Ok, I understand that a need to install a very budget friendly sound damping solution, and that results in trying out products meant for something else to be put in the automotive environment. The reason why a lot of R&D goes into developing certain products is to ensure the product serves its purpose.
I strongly advise against using civil/home materials in automotive environment. A simple analogy as you can relate to is that you dont put home audio speakers into a car. Why, cuz they dont work that well, even though they are speakers as well. Same goes for sound insulation products. car sound insulation works in a car, not in the home and vice versa.
You can experiment as much as you want but the best results will be achieved by using the proper material that is designed for the purpose. So I would advise to use the proper materials. All materials are locally available. They are more expensive then jugars, but that is because they are meant to do their job right.
The Hy-grip bitumen based sheets seem great but its meant for adhesion to concrete. Also to consider is the smell that is associated with bitumen based products. Your car might smell like aroad at all times. And once this stuff goes inside, it stays inside. You also need more bitumen compared to butyl rubber to work well. Hence the added weight to achieve equal damping quality compared to butyl.
