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1. ## Q: Can Kerdi Board e used with steel stud framing? A: No, Kerdi-Board is not designed

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2. ## Q: Can Kerdi Board be used in a Steam Shower A: Yes - but should it?

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3. ## Q: Which is better Kerdi Board or Kerdi DS? A: Kerdi DS by a long shot

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4. Oh, boy...I'm not sure where to even start here. Your "little bit of knowledge" quote works both ways.

Let's take the slide above:

1. A perm is a rating of 1 grain per sq.ft per hr at a vapor pressure differential of 1" Hg. (http://en.wikipedia.org/wiki/Perm_%28unit%29). There are 7000 grains per pound of water. If you convert pounds to ounces (weight..not fluid) then you get the conversion factor in the first column.

2. The second column takes that info in column 1, multiplies by 100 sq.ft, and then multiplies by the number of hours per week (24*7).

3. The 3rd column does the same as column 2, but for 1000 sq.ft

So, the problems with the slide includes:

1. The values in column 2 & 3 (especially 3) are more for "shock value". How many steam showers have you built that are 1000 sq.ft and run constantly for a week??? We could really create "shock value" by assuming that the shower is the size of a football field and is ran 24/7 all year. It would make the values look huge, but doesn't mean that this is a realistic comparison.

2. A more minor point, but these numbers are ounces in terms of weight (not fluid). The two values can be similar, but it depends on the density of the water that you assume.

Now, for your numbers...they aren't even close. Maybe you have major typos or you don't understand what you are looking it. Let's look at Kerdi-Board (0.45). The calc would be (0.45*384oz = 172.8 oz). This is for 1 week of continuous use for a 1000 ft^2 shower. This is like a 16'x16' shower (including all walls, ceiling, and floor (with little to no glass)). It also ignores the fact that the tile itself can have a low perm rating.

All this also assumes that the vapor pressure differential will be maintained over that time and that no drying will occur on the other side. You have to also understand that typical building materials (such as drywall) will have a much higher perm rating that the membrane that you use in the steam shower. This means that the wall can dry out as fast as the moisture entering it.

You could wrap the inside of the shower with aluminum foil to have even a better perm rating, but that doesn't mean it is a good material to build a shower with.

5. Posts removed by John Whipple

6. I got my money on the Nuclear Engineer.

7. Used as intended, Kerdiboard works. All of the people you asked said it should not be used in a commercial steam shower. So, why consider that? For safety purposes, a person should not stay in a steam shower for more than about 15-minutes on average, and even if you have a large family, and each person wanted to take their steam shower serially, the thing would still have the majority of the day to dry back out in a residential setting, where they will warranty it (if you ask, it's not in the manual). I think that there's a reason why the shower construction manual does not list Kerdiboard (at least in the version I read online last week) and only lists Kerdi and KerdiDS depending on the perm rating you want or need. A second reason why is the specified heat rating. There's a bit of confusion here, because in one document I saw 70C, and another 79C, but one of them could have been a typo. But let's take either one: to be steam, it must start out at boiling, and can go hotter; i.e., at least 100C at sea level. If you want a fog generator, you can get droplets at any temp above freezing and below boiling, but that's not what the steam generator produces in a steam shower. Certainly, you could not stand a steam shower that was literally filled with steam (except for a short distance out of the head, it's a hot fog, not steam), you'd cook like a lobster, and maybe before that, die from asphyxiation, but the supply line and head will exceed the temperature rating. Why that temperature is listed, I don't know, and Schluter hasn't said, but it may be because of the bonding of the faces to the extruded polystyrene core (BTW, did you realize that Styrofoam, a registered trademark of Dow, is made of the same generic stuff - polystyrene foam - the stuff billions of coffee cups are made of every year? Why I said, and still say the foam is waterproof.).

Every product has it's place, any product can be installed incorrectly and abused. John is pointing areas where it is not designed for, not the areas where it is, and works well.

One has to consider the cost/benefit/risk - Kerdiboard can allow you to do things you'd never think of, or could afford to do building with conventional means. So, in those situations, it's invaluable, if you want it. When you consider the labor to build say a shower seat, or a tub deck out of conventional means, then waterproof it, and how fast you can do it with Kerdiboard and not have warping, and built-in waterproofing AND a guarantee, how much is that worth? Again, cost/benefit/risk. Now that we know the faces are waterproof, and the extruded polystyrene foam always was, there are three layers of protection built-in. Professional labor is not inexpensive, and it is often a significant part of any contracted job. If it can be done significantly quicker, flatter, and with a full warranty from the factory, the cost of materials becomes somewhat of a non-issue. For a DIY'er, the cost can be a factor, but when you compare that to his inexperience, consider how much more reliable a project can be made with the product.

I still stay, John does not understand the product...or, how best to make use of it.

8. John,

I don't know of any commercial steam shower that would operate 24/7. Sure, they may run 9, 10, or even 12 hr a day, but I don't see one running 24/7. Also, 1000 sq.ft of wall/ceiling space would be quite a monster of a steamer. Yes, the results are proportional, so you can compare based on perm ratings, but then you are back to saying that 1 perm flows 10x the vapor as 0.1 perm under the same conditions. It is like saying "Guess what...10 lbs is 10x heavier than 1lb and 100 lbs is 10x heavier than 10 lbs". In other words, without the shock value, it is a worthless slide.

You obviously have the units mixed up on column 2 and 3. These aren't per sq ft or per hr. They are per week and for 100 sqft or 1000 sqft. The 100 sqft might be reasonable for a residential steamer, but you are saying that the customers are maybe using it 1hr per week (not 168hr per week as assumed in the slide).

Your big commercial steamer (in your example) would be in the ballpark of 1000 sqft (maybe more/less depending on the amount of glass). I don't see how your value of "255,780 Oz of water" for a Kerdi shower is "close enough" Taking data from the slide, the Kerdi case would be 0.74*384oz = 284 oz (this is the amount of water per week through all surfaces with it running 24/7, no credit for tile, no drying, etc. for a 1000 sqft steamer). You are only off by a factor of 1000. I guess that is close enough...

You know that if Jim had post any of that info, you'd be saying "Oh, that's just from a bunch of lab tests. They aren't real world. I build real world"...etc.). If he posted numbers that were so wrong, you'd be posting all over saying that John Bridge must have told him or maybe he got the numbers from some rep.

Point is...there could have been some good discussions in these threads instead of throwing mud. You may set tile as a profession, but your behavior, especially lately, has been anything but professional. That's my 2 cents anyway.

Jim: For the temp rating, I know that standard XPS has a max service temp of 165F (74C). (see here: insulation.owenscorning.com/assets/0/428/429/440/49071852-85cb-495f-b5a2-b1eccb50619d.pdf). Either number that you posted is probably in the ballpark. I think that I would assume that the 70C value is correct (74C rounded down). However, we know that it isn't rated for 100C, so you'd have to be careful with the steam lines. Once the steam exits, it will quickly cool. Also, the tile and thinset will offer some protection. However, if that steam is constantly jetting on a tiled surface, I could see the temperature in that location exceeding the Kerdi-Board max service temperature.

9. I guess when its close enough...its good enough and not quite perfect.

I guess when its close enough...its good enough and not quite perfect.
Not quite getting it...whose deciding what perfect is? Nothing man produces is perfect, depending on what set of parameters you're using. Done according to one of the approved methods with good workmanship, even a simple design and install could be considered perfect. Some people think it's only perfect if it has 2-3-4 or more layers of redundancy. Nowhere have I been saying to cut corners, but even a pretty mansion can fall down or have problems if it's not built with care and understanding. That owner may have different opinions on what perfect means, but we're talking about building something that is reliable, whether simple or complex...

11. Its a play on Whipple's red tagline.

12. ## Tiling a Kerdi-Board Niche

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13. ## Kerdi Board Flood testing: They Leak after a four day soak

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14. And what in a shower niche is going to have 2+" of liquid water on it for 4-days? After covering with tile, what is possible to sit there?

15. ## Fully Waterproof and Vapour Tight - aahhhh NOT

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