Dpm not bedded into inner skin!!

[jimal1969]

Along one of my walls the Dpm hasn’t been over lapped into the inner skin, it’s also in places not long enough to get in there anyway. 
is the best option to grind out a channel in the Dpc course and mortar it in and also tape more to it where it’s short ? 

[Brickie]

Was it the same company who cast the slab (& didn’t leave much dpm free for lapping) as have started the blockwork? 
For that little amount of work I’d tell them to take it down,tape & lap some dpm in & rebuild. There’s only about £200 worth of work there. Also,are they using wall starter kits where the blockwork meets existing? I’d expect to see it poking out the top of what’s built. Have the cut a slot in the existing wall to slide a vertical dpc into where the new cavity meets existing? Otherwise you have an external wall becoming internal with potential for penetrating damp. 

[jimal1969]

Yes we’ve got wall started ties in, you can’t see them because they don’t go on a rail they drill in every few course see… https://www.selcobw.com/staifix-stainless-steel-wall-starter-tie-pack-10

there is also a vertical Dpm in the adjoining. That’s there because BC told us to put it there. 

Look if I’m honest it’s partly my fault, I knew it needed to tuck in but was distracted and before I knew it the time went by. I’m paying the bricklayer on a day rate and don’t want to demolish and start again. But do you have any better ideas other than grinding it in? Appreciate the reply
 

[Brickie]

Others who’ve done refurbs & cast a slab will be better informed than me on this-I believe taking the DPM up the wall a certain way (rather than cutting it in) is more the done thing in that scenario. 

[jimal1969]

2 hours ago, Brickie said:

Others who’ve done refurbs & cast a slab will be better informed than me on this-I believe taking the DPM up the wall a certain way (rather than cutting it in) is more the done thing in that scenario. 

Cool, no worries, not an urgent issue, will get it sorted one way or another 👍🏽

[Gus Potter]

10 hours ago, Brickie said:

Have the cut a slot in the existing wall to slide a vertical dpc into where the new cavity meets existing? Otherwise you have an external wall becoming internal with potential for penetrating damp. 

Good point.. but remember that you could be weakening the existing house wall in terms of horizontal stability if you cut it. I would check with the designer before you do this.

 

@jimal1969 where the new wall interfaces with the existing rear wall looks like it is in a pretty sheltered spot so less risk of driving rain causing a damp problem. I would try all other options before cutting the existing brick first. I would imagine that you are going to strap the existing rear elevation wall and line with insulated plasterboard anyway so the any occasional increase in mosture is not going to pose much risk. If you are just going to plaster onto the existing brick then.. could be an issue for condensation and so on.

 

In terms of you DPM. Are putting solid insulation on the slab with screed or some kind of floating floor? You usually need some perimeter insulation vertically so should be able to cobble up something with tapes and some extra DPM / DPC to protect everything from the masonry below DPC level.

 

Anyway you are now into spring.. good building weather.. what more could you ask.

 

 

 

[jimal1969]

4 hours ago, Gus Potter said:

Good point.. but remember that you could be weakening the existing house wall in terms of horizontal stability if you cut it. I would check with the designer before you do this.

 

@jimal1969 where the new wall interfaces with the existing rear wall looks like it is in a pretty sheltered spot so less risk of driving rain causing a damp problem. I would try all other options before cutting the existing brick first. I would imagine that you are going to strap the existing rear elevation wall and line with insulated plasterboard anyway so the any occasional increase in mosture is not going to pose much risk. If you are just going to plaster onto the existing brick then.. could be an issue for condensation and so on.

 

In terms of you DPM. Are putting solid insulation on the slab with screed or some kind of floating floor? You usually need some perimeter insulation vertically so should be able to cobble up something with tapes and some extra DPM / DPC to protect everything from the masonry below DPC level.

 

Anyway you are now into spring.. good building weather.. what more could you ask.

 

 

 

Hi Gus. We had to grind a vertical Dpc into the existing wall because bc insisted it. It’s only 15-20mm in so not going to compromise the brickwork in any way and in my mind it does seem like good practice. You are right in it being a sheltered spot however. We will be going with 100mm celotex with screed on the top but I don’t understand what you mean but perimeter vertical insulation?  The walls will be bonded and plastered. At the moment I think my best option is to grind a 25mm groove into the blockwork a fraction above the Dpc and gripfill the Dpm in and then cement it in completely. It would give me peace of mind. I’m open to other suggestions however 😃

[Gus Potter]

9 minutes ago, jimal1969 said:

Hi Gus. We had to grind a vertical Dpc into the existing wall because bc insisted it. It’s only 15-20mm in so not going to compromise the brickwork in any way and in my mind it does seem like good practice. You are right in it being a sheltered spot however. We will be going with 100mm celotex with screed on the top but I don’t understand what you mean but perimeter vertical insulation?  The walls will be bonded and plastered. At the moment I think my best option is to grind a 25mm groove into the blockwork a fraction above the Dpc and gripfill the Dpm in and then cement it in completely. It would give me peace of mind. I’m open to other suggestions however 😃

Hiya.

 

If the floor screed touches the outside wall you get a cold bridge. What you do is stop the screed often 25 to 50mm from the wall and put a bit of insulation that is vertical. Like below from screen shot of Kingspan detail

 

To finish the existing house walls I always want to know if the existing wall has a clear cavity or if it is fully filled with insulation. If not fully filled then you often get a cold draft in the cavity so the existing wall is cold. Plastering this is not my preference as it can attract condensation at the bottom / top if a kitchen area. My first choice is to strap and line with 40mm insulated plasterboard. Yes it thickens the wall a bit but you can lose quite a lot of heat on a windy winters day due to a drafty cavity!

 

I would look to see if you can tape and seal the DPM as best you can, avoid raggling (grinding a groove) out the block to rebate in the plastic.. not a good structural option over that length of wall. Try and lap a bit of DPM up the wall, tape and seal and take it above the top of the screed. The vertical insulation (perimeter insulation) is often water  proof anyway so you have belt and braces.

 

 

 

[jimal1969]

7 hours ago, Gus Potter said:

Hiya.

 

If the floor screed touches the outside wall you get a cold bridge. What you do is stop the screed often 25 to 50mm from the wall and put a bit of insulation that is vertical. Like below from screen shot of Kingspan detail

 

To finish the existing house walls I always want to know if the existing wall has a clear cavity or if it is fully filled with insulation. If not fully filled then you often get a cold draft in the cavity so the existing wall is cold. Plastering this is not my preference as it can attract condensation at the bottom / top if a kitchen area. My first choice is to strap and line with 40mm insulated plasterboard. Yes it thickens the wall a bit but you can lose quite a lot of heat on a windy winters day due to a drafty cavity!

 

I would look to see if you can tape and seal the DPM as best you can, avoid raggling (grinding a groove) out the block to rebate in the plastic.. not a good structural option over that length of wall. Try and lap a bit of DPM up the wall, tape and seal and take it above the top of the screed. The vertical insulation (perimeter insulation) is often water  proof anyway so you have belt and braces.

 

 

 

So basically do a dot and dab with insulated plasterboard and rather than grind the Dpm in, extend it and tape it?

[tonyshouse]

Run a couple of miles away from d&d

[Gus Potter]

Yes, sorry to confuse. I put up that screenshot to show what the perimeter insulation looks like, not appreciating that there was dot and dab above. Agree with Tony, strap and line. Dotting and dabbing onto old walls can sometimes cause patches of condensation.

 

All the best.