Electric radiant under ceramic tile

[zeeto]

The other day I went to start tiling over the radiant mat (Suntouch 10'x30") I layed down our upstairs bathroom I'm remodeling. Checked the resistance right before I started and it was within the model specs (~45.3ohm; specs are 39-48). I ended up taping the wire ends to my multimeter prongs to monitor it while I was laying the tile. I started the first row and noticed it increased a bit, to around 46ohm. Didn't really pay attention for a bit and when I looked again it was around 49, and increasing about 0.1ohm every 30 seconds or so. At that point I decided to scrap it, just incase something was really wrong. Pulled all the tile, cleaned the thinset up, and started to trim out the mesh covered in thinset. By the time I was done the resistance was ~70ohm or so, but the neutral was still nothing. Figured the mat had a nick somewhere, so I said I'd go over the wires the next day. Checked the resistance the next day and it was right back to 45.3ohm, and then spent about an hour going over the wires and didn't find anything.

I called up the manufacturer to find out if the increase would be normal, since I figured if it weren't it wouldn't have gone back to the original number. Well, they weren't any help. Wouldn't give me any info and just said there are too many variables to help me out.

So now I'm kind of stuck on whether or not to take my chances on the mat. Anybody know if an increase during install is normal?

[HayZee518]

the resistance went back to the original reading is ok. the spacing of the heating element is spaced apart by a good distance. when the thinset cures it should be ok.

[pushkins]

Yeah, I've had that happen before when using the "Mat" radiant heat systems (esp. the one sold at Lowe's)Client supplied, I always figured it was something to do with the curing thinset, perhaps the heat as it cures.
Never had the problem with the coiled wire version.