I can't help you, but I'm wondering if you asked the Oakland Building Department? When they said RedGard wouldn't be accepted, did they refuse to tell you what would be accepted?

No. They have not refused to tell me. But, until this morning, I had not actually posed that exact question. This morning I did and I will let this disc know what they say.

It’s not a matter of the type of flooring unless I can get a type of flooring that meets the Oakland Building Department‘s requirement for a permeance of 0.06 perms or less. If a flooring product can do that unilaterally, then I can just propose that flooring product. But, it would have to be demonstrated and documented through independent lab results

...As things stand right now, the Building Department doesn’t regard RedGard as overkill because it has a permeance of 0.35 — seven times the allowable permeance of 0.06 perms that an under-slab HDPE vapo barrier provides.

...in the world of permeance, lower numbers are better. Higher numbers are worse...

there Is a diference between vapor barrier and water proof redgaurd waterproof well maybe not if you only apply 1 coat? I would reach out to a flooring company and they can point you to what would work.

What kind of floor are you installing? Glue down or floating application?

My original thinking was to go with a floating floor, such as the GemCore Topaz stone plastic composite (SPC). But, I would go with a different flooring if it was rated as a vapor barrier good enough to satisfy the Oakland Building Department. For example, I spoke with the manufacturer or RedGard this morning and they suggested a porce tile flooring with TechMV underneath. TechMV is paint-on like RedGard, but has a permeance of 0.085. That is three times better than RedGard but, still not to the 0.06 perms that the Oakland Building Department is requiring.

...They are suggesting that Dal-Tile might have a porcelain tile rated with TechMV underneath that would achieve a permeance of 0.06 perms or less. I have not yet spoken with Dal-Tile. But, I inten to.

Why don't you lay down 6 mil poly then install a floating floor over that?

6 mil poly over the slab does not get the same permeance rating as the same 6 mil poly underneath the slab. Because of the weight of the slab bearing down on the poly and ground vapor underneath the slab, the combination of slab-over-poly achieves a permeance rating much better that that same poly over slab does. And, further, when it comes to permeance, a thicker barrier of the exact same materia does not, necessarily, translate into lower permeance. That is why three coats of RedGard does not achieve a lower permeance than two coats of RedGard.

Mr Memes - You might just have hit the jackpot for me. I had never heard of Schluter Ditra. But, I just called Schluter Systems and they are telling me that the Schluter Ditra barrier achieves 0.006 perms. If that is correct, then it is ten times better than the 0.06 perms required by the Oakland Building Department. They are sending me the documents and I will review them. So far, so good. Fingers crossed. Thank you so much for that suggestion...

Kerdi is .75, which won’t cut it for your purpose, or steam shower either. You have to move to Kerdi DS, which is .18. It’s 20 mm thick, and harder to work with. It holds the roll curl. A little heat usually sets it right.

Hydroban sheet is thinner than DS, more workable, and is rated .06, which would easily meet your goals. You can also use modified thinset with it, whereas Kerdi requires unmodified.

If vapor permeability is the goal, the products with less vapor permeability is very relevant to the discussion.

Might get you close... link

Check out with Surecrete, they have a few solutions

there Is a diference between vapor barrier and water proof redgaurd waterproof well maybe not if you only apply 1 coat?

Wrong.

Taken from CBP redgaurd tech sheet.:

Redgard can be used as a slab-on-grade moisture vapor barrier under all types of floor coverings.

Dennis:

always go direct to the product tech spec( as you did) never fight with CA inspectors :).

Ditra has been tested for California.exceeds both vapor perm and is VOC compliant theres many better products regardless and sounds like youve found one that will be fine..

DITRA and DITRA-XL were evaluated according to the "Standard Method for the Testing and Evaluation of Volatile Organic Chemical Emissions from Indoor Sources Using Environmental Chambers, Version 1.1" for California Specification 01350 and found to comply with the VOC requirements. California Specification 01350 is referenced by various green building standards and rating systems.

The manufacture of RedGard tells me that, in order for RedGard to be used as a vapor barrier, two coats — and only two coats — must be applied. This resulta in a barrier that is 30 mils thick and has a permeance of 0.35 perms. This is probably not a low enough perm rating for the Oakland Buil Department standards. However, I am told that it has met requirements of a number of cities in Southern California.

Yes and true. Oaktown is another planet

Clarify's exactly why I corrected the other poster it is a vapor barrier and is ONLY to be used as they advised you (there is no in between). . I would simply comply with your inspector. Roll on membranes are very much like guesswork regardless brand. IMHO.

There are local schluter reps in your area you may call them in if you feel you want to use ditra and get them involved .

" Idk may said stupid idea but I'm out of ideas lol"

Poor english but TRUE

The question that follows is, what can you put over Redgard? I'm told a self leveler like Ardex would delaminate from the Redgard. And Floor glue is solvent based and will react with it. So what does that leave if you don't want tile or a floating floor? My clients all want to see polished concrete.

Same dilemma here with City of (J)Oakland. What did you end up using? Koster doesn't seem very attainable in our parts.