Sealing a cavity wall

[bashypack]

Hi - I need to build a single block wall on top of an existing cavity wall for a first floor extension but can't find anything to 'seal' the cavity with prior to building .. can someone point me in the right direction?? Thanks!

[stoneyboy]

bashypack,
Not sure what you mean by sealing but google 'cavity closers' and see if this meets your requirements.
end

[bashypack]

..Thanks - yes that is more what I meant something to close (rather than seal) the cavity so I can build a single block wall on top of a cavity wall - I wasn't sure what they were actually called so I am sure that will help!