24. Installation – seal and flaunch the chimney head/liner It is also essential to seal and flaunch the chimney head and liner so that there is no possibility of rainwater penetrating through the the void. If you leave a reasonable section of liner protruding up into the pot it is a simple matter to backfill around it with a mix of sand and cement which sits down onto the closing plate & clamp making everthing secure and weatherproof. A REMINDER Since this section has discussed only the principles that apply for flexible liners it is essential that you study the manufacturer's instructions for the product you buy and comply fully with all requirements.