I have a square cast iron manhole cover in my garden that does not block the smell of toilets. It measures 655 x655 millimetres with a gap of between 5 and 6 millimetres all around between base and cover. The waterboard claim there is nothing they can do!! Is there anything I can use to make it airtight but also to be able to open it for inspection or repair? Apparently, the manufacturer of EVERBUILD THERMOFOAM AIRTIGHT ACOUSTIC EXPANDING FOAM EVTHERM7 that I originally enquired said that these foams are not suitable as they are not even waterproof. They said that probably I should be looking at closed cell foams. I wonder whether a foam of some sort blocking the surrounding gap might be better than a sheet of closed cell foam on which a heavy cast iron cover would be sitting? If a foam is suitable, will it be permanent, or will it allow access for inspection or repair with the possibility of reapplying the sealant? I read in earlier replies that silicone grease might be suitable but given that it is exposed to the sun almost the whole day, the silicone grease might last only for a few days?
Your help will be appreciated
Your help will be appreciated