The only thermostats that run mechanical relays are the herpstat 1 (not the basic) the 2 and 4. this feature needs to be enabled. Many duck tapes are not for use with high temps the max temp for 3M for example is 130º for less than one hour. there are great risks involved in the method you have chosen to follow. Be careful misuse of products can be serious. Again I would suggest products designed for in floor heating and use the set up that is approved for that application or use products that are intended for direct contact. Do be careful and keep an eye on what you have done.