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Unread 09-28-2002, 05:50 PM   #1
John Bridge
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Over in the shallow end, Todd (tileguytodd) made mention of what he termed "hydraulic pressure" building up in a mortar bed shower floor if the drain weep holes become clogged. I've heard this theory before, and I think it's incorrect.

Now, everyone knows I never argue with Todd, but I can't help it this time.

There is no way that pooled water can exert hydraulic pressure except downward and laterally (through normal gravity). It cannot cause tiles to push up from the setting bed. There can be no upward pressure in that regard.
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Unread 09-28-2002, 07:29 PM   #2
Jason_Butler
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Hi John,

I seem to remember a fella named Tyler that claimed the same. This is the guy that "repaired" shower floors by cutting along the wall/floor junction and resealing. Bringin' back any memories?

Anyway, we got a few engineers here on this board to go along with the field experience so let's get some opinions. The way I see it, if water was to make it to the pan and be denied by clogged weep holes, the water pressure ( as minimal as it is) would be alleviated through the very hole/orifice/crack/porous surface that allowed the water to reach the pan in the first place.

In order for water ( an incompressible fluid) to exert pressure from below, it would have to originate from a source below the floor. Right????

Only if the water made the phase change from liquid to vapor would this seem to be an issue. I never saw water boil beneath a tile floor...if in the Texas summers

Am I totally off my rocker with this train of thought ??

Jason
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Unread 09-28-2002, 08:07 PM   #3
John Bridge
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Hi Jason,

I'm not forgetting that you are an engineer in some discipline or another.

Yes, hydraulics. The only way water can exert pressure upward is if itis under some external pressure, sort of like when you squeeze the trigger of a squirt gun, causing a plunger to push against the trapped water, which causes enough pressure to cause the water to come out the front of the gun in a "squirt."

Now gravity and a water "colunm" can exert a tremendous pressure, but not upward.

I learned the principles of hydraulics (mechanical values) in high school physics (before I dropped out).
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Unread 09-28-2002, 10:31 PM   #4
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Water (or any matter in it's liquid state) is going to take the route of least resistance. This is how the grand canyons were made.

If you were to consider the shower wall as if it were a column of water it would have X amount of pressure in a downward direction. (Due to the mass of the earth, Gravity.)

If the weep holes are clogged the water under pressure will take the path of least resistance, whether that is up or down.

Would the pressure in a normal shower be enough to damage tile? I don't think so... Where the H%#$ is Bob Camp when he's needed?
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Unread 09-29-2002, 12:48 PM   #5
tileguytodd
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I stand corrected (prob wont be the last time either )
I have an excuse though,Sonny made me do it!!!!!
He kept me up all night and my actual brain wasnt functioning
And i dont call it arguing john, I call it training technique,I screw up,you fix it there ya go i 'm trained

You must note though that on another post i did indicate while after 20 years in this trade i still dont know it all,and I am still man enough to admit when i am wrong.Just remember that though John when I am right
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Unread 09-29-2002, 02:45 PM   #6
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Hydraulic pressure acts equally in all directions.

Hydraulic pressure in this case is hydrostatic pressure, or the pressure generated by the weight of the water column above the point in question.

Lets say that the water in the mortor bed is at the full depth of the bed. That would be no more than a couple of inches, right? The pressure of a couple of inches of water is about .86 psi. For a 3x3 inch tile, there would be about 8 pounds of force trying to lift the tile. Is that enough force?

I think Jason is probably correct. Unless the grout, tile and liner are impermeable and completely rigid, the pressure would be relieved through weepage. That is the usual result in a damp basement, where the hydrostatic pressure is measured in feet of water, not inches.
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Unread 09-29-2002, 03:11 PM   #7
John Bridge
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Okay, so Bob, I think that means in this scenario that the floor tiles might simply become immersed in water.

But are you saying gravity has no effect? What I was assuming is that the tile would not act as a barrier and that the column would be open at the top. I realize that rising water exerts an upward force. I was thinking more of a static body of water, which exerts force only downward and laterally due to gravity.

If a tree fell in the forest . . . . ?
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Unread 09-29-2002, 04:21 PM   #8
Jason_Butler
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Talking

...yes it would make a sound ....
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Unread 09-29-2002, 04:55 PM   #9
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I'm not quite with you there Bob. The tiles next to the wall are at the highest part of the bed, and there is no water higher than them. They would have no pressure on them. The tiles next to the drain would be slightly lower, but not two inches unless it's a really big one.
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Unread 09-29-2002, 05:18 PM   #10
John Bridge
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Oh, man. I just love it. We've got a couple engineers engaged in an engineering discussion, and it's all happening right here on the JB Forums.

Folks, it just doesn't get any better than this.
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Unread 09-29-2002, 06:39 PM   #11
Jason_Butler
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The only way I could see a significant amount of water accumulating ( and causing pressure) is if the walls became saturated. This would happen if the weep holes became clogged and all of the trapped water "wicked" it's way up the wall. At some point, there could be enough water in the wall to exert enough downward pressure to cause damage ( I think?)

In this case you would have a "column" of water exerting pressure ( pressure = constant*gravity*height). If this pressure were to act below the bed, it would look for a way to equalize. This is the same principle as a water level. In this case, their may be sufficent water pressure to loosen a tile.

I have seem a number of walls where wicking has occurred but not to the extent described above.

Jason
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Unread 09-29-2002, 09:14 PM   #12
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Interesting thought Jason. I don't see water wicking up a wall and then pushing back down though. If it wanted down, why'd it go up? I'm picturing a water level that just had a sponge jammed into one end. The water would wick up the sponge, and that's it. It wouldn't saturate and then start pushing back down. Now if there were a plumbing leak that supplied more water than the wall wanted to hold, that would increase the height of the water column.

John's gonna love this, three of us going now. c'mon Bob, it's your turn!

[Edited by davem on 09-29-2002 at 11:39 PM]
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Unread 09-29-2002, 10:10 PM   #13
Bud Cline
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John we...er-a you may just learn something when this is over.

Carry on guys.
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Unread 09-30-2002, 02:36 AM   #14
Sonnie Layne
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So, the last piece of property I owned was about ohhh 1/4 mile as the crow flies from this lake. I had this spring on my property that was rightfully called a "spring spring" 'cause of rise of the elevation in this reservior during spring rains, the force of the pressure, gravitationally speaking, would force this plane of water up through it's sands and out into my 'forest'. Now upon aquiring this land (and this was a big factor to me, that I'd have a spring throwing out about uhhhmm 2 gal per min., I've always been kinda romantic in that Libran kinda way anyway, where does the other parenthesis go? Ahhh forget it, what was the subject? oh... yeah. I was told after the first hard dry summer that my spring was hydrostatically controlled. But the mouth of the spring was hmmm I think I remember it being around 50 feet above dam height. Is this the same principle on a smaller scale? Am I talking to my coffee? Please someone tell me I'm not totally kibitzual??? I really wanna know, and no, I don't read the Enquirer.
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Unread 09-30-2002, 06:10 AM   #15
John Bridge
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Yeah, I love it. Where are the other 40 engineers we have among our membership?

Sonnie, I think you are talking about gravity. You may not be, but that's what I think you are talking about.

And a "spring" is a spring not because it occurs in spring. It's because it springs from the Earth.
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