Lintel over pipework opening - masking in practice

[Olf]

NHBC shows such a schematics:

 

 

How is the 'masking' done in practice? I could not find any ready made solution, it should be easy to cut out of a sheet, but what material?

It needs to be man enough to withstand pressure of the ground, that suggests something rigid, and that means 2 part barrier (if installed around existing pipe, a sewer in this case).

 

 

[Oz07]

Lintels over an 8inch (I used 6) pipe built into the wall. Fill gaps in with compo and crap. 

[Temp]

I think a lot of builders wrap the pipe in some sort of insulation like rock wool and just fill trenches either side with gravel. 

 

Something like perspex or similar plastic sheet would work but its not cheap. Note it isn't fixed to the wall just slipped over the pipe.

[Faz]

Bedded and topped mine in building sand - as much to find it without damaging it when we have to dig back down to it as anything else.  All goes into the sub-floor so no need for anything elaborate.

[Olf]

I failed to mention that on one side I'll have void under beam and block floor -  so there would actually be a gap through the opening.

However SE came back and suggested using rigid insulation boards as the masking on both sides - I'm happy with that, as it is easy to cut to the actual profile.