DIY Hydronic Floor Heating

[webaware]

Here's the photos.

[webaware]

A bit more data:
Steel panels weight (/m2): 4.5kg
channel grout weight (/m2): 16kg
I've got 27m2 of the panels, giving a total weight of 553kg
I figure that the cladding is a good compromise between a screed floor and the alluminium nail-up panels:
Greater surface area (they go over the joists, not just between).
The channel grout provides a thermal mass as well as a conduction passage between the PEX and the panel.
Some more photos then:

[Drake]

Very inventive webaware. Did you space your joists to fit metal or did they happen to fit standard joist(cc) spacing? Typical steel roofing/siding here has 9"(cc) spacing between channels. Though steel is not a better conductor than alum I bet the difference is minimal. I wonder if the corrosion reaction with cement product(grout) would be similar to alum. I have used galv flashing in cement projects with now ill effect that I've seen. I think stucco mesh could be fastened right over it as well if one wanted to lay a ceramics floor as well.

[AC_Hacker]

Originally Posted by webaware

Some more photos then:

I'm very interested in what you're doing. I understand what's going on, but if you have more photos, I'd like to see more.

Is this a technique that you developed, or is it being used elsewhere in your area?

Very interesting that such a curious coincidence could be utilized in this way.

Regards,

-AC_Hacker

[webaware]

Hi Drake and AC Hacker!
joists are normally 400mm centred in the UK, so it's a happy accident that the panels fit.
The panels are painted, so in the dry location i'm not anticipating any reaction between the grout and the panels. I'm not aware of anyone else using this technique. It came to me as a flash of inspiration when looking at the roof of our garage, which is covered in such panels. In the UK, extension work is overseen by a building inspector from the local authority's Building Control dept.. My building inspector approved the technique, and he's not aware of anyone using it.

[webaware]

I should mention that I got the panels from the local panel suppliers - they're all seconds - different colours, scratched etc. so I got them for less than half the price of new panels - they would have gone for scrap, so my recycling index has risen.

[Ko_deZ]

Looks like a great solution you have there. The grout will be able to store and somewhat distribute heat, and the metal will do the distribution. Steel is not the best thermal conductor, but it should do the job. In your case it only needs to spread the heat 10cm to either side of the pex. I am thinking that the grout will help somewhat in getting the heat from the tube into the steel so that it spreads better. The normal way is of course to have a heat spreader that is bent around the tube, but I cannot see any reason for this not working just as good. Good thinking!

[Drake]

Webaware do you have living space above and below radiant floor? Do you plan to insulate under it to isolate space below?

[Drake]

Exploring possible reactions of cement with galvd metal found; "The reaction time between galv rebars and concrete are only of concern during the the curing stages of the concrete. The initial curing include the time when still wet. Ph of wet concrete is approx 12.5, very alkaline. It reacts with zinc(in galv) to form hydroxyzincates which protect zinc from further corrosion, but can evolve hydrogen gas. Excessive gas can result in a more tenuous interface(bubbling), reducing bond strength. Mixes with ph over 13.5 have shown significantly higher and should be avoided with chromates"

"The admix at the mixer is chromium trioxide. It is added to the water before depositing into mixer @ dosage of about 300 parts per million by weight of mortar's or concrete's mix water. However, a substantially smaller proportion (100 parts per million) may be sufficient to prevent hydrogen evolution. All that works out to approx. 5 to 13 grams or a level teaspoon of chromium trioxide powder for every 100 pounds of mix water."

Tom Rapenske
- Richmond, KY, USA

----
Ed. note: Tom reminds the readers that chromium trioxide is a dangerous chemical and a potential environmental issue; you must be thoroughly familiar with these issues before attempting to work with it like this.


"Abstract: The major concern regarding the use of hot-dip galvanized (HDG) steel as reinforcement in concrete has been the high rate of corrosion experienced by the zinc during the first hours in the fresh, wet, and highly alkaline concrete. The present work was aimed at clarifying three issues associated with these concerns. The first involves the metallurgical phases at the surface of the zinc coating. The concentration of zinc at the surface is a function of processing procedures, surface treatment, and exposure to weathering. Differences in the coating surface composition influence the corrosion behaviour of HDG steel reinforcing bars when they are embedded in concrete. The second issue involves the increasing use of supplementary cementing materials in concrete, which change the chemistry of the concrete pore fluid, and also influence the corrosion. The third issue is that the initial corrosion is accompanied by hydrogen evolution, which could increase the pore volume of adjacent cement and thereby, decrease the bond stress between the concrete and the steel. In order to limit the hydrogen evolution, a chromate layer is applied after galvanizing. The results of the project have demonstrated that, during zinc corrosion in ordinary Portland cement (OPC) concrete, calcium hydroxyzincate formed on untreated HDG steel provided sufficient protection against corrosion. Therefore, it is concluded that treating HDG rebar with dilute chromic acid is unnecessary as a method of passivating zinc. A layer of zinc oxide and zinc carbonate formed through weathering on HDG bars slightly increased the initial corrosion rate and passivation time compared with the non-weathered rebars. HDG steel with an alloyed coating, i.e. consisting of Fe-Zn intermetallic phases, required a longer time to passivate than those with a pure zinc surface layer. The lower zinc content of the surface limited the rate of CHZ formation and, hence, delayed passivation. However, regardless of the surface condition, the coating depth loss after two days of embedment in OPC concrete was insignificant. In concretes containing 8% cement replacement with silica fume, or 25% cement replacement with slag, the initial corrosion rates were higher than those in OPC due to higher pH and lower calcium contents of the concrete pore solution. The higher corrosion rates lead to initial depth losses which are considered significant. However, in these concretes, chromate treatment was also shown to be unnecessary. Through porosity assessment of cements adjacent to HDG bars, it was found that hydrogen evolution accompanying zinc corrosion did not have an impact on the pore volume of cements: any additional pores created by hydrogen gas are filled by the zinc corrosion products. The negligible difference in pore volume between cements adjacent to chromated and non-chromated bars further confirmed that chromated treatment was unnecessary."

Webaware use of "painted" metal might also help limit reaction. "Paint" might reduce thermal transfer effic some.

It can be a hard thing to quantify how much efficiency is worth with all the possible variables in any project. Significant savings in materials, DIY capability or just the "realness" of a project, a lower efficiency can still be preferable than nothing.

Webaware approach has simplified how I was considering to use steel siding in hydronic radiant in second floor where I plan it under a tile floor that also has passive solar exposure. I am lucky it is new construction and can build to fit.

Web, did you notch joists for PEX crossover?

P.S. In most "under" floor PEX installs I've seen large bends of PEX are shown exposed, uninsulated. Isn't this a potential significant thermal loss easily solved with flex foam pipe insulation or something?

[Drake]

More info:GUIDELINES FOR MIXING AND PLACING THERMALLY CONDUCTIVE
CEMENTITIOUS GROUT (Mix 111) http://www.osti.gov/bridge/servlets/...ive/751159.pdf

This for a high thermal grout that might be used in several DIY applications that I can think of.