elaborate on why you "would NOT keep the existing slab

Maybe you could explain more clearly what the options are. What the contractors want to agree to and what you want to do.

You can google for "gypcrete cracking" to find lots of similar discussions. I suspect that your concrete is about the strength of gypcrete.

What I do know about the mix at this point

What else do you know? In this entire thread, we still haven't learned too much about your actual situation. For example;

1) Where is this build located?
2) Why do you consider it passive solar? In other words, what shines on it and what does the insolation pass through on its way to the slab?
3) Does the slab have radiant tubing in it and what kind? How much? What is the design temperature?
3) You have never told us what the actual size or dimension of the slab(s) are. What rooms?
4) You haven't ever detailed the structure which would include joist size and type, span, spacing, subfloor, etc.
5) What is the actual makeup of the slab? Is there a vapor barrier at the bottom? What is the reinforcing in the slab?
6) What was the procedure? Did they pour it one afternoon and "seal" it a couple hours later? Next morning? A week later? Has it been stained or sealed or patterned? Did it crack before all that?
7) Haven't even figured out if the cracking has continued or stopped and after how long.
8) Haven't described how this looks much at all, other than for the word "efflorescence". Is that what it actually was or did a concrete stain go bad? Is the surface rough, glossy or punky? Soft? Hard?
9) At one point, cracks were 3/16" by your description and then they became 1/4" and 3/8".
10) What is proposed? Raising entire slab with overlay 1/16"? 1/4"? Will doors need to be raised? Thresholds? How many?
11) And finally, since you seem to like the "passive solar" characteristics of the slab, I'd like to know how you determined that. Is there any data or is the surface just warm to the touch?

In short, without meaningful input on what is happening, no one here can help you much except to feed you an answer you may have been looking for in the first place.

Posted By ICFHybrid on 18 May 2013 10:23 AM

What I do know about the mix at this point

What else do you know? In this entire thread, we still haven't learned too much about your actual situation. For example;

1) Where is this build located?
2) Why do you consider it passive solar? In other words, what shines on it and what does the insolation pass through on its way to the slab?
3) Does the slab have radiant tubing in it and what kind? How much? What is the design temperature?
3) You have never told us what the actual size or dimension of the slab(s) are. What rooms?
4) You haven't ever detailed the structure which would include joist size and type, span, spacing, subfloor, etc.
5) What is the actual makeup of the slab? Is there a vapor barrier at the bottom? What is the reinforcing in the slab?
6) What was the procedure? Did they pour it one afternoon and "seal" it a couple hours later? Next morning? A week later? Has it been stained or sealed or patterned? Did it crack before all that?
7) Haven't even figured out if the cracking has continued or stopped and after how long.
8) Haven't described how this looks much at all, other than for the word "efflorescence". Is that what it actually was or did a concrete stain go bad? Is the surface rough, glossy or punky? Soft? Hard?
9) At one point, cracks were 3/16" by your description and then they became 1/4" and 3/8".
10) What is proposed? Raising entire slab with overlay 1/16"? 1/4"? Will doors need to be raised? Thresholds? How many?
11) And finally, since you seem to like the "passive solar" characteristics of the slab, I'd like to know how you determined that. Is there any data or is the surface just warm to the touch?

In short, without meaningful input on what is happening, no one here can help you much except to feed you an answer you may have been looking for in the first place.

I don't see the need to answer all these questions on this forum--especially if you go back to the question I asked initially, before the discussion got far off onto other aspects of the defective work. If you have expertise in this area and let me know what it is, I'll be happy to talk with you directly, individually. I will say here that the house is absolutely true passive solar. I had a passive solar expert design the house so the house angle, amount of glass on each side, type of particular low-e glass, overhangs, calculations of solar thermal heating/cooling, slab, etc. were all done very precisely in the design of the house. I am not using the term passive solar informally like I know many people do. I'm in the northern Rockies and get almost all my heat, except on the coldest nights, from the passive solar. True passive solar works amazingly well (and it doesn't overheat at all in summer of course, as well). Also be aware the house is very green. I'm 100% off-grid with solar, wind, solar thermal as well.

Posted By ktot on 13 May 2013 12:48 AM
I have a passive solar off-grid home that works very well with a 2 in. concrete slab that is finished with decorative concrete stain/paint. However, the slab and stain/sealer are very defective and very likely have to be replaced, but one party is proposing a concrete overlay product be put atop the existing slab. The overlay product (ArtCrete Deck Coat, I think it is) consists of two parts--1) Portland cement, aggregate, and a stain, and 2) a modified acrylic latex resin. My belief is this is not good thermal mass (atop the concrete) as the resin component synthetic or at best partly plant material and only earth materials such as stone, clay, water, concrete, provide optimal thermal mass. That in fact the entire slab needs to be removed and the floor rebuilt from scratch to resolve the serious problems and still provide me with optimal thermal mass.

Does anyone have experience or knowledge about this? Using or not using a concrete overlay product for the top layer of a floor for thermal mass, vs. a plain darkly stained concrete slab.

I have a similar floor and use it as thermal mass - concrete with stain/sealer/wax.  Here is a pic.



I believe you are correct to be concerned about the acrylic component.  I think it depends on the mix.  Acrylic can be like plastic, which could "block out" your thermal mass, or it can be a very minor part of the mix, like an acrylic stucco.  Basically, you want something with a very low (near zero) R factor.  You should be able to contact the manufacturer and get this information.  My gut feel is that you're OK, but it doesn't hurt to check.

Your concerns are very valid!  The last thing I would want is to lose my thermal mass from my floor.

Jim Gagnepain, What sealer and wax did you use?

Posted By vb on 07 Jul 2013 10:53 AM
Jim Gagnepain, What sealer and wax did you use?

Sealer: PermaPro Aqua Klear Koat
Wax: Direct Colors DCI Residential Floor Wax and Polish

We find that the wax protects the sealer.  The sealer scratches fairly easily, without the wax.

I'd be tempted to use a two part clear polyurethane. Works well on my garage floor.