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tlovesb 02-03-2011 06:32 PM

Tiling a bathroom floor and installing under floor heating
Hi, My husband and I live in a house that my Dad and I built ourselves three years ago. We hadnít quite finished the house (trim work, kitchen counter tops, etc. still to do) when we moved in and for the last three years our bathroom floor has just been the plywood subfloor. We are getting ready to put down tile and a under floor heating system. Iíve been trying to decide whether to use Hardibacker or cement board over the plywood. Does one work better than the other? Is there any benefit or extra prep needed when using these products with the radiant floor warming mats? Also, is there something extra Iím supposed to do to waterproof this stuff? I keep seeing that mentioned in forums and Iím not really sure how that applies.

Also, any input on brands of under floor heating systems? So far I've been looking at ThermoSoft or Watts Radiant.


LIHR 02-03-2011 07:59 PM

What is your home heating system? is your intention to just warm the bathroom floor? Do you have heat in the bathroom now?

What is the span and spacing (and size) of your floor joists?

What thickness is the plywood sub-floor?

What is the size of the bathroom?

Sorry for the third degree... but answers will help you much better in the long run

tlovesb 02-03-2011 08:12 PM

Hi Gary,

The bathroom is heated - our house uses a heat pump.

The floor joists are 2x10s - 12 ft span and 16 in spacing.

Plywood subfloor is 3/4" t&g

The area we will be tiling/installing the heating mats is approx. 175 sq. ft. - it is a bathroom/dressing area combo.


Bud Cline 02-03-2011 09:00 PM

You can install your heat mat system over your existing subfloor material. Use the Watts Radiant mat product. Fax them a drawing and they will give you the required layout and materials list at no charge.

You will need the required mat(s), a thermostat, a heat sensor bulb, and a Loud Mouth Detector. The system will run on a single 120v. dedicated circuit and actually could be branched off of an existing lightly used circuit if necessary.:)

Once the mat is installed bury it in 3/8" of Self Levelling Compound and proceed with your tile.:)

LIHR 02-03-2011 09:21 PM

Bud I like the way you think and I like your tag line. TCNA Handbook would confuse most of the so called "tile setters" out there.

Teresa, your floor framing is good for ceramic tile and as Bud
(floor deflection is well within what is required)

SLC will give you a very flat surface for your tile install. Follow instructions carefully.

I'm not familiar with the mentioned heat mats, have used nuheat but most of my floors are hydronic in-bedded in mud.

have fun

Bud Cline 02-03-2011 09:45 PM

This is a clean straight-forward installation, I've done scores of them just like it.

Install your Loud Mouth first thing. The Loud Mouth will tell you if you have caused any damage to the circutry during installation.

Buy twelve bags of SLC, should have one left over. Be sure to hot glue all the wires approximately every 6-8 inches. If you don't the wires will float above the SLC. Staple the mats generously. Staple across one end then stretch the mat and staple the other end. Then go back and staple the field areas.

Install foam-sill-seal around all the walls for later expansion of the SLC thermal-mass. Dam any door openings and seal any floor vents and toilet flange. If there is a way for the SLC to leak out it will find it. Caulk along the tub.

After the SLC has set the remaining sill-seal can be cut away.

Once you have the layout recommendation from Watts you'll have a better idea of what you are doing.:)

LIHR 02-04-2011 06:01 AM

Don't expect to mix one bag of SLC at a time in buckets. Use a heavy duty mixing drill and mix in a large Hvyduty garbage-can and float it all at the same time.

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