Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I installed a radiant floor heating mat under ceramic tiles using a premix mortar. I now understand this was not the right thing to do. After further research the only reason I can find that suggests this is not recommended is that the pre-mix is not as heat resistant and doesn't seem to conduct heat well. Too late...

Before I turn this on, are there any other dangers of using the pre-mix with the mat? I used an expensive premix that is extremely hard. Are there dangers of fires or risks of the premix expanding and causing cracks, etc? Any other risks?

If it means that I will spend more to get the heat up on the floors because the heat does not conduct well enough, then I will have to live with that. I just need to know if there are any dangers or risks.

share|improve this question
I would try to talk to a technical representative from the mastic manufacturer and ask these questions. I expect they will want to know the maximum temperature at the wire-mastic interface. – HerrBag Sep 9 '13 at 4:52
I called both the mat and mortar manufacturing company. They both said I should do no it, but neither could give me a definite answer as to what my implications could be. The mat company said the chemical in the thin set would eat the cable coating. The mortar guy just kept saying don't do it, but could not say why I should not do it. I asked if there was a fire risk and he said the mat could cause the plywood to burn. Really? I just need to know there is a risk of fire. I just wont turn it on if there is a risk. Anyone know? – Andrew Findlay Sep 9 '13 at 18:07
obviously im late responding. hopefully this will help some who accidentally use premixed or modified thinset mortars over heating mats. It is my understanding that the problem is that the heat drys the mortar from the inside out. this makes it brittle and weak and can cause the tile to break away from the floor. modified mortars are designed to dry from the outside in. they can take from 14 to 60 days to dry. drying them with heating mats – user33820 Feb 17 '15 at 14:36

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.