Alternatives to Plastic DPC

[ChrisDYI]

Hi

I am planning to build an extension on my house and have been doing some research on standard building practices. One thing I cannot get my head round is the use of a plastic layer between the mortar for the DPC layer. I have done a small test to see if my concerns about this creating a weak point in the wall with a couple of bricks mortared together with a plastic DPC between them and to be honest the results were shocking, the bricks came apart very easily. Is there an alternative to this approach which seems to be standard building practice in the UK - The idea of putting plastic sheets in a wall which do not seem to bond with the mortar seems like madness to me. I was thinking a layer of water proof bricks combined with water proof mortar could act as a DPC layer, not sure what the building inspector would say about it.

Thanks,

Chris

 

[freddiemercurystwin]

Build up two leaves of masonry, tied together and three + meters tall, throw some masonry returns in too and see if it moves then.

 

[Munroast]

when you get the entire weight of the house on top of the join, it doesn't usually slide off, even on a windy night.

 

[ChrisDYI]

Build up two leaves of masonry, tied together and three + meters tall, throw some masonry returns in too and see if it moves then.

I get that the weight of the wall will hold it in place but it is clearly a weakness in the wall. You might as well have a row of bricks with no mortar between then and just use gravity to hold the wall together. I am sure if you just left the mortar out of an entire row of bricks because gravity will stop it moving the building inspector would tell you to pull the building down.

 

[freddiemercurystwin]

No it's not a weakness, it's been used successfully in building since the invention of dpcs.

 

[Larry1990]

You could go old school and use a slate DPC. You could use dry rods or chemical DPC. Staffordshire blues and sbr mortar.

I've not heard of any houses falling down so I am sure you would get away with a standard Plas DPC.

 

[cdbe]

You need the right mortar. Some mortar doesn't stick properly, if you get the right stuff it sticks to anything - I've had some where I've struggled to chisel the dpc off the mortar. Don't worry if you get it wrong - it's generally only an issue on garden walls where they can easily be pushed over.

 

[Notch7]

Hi

I am planning to build an extension on my house and have been doing some research on standard building practices. One thing I cannot get my head round is the use of a plastic layer between the mortar for the DPC layer. I have done a small test to see if my concerns about this creating a weak point in the wall with a couple of bricks mortared together with a plastic DPC between them and to be honest the results were shocking, the bricks came apart very easily. Is there an alternative to this approach which seems to be standard building practice in the UK - The idea of putting plastic sheets in a wall which do not seem to bond with the mortar seems like madness to me. I was thinking a layer of water proof bricks combined with water proof mortar could act as a DPC layer, not sure what the building inspector would say about it.

Thanks,

Chris

I once had a roll on roll off skip lorry reverse into a projecting pier on my industrial unit, which is made of 9” concrete blocks - that shifted on the DPC by 3”

I have to say you are overthinking it - its a proven established method that has been in use for decades

DPC is embossed and mortar does stick to it. Plus walls are cavity construction and most extensions have 3 sides and butt up against the house.

You are thinking of a problem that doesn’t exist

 

[ChrisDYI]

Thanks for the advice. I agree I am probably over thinking it and should just stick to standard building practice but I think it is obviously a compromise in the walls integrity - although it might not ever be an issue. I might phone the building control and ask if they will accept it if I use a layer of SBR or similar water resistant mortar with blue water resistant bricks.

 

[freddiemercurystwin]

It is not a compromise.

 

[Notch7]

but I think it is obviously a compromise in the walls integrity

You need to get past this.

There are loads and loads of challenges in building an extension….and this is not one of them.



Have a think about it in more detail: yes a DPC does in theory create a potential slip line in the construction….but masonry construction is not subject to massive side loads.

masonry construction is subject to vertical loads from weight of stuff above, moderate side loads from wind and potential side loads from pitched roofs on the upper courses and none of those are enough or in the direction to cause slip at the DPC.

 

[john4703]

I agree with everyonevwho has said that plastic DPC is designed for the job and is perfectly safe.
The old material for a DPC was slate. Mortar stuck well to it but I'm not sure anyone would use it these days.