Sealing Exposed Mortar in Bathroom

[Drakkith]

TL;DR Summary

Do I need to seal exposed mortar in my bathroom?

Hey all. Long story short, I just installed tile around my new bathtub and I have some exposed mortar at the edges that I'm worried will be vulnerable to moisture. I could use caulk to cover and seal it, but I don't think it would look good. Can I seal it like grout, or will it be okay if left exposed? It's Mapei large format floor and tile mortar and won't be subject to getting directly doused with water, just vulnerable to moisture and the occasional splash while someone dries off.

Thanks in advance!

Edit: Forgot to mention that the tile and mortar sit on top of a waterproofing coating which was rolled onto cement board that's used as the backerboard. Everything except for a small quarter-inch to half-inch section that runs up the edge of the backerboard-drywall joint. This section sits on top of the painted drywall, as I somehow installed the backerboard slightly crooked. It is this section that is the exposed part that I'm worried about. The rest of the mortar around the edges is not visible and can be sealed with caulk.

 

[ChemAir]

I would seal the grout, and use caulk in the corners or at joints, where there may be some expansion/contraction where the tub/shower and the walls/trim meet.

If you have gaps, you may be able to use some trim pieces, like 1/4 round, either polyurethane or PVC that won't really have an issue with moisture, to cover those (caulk/silicone at the edge). Wood will work, but can rot, and you need to be sure it can dry out between each use.

 

[Drakkith]

The grout doesn't require sealing, so that's fine. It's just the edge of the tiling area that has exposed mortar that I'm worried about. The joints between the tub and the tile are already sealed with caulk.

If you have gaps, you may be able to use some trim pieces, like 1/4 round, either polyurethane or PVC that won't really have an issue with moisture, to cover those (caulk/silicone at the edge). Wood will work, but can rot, and you need to be sure it can dry out between each use.

It's not so much a gap as simply the place where the tiling ends and the rest of the wall begins. See the following image:

 

[ChemAir]

Can you find a piece of trim that will cover that raw edge, and not be an eyesore? Something like 1/4round would do a pretty decent job of covering that, if the clearances and dimensions work, but it looks like the root will be filled and foil any attempt at a cover.

You may be able to use a thinner moulding, or a piece that is designed to cover that. May be able to repurpose a molding that has a hollow back, to hide it. If you have a table saw or other, you might can rip an edge off to make it fit, if you can't find what you like.

If you have good grout skills, you also may be able to smooth it out and not worry about it.

I don't (have good grout skills), so I would be going for beauty strips of some sort.

 

[ChemAir]

Can you find a piece of trim that will cover that raw edge, and not be an eyesore? Something like 1/4round would do a pretty decent job of covering that, if the clearances and dimensions work, but it looks like the root will be filled and foil any attempt at a cover.

You may be able to use a thinner moulding, or a piece that is designed to cover that. May be able to repurpose a molding that has a hollow back, to hide it. If you have a table saw or other, you might can rip an edge off to make it fit, if you can't find what you like.

View attachment 333092

If you have good grout skills, you also may be able to smooth it out and not worry about it.

I don't (have good grout skills), so I would be going for beauty strips of some sort.

 

[Drakkith]

Can you find a piece of trim that will cover that raw edge, and not be an eyesore?

Possibly, but I think it would look very awkward. I also like the way it looks now. I just need to smooth it out a little.

If you have good grout skills, you also may be able to smooth it out and not worry about it.

If it was grout I wouldn't be asking this questions, as the grout I used is sealed to moisture. But this is mortar, not grout.

 

[ChemAir]

Possibly, but I think it would look very awkward. I also like the way it looks now. I just need to smooth it out a little.If it was grout I wouldn't be asking this questions, as the grout I used is sealed to moisture. But this is mortar, not grout.

I've had one like what you have, and mine was smoothed mortar, rather than a beauty strip, but I didn't do that, myself, and it looked very nice (probably because I didn't do it). The mortar/grout was slightly rounded at the edges.

I believe they laid it and waited for it to mostly set. Then used a fillet device of some sort, followed by a wet rag/sponge to wipe it and bring it to the desired profile, and clean the edges.

I've done the beauty strip, but, often, there's more to making it look good than just covering it. You may be able to just fillet/round the edge grout/mortar.

 

[Drakkith]

I can make it look nicer, I'm just worried about moisture seeping into and through the mortar and causing problems.

 

[dlgoff]

How about just painting it with a good waterproof paint?

 

[marcusl]

I would cut a spare tile into thin strips whose width matches the buildup thickness (distance from wall to tile face). Glue these with mortar to the side of your sandwich and grout the gaps as usual. It will look professional. Just remember to ease the sharp edges.

 

[Drakkith]

How about just painting it with a good waterproof paint?

I guess I could. I might paint a small bit to see how it looks tonight or tomorrow.

I would cut a spare tile into thin strips whose width matches the buildup thickness (distance from wall to tile face). Glue these with mortar to the side of your sandwich and grout the gaps as usual. It will look professional. Just remember to ease the sharp edges.

I'd still have to buy more mortar and grout, something I was trying to avoid if possible. The simplest solution is probably to go buy a small bag of grout and cover the existing mortar with it. It would look just as nice, if not more so.

Thanks for the suggestions all.

 

[Lnewqban]

It's not so much a gap as simply the place where the tiling ends and the rest of the wall begins.

What is the material of the wall?
Do you know what that mortar was made of?

Please, see:
https://en.wikipedia.org/wiki/Mortar_(masonry)#Ordinary_Portland_cement_mortar

https://redblockindustries.com/blog/shower-remodel/shower-tile-installation/

 

[Drakkith]

What is the material of the wall?

Regular drywall with paint over it. The moisture resistant kind like this.

Do you know what that mortar was made of?

No, but this is the exact mortar I used.

 

[Tom.G]

There at least used to be quarter-round tile that was used for covering that tile-to-wall joint, I seem to remember even corner pieces. Just set it like setting flat tile.

Cheers,
Tom

 

[Drakkith]

There at least used to be quarter-round tile that was used for covering that tile-to-wall joint, I seem to remember even corner pieces. Just set it like setting flat tile.

At this point the tile work is done. I'd have to risk damaging the main tiles to rip out the current border just to replace it with quarter round.

 

[Rive]

A good paint should be able to take care of the water-issue, but

I'd have to risk damaging the main tiles to rip out the current border just to replace it with quarter round.

Sharp edges are generally considered as risks in a possibly slippery area. If you are OK with that, then a good paint should be able to do the job.

 

[Drakkith]

Sharp edges are generally considered as risks in a possibly slippery area. If you are OK with that, then a good paint should be able to do the job.

If you're referring to the tiles, the border tiles are bullnose and are not sharp except perhaps at the corners.

I'll probably end up adding grout on top of all the mortar. Turns out I forgot we had a spare bag and I can use it elsewhere to pretty things up a bit more.

 

[Lnewqban]

Regular drywall with paint over it. The moisture resistant kind like this.

No, but this is the exact mortar I used.

Please, excuse me late response.

If that edge is exposed to water splash, the moisture resistant drywall is the weakest link.
It is rated to only resist exposure to humid air.
For eventual direct water contact, a cement-based drywall (like Durarock) is normally used for walls and floors of showers (just in case water eventually finds a breach trough grout and mortar, or through broken tiles).

https://www.lowes.com/pd/DUROCK-Brand-0-5-in-x-36-in-x-60-in-Cement-Backer-Board/1000383889

That mortar should be technically impenetrable by water: nothing to worry about.

For trimming edges like that one, a Schluter tile edge trim is frequently used before the mortar hardens.

https://www.lowes.com/pd/Schluter-S...W-x-98-5-in-L-Aluminum-Tile-Edge-Trim/4220124

 

[Drakkith]

For eventual direct water contact, a cement-based drywall (like Durarock) is normally used for walls and floors of showers (just in case water eventually finds a breach trough grout and mortar, or through broken tiles).

Exactly. I have cement board under the tile everywhere except a quarter to half an inch of one edge along with an extra bag of grout I forgot I had that I plan to use to seal up the border.

Perhaps I'm worried over nothing. Now that I think about it a little more, the section of wall I'm worried about is no more exposed than it would normally be.

 

[marcusl]

Please, excuse me late response.

If that edge is exposed to water splash, the moisture resistant drywall is the weakest link.
It is rated to only resist exposure to humid air.
For eventual direct water contact, a cement-based drywall (like Durarock) is normally used for walls and floors of showers (just in case water eventually finds a breach trough grout and mortar, or through broken tiles).

https://www.lowes.com/pd/DUROCK-Brand-0-5-in-x-36-in-x-60-in-Cement-Backer-Board/1000383889

That mortar should be technically impenetrable by water: nothing to worry about.

Sorry, but neither grout nor thinset mortar is waterproof (look it up). That’s why the underpayment prep is so important. Cementitious board over a waterproof membrane is a favored preparation, but you should always check with your city’s building code office. The city I previously lived in insisted on green water-resistant drywall instead, with no vapor barrier over the studs. They decided after years of experience that it was better to provide paths for moisture to evaporate and dry out. In the end, you have to follow the local building code.

 

[marcusl]

BTW, Durock and other cement boards are also permeable to water.

 

[Drakkith]

Sorry, but neither grout nor thinset mortar is waterproof (look it up).

I guess that would explain why grout appears to absorb water and darken when we shower instead of having the water bead up and run off. I guess I've been worrying over nothing then.

 

[Tom.G]

Another fun fact about ordinary cement, as found in sidewalks and concrete buildings.

In coastal environments, within a few miles of salt water, the cement can carry salt and water far enough in to corrode any steel reinforcement bars. Such an environment requires a concrete additive (I don't know the details) to prevent this.

Several years ago I lived in a building with an underground garage. The apartments were on a continuous slab that was the garage ceiling. Some outdoor stairs were also concrete.

First the steps started cracking in two. Then the slab developed a crack all the way across it... right thru my living room, bath, and bedroom... had to stuff the sliding windows because the openings were no longer at right angles

That's when I moved out.

A few years later, chunks of the garage ceiling started falling off.

When the steel reinforcement bars corrode, the rust grows to 13 times the volume of the steel, thus cracking the cement.

The building is still standing, all be it borrowed time. The next earthquake could be 'interesting.'

Cheers,
Tom

 

[chemisttree]

It won’t leak but it WILL grow black nasty mold. Seal it with a silane sealer to reduce that growth.

 

[chemisttree]

Another fun fact about ordinary cement, as found in sidewalks and concrete buildings.

In coastal environments, within a few miles of salt water, the cement can carry salt and water far enough in to corrode any steel reinforcement bars. Such an environment requires a concrete additive (I don't know the details) to prevent this….(snip)

Cheers,
Tom

I’ve done a bit of work in the field of concrete. There are numerous additives that make that claim. Most work by filling in pore spaces (silica fume, fly ash, polymers, soluble silicates) or by reducing iron oxides to “black” iron. But chloride is very aggressive on steel regardless what is used.