What adhesive do i use in General Maintenance and Repair Posted July 27, 2018 Hi Pegleg, When I refurbished my heater box assembly (non-ac), I used spray on adhesive. The gaskets and seals I made myself out of foam. Its not original but they seal and do the job. I had re-used the pads on either side of the core. I just cleaned them up and re-installed them. Spray- on adhesive can be purchased locally at hardware store or even at a upholstery shop. Be careful when re-assembling the unit with the rivets as the fibre-glass body cracks easy if too much pressure is applied. Choose rivets that fit snug in the existing slots. Good luck! Thanks Marco. Do you mean a heat resistant adhesive? Is the rubber around the heater core glued? Taking my old rubber off the old heater core i saw no adhesive and the longer lengths were coming away. the rubber surround appears to have adhered to the heater core through the cores tempreture. I did not need to remove any rivets. However, where one of the brackets that attach the box to the car was starting to crack so i used some fibreglass to strengthen it. Pegleg, If I remember correctly, on my car the rubber caps around the core weren't glued just stuck due to age and hundreds of heat cycles. As others have mentionned, the adhesive is used to secure the gaskets during the re-install and not used necessarily for sealing purposes. Once the unit is put back into the car and hot coolant starts to flow it will heat and cure any adhesive applied. It may even make the gaskets stick simply due to the heat generated inside. Let me know if you have any other questions!