Micro Topping over Hydronic radiant heated floors???

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Old 12-25-09, 08:43 AM
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Micro Topping over Hydronic radiant heated floors???

Hello all, this is my first time posting here so I would like to thank everyone on here who is kind enough to help people like me. I am a noob when it comes to the world of decorative concrete. I have been impressed by the results overlays can produce. I have decided to install (retrofit) a hydronic radiant heat system in my newly purchased home and I would love to do an overlayment over the system. I plan on placing the either 1/2" or 3/4 pex right on top of the plywood subfloor wedged in between 6-8"x 3/4" plywood sleepers. The tubing will be spaced every 6-8". I need to know what my options are for putting an overlayment/Micro topping over this type of set up. I was hoping I could put a strong skim coat of some type directly over the plywood sleepers allowing the material to fill the seams, screw holes, and tubing channels. Then I would apply diamond metal lathe over that followed by my base coat and finish coat. I would like to keep the micro topping as thin as possible without sacrificing structural integrity. Any advice will be hugely appreciated. Thanks folks
 
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Old 12-25-09, 05:55 PM
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What you describe should work. The diamond lathe/scratch coat/finish coat is right on anyway. For the underlayment/space filler, you may consider a self leveler like Ardex or Mapei, which you would just pour in and let it seek it's own level. However, be advised that this stuff is expensive.
I'd call the manufacturer of the heating system and ask for detailed installation instructions. I'm sure that someone else has done what you're describing. Good luck.
 
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Old 12-25-09, 06:45 PM
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Thanks for the input. Do you think that there will be any type of ghost effect from the tubes? If so, is there anything that I could do to prevent it without making the overlayment really thick. Is there a minimum thickness for overlays/micro toppings over wood with radiant heat? I would like to keep it as thin as I can.

I appreciate the advice. Thanks
 
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Old 12-31-09, 09:46 AM
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I apologize in advance for my lack of knowledge with radiant floors, but I live in Texas & we don't have too many of them around here. I am however very familiar with installing cementitous overlays over wood substrates. The most common practice for a wood substrate is to:

1) Lay down Roofing paper.
2) Lay your metal lathe & staple it well (about 25 staples/sqft)
3) Apply a polymer modified repair mortar over the lathe & allow to dry completely (8 hours+)
4) Apply a water proofing agent (this also serves to eliminate ghosting)
5) Overlay, Stain & Seal as usual. I would recommend an overlay that needs to be mixed with LIQUID polymer, as the dry polymer (aka just add water) overlays don't have the tensil strength to hold up to movement. This is especially true when applied over wood, which moves more than a foundation would. Not to mention the just add water overlays will not hold up to more than a couple freeze thaw cycles.

It sounds like you're on the right path. If you don't follow the above instructions the make sure to apply a primer over whatever repair mortar you use to prevent ghosting ML Primer from Miracote is what I sell at my store for just this reason. What will happen is the depth of the repair mortar will vary & will cure at a different rate & when a decorative coating is applied it will typically color differently at the deeper areas than at the shallow areas creating the ghost lines that nobody wants to see. I have included a link below to the instruction sheet for applying overlays over wood substrates. I hope this helps. Good luck with your project.

http://www.miracote.com/installguide...Rev%200309.pdf
 

Last edited by Al Smith; 12-31-09 at 09:47 AM. Reason: oops, I forgot the link.
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