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Old 03-13-2013, 12:59 PM   #1
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Cement board behind the sink?


Thinking on redoing the plumbing in the kitchen. I'm going to put in a tile floor, a double sink, and also adding a dishwasher, so while I'm there I may as well replace the plumbing coming up the walls and in that process reroute the very poorly routed plumbing in the basement (there are 5-6 90 degree bends in JUST the hot water line that wouldn't be there if it was run started on the inside rather than the outside--one section of pipe needs to be 6 inches longer, and the rest is 2 straight runs connected by a 90 degree bend instead of a jungle of bends to swap the pipes around 2/3 of the way down).

So, a question comes up: Should I use HardiBacker behind the sink/dishwasher and use a seal around where the pipe comes out? That would effectively waterproof the wall. I'd have to cut the whole section of drywall out and replace it with cement board, but I may end up going in there anyway.

The perceived advantage is that if the sink leaks (right now, it does: if I drain too much water too fast it leaks; if I turn the in-sink disposal unit on, 95%+ of the water bypasses the plumbing and dumps into the cabinet), it won't damage the drywall. Also errors with the sprayer head that spray the back wall are harmless, but generally drywall isn't that fragile.

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Old 03-13-2013, 01:44 PM   #2
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Cement board behind the sink?


First off Hardi backer isn't waterproof. I'd try and fix the leaks.

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Old 03-13-2013, 02:17 PM   #3
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First off Hardi backer isn't waterproof. I'd try and fix the leaks.
Leaks are being fixed by replacing all the plumbing, which is consequential. So I figured I'd address all this at once.

Don't you run a potential problem analysis on everything? Let's take a situational analysis of tiling the kitchen floor...

I'm getting a dishwasher, so I'm using kerdiband to waterproof the kitchen floor while I put in tile floor. Potential Problem: Dishwasher [or ice maker] leaks and water penetrates under the tile floor, damaging the subfloor. Likelihood LOW, Severity HIGH. I've seen it happen, and if the damage is bad enough you need to rip up the whole floor and start over. It WILL happen if someone uses dish soap in the dishwasher instead of dishwasher detergent.

Decision analysis: Waterproof the kitchen floor?

This decision is hard: it scores quite high because the important factors are all better than not. So compare it against an ideal solution. I'll have the dishwasher in an area against an additional wall, so it will have waterproofing such that it is unlikely for water to flow out the kitchen entrance and into the living room; I can mitigate that some as well with caulk (caulk the threshold down to the tile, caulk the cabinet next to the dishwasher to the tile as well).

Against an ideal solution, "protecting from water damage" is 90% as good. Cost is also 90% as good--the cost is about $200 from end to end (kerdi-band, Kerdi corners), where an ideal solution would reasonably cost, oh, $30 (caulk the edges of the floor and call it a day); since the floor is several days of work, around $1000-$1200 (including subfloor, wall damage, etc), and damage would extend into the next room's hardwood floor because of my topology (raising time and costs maybe up to $2000+), cost is 80% as good as ideal. Additional labor is so small it's reasonably equivalent to ideal, 100%.

By these numbers, with "protecting from water damage" at 10 points, cost at 8 points, and front labor at 5 points (I'm not afraid of extra work), waterproofing with Kerdi versus ideal is Kerdi=212, Ideal=230, 92% as good as ideal. That's acceptable, so I'll take steps to waterproof the kitchen floor.

Problem, Decision, Adverse Consequences, Potential Problem, Decision, etc...

I guess cement board isn't waterproof, so there's a whole extra layer of work that has to go into this, or just something else entirely. That would tend to change the dynamics for that decision. Also likelihood of wall damage from a leak is ridiculously low because even in a failure situation the leak is confined to the floor and inside of the sink cabinet, so maybe it's not a big enough risk to deal with. Severity would be lower too, since I can easily repair the wall.
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Old 03-13-2013, 02:31 PM   #4
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Is there a doorway in your kitchen?

I like taking extra precautions too but if you have a severe water leak and it is localized to your kitchen because of your water proofing membrane and somehow doesn't go anywhere else then what?

It will just seep thru the semi permeable layer of tile and grout and just sit under your visual layer to get musky?

Best case scenario?

What if it doesn't stay in your kitchen? lets say your water line breaks when you're at work. Where would your water go once it stops at the Kerdi.

Seems over kill to me but I'm open to constructive debate.
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Old 03-13-2013, 03:17 PM   #5
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See, that's what I'm talking about. What could possibly go wrong?

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I like taking extra precautions too but if you have a severe water leak and it is localized to your kitchen because of your water proofing membrane and somehow doesn't go anywhere else then what?
Wet-dry vac.

Quote:
It will just seep thru the semi permeable layer of tile and grout and just sit under your visual layer to get musky?
Good question. Difficult to address, even with a drain (the floor is level). Also important because of the sweep vent for the vacuum power unit, which would fill with water and take it to the power unit, destroying it (unless I have an interceptor bucket).

Less severe than the subfloor being destroyed, though.

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What if it doesn't stay in your kitchen? lets say your water line breaks when you're at work. Where would your water go once it stops at the Kerdi.
Too many bad places.

Because of kitchen sinks this is impossible to address completely. As for an ice maker or dishwasher... only so much water should flow at once continuously.

Is there a device I can place on the water line that measures how much water actually flows in one run, and if it exceeds a certain volume (i.e. if you turn the water on/off/on/off it's fine, but on and draw 10 gallons it's not fine) it shuts the water line off permanently? This should work for ice makers and dish washers, which absolutely draw limited amounts of water at once.

How about a device that is aware of the maximum flow rate of a line? For a sink or dishwasher, the appliance itself is limiting (the faucet on a sink won't pass full line flow...), so greater flow indicates something is wrong on that line. Think of water pressure as voltage and water flow rate as current, and what we have is a (fluid) circuit breaker throwing when the current gets too high.

Such devices don't exist, unfortunately. (However, unrelated, I'm going to put a thermostatic mixing valve on the dishwasher to prevent temperatures above 125F, which may damage dishes--irrespective of the setting of the water heater.)

Maybe the reason these devices don't exist is if you cared that much you'd have a shut-off valve at the kitchen and you'd shut it off when you leave for work. Oddly there's a shut-off valve in the basement to disable the garden hose. My parents actually turn the main off when they leave the house, but they leave for a week. (They also disable the pump so there's no water pressure)

Decision seems to be between A) Accepting the risk; or B) shutting off the water when I leave. (B) seems ridiculous, but takes 15 seconds. Note my parents shut off most of the power (notably, to the kitchen electric stove they have, and to the water heater and water pump) when they leave; but the breaker box is in the garage. If I got a heat pump and heat pump water heater, I'd be inclined to shut off the gas when not using my electronic ignition gas stove.

EDIT: Actually. I'm over-complicating things. A floor-level drain next to the exit from the kitchen into the dining room would drain any water that could possibly flow over the threshold and out, if I caulk-sealed the threshold. The water level would have to exceed half an inch locally, hence the drain. Drain could go to the sump. It could be hidden behind a cabinet, with a hole cut in the side near where moulding would run behind the cabinet, nice and discrete.
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Last edited by bluefoxicy; 03-13-2013 at 03:25 PM.
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Old 03-13-2013, 03:30 PM   #6
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I suppose you could plumb a pressure transducer in line and run it to a computer. Then you could measure your pressure via voltage drop, write a simple program which will then talk to an electric shut off valve.

Assuming of course that your pressure would change when the water is flowing vs not. I dont know if that is the case.
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Old 03-14-2013, 02:14 PM   #7
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Cement board behind the sink?


How about, stop all this nonsense and use one of these options:

http://www.watts.com/pages/whatsnew/floodsafe_connectors.asp
or
http://www.rewci.com/floodstopsystems.html (there are other manufacturers too, including watts. I've given you a start in the right direction)

Last edited by Seattle2k; 03-14-2013 at 02:20 PM.
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Old 03-16-2013, 09:16 AM   #8
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How about, stop all this nonsense and use one of these options:

http://www.watts.com/pages/whatsnew/floodsafe_connectors.asp
or
http://www.rewci.com/floodstopsystems.html (there are other manufacturers too, including watts. I've given you a start in the right direction)
I like these!

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