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Minimum Topping Slab Thickness for Terrazzo Floor

<span style="font-size:12pt">I have a heating-only radiant slab with a tight slab sandwich condition.   My rule-of-thumb regards minimum topping slab above the radiant tubing is typically 1.5”.  Less than that and I'm worried about ‘ghosting’ of the tubing (it being visible from above) & having enough slab thickness to protect the tubing.</span>

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<span style="font-size:12pt">In our case, we have, in order from the bottom:</span><span style="font-size:12pt">

·         Structural Slab

·         Insulation

·         Wire Mesh

·         ¾” OD PEX

·         Topping slab (thickness tbc)

·         ½” of epoxy mortar

·         3/8” terrazzo floor

<span style="font-size:12pt"> </span></span><span style="font-size:12pt"> </span>

<span style="font-size:12pt">The topping slab is non-structural (the project structural eng’r is not worried about thickness).  Regards ghosting, I'm imagining that the terrazzo covering would be a lot less likely to show ghosting than a typical concrete topping slab on its own.</span>

<span style="font-size:12pt"> </span>

<span style="font-size:12pt">Do you have any experience about the minimum toppings slab coverage thickness for this type of application?  The field conditions are indicating that we may only have 1" including the epoxy mortar....seems too shallow, but I don't know where to draw the line.</span>

<span style="font-size:12pt">Any first-hand experience?  Thanks!</span> 


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    An inch should be good...

    Many homes have 3/4" cover and it is with a less dense (Gypcrete) product. You should be fine. As for striping, consider constant circ with ODR and indoor reset and striping should not be an issue.

    As for ghosting (bubble traces) if the pour is done in two lifts, ghosting is also non existent. The tube is barely covered with the first lift, and the second lift caps it off.

    If in doubt, run your assembly by the tubing manufacturer. They have more experience with their product than anyone :-)

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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