Urgent answer.. builders have built on plastic DPM ??

[tvrbeaver]

Hi All

The builders are back tomorrow so I need an urgent answer to a question if you could please...
We've brought the build out the ground on foundation blocks. As I want a space under the floor, ive put DPM around the outside of the blocks to stop and damp coming through into the voide... as I did this i lapped it over on top of the blocks and put bricks on it to hold it in place whilst I've back filled the outside. Today, the builders put the inside blocks up and have made a great job... but they also put one row of bricks on the outside face straight onto the DPM????...
Unlike DPC that has diamonds in it to help it key and grip, this stuff it 1200 gauge DPM thats smooth.
I did expect them not the key it in if I'm honest or if they did, only 10mm or so... but they have put it the full way under the outside course... what stops the bricks 'slipping' off in future?
or am I worrying too much?.. it may have been better if they had a bit of weight on it if they had done 3 or 4 layers.. but just one layer?.. it's hardly pushing it into the blocks below?.. so very little key?.. and when they do build on top and it crushes a bit, does that further break any bond there may be???...

 

[tony1851]

You would never get a bond.with either dpm or dpc. The building stays stable because of the sheer weight of the structure. Nothing to worry about.

 

[freddiemercurystwin]

I don't really understand the detail, got a section to show us? On another subject are you saying you are effectively using some plain old dpm as your tanking?

 

[tvrbeaver]

Im told by building control that tanking is not required,, we are well drained so should not be a problem... and its on the outside of the build so should be okay.. just a OTT precaution as I had to buy a big roll of the stuff.
.
On the DPM v DPC... The DPM being Visquene... but at least DPC has small diamonds moulded into the surface to give it some grip to both faces.. this has nothing and is slippy as hell when wet....

Are you sure it's okay ... its easy to take a layer off now whilst it's only a brick high...

Cheers...

 

[freddiemercurystwin]

I don't really understand the detail

 

[tvrbeaver]

I don't really understand the detail

OK.. so I have a small 3mtr extension being built... I've dug a hole 3 x 3 and put strip foundations in... I've then got about 1 meter of solid foundation blocks to bring the build out of the ground just below surface level.... On the outside of this I've put Visquene in a Z shape.. so it sits on top of the foundation strip... comes up the wall... and goes over the top of the foundation blocls where its been held with bricks until I've back filled the chanel between the blocks and the earth. The inner wall on top of the blocks was done before so it's lapped over into what will be the cavity... they have now put the first layer of external wall bricks down to bring the outside up to DPC, but have put them on top of the Visquene membrain... I would have thought they would have cut the top section back so it only sits under 10mm or so.. or maybe even cut it off ( to give it a L shape sitting on the foundation strip and against the wall only)... so does this give issues in that its not DPC with the small diamond grips moulded in it?.. and is actualy smooth visquene that the external wall now sits on (although its only 1 brick high at the moment).. cheers

 

[tony1851]

@OP;

OK, so if the structure is built on conventional dpc with the little diamond-shapes on it, the building won't move, right?

But if the same structure is built on visqueen, the building will slide about?

So on that basis, you would argue that the little fraction-of-a-millimeter diamond shaped protrusions stop the building from sliding off?

The coefficient of friction may appear to be low, but the applied load is very high.

 

[tvrbeaver]

Like using slicks in the wet LOL. Sure I know what you mean. So will be fine. Cheers

 

[tvrbeaver]

intersting though... I've just put a block on a strip of Visquene and pulled it out... you do that with DPC and it won't move (the block falls over).. so even if they are small 1mm diamods imprinted in the surface, it does prevent any sideways movement for sure

 

[Deltamale]

Stop worrying, as already mentioned the imposed weight of the superstructure will more than overcome any risk of slipping. bear in mind plastic DPC has not always been keyed and was never much of a problem when smooth.

Try putting a piece of the DPM in a vice and try pulling it out, well that's what it will be like when the wall is built.

 

[SimonH2]

Work out what pressure is going to be on top of that sheet. It'll deform to conform to the textured surface of the block underneath and the texture of the cement course on top - yes it'll still have a texture even if it's very fine.

Not only that, but a small piece won't move in isolation. In one direction, the entire length of teh wall would have to move. In the other direction, both leaves (they are keyed together with ties) will need to move along the length of several blocks.

In theory it'll make the building "very very slightly" more likely to move if a car runs into it - but if that happens then moving at the DPC is the least of your problems. At work, a car drove into the building and the bricks/blocks had moved about around the impact point even without a DPC in the mortar bed. I can't help thinking the poor lady sat the other side of the wall most have "had quite a surprise" when teh wall next to her desk moved in by 2"