Outbuilding / Internal render query

9 Jun 2010
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United Kingdom
Having an 5m x 2m outbuilding put up. 4" concrete block walls, walls and roof are up. It has a damp course. It will not be heated

The builder is going to cement render the inside walls (with water proofer), and keeps going on about dot and dabing plasterboards onto the cement render. internal walls. Says how the rear wall blocks are damp (but they have been out in the rain prior to going up?)

I thought either
a) put a good finish on the cement render and use external masonary paint on it (yes i know its not a smooth finish) or
b) plaster skimming the rendered wall (which with the waterproofer won't let water in?)
but he keeps saying i'm going to regret it later on by not spending the extra on plasterboards.
With b) skimming the rendered wall he's insistent there will be damp

I don't understand how dot and dab stops the damp he says there will be, if waters getting in of there will be damp, it will get to the plasterboard?..

For me, it's an outbuilding mainly for storage i don't need it kitted out like a room, and hes on a day rate with the labourer, and doing as he suggests Plasterboard and Labour will probably cost me £350 extra. I'm sure he's stretching the work out

What's the sensible thing to do?

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plasterboard -no not a good idea, it will get damp

is the building single skin or cavity?

render with sbr is a good idea.
external 4" conc block walls are typicly rendered on the outside - takin care not to bridge the dpc.

internal wall surfaces can be sand & lime rendered but dont use any gypsum skim finish, only a remedial finissh.

dont dot an dab.
Thanks - just confirms what i was thinking! it didn't make any sense to me

Single skin 4" concrete blocks, it's built next to the back fence so not possible to render the back (the sides can be). Is there any liquid sealer that can be rolled on the back on the concrete blocks to give some water ingress protection? as there is a gap to get a roller and pole down, or is that pointless.

I will definitely insist that it's just a render on the inside - the "damp" blocks are drying out despite the rain. The ceiling can still be plaster boarded and skimmed? I was going to have some insulation put in the ceiling joists (if it makes a difference) to retain some warmth if i was ever working in there
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render with sbr is a good idea.
Difficult one, I've used him before and he has lots of experience, but i don't think he would appreciate me telling him what to put in the render, he gets irked when I get involved, bits I do to save time i do when he's left lol. Waterproofer is all he uses which i suppose is at least something. When I do something like this myself I will definitely remember this

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