[Greenbuilding] Passive solar home--concrete overlayre thermalmass

KTOT (g) ktottotc at gmail.com
Fri May 17 15:15:01 CDT 2013


I read your other response before this one so see now what you were saying about 2 in. To comment on some of your remarks here. Yes, the framed floor is strong enough—a comprehensive analysis has been done and this is a known fact at this point. No, there probably is not adequate reinforcement nor enough control joints. Both those were the responsibility of the concrete contractor and are questions being raised and pursued. No, the designer was not specifying a gypsum floor. He was specifying a concrete slab that would be directly stained; gypcrete cannot be stained from all I’ve read and learned.

The floor IS designed to hold the 2 in. This research was done before my builder OK’d the slab being poured at 2 in. and further more detailed analysis (or at least documentation of it) has been done/made available more recently.

Do note at this point I’m not at all concerned about “removing and replacing.” I’m only concerned about the “removing” part. Once I am paid for the rework, I will be doing extensive research on how to optimize a new floor for the passive solar and radiant heat.

From: John Salmen 
Sent: Tuesday, May 14, 2013 8:00 AM
To: 'Green Building' ; topher at greenfret.com 
Subject: Re: [Greenbuilding] Passive solar home--concrete overlayre thermalmass

I said ‘usually’ requires. Building is about understanding how materials work and how they work together. Concrete expands and contracts – the ground or structure underneath it expands and contracts. It is like two people dancing to different songs. This is why we put control joints in slabs (to relieve stress and create predictable cracking). This is also why we separate materials (a layer of sand between the ground and the concrete to allow for movement) or we increase the strength of a material to resist cracking (eg. Reinforcement in concrete or increasing the thickness of a material)

 

I read in a later post that this slab you don’t like is only two inches and supported by wood framing. You also said that it is thicker than the designer wanted? This is an atypical floor so it raises lots of questions. Is the framed floor strong and stiff enough to support a 2” slab (if it is thicker than the designer wanted then they were probably specifying a gypsum floor with something over it). Is the slab designed to resist movement (sufficient reinforcement and control joints)?

 

I have the feeling that this was a conventionally framed floor and the concept of adding mass as a finished concrete slab floor was an afterthought and not well thought out. If the floor is not designed to hold the weight of 2” concrete it will fail in some way or compromise the structure – it will definitely continue to cause the concrete to crack. Anything you put over the concrete will show the cracks through it or form new cracks. Removing and replacing the concrete is not really a solution. 2” concrete has to be reinforced substantially and control joints cut in a tight grid pattern and still there will be odd cracks. Going thinner means you are basically pouring concrete tiles and even a 2’ grid pattern will crack over a framed floor.

 

The only reliable way of achieving mass of consistent density would be tile on a thickset (tile on 1-1/2” of mortar) and that is tricky. Tile on a couple of layers of cement board is a possible option if the tile is fully bedded (no air gaps)

 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of KTOT (g)
Sent: May-13-13 10:20 AM
To: 'Green Building'; topher at greenfret.com
Subject: Re: [Greenbuilding] Passive solar home--concrete overlay re thermalmass

 

I am not clear on what you are saying. Are you saying simply applying overlay material (as was originally used in a bathroom, which is not thermal mass so was not an issue re overlay vs. bare concrete) will not work, that something else is required? Or a layer between the concrete and the overlay?

 

Also my understanding is density isn’t the issue specifically re thermal mass, rather is an issue of earth materials (stone, water, clay, etc.) vs. non-earth materials.

 

Re the slab, it appears the cement was left sitting in the truck multiple hours with no retardant added and a very excessive amount of water was added, curing/finishing was likely improper, and possibly more. I probably didn’t mention the very severe cracking throughout the floor in my original post. People also have different opinions on whether one can just cover a defective slab or if cracking will cause problems in the future as well. Some of those issues are still be sorted out. Meantime, I’m focusing on the thermal mass aspect of overlay atop a slab.

 

From: John Salmen 

Sent: Monday, May 13, 2013 10:58 AM

To: 'Green Building' ; topher at greenfret.com 

Subject: Re: [Greenbuilding] Passive solar home--concrete overlay re thermalmass

 

The bonding of a tile or dissimilar material to a concrete slab usually requires a separation or slip sheet of some sort as well as a trowel pattern that will create air pockets. This is different that simply a concrete resurfacing material. Resurfacing is typically a very finely graded cement product with modifiers to allow for bonding and movement. The density of these materials would be typically high possibly exceeding the concrete slab. I can’t see an issue that would involve removing a slab unless it is totally f_____ for other reasons.

 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Vadurro, Rob, EMNRD
Sent: May-13-13 8:07 AM
To: topher at greenfret.com; Green Building
Subject: Re: [Greenbuilding] Passive solar home--concrete overlay re thermal mass

 

I believe the concern is the transfer of heat between different materials. I can’t remember where I saw it, but there was a table showing the transferring heat between base and finish materials, say tile to concrete slab below in passive solar conditions and the rate of transfer was much less than one might think. The joint between the two impeded the heat transfer, in other words. I would think an acrylic additive may impede the transfer even more. The best is always to not cover the slab, only color it, if heat retention in the slab is the goal.

 

Rob Vadurro, AIA

Park Architect

New Mexico State Parks

1220 South Saint Francis Drive

Santa Fe, NM 87505

505-476-3383

505-476-3361 fax

 

From: Greenbuilding [mailto:greenbuilding-bounces at lists.bioenergylists.org] On Behalf Of Topher
Sent: Monday, May 13, 2013 8:39 AM
To: Green Building
Subject: Re: [Greenbuilding] Passive solar home--concrete overlay re thermal mass

 

On 5/13/2013 1:07 AM, KTOT (g) wrote:

  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 


A concrete overlay product is likely to be roughly similar in thermal characteristics to a concrete slab.  Meaning that you will just have a thicker thermal mass.  It seems unlikely that you should be worried about too much thermal mass in a passive solar house.  The overlay product might have a lower specific heat, or conductivity, wither of which will reduce it's effectiveness somewhat.  Remember to stick with a dark color.

Thank You Kindly,

Corwyn

-- Topher BelknapGreen Fret ConsultingKermit didn't know the half of it...http://www.GreenFret.com/topher@greenfret.com
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