DPC sticking out

[MortarThePoint]

My brickie and BCO both say that the DPC/cavity tray at the bottom of wall (above splash) can stop just short of the edge of the mortar so that it isn't visible, but my warranty inspector says that he would require it remediated if that was the case. He says it needs to stick out by 10mm so that capillary action doesn't allow water to bypass the DPC. I think that's going to make things much worse as rain could collect on the surface of the part sticking out and then get sucked into the wall at a much greater rate than any rising damp could possibly bypass the DPC.

 

Here's how NHBC draw it in their guidance:

 

I'm wondering if I can keep everyone happy by using some kind of liquid DPC in addition to having a recessed DPC/cavity tray. Either:

1. painted on the top of the lower course forming a DPC (e.g. Black Jack ) though ideally clear
2. use a waterproofing admixture in the mortar to make the mortar waterproof and effectively a DPC in its own right (e.g. Sika 1 )

 

My brickie is going to think I've lost the plot, but the thought of the warranty inspector kicking up a fuss about the DPC would give me nighmares as remediating that would cost a fortune.

[Mr Punter]

10mm seems excessive and may look crappy.  As long as it is just visible it will be OK.  Could see no mention of 10mm projection in NHBC.  The drawing shows a slight downstand, which will not happen with the stuff on a roll.

[MortarThePoint]

1 minute ago, Mr Punter said:

10mm seems excessive and may look crappy.  As long as it is just visible it will be OK.  Could see no mention of 10mm projection in NHBC.  The drawing shows a slight downstand, which will not happen with the stuff on a roll.

 

I agree, 10mm would look terrible. I think it would look best if it didn't stick out at all. also I think any amount of sticking out has the rain issue that is likely greater than the risk of rising damp.

[nod]

He’s being picky Most just follow BC 

In any case the Warrantee companies hardly ever pay out 

[joe90]

Leave it at 10mm then trim with a Stanley knife after he has left  ?.

[Mr Punter]

10 minutes ago, joe90 said:

Leave it at 10mm then trim with a Stanley knife after he has left  ?.

 

It will be a pain to get a neat cut.  Probably skin your knuckles tying.

[epsilonGreedy]

A 10mm dpc projection is bonkers and as suggested it will stick out horizontally due to the rigidity of dpc plastic and act as a rain catcher.

 

I suggest the OP makes a stand against this errant warranty inspector and raise hell with the superiors. It is important to get the upper hand at this stage as there will be subsequent disagreement so it is necessary to gain the psych-ops warfare advantage.

 

 

[Timedout]

Went through this a long time ago. BC wanted it to stick out so the masons complied. The SE who was providing certification said stuff off I want it flush. I trimmed it flush when we finished, inc skinned knuckles, and it looked poor. Not a squeak out of BC. Thereafter, DPC flush like a pencil line in the mortar.

[MortarThePoint]

1 hour ago, epsilonGreedy said:

A 10mm dpc projection is bonkers and as suggested it will stick out horizontally due to the rigidity of dpc plastic and act as a rain catcher.

 

I suggest the OP makes a stand against this errant warranty inspector and raise hell with the superiors. It is important to get the upper hand at this stage as there will be subsequent disagreement so it is necessary to gain the psych-ops warfare advantage.

 

Agreed, it's bonkers. Into the cavity I wouldn't argue with, but sticking out like that it would catch rain and have things growing on it. I need to take a stand on this as, in my mind and pretty much everyone else's, it it is a thoroughly bad idea to have it sticking out like that.

 

1 hour ago, Timedout said:

Went through this a long time ago. BC wanted it to stick out so the masons complied. The SE who was providing certification said stuff off I want it flush. I trimmed it flush when we finished, inc skinned knuckles, and it looked poor. Not a squeak out of BC. Thereafter, DPC flush like a pencil line in the mortar.

 

I think this is where I'd like to get to, so that the inspector can see it has been installed, but it doesn't act as a rain catcher. My brickie talks of having minimal mortar under the DPC, whereas where I have noticed DPCs they appear to be in the middle of the bed. A complication of this though is that the outer course brick would have to be laid before, or at the same time as, the inner blockwork so that it could be aligned appropriately.

 

[Brickie]

11 hours ago, MortarThePoint said:

complication of this though is that the outer course brick would have to be laid before, or at the same time as, the inner blockwork so that it could be aligned appropriately

You would expect to see your brickwork completed to dpc height before any internal blockwork is done. You want to be able to set any openings out so that they work to bond where possible. 

[epsilonGreedy]

16 hours ago, MortarThePoint said:

I need to take a stand on this as, in my mind and pretty much everyone else's, it it is a thoroughly bad idea to have it sticking out like that.

 

 

My brickie automatically inset the dpc a few mm so that the external pointed finish did not expose the edge of the dpc. I questioned this practice in the first hour of above dpc laying and he offered to change to marginally exposed dpc if that was my preference but he advised the amount of moisture uptake through a thin crust of pointed up mortar was trivial. I am in  low rainfall area and as with many building debates, local practice may reflect the local environment.

 

How old is this warranty inspector?

 

p.s. I have 3 courses of engineer blues below damp which form an additional barrier to rising damp.

Edited July 25, 2020 by epsilonGreedy

[joe90]

3 minutes ago, epsilonGreedy said:

he advised the amount of moisture uptake through a thin crust of pointed up mortar was trivial

totally agree ?

[MortarThePoint]

4 hours ago, epsilonGreedy said:

How old is this warranty inspector?

 

He does seem pretty young and inexperienced. He may be right 'on paper' though which makes it hard to swing him round or to get a second opinion from his firm / the warranty provider.

Edited July 25, 2020 by MortarThePoint

[PeterW]

Are they doing combined warranty and BRegs approval .??

[MortarThePoint]

54 minutes ago, PeterW said:

Are they doing combined warranty and BRegs approval .??

 

Thankfully not, though I did consider it back at the time. BCO is fine with / expects the DPC recessed slightly

[PeterW]

Ok so BRegs trumps warranty as one is legal compliance ..! Suggest you get both on site together and get BCO to explain what compliance means. 

[Timedout]

         

Quote

My brickie talks of having minimal mortar under the DPC, whereas where I have noticed DPCs they appear to be in the middle of the bed

Your brickie is correct. DPC should be bedded on mortar and have mortar over it too. This is disregarded by some but is technically correct.

[MortarThePoint]

8 minutes ago, Timedout said:

 Your brickie is correct. DPC should be bedded on mortar and have mortar over it too. This is disregarded by some but is technically correct.

 

Yes, but he's saying most of the mortar in the joint is above the DPC, rather than the DPC being smack in the middle.

[MortarThePoint]

I found this LABC guidance:

"The bottom of the tray should be taken across the external leaf and preferably just visible at the external mortar joint."

 

That's preferably just visible, possibly not, and definitely not sticking out 10mm.

 

This LABC guidance on the other hand is perhaps clearer:

"5. Ensure the external edge of the DPC is visible and not bridged by mortar when completing pointing of the mortar joint."

Edited July 25, 2020 by MortarThePoint