dpm

[jamesarm]

Hi Guys,

Couple of questions relating to DPMs if anyones up for it;

1. I have got to join a new poly DPM with an existing slate DPC. Plan was to chase out the underside of the DPC and wedge the DPM in with a bit of Silicon. Any better ideas?

2. Got to join up different bits of the new DPM together;- Duck Tape, 200mm overlaps, tape on both sides?

Cheers,

James

 

[r896neo]

Don't be shy with the old overlaps, a foot would be better and just tape it up on one side for good measure. The weight of the concrete forms a good enough seal on its own usually.

 

[RedHerring2]

A bit confused here:

1. I have got to join a new poly DPM (Damp Proof Membrane) with an existing slate DPC (Damp Proof Course). Plan was to chase out the underside of the DPC and wedge the DPM in with a bit of Silicon. Any better ideas?

James

OK, so you're laying a new floor slab and you want to tuck the DPM into the DPC course, yeah?
I think the dpm is just taken 50mm or so higher up the wall, held in place by the 'timber tamping guides' until plaster/board/skirting is fixed.

2. Got to join up different bits of the new DPM together;- Duck Tape, 200mm overlaps, tape on both sides?

Well, that's straightforward. No problem. I believe some BCOs may want double-sided tape, judging by some posts but I have no experience of that.

However, this really confuses me:

Don't be shy with the old overlaps, a foot would be better and just tape it up on one side for good measure. The weight of the concrete forms a good enough seal on its own usually.

how the 'eck does one overlap a new dpm to an old dpc by 300mm? Or was " the old overlaps" just a 'turn of phrase'?
Clarification needed, I think

 

[jamesarm]

RedHerring,

I think it was just an 'old' turn of phrase. I am talking about the new DPMs.

Regarding the new DPM to old DPC; The slate is a bit knackered, so I dont think I will get a good joint unless I chase out the underside. I see what your saying about bringing it up 50mm, but it will be behind an expansion joint so will not be able to fiddle with it after.

Cheers,

James.

 

[r896neo]

sorry by 'old' i meant nothing as in how you would say, 'oh yea the old girl is going well'

Which in this context was pretty confusing.

 

[jamesarm]

No worries, does the missus like being called the old Girl? - mine isn't too keen

 

[r896neo]

i was more referring to a car etc. Yet again my enigmatic reply confuses.

 

[theoldun]

James,
Just to finish this post.
Do as RH2 has suggested, bring DPM up above proposed finished concrete and screed level and tack to wall temporary.
You say you have an expansion joint round the perimeter, it must be a good sized slab to warrant expansion joint, or did you mean perimeter insulation?
What ever you did mean, expansion or insulation, the DPM at the back is no problem as long as it is above finished floor level.
Cut DPM of 25mm above screed on completion.

oldun

 

[jamesarm]

Cheers Oldun,

It is about 60m2, a thickened raft. Site is in the Fens, so expecting movement. Formwork is ICF, with Monolithic pour. Thanks, I will bring the DPM up above ffl.

James