Silicone every time, always use low modulus neutral curing silicone, mastic is a generic term used to describe (usually) cheap builders quality mastic with very little elasticity that will invariably crack in a short time and not bond with the UPC
If you need to find a tradesperson to get your job done, please try our local search below,
or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Please select a service and enter a location to continue...
Are you a trade or supplier? You can create your listing free at DIYnot Local