I am about to lay some screed and there is about 4 inches of dpm around the edges at slab level. It goes under the blocks and at present is sitting on the concrete. I have 50mm to go down, do i lay screed on top of this or cut back the dpm???

not quite sure what your describing there mate?
is the dpm under the concrete, lapped up the edges and under the blocks at dpC level? or are you saying theres some dpm just sticking out from under the blocks?
is this a newbuild / extension or a refurb?

if a general answer will suffice... stick it on top...
dpc is used to separate a wet substrate from a dry one... e.g. any bricks below the level of the dpc will be 'wet', bricks / blocks of an internal skin above the dpc will be 'dry'..

if the concrete youre screeding over hasnt got a dpM under it... put one under the screed... or better still, some cellotex then dpm...

dunno if any of that helps at all?

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