Hardwall and then screed?

Marina

New Member
Hi. We are building an extension and laying new floors inside the existing house as well. We are managing the job ourselves, but seems like we are making lots of mistakes, relying on "specialists" trades instead of doing our own research to get the right solutions.
I know we got it wrong, so please just help if you can.

Problem no 1
We have hardwall on most of the existing and new walls which was installed all the way down to the concrete slab level. We used Thistle hardwall. A few of the are also done with multifinish, ready to paint them.

Insulation and screed with UFH (I believe it will be liquid screed- 50mm)will be installed in a few weeks time.

Doing things in this order made sense as I have seen how messy some of the plastering can be and we wanted to make sure that the screed will be nice an clean at the end.

Where we have plasterboard, we will cut it to make sure it sits above the screed level to avoid it getting wet. Will we need to do somethign with the hardwall where it will sit within the depth of the screed?

Problem no 2

The dpm will go over the concrete slab, then insulation and UFH with screed.
We have a 300mm step down from existing house into the new extension generrally, except for one room which is level with existing floors.
The dpc was installed on external skin to suit external levels and then it comes up in the cavity and laps over the block and then down the inside face of the blockwork and will lap with the dpm.
The dpc was installed to suit the higher level of the floor as that was where they started building the walls, meaning that in the bulk of the extension the dpm/dpc membrane is close to 300mm above FFL. Again, we are using hardwall rather than dot and dab plasterboard.
Is there a way to plaster or fix something over the membrane?
We will have tiles in this area.

Thank you in advance for your help
 

Marina

New Member
Thank you for all the messages about my name. I am an engineer not a builder. Like some of you don't know how to calculate a 10 storey concrete frame I don't know how to plaster a wall.

Like I said, I know it is messed up but we need to find a solution to make it work.

Picure of plastered wall all the way down to concrete slab. Insulation and screed to go on top of slab. If hardwall and multifinish can't sit in screed we will remove it, it will take someone a few hours, but that is doable. If that is the only solution.

Pictures of membrane lapping the inside face of the wall. This will lap with dpm on top of concrete slab.
In one room the level will work as the membrane will sit within the insulation/screed buildup. But in the other room it is much higher up the wall so we need to find a solution to cover about 150mm of it.

External levels are higher which is why the membrane was laid like this. I know it should have been done in a different way and that was what was drawn, but too late for that now.

I spoke to permaguard yesterday and they suggested using a SBR adhesive on the black membrane and then to stick a fleece tape. Then we should be able to plaster on that.
Another suggestion was to cut a bit of the hardwall on top of the membrane and fix a cement board. This would be held in place at the top only. Again, can't find any info on their technical data sheets regarding casting screed against this cement board.
I could not find any screws that are suitable to mechanically fix the membrane to the wall. The ones that have the rubber washer are all for the cavity membranes that look like an egg crate.

If you have some better ideas, please let me know.
 

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essexandy

The Lake Governor
Thank you for all the messages about my name. I am an engineer not a builder. Like some of you don't know how to calculate a 10 storey concrete frame I don't know how to plaster a wall.

Like I said, I know it is messed up but we need to find a solution to make it work.

Picure of plastered wall all the way down to concrete slab. Insulation and screed to go on top of slab. If hardwall and multifinish can't sit in screed we will remove it, it will take someone a few hours, but that is doable. If that is the only solution.

Pictures of membrane lapping the inside face of the wall. This will lap with dpm on top of concrete slab.
In one room the level will work as the membrane will sit within the insulation/screed buildup. But in the other room it is much higher up the wall so we need to find a solution to cover about 150mm of it.

External levels are higher which is why the membrane was laid like this. I know it should have been done in a different way and that was what was drawn, but too late for that now.

I spoke to permaguard yesterday and they suggested using a SBR adhesive on the black membrane and then to stick a fleece tape. Then we should be able to plaster on that.
Another suggestion was to cut a bit of the hardwall on top of the membrane and fix a cement board. This would be held in place at the top only. Again, can't find any info on their technical data sheets regarding casting screed against this cement board.
I could not find any screws that are suitable to mechanically fix the membrane to the wall. The ones that have the rubber washer are all for the cavity membranes that look like an egg crate.

If you have some better ideas, please let me know.
What a mess.
 

Monkey Boy

Well-Known Member
I have no idea on the solutions
You may find screws your after on roofing superstore?
As for everything else I’d think you need to stop works and leave off till new year and between now and then do alot of research and pay a professional builder with decades of experience to help you come to the right way forward
 

Brimstone

Well-Known Member
Well I can plaster a wall and design a reinforced concrete structure, and so can a few others on here. Research and know your subject before you start, but too late now..

1st The Building Control Inspector is your friend, without their sign-off you do not have a house, it's an unapproved hut. They are genuinely very helpful, talk to them, listen, get buy in.
Thank you for all the messages about my name. I am an engineer not a builder. Like some of you don't know how to calculate a 10 storey concrete frame I don't know how to plaster a wall.

Like I said, I know it is messed up but we need to find a solution to make it work.

Picure of plastered wall all the way down to concrete slab. Insulation and screed to go on top of slab. If hardwall and multifinish can't sit in screed we will remove it, it will take someone a few hours, but that is doable. If that is the only solution.
Yes, cut back the water absorbent plaster, it is the only way and not a big deal.
Pictures of membrane lapping the inside face of the wall. This will lap with dpm on top of concrete slab.
In one room the level will work as the membrane will sit within the insulation/screed buildup. But in the other room it is much higher up the wall so we need to find a solution to cover about 150mm of it.

External levels are higher which is why the membrane was laid like this. I know it should have been done in a different way and that was what was drawn, but too late for that now.
a) You stated that the DPM was laid externally up and over the wall, before coming down. If so, you have an external DPM and do not need the internal one and could cut it back. In theory, any water at the higher level will press the external DPM against the wall and flow around the building.
b) glue the internal DPM to the higher back wall then put plaster board over it, support the bottom edge with a batten or dotndab. It will be "floating" and not joined or bonded to the DPM. If you are still worried about damp, condensation, leaks -use say floor cement tile adhesive to D&D,as not affected by water. If you screw thru it you will have holed your DPM. (Hilti gun nails are so hot the DPM usually melts and seals around the nail). I don't like holes - you could cut the DPM back and paint Synthaprufe onto the concrete/blockwork, dob enough over the edge of the DPM and it should, should, seal the cut line.
I spoke to permaguard yesterday and they suggested using a SBR adhesive on the black membrane and then to stick a fleece tape. Then we should be able to plaster on that.
SBR 'twixt membrane and blockwork you mean? if only on the pleaster side the DPM is not fixed and in future might move and crack the plaster,..or might not.
Another suggestion was to cut a bit of the hardwall on top of the membrane and fix a cement board. This would be held in place at the top only. Again, can't find any info on their technical data sheets regarding casting screed against this cement board.
It is made of cement, the constituent part of concrete, of course you can cast against it. Go back to yr 1 materials and science course book. Held in place at the top with floor tile cement (90-95% OPC) if you must.
But, will be proud of the wall surface above so you either skinny the plaster to make it all level -may crack along the join, or dub out the wall, and it might still crack. Or use a horizontal pencil bead and make it a feature somehow.
I could not find any screws that are suitable to mechanically fix the membrane to the wall. The ones that have the rubber washer are all for the cavity membranes that look like an egg crate.

If you have some better ideas, please let me know.
Who drew the originals details and why? go challenge. As an Engineer you should have studied this as part of your course, in some detail, it is a critical element of a successful office or block of flats, or civils engineering. As a professional, go back to your books and relearn this. In London a 9 year old block of flats is being demolished this year because of these failures up and down the building. There are lots of others.
 

Smudger1

Well-Known Member
Disc level plaster 2" above screed and remove, skirting hides gap.

Remove membrane to just above screed level, inject dpc. Tank and plaster over following procedure permagaurd recommend.
 

Topspread16

Well-Known Member
I’ve not read all this palaver, it boils down to trying save a few quid on not having a project manager. It’s crudely bit you on the arse. The standard of work is abysmal, probably tried save money here and there to for the glorious kitchen that will be fit, totally forgetting the integrity of the build is what really matters.
 

Marina

New Member
Thank you all for your replies.
I have said from the start it is a mess, so all I am trying to do is fix a mistake the best I can.
 

Marina

New Member
Just from all replies, this is what I am thinking. Glue membrane to wall so it stays in place. Cut 10cm of the hardwall above the membrane and fix a sheet of cement board to the wall. It will be mechanically fixed above membrane (so as not to puncture it) and held in place at the bottom by the insulation and eventually the screed. We will add mesh to the wall before they do the multifinish. Hopefully that will help with the cracking at the joint between hardwall and cement board. This will only be visible for a lenght of about 2.5m, everywhere else it will sit behind furniture, so if it cracks it is not that bad, as long as this is a working system.
Would it help if we also apply a Liquid DPM? What make do you recommend and is that going to cause issues if we glue the membrane to the wall?
 

Stevieo

Royal Spin Doctor
Just from all replies, this is what I am thinking. Glue membrane to wall so it stays in place. Cut 10cm of the hardwall above the membrane and fix a sheet of cement board to the wall. It will be mechanically fixed above membrane (so as not to puncture it) and held in place at the bottom by the insulation and eventually the screed. We will add mesh to the wall before they do the multifinish. Hopefully that will help with the cracking at the joint between hardwall and cement board. This will only be visible for a lenght of about 2.5m, everywhere else it will sit behind furniture, so if it cracks it is not that bad, as long as this is a working system.
Would it help if we also apply a Liquid DPM? What make do you recommend and is that going to cause issues if we glue the membrane to the wall?
Just stop.

Stop and get a fekkin builder.
 

Retired Spread

Well-Known Member
Thank you for all the messages about my name. I am an engineer not a builder. Like some of you don't know how to calculate a 10 storey concrete frame I don't know how to plaster a wall.

Like I said, I know it is messed up but we need to find a solution to make it work.

Picure of plastered wall all the way down to concrete slab. Insulation and screed to go on top of slab. If hardwall and multifinish can't sit in screed we will remove it, it will take someone a few hours, but that is doable. If that is the only solution.

Pictures of membrane lapping the inside face of the wall. This will lap with dpm on top of concrete slab.
In one room the level will work as the membrane will sit within the insulation/screed buildup. But in the other room it is much higher up the wall so we need to find a solution to cover about 150mm of it.

External levels are higher which is why the membrane was laid like this. I know it should have been done in a different way and that was what was drawn, but too late for that now.

I spoke to permaguard yesterday and they suggested using a SBR adhesive on the black membrane and then to stick a fleece tape. Then we should be able to plaster on that.
Another suggestion was to cut a bit of the hardwall on top of the membrane and fix a cement board. This would be held in place at the top only. Again, can't find any info on their technical data sheets regarding casting screed against this cement board.
I could not find any screws that are suitable to mechanically fix the membrane to the wall. The ones that have the rubber washer are all for the cavity membranes that look like an egg crate.

If you have some better ideas, please let me know.
james franco.gif
 
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