Hardibackedr over sheetrock on exterior wall.

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Bmusgrove

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I have mold in my backer board and had to remove it . Builder had used a paper faced green board over sheetrock.


On the outside walls, I am not sure how to install the vapor barrier as there is not one know. Where would it go whn using backer board over sheetrock?

Insulation - vapor barrier - sheetrock - backer board-tile?
Insulation - sheetrock - vapor barrier- backer board-tile?

Currently the insulation on the outside wall is unfaced. Shouldn't this be faced insulation or is it different when sheetrock and backer board is installed over it?
 
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JohnfrWhipple

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As a backer board Hardie Backer is not one of my favourites.

I have seen many tile books showcase the boarding method you have. Not sure why. I would track down WonderBoard Lite as a backer board and call Custom Building Products technical support line.

Not sure what the vapour proofing requirements are in Texas. You best talk with city hall here.
 

Bmusgrove

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As a backer board Hardie Backer is not one of my favourites.

I have seen many tile books showcase the boarding method you have. Not sure why. I would track down WonderBoard Lite as a backer board and call Custom Building Products technical support line.

Not sure what the vapour proofing requirements are in Texas. You best talk with city hall here.
Apparently in 1992 it was not against code here and was common.
 

Jadnashua

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The location of a vapor barrier on a typical wall will depend on whether you are in a predominately heating or cooling zone. On a heating zone, it is placed on the room side to keep moisture out of the colder walls where that vapor could condense and create problems. In a predominately cooling location, where you have hot/humid air outside most of the time, you typically put the vapor barrier on the outside of the wall so that your dew point which will be inside the wall doesn't have any appreciable moisture to condense...this is the reason why the location is important.

Keep in mind that cbu (Hardie is technically a fiber-cement backer unit) is NOT waterproof by itself, but it is generally not damaged by being wet. A fiber cement board requires slightly different installation techniques verses a 'real' cement board (Hardiboard can contain up to something less than 15% cellulose, i.e., wood pulp or paper).

A shower can provide a fairly substantial vapor pressure, and personally, I would not want any cbu to be directly on drywall...it would hold any moisture against the paper facing, and create problems. So, your job is to prevent both the shower's vapor pressure and that from outside to be managed properly. Your local building inspector should be able to tell you what is required in your locale.

If I were considering this, I'd probably ensure there was a proper vapor barrier based on codes, then I'd use a surface waterproofing IN the shower to limit any vapor that might get into the walls. If this were a steam shower, you'd want to select that waterproofing for its vapor barrier characteristics (there's a big difference between vapor proof and water proof - think Goretex - it's waterproof, but specifically is designed to let water vapor go through it). A typical shower really only needs water resistant on the walls since the vapor pressure isn't high, and not much moisture can get into the walls, and they dry out between uses (slightly different thing on the shower pan, though...long topic - that needs to be waterproof).
 

Bmusgrove

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I will probably go with a kerdi system for the walls, whether I go dire to studs or sheetrock > kerdi Board > kerdi membrane
 

JohnfrWhipple

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I will probably go with a kerdi system for the walls, whether I go dire to studs or sheetrock > kerdi Board > kerdi membrane

Good luck with that. Kerdi Board is most likely the crappiest product I have ever reviewed or tested. You know they use a paper based product to make it strong right? And you understand it's made from foam? Foam.... When a home is build part of the earthquake strength comes from a rigid backer board & Drywall being installed to both sides of a homes wall. You will weaken this as well with foam based backer boards. Check with your local building inspector and architect if this is OK. With my little girls sleeping under our roof I would never want to worry about that.

If you are trying to save money and buy into the drywall is OK for the shower then go with a more premium waterproofing system like those from Laticrete and Ardex. This way you can keep your waterproofing system and setting materials all in one family. I'm aware of no thin-set suppliers than allow the over watering on the thin-set that Schluter asks for. If you find one let me know. I asked Mapei and they said not to. I asked Laticrete and they said to use their system. I asked Ardex and they recommend 8+9. There must be one company but it's really important to get this is writing since the mix ratios on thin-set bags are most time to stiff of mix to use with Kerdi.

Keep in mind, also when you choose to use Kerdi you also need to go against all most every single tile manufactures recommendation to use a modified setting material to apply the tile. In fact I have never seen a tile supplier specify non-modified thin-set. At least not in the past 20 some years.

It's your shower so it's your call. None of the tile pros here use it. None like it. We do have a member who has been selling Kerdi online for over ten years. Before you go ahead with his recommendations ask him to show you his showers. I bet he won't.

I know John Bridge used Kerdi Board for a project. But he needed to use a liquid waterproofing called Hydro Ban to finish the job.
 
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JohnfrWhipple

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Laticrete's sheet membrane is superior to Schluters.

So is Noble Company's.

If you are worried about thin-set restrictions with these two products. Don't. There is none.
 

Jadnashua

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Listening to John is like a broken record. There are lots of decent waterproofing products out there. Kerdi has been used worldwide for nearly a quarter century, most of the others are much newer - the Laticrete sheet product came out this past April...while I believe it is good, they have no track record with it. Kerdiboard, when used in a shower, has all edges and penetrations sealed...the surface is waterproof. The foam is an extruded version of the same chemical foam that millions of foam coffee cups are used every day are made of...they don't leak. Then, throw in the stiffening, thinset holding surface, and you've added additional water/vapor/thinset features to the material. If you use DitraSet, you'll notice on the spec sheet that it works as both a thinset and a medium bed mortar, and that they have a range of water you can add to it. Most thinset manufacturers magic mix is designed to only work with a very specific amount, Ditraset does work fine as long as you are within that range. Anyone that says to overwater the thinset does not understand the Kerdi/Ditra installation instructions. Use the max for embedding the fleece of the membranes, and you can use less, especially if you have a larger format tile where a medium bed mortar might be needed. Mapei also makes an uncoupling membrane mortar that works quite well.

If you read any of the spec sheets for any available thinset mortar, dryset or modified, it will list bond strengths to various types of tile, porcelain included. What some people just don't seem to be able to grasp is that there is a big difference between bonding to a solid surface like cbu, plywood, or a concrete slab and bonding to a membrane which acts somewhat like it's own microscopic cleavage plane. While you may find bond failures using an unmodified where a modified was specified, you really do not see failures when a dryset mortar is used, as specified, when used over a membrane designed for it unless there is some workmanship error (like poor coverage, letting the thinset skin over before setting the tile, improper substrate prep, or excessive deflection, etc.).

The industry guidelines as outlined by the TCNA (Tile Council of North America) give some specific warnings about a latex modified mortar used between a waterproof membrane and an impervious tile. They are there for a reason.

FWIW, most internal walls are not load bearing, and it makes little difference what is applied to them. A properly installed sheet of Kerdiboard, covered in tile isn't going to make your house fall down in an earthquake!
 
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