Interview Transcription by Alice Dean

Photos  Courtesy Pavlo “Pasha” Starykov

Professional stone and tile installers have skin in the game when it comes to understanding what causes moisture discoloration on marble and other natural stone installations, especially white Carrara marble floors. If installations are performed properly with the appropriate materials, why would there be a problem? It all boils down to understanding how water molecules penetrate natural stone and other porous building materials.

Pavlo “Pasha” Starykov of Star Tile & Stone LLC consulted with one of the most prominent natural stone experts in the industry, Fred Hueston of Stone Forensics, to test and research possible solutions for moisture discoloration. They continue to compare notes with other industry experts, including Foster Lyons of Foster Lyons Building Science, to provide reliable, fact-based technical information regarding this ongoing problem. 

Hueston interviewed Lyons, a building science consultant who specializes in water and moisture dynamics. He offered unique insight into how water molecules interact with each other, penetrate natural stone and other porous building materials, and contribute to various processes, including the problem of moisture discoloration. This article is not a complete transcription of that interview and has been edited for clarity, flow, and brevity. You can listen to the full interview at Fred Hueston’s The Stone and Tile Radio Show Podcast.

This 20-year-old marble shower has had no water discoloration problems, likely due to the dry-pack mortar bed and traditional water-in/water-out installation system.

This 20-year-old marble shower has had no water discoloration problems, likely due to the dry-pack mortar bed and traditional water-in/water-out installation system.

: In general, in the building industry, most materials used have one awful characteristic. They’re porous. 100% of the natural stone materials in tile applications have some amount of porosity. Depending on the porosity and characteristics of stone, water enters in different ways. 

One such way is called capillary action, like sticking a straw into a soda and it wicks up into the straw. The surface tension of the liquid is attracted to the interior surface of the straw and literally gets pulled up against the force of gravity. 

For a natural stone tile, slab floor, or a wall installation, if the water sits on the surface and the surface isn’t sealed with a surface sealer (not a penetrating sealer), the water will get sucked into the pores of the stone. 

Fred, you have spent a lot of time speaking with Pasha about this: the grout that is on either side of the stone and setting bed and the thinset mortar beneath the stone have a different porosity than the stone tile. They’re both porous to some degree, so they both also pull water into them by capillarity.

Now, the second mechanism for getting water into stone, the grout, and the setting bed underneath is gravity. If water is poured on a floor, gravity will try to pull that water into that material. 

Take a very close look at a grouted tile floor with no apparent gaps, holes, or cracks. How the heck could gravity possibly pull water in? Water molecules, themselves, are incredibly small, but liquid water doesn’t move around as individual water molecules. It moves around in clumps of water molecules that are maybe 25 to 200-300 molecules all clumped together. The molecules are constantly changing with their neighbor clumps. But, a liquid ball of 100 or 200 water molecules is still incredibly tiny. 

A very microscopically tiny crack will look like the Grand Canyon to a clump of two or three hundred water molecules. Imagine a ping pong ball on top of the Grand Canyon and gravity pulling it down. It’ll go down. There’s plenty of room for it and all its neighbors, too.  

The water molecule clump will be pulled into a tiny crack between the grout and the tile, in the tile itself, around the edges, around the drainpipe, or any other place there are microscopic cracks. It drops in by gravity and gets pulled in by capillarity, and then it gets further pulled into all the tinier pores or crevices that are in the stone, grout, the thinset mortar, the cement setting that’s underneath, and any other crack or crevice that’s available. Water is very mischievous. If it is allowed to hang around, it’ll cause trouble! 

Water can also go in as a vapor. Imagine a steam room, which has 100% relative humidity, basically. That’s a lot of water vapor, and water vapor is not like liquid water. Water vapor kicks around and goes through life as single molecules bouncing around with oxygen and nitrogen molecules. They collide amongst each other and the surrounding surfaces, like the walls, floors, and ceilings. Some number of them will zip right into those pores that exist in that material. 

I think that’s an excellent point. We seal the floor with these impregnators, and their manufacturers say: “Oh, this stuff is breathable. It’s vapor permeable.” …or whatever other terminology they want to use. Even though these floors or walls are sealed with those impregnators, vapor can still get in. Is that correct? 

Lyons: That is 100% correct. Sealers do a very good job of making surfaces hydrophobic, meaning, they don’t like water, but sealers do nothing for cracks or holes. Sealers of the variety that you’re describing work on a microscopic level, so they’re literally coating the interior of the pores in the natural stone. But if there’s a tiny, little hairline crack around the drain, between two tiles, or where the floor meets the wall and that sort of thing, the sealer does nothing for that. It’s not waterproofing. 

I’m still looking for a single manufacturer to tell me what the vapor permeability of their material is. Now, I know why they can’t, and I’ll talk about that in a minute. But whatever the number is, what I know for sure is they’re not increasing the vapor permeability of the stone-to-air boundary. They’re decreasing the vapor permeability of the stone-to-air boundary. They’re making it more difficult for vapor to move. 

One of the ways liquid escapes is through the surface of the stone as vapor. Sealer decreases the speed at which that can happen. 

Suppose you take a hot shower. You turn the shower off, and suddenly it gets cold. What about condensation? Can condensation occur in these installations? And if so, explain that. 

Lyons: Yes, it can. Everybody who drinks cold beer understands condensation. I don’t think condensation is nearly as much of a factor as the volume of water created by running the shower. 

The wettest place on the surface of the earth is a shower stall. Do the math. There are more inches of rain per year in a typical shower stall than in the rainiest town in the mountains in Colombia, South America!

Let’s just, like, shrink our minds down, as if we went into Alice in Wonderland or the land of the Lilliputians. You’re a water molecule that just flew into a pore in the stone where there are a bunch of chemicals or salts, silicon dioxide, aluminums, etc. The water can be attracted to these surfaces. In other words, the overall energy state of the system will be lower if the water molecule sticks to the pore wall. The universe just prefers that. The molecule would rather stick itself to the wall than fly around the room. 

Just take my word on that. Every stone is going to have a different level of attraction for these water molecules. 

Water that’s in the air in the room is going to end up inside the stone by vapor diffusion and normal physics. But it gets a little worse than that. 

In the tiniest of these pores, molecules have very little room to move around. We’re no longer in the Grand Canyon. The forces of attraction between the molecules and the sidewalls changes dramatically, and liquid water condenses at a much higher temperature than it would otherwise. It’s like pulling a warm beer can out of the fridge and still seeing condensation on it.

If the relative humidity is high enough for long enough, stone could very well be saturated with water. The tiniest pores fill first. That’s called capillary condensation. Then the larger pores, and when that’s filled up, it goes to the next largest pores, and it continues in that way. 

The cause of the moisture discoloration was not clogged weep holes, but an improper assembly/system for marble.

The cause of the moisture discoloration was not clogged weep holes, but an improper assembly/system for marble.

This is great information. I just want to back up a second and mention that I’ve asked sealing manufacturers about perm rates for years, and half the time, they look at me like a deer in the headlights like: “What’s a perm rate?” And then that’s when I walk away. It’s like they don’t know what they’re talking about.

Lyons: I understand why they don’t quote it, because they would have to ask, “Exactly what stone? Where was it quarried? Which corner of the quarry it came out of?” They’d have to test the stone, with and without sealer at multiple different relative humidity levels and temperatures. It’s very easy to quickly realize that there’s 10 billion different measurements they’d have to do here. This is not possible, right?


Lyons: I get it; I just don’t like it!

Hueston: Yeah. I’m with you there, believe me. Let’s talk a little bit about the installation systems and how water affects these or how the installation system affects the travel of moisture, etc. I remember back in the day; my dad would use white marble and never had this issue. Today we have new technologies, shower and floor systems, resin-backed tiles, etc. In your opinion, what have the new technologies done to moisture? We can talk about impregnating sealers, resin-backed materials, and things of that nature. 

: There are no bad materials, there are only bad assemblies or poor installations. Pretty much all materials can be made to perform well if they’re in the proper assembly and installed properly, according to the manufacturer’s recommendations.

My guess is your dad was a very smart, skillful guy, but two-stage drains are a stroke of genius for systems or assemblies like shower floors or roof assemblies. In your dad’s systems, I’m assuming, water is going to get underneath the stone surface. There were holes in the side of the drain above the waterproofing membrane (called weep holes) to allow incidental water to drain. That’s how it was done for a very long time.

Then a chemical engineer in Waterbury, Connecticut, who went on to found the Laticrete company, invented thinset mortar, which is basically just sand, Portland cement, and latex rubber mixed in with it. This allowed for thin setting beds underneath tile installations rather than thick beds, but without this thick bed of very porous sand and cement, it’s latex-modified – sand-cement glue, effectively. It drastically changes the porosity of that mixture. It is harder for liquid water and water vapor to move through. 

Imagine an Erector Set, but then building a second Erector Set within the first Erector Set. They’re not technically touching each other, but clearly one is inside of the other, and that’s the way we should think about a latex additive. 

Now, advance the clock from 1950 to 2020. Well, I don’t know. Are there 10,000 or 100,000 different additives that they put into this important cement-sand mix to make thinset mortar?

All I know is that there’s thousands of them, and good luck figuring out exactly what they are or at getting any manufacturer to tell you what their magic ground unicorn horn dust is that they put into their stuff. 

Water still gets into that latex-modified thinset. You’ve probably changed your drain to a linear drain that has no second stage. It’s a single stage drain, and the water just doesn’t move through that thinset the way it would move through an old-school sand-cement setting bed. 

Water that hangs around is mischievous and needs a place to go as quickly as possible. Don’t let water hang around, that’s the secret to success, most of the time. 

Pasha’s got a different assembly, and I believe he is completely right for that assembly and those conditions. But in many applications, if you can do a thick, porous bed with a two-stage drain, that’s great. Do it. 

Integrated bonding flange drains create a little dam around the drain opening; not what you want in your marble tile shower installation.

Integrated bonding flange drains create a little dam around the drain opening; not what you want in your marble tile shower installation.

Yep. I agree. Now, what about mosaics? Almost 100% of them have a mesh backing, and they’re also resin backed. Since the resin is pretty much, I hate to use the word, “waterproof,” because nothing is really waterproof in my opinion, how does water get through? 

Lyons: It gets through in the same way as applications that don’t have it. Imagine it’s a one-by-one, resin-backed, square stone tile. Well, there is still a grout joint between all the tiles, and plenty of water can get through that grout joint and go into the thinset mortar or setting bed. 

In a system that allows the water to drain, it will move by liquid flow to the drain or back up and out through the grout joint between the tiles.

Imagine a big shower, like 100 square feet. The area of the grout joint is probably like 5 square inches or like one tenth of 1% of the floor area. 

Without the resin, arguably, the vapor could slowly move back up through the stone. The resin on the thinset or the sand-cement setting bed below the stone is going to get wet, because there are cracks in the flooring etc., and its only way to dry out now is through that one tenth of 1% of the floor area. 

Will it dry out eventually? Sure. It’s just incredibly slow.


This marble shower floor was installed using the epoxy method by Pavlo “Pasha” Starykov.

This marble shower floor was installed using the epoxy method by Pavlo “Pasha” Starykov.

Hueston: Obviously, you know Pasha’s opinion and my opinion on sealers. Would you recommend, with the type of assembly system that is being used, to NOT seal a shower floor?

Lyons: Between Pasha’s system and the kind of traditional system, no, I wouldn’t. I don’t see the great necessity for it. In other words, for any stone that somebody thinks about using in a wet area, if it needs a sealer, they already went down a wrong path. 

There is a huge amount of historical evidence that unsealed stone would behave and function very well. The Iraqis, Greeks, Romans, and French did this for thousands of years, by some miracle, without the help of DuPont or Dow Chemical. Arguably, the addition of sealer is more suspect than non-use.

Sealer companies do great marketing, but sealers are not the solution. In porous materials that are going to get wet, any reduction to their ability to dry out is a bad thing. We want maximum drying potential. 

Pasha has been working on an all-epoxy system: epoxy setting mortar, epoxy grout, and a sealer on top of that. He’s going to do more work on more modules, but what’s your opinion there?

Lyons: Overall, I think he’s got it. I think he’s perfectly correct for those systems. He’s making what I’d call a “barrier system.” Liquid water cannot get past the epoxy grout or the stone. Of course, the stone is porous, and water can get into those pores, as we’ve discussed. But now, because of the epoxy grout, there are no cracks.

That stuff is gooey, sticky, flexible, and all the other great things. It’s not porous. Zero porosity. It’s like sheet plastic when it’s all sets up. A barrier has been created.

So, his system is epoxy grout and epoxy thinset. There’s no place for water to hang out, right? Even if 10 molecules of water got past some little crack, it’s got nowhere to go. No water builds up. 

Hueston: I would think even if you did that system, and even if you sealed it, and when I say “seal it,” I mean impregnators: – if water does get in there, it’ll probably evaporate quicker than a system that doesn’t have that.

Lyons: Yes. Well, it’s going to evaporate faster than a system that’s got non-epoxy grout and non-epoxy thinset. The reason is only the water that is in the stone is evaporating. Water doesn’t fall quickly to the underside of the stone, because it takes time to go through these tiny pores. When the shower ends, water goes down the drain. There might be a little water in the top couple of millimeters of stone, but now it can dry out and there’s no additional water coming up from below or in from the sides. 

This system reduces wetting potential and maintains drying potential, tipping that balance of wetting and drying. It’s more favorable for being dry. 

I do like talking to Pasha about the sealers on those floors. I’m of the opinion that the reason that sealer helps in that assembly, and I’m pretty sure I’m getting this right… Pasha is probably screaming into his radio right now!

But he believes the assembly functions better with a particular sealer. In my opinion, it functions better because it reduces the amount of wetting of the stone by just allowing the water to sheet off the stone a little faster, rather than hanging out on the stone, meaning that the surface of the stone with the sealer on it is hydrophobic. 

It’s kind of like a super-hot frying pan. You drop a tiny little drop of water on it, and it dances around a while before it evaporates. If the pan wasn’t quite so hot, it would just quickly evaporate. 

That’s kind of what sealer does to a surface. The water doesn’t like it as much, so it literally runs across the surface faster and gets to the drain faster. If you’re not putting a plug in your shallow floor, it’s helping this mischievous water get to another place where it can’t cause trouble.

Lyons: In my opinion, the sealer is reducing the quantity of water that gets into the stone to begin with, and therefore, it dries out even faster. That’s the reason that assembly works better. 

It’s not as if the sealer improved the drying potential. If anything, it reduced the drying potential, but the fact that it’s on the surface of the stone helps reduce the wetting potential. 

An example of moisture discoloration around a drain in a marble shower floor – a common problem arising from faulty construction.

An example of moisture discoloration around a drain in a marble shower floor – a common problem arising from faulty construction.

In conclusion, what would you recommend to an installer? 

Lyons: You would have to tell me exactly what kind of stone and drain is being used. If you’re using absolute black granite and a two-stage drain, you’ve got choices, but if this is a slab marble floor and it’s white Carrara, that’s different. 

Long story short: if it’s a translucent marble, you either don’t have the room or your drain is such that you can’t put a two-stage drain in. If It’s a single-stage drain, like these modern linear drains, then I would recommend exactly what Pasha has come up with: 100% solid epoxy thinset and 100% solid epoxy grout. 

I don’t disagree with Pasha on the sealer, I just get a little nervous about it, because there’s one that I’m okay with, but I don’t control what the contractor buys. 

Yeah. And then they all differ, and there’s literally hundreds of them out there. 

Lyons: Now, if they say, “No, no, no. We’re putting in a beautiful, old school, two-stage drain. We’ve got plenty of room. We framed the floor down, and we can put a 6-inch bed or whatever you want…” then I’m, like, “Great!” If your contractor is comfortable with that, and he’s done it before and had success, go for it. Go ahead and do that. It’s going to be OK, if properly installed.

A lot of design decisions have to be thought of before the house is framed. If you need to drop the floor for a shower stall, guess what, your structural engineer has to be involved. You’ve got different floor joists, etc.

So, it’s a little complicated, but I love Pasha’s system. I believe in it. It works. 

I love the old school system. I believe in it. It works. Just don’t mix the two. 

Well, Foster, this was really great. I’d love to have you back on my podcast sometime to talk about some other things concerning building science. Again, thank you. 

Lyons: Thank you very much. It’s a great honor, and it was fun for me. 

Alice Dean is a technical writer for SurpHaces, a professional resource and support organization for quality surface care pros and their customers, and she also writes for home and property service providers at Top Floor Writer.

For more information, check out these articles:

Sealing Stone in Wet Areas, by Fred Hueston

Marble Moisture Discoloration: Don’t Blame the Stone
, by Pavlo Starykov

See the Archives, September 2020 issue

Eliminating Marble Moisture Discoloration,
by Pavlo Starykov

See the Archives, January 2021 issue