This is for a radiant floor overpour. The gypcrete sights all point out the flaws of concrete, but it seems to me that concrete has the distinct advantage of being mold resistant. This would be an 1 1/2″ slab & if using concrete, I would add fibermesh & an isolation membrane between the crete & the subfloor.
Anyhoo, I’m looking for the pros & cons of each. I’m not looking into regular concrete due to the weight – I imagine lightweight concrete uses a lighter aggregate (hollow or pumice or something).
I apologize if this topic has been hashed out before (I searched on gypcrete & concrete & didn’t turn up anything). If there is a thread on this you can point me to it.
Replies
The aggregate is lighter in lightweight concrete..It is alot more weight than the gypcrete..
If your floor is sized to accept the lightweight concrete, then go for it. As far as radiant systems go, the denser the medium the tubing is set in, the more efficient the system is..
Check with the arch/eng to make sure the joists can handle the added dead load...
Edited 1/24/2006 12:25 pm ET by MJLonigro
I already called my archy & he said that gypcrete or lightweight concrete would be fine.
What did you mean by the tubing being sized to accept lightweight concrete? I'll be using 1/2" PEX...
in either case, stick to 9" o.c. or less and make sure you're dealing with the lead/lag times effectively. This generally means at least PWM thermostats or even better indoor feedback sensing w/water temperature modulation. Depends on the house and climate though.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Another suggestion I had heard was to nail sleepers on top of the floor & run the tubing between (~8" OC) & then fill w/ sand.
The main pros for this method would be 1) I could do the entire job myself 2) sand is even lighter than gypcrete.
The cons 1) the sand would not be structural at all - concrete w/ fibermesh would be - don't know about gypcrete & 2) lighter also means less thermal mass
thermal mass is not a benefit for radiant. If you're doing passive solar, then mass is a factor. Conductivity is the key element of radiant.Sand is a bad radiant method. Do not use it under any circumstances.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Sand not so good, but if you wanted a nailing base, you could layout sleepers and pour concrete in between. Also, there are the subfloor 'systems' with preformed channels, and some folks make their own with plywood strips and aluminum plates (some also omit the plates).
The difference in weight between gyp-crete and concrete is not very significant IMHO. In fact the density of the concrete is an advantage, as it is more conductive.
I think the primary benefit of the gyp-crete is not its weight, but its self-leveling nature.
Here is a 'thin slab' RFH concrete mix with proven results known as the "Youker Mix" (attributed to a fellow by the name of Harvey Youker).
Type 1 Portland cement 517 lb.
Concrete sand 1,630 lb.
#1A (1/4" maximum) peastone 1,485 lb.
Air-entrainment agent 4.14 oz.
Hycol (water-reducing agent) 15.5 oz.
Fiber mesh 1.5 lb.
Superplasticizer (WRDA-19) 51.7 oz.
Water about 20 gal.
Footnote text from figure:
Note: These mix proportions make one cubic yard of 3,000-psi concrete floor topping (strength rated at 28 days). The high-slump concrete recipe creates an easy-to-pour mix that flows well around the tubing, providing excellent thermal conduction between the tubing and the concrete.
Interesting. Do you know where I'd find an air-entrainment agent? Same place as I buy the cement?
Yes. It's what they put in for outdoor flatworks, such as sidewalks/driveways. Prevents cracking.
What about aggregate? Would it be a good idea to use something like vermiculite instead of pea gravel? I'd like to keep the weight under 100 psf
I don't know enough about vermiculite to say either way.