do I even need to? I’ve read through a LOT of the comments, but have found conflicting information. Thanks!

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Roger

Hi Renee,

No need for silicone, just tape and thinset. You can tile directly over it in dry areas. You do not need a liquid membrane.

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Dave Schmidt

Well here goes.
Have studded in. rough opening is 37 X 54. Will be tilling to ceiling. Want to tile floor.
Question one. Do I need to support the floor trusses in the basement?
Question two. Would like to get your books. I’m old (67). Like to read on the bathroom potty fixture. Want to do the job right, preparing and tiling the walls that is.
Need info in book form with pictures. Need to do the whole thing right. What books would you suggest?
Thank you for any suggestions and advise you could give. Love your text in the readings I did.
Dave

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Roger

Hi Dave,

1. No, they should already have sufficient support.
2. It depends on how you plan on waterproofing the shower. If you download my free waterproofing manual it will walk you through the different methods and pros and cons of each. You can decide from there. You can find it here: Shower waterproofing manual

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