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Old 11-13-2018, 08:33 AM   #1
jeff meeks
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"Perk" time through a mortar bed?

Is there any research or numbers on the amount of time it takes for water to drain through a mortar bed and then follow the pan liner to the drain. I imagine its a function of gravity, the grain structure of the mortar and any surface forces between the water and the grains and how much water is in the bed. Obviously if the rate of drainage out of the mortar by either flow of evaporation is less than the rate of water flow into the mortar bed then it will tend to stay wet. I know this is a bit of a moot point now that there is Kerdi and Hydroban etc, but I was just thinking.
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Old 11-13-2018, 09:50 AM   #2
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Welcome, Jeff.

I know of no perk test data for shower mortar beds and it would be difficult to quantify due to the variation in size of shower receptors even if you tried to duplicate the precise mortar mix, the precise slope of the pre-slope, the precise packing of the mortar before carving, the type and size of the drain weep holes, etc, etc. Could get a bit complicated.

Not a moot point at all. There are still thousands of traditional shower receptors being constructed, but the numbers are certainly diminishing due to the more modern methods available with today's direct bonded waterproofing membranes.

But a heavily used traditional receptor may, as I think you're suggesting, remain damp all the time, but the water in - water out function generally ensures that there is minimal problem with that condition. And, depending upon the construction of direct bonded waterproofing membrane receptors, they are at least as likely to remain damp between uses in a heavily used shower.


Is there a specific problem you're seeing that has prompted your question?

My opinion; worth price charged.
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Old 11-13-2018, 05:05 PM   #3
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No specific problem with my shower as I had Hydroban installed, but in the process I got to thinking about shower pan liners particularly because I live in MA and copper pans are still in use. I think lots of people think of water running down a pre-sloped liner without considering that it's surrounded by sand grains and air channels and not just air. The thing with doing some research would be to derive a set of requirements for good flow....that would include slope, mortar mix and bed thickness and size. It's a complicated matrix, but I would have expected the industry standards organizations to have done some research on this. It would be easy enough to put a liter of water in a tube sealed to the surface of a mortar bed and see how long it took to emerge at the drain.
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Old 11-13-2018, 06:24 PM   #4
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I think most of us who grew up with that type of shower receptor are content to know that, when properly constructed, they've work quite well. If you've never poured water in the far corner of a traditional shower receptor before tiling you might be very surprised to see just how quickly you begin to see water in the drain through the weep holes.

We have a member here who has been involved in creating the ceramic tile industry standards for many years. I'll see can I get him to comment on whether he recalls any discussion or call for discussion on the matter.
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Old 11-13-2018, 06:39 PM   #5
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We played with it some over the years. Never studied it thoroughly because it was a non-issue. There are a lot of variables that would have to be considered. That would be even more so now that there are so many bag mixes to consider. When we did look at it we had samples from all over the country. Each had variable sand particle size and mix make up. Cement types and ratios varied widely as well.
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Old 11-13-2018, 07:22 PM   #6
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I know that the higher the water to cement ratio the weaker the resulting concrete/mortar, but it will end up more permeable....so I imagine having a lean cement to sand dry mix mortar is sort of a compromise.....dry to give a strong result and a lot of sand to try to keep it porous? The installers that put in a sloppy mix will get good perk, but a weak bed.

Google produces quite a lot of research on the water permeability of different concretes and mortars, but there's no real world idea about how water moves through a real shower mortar bed which is probably well understood on the way down to the pan liner, but once the surface of the pan liner comes into play I bet that complicates things a lot.

Can you give me a rough idea of the drainage times in a standard type shower application...is it seconds, minutes or days? My feeling is that it might be minutes, this is all really just out of curiosity.
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Old 11-13-2018, 07:57 PM   #7
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Quote:
Originally Posted by jeff meeks
...the higher the water...will end up more permeable....
No, not true. With deck mud, the less water you use, the more permeable it is. You only want to use enough water in your mix to make the mud stick together when you ball it up in your fist. This isn't concrete mix we're working with. There is good information out there from shower forensic experts to support my statement. Otherwise you can make a mock up and see for yourself firsthand.

If I poured a pitcher of water on a 3'x3' bare mudded shower pan that was a few days old, it would all be sunk into the mud within a few seconds. But the more water and harder you pack the mud, the less permeable it will be.


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Old 11-13-2018, 08:02 PM   #8
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I've always mixed my own dry pack out of sand and Portland. 5 to 1 is a standard mix with enough water to make it damp. The day after mudding a shower floor, I can take a 16 oz cup of water and dump it on the mud and it disappears in 2 seconds. A while back, I thought I would try the Mapei 4 to 1 mix. I dumped a cup of water on it the next day and it was still wet 15-20 seconds later.

These days we have a lot of installers that think sand mix mixed dry is dry pack. Not so, it needs sand added to it.
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Old 11-13-2018, 08:39 PM   #9
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The technical papers I have read say that the final mortar becomes more permeable the greater the water to cement ratio because the hydration reaction creates more pores and more connected pores, this is also what leads to reduced strength. Here is a link, look at Figure 3. There are many more papers that show similar data.

https://www.hindawi.com/journals/amse/2014/273460/

But I'm more interested in a rough idea of how long water takes to get from the surface of a mud job into the drain weep holes via the liner....So what's the best guess /observation for a 5:1 sand to cement dry pack with a cup of water poured onto the surface a couple of feet away? I've seen water get sucked into dry mortar in a few seconds so I was thinking the answer to my question might be minutes rather than hours.
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Old 11-13-2018, 09:41 PM   #10
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Jeff, the article you linked is talking more about concrete than the mixture the tile industry refers to as deck mud or dry-pack or, frequently, just as mortar. Mortar being a term used somewhat haphazardly in the industry.

But when you're talking about placing mixes with a water/cement ratio in the .45 to .60 range as in that article, you're dealing with something closer to concrete with a lot of water of convenience. It will be much more dense and less porous than deck mud and the higher porosity they're talking about is a relative thing, but would all still be far less porous than properly mixed and placed deck mud. The deck mud is a very porous product when cured. I've never tried to calculate the water/cement ratio of deck mud.
Quote:
Originally Posted by Jeff
The installers that put in a sloppy mix will get good perk, but a weak bed.
Give that a try and let us know the result. I think you'll find that not to be the case with the "good perk."

[EDIT] How long for water poured on a dry pack shower floor to get to the drain a couple feet away? Seconds for the part not held in the mortar. Most of it will go through to the liner and to the weep holes rather quickly. Some of it will evaporate back through the surface.

Build you a test floor and give it a try for yourself. The materials are dirt cheap and you can experiment with as many mixes and water ratios as you like 'till you see whatever it is you're looking to prove or disprove. Look in the Shower Construction section of our Liberry for a thread on the proper mix for the deck mud and experiment from there.
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Old 11-13-2018, 11:20 PM   #11
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The article is testing cement mortar ie just cement and water...there is no aggregate. It finds that in that, the more water you add influences how the calcium silicate hydrate crystals form and you get a more porous end result. This is not deck mud as you need a lot of sand for that and so I concede that things will be different and maybe physical packing of the sand rather than chemically created crystal structures and pores might be the bigger factor. But generally speaking the more water to cement you have even with sand or larger aggregate the weaker the final result and I think the idea that that's because it has a larger volume of pores holds water......or maybe it doesn't.

The dryness of drypack might not allow the chemical reaction between water and the cement to go to full completion so maybe this is a special case and the paper isn't applicable. So maybe if it gets wet in the shower it will continue to react. I'm just thinking.

I like the idea of doing some tests. Some sloping plywood, poly, some Quickcrete topping mix and extra sand might be in my future. Maybe just start with straight Quickcrete made up dry and wet to compare.

Thanks for everyone's contributions.

PS
For anyone interested here is a paper that is directly applicable as it measures mortars.

https://ciks.cbt.nist.gov/~garbocz/paper64/

The conclusions are that mortar does get less permeable the higher the degree of hydration so Davy and Tool Guy are correct, but that as you increase the water to cement ratio the permeability increases. It took me a while to realize that those two statements are not necessarily contradictory.
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Old 11-16-2018, 08:55 AM   #12
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I'll go back to what was said in the first few posts of this thread. How fast the water disappears from a shower mud bed isn't all that important. What is important is that the water in-water out process works continuously as long as new water is introduced, as CX said. If a properly built shower floor is left unused for a month or two there is a good chance it will dry out completely through surface evaporation (via the grout joints). As long as the shower is used (or wetted) more frequently than that the floor will never dry out. As Gobis said, this issue is really a non-issue.
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Old 11-16-2018, 09:25 AM   #13
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I would think any way to facilitate water quickly passing through would be best practice.

When y’all say non issue are you saying how it affects the maintenance of the shower through it’s lifespan?

If it’s a non issue why do arguments arise about a liner system being inferior to modern techniques for mold growth and dampness?
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Old 11-16-2018, 11:36 PM   #14
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How wet a shower bed stays is going to depend on a lot of rates...rate of water in, rate of absorption at the surface, rate of travel through the bed and out of the drain and also rate of evaporation. I started this as I had no feel for the basic rate of flow through a standard 5:1 mud bed, but thought that there should be some ballpark figures as it's the basis of the whole system. Through reading I have now learned that the permeability of mortar goes down the more water it contains. So maybe over a number of years if the bed does not fully dry between showers it could slowly reduce in permeability and we have positive feed back and the mud bed saturates. Again without knowing the rates there's no way to know if this is ever a problem other than through the experience of shower tear outs, it could only be an issue over many decades or not at all.

I think I'll go to Home Depot tomorrow and get some materials to make a test rig.
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Old 11-17-2018, 07:56 AM   #15
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Yeah there are going to be a LOT of variables but like you Jeff, I hoped for a average baseline even if it +/- a percentage of error. We'd have some kind of answer. The reason I'm interested in such answers on anything with mud is because it's how I build showers. More information on mud specs the better to explain to people the negative connotations the industry pushes on it are from bad installs not proper work.
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