DPM is too high - need a solution

[mk2phil]

Hi there,

I've just had a conservatory built but the floor level has had to be lowered slightly. As a consequence, the DPM on the inner wall is about 2" higher than the floor.

I'm worried that if I get it plastered, instead of any damp being stopped by the DPM, it'll use the plaster to creep upwards - the plaster will bridge the DPM. So I basically need to seal the sides also as the bricks beneath the DPM are above the ground now.

I've mentioned this to the builder and said that we could use something called 'Black Jack' to solve it. Presumably this is some kind of adhesive that I paint onto the bricks that effectively provides a liquid DPM which I can then plaster over?

Does this sound correct?

 

[Shytalkz]

It's just a nickname for Synthaprufe or RIW. How come the DPC/M has ended up higher than the finished floor level though?

 

[mk2phil]

Well when I say the floor has been lowered, I mean that it isn't going as high as originally planned; we have french doors opening into the conservatory so the floor is at a level that allows this.

Oversight by the builder, but I've only just realised and am too far down the road to get him to rip it all out again. If this Black Jack stuff will do the job then thats fine with me.

Presumably I just paint it on, up to the bottom of the DPM - effectively sealing anything below the DPM.

Do I then just plaster straight onto it?

 

[^woody^]

Do you mean DPC is higher so that there is a section of wall below the DPC which you fear will allow moisture to bridge the DPC via plaster?

Yes, any waterproofing compound will do. Or you can tuck a bit of polyphene against the wall behind the skirting and into the DPC.

But if the bricks imediatly below the DPC are not and never do get reallly damp, then you wont have a problem if you just plaster it.

 

[mk2phil]

Do you mean DPC is higher so that there is a section of wall below the DPC which you fear will allow moisture to bridge the DPC via plaster?

Exactly that.

In some places the bricks (well, white thermalite blocks) are exactly the same colour below the DPC as they are above, but in others they are darker below and feel colder than those above.

Essentially all I want is something that will effectively seal the brickwork to stop any moisture bridging the plaster. I think the best way to explain it is if you had the DPC twice as wide as the brick and you then folded it 90 degrees downwards to cover the wall below the DPC too - this would be ideal.

I'm hoping that I can use the Black Jack DPM stuff to effectively paint on a vertical DPM that will seal the wall and prevent moisture entering the plaster afterwards.

I suppose I need to know if this what I need, and whether a plasterer can plaster over it afterwards as normal.

I will try to get some photos over the weekend.

thanks in advance

 

[^woody^]

yes the plaster will stick to it

 

[mk2phil]

So the product in that link will do the job of adequetely damp proofing the wall..?

Thanks Woody

 

[Shytalkz]

Yes that will work fine - and I never knew that it actually existed as a trade name, which goes to show you really do learn something new every day!

If you want to plaster over it, apply at least two coats and chuck some sand at the top coat as a plaster key.

 

[tawelfryn]

You want to check that there is any DPM in the floor, because it should have been lapped up and over the DPC on the internal leaf. Seeing the blocks below dpc in an internal leaf is a no no

 

[mk2phil]

If you want to plaster over it, apply at least two coats and chuck some sand at the top coat as a plaster key.

Does it matter what type of sand? Builders, sharp etc..?

Thanks

 

[Shytalkz]

Either will do.