Build internal block walls off the floor screed - yay / nay?

[larrylamb11]

I am having an issue with potential damp in an (unfinished) new build extension, part of the solution is to call in a specialist company who are going to put down a Newton 520 membrane, insulation and new DPM. All the internal walls (Durox Supabloc) have been taken down to facilitate.
The damproofing co. suggest laying the floor screed immediately after they are done to avoid any potential damage to the membrane... then rebuild the internal blockwork walls off the screed.
Talking to the builder, he doesn't seem as comfortable building off the floor screed, suggesting the screed should be reinforced or build internal walls out of stud. We are looking at a 75mm screed. Is this overkill? or do I need to reinforce the screed under where the walls are planned with wire mesh?

 

[theoldun]

Newton 520 is basically the same product, under a slightly different name, material and packaging as Newtonlite lathing that we used so extensively in the 50s and 60s.
These days people say they have had a DPC injected, in those days you said your house had been Newtonited.
Out of interest I have read Newtons technical information and drawings and your builder is one hundred per cent correct in not wanting to build partitions on top of screed.
Course of engineering bricks on top of oversite, Newton 520 cut up to brickwork and Newton 501 slim line lapped over 520, over engineering brick and over 520 other side. Partition build of off engineering brick.
Google Newton 520, click on technical information and read yer fill.
Your DPC company is going the cheap skate way round doing the job.
How ever, after saying all that, If you lay 75mm screed reinforced with fibre, and chicken mesh under where walls sit, use light weight blocks or stud partition, then you should be okay. Ask your DPC company if they agree, and to put it in writing that they will accept responsibility for any failure.
How you managed to get into a situation with a new build, that you require such a system as Newton is a mystery. Newton is for really wet situations.
One other point where is floor insulation?
old un.

 

[larrylamb11]

We're in this situation because of DPM failure at wall/floor junction - its been damaged in construction and is no longer watertight. Also oversite is below external ground level - in the depths of the winter we found water would stand, rise and fall on the oversite.
Personally I think we have fixed it with a french drain right around the perimeter and a perforated pipe on top of the foundation, but knowing we have had water inside we can't afford to take the risk and are 'belt and bracing' with Newton etc.
The complete order is Newton 520, 50mm Dow Floormate 300 insulation, Newton slimline membrane, then 20 or 25mm Cellotex topped off with 75mm screed.

So the best solution would be to get the walls laid out on the oversight and upto approx membrane height, cut the Newton 520 around the walls, insert the insulation, then slimline membrane over the whole lot? then build off the pre-laid-out walls on top of the membrane?

 

[theoldun]

Can see your problem. Did you find the technical information and drawings?

Quote:
The complete order is Newton 520, 50mm Dow Floormate 300 insulation, Newton slimline membrane, then 20 or 25mm Cellotex topped off with 75mm screed.

So the best solution would be to get the walls laid out on the oversight and up to approx membrane height, cut the Newton 520 around the walls, insert the insulation, then slimline membrane over the whole lot? then build off the pre-laid-out walls on top of the membrane?

Seems the way to go. Only thing worries me, is if water is penetrating through external walls between oversite concrete and DPC, what stops it soaking Dow 300. Never used Dow 300. Is it closed cell? Remember engineering bricks on oversite.
old un

 

[larrylamb11]

Thanks for that, yeah Dow 300 is closed cell and suitable for this application apparently. Yes, read the technical sheets on the Newton site - thats kinda what prompted me to ask the original question as I was looking at the compressive strength and thinking about loadings.
Will get my walls laid out in engineering brick on the oversight and go from there... I think I feel much more comfortable with that route anyway as is significantly reduces the number of things to go wrong!