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#206407 - 06/29/12 06:41 AM Deteriorated mortar caused by electrolysis?
WNYJim Offline
Member

Registered: 06/06/02
Posts: 39
Loc: Rochester, NY, USA
I was asked to take a look at an old cobblestone building with some deterioration of the mortar next to the meter channel.

The motar is question is powdery and white.

The service was installed in 2004 with the meter channel mounted on two vertical sections of kindorf.

From the lower left section of the kindorf (the starting point of the deterioration) to the furthest point of the damaged mortar (about8 feet) there was a reading of 52mV

There's a frost proof sillcock about 2 feet to the other side of the meter channel, the reading to that was 116mV but there is no damage to the mortar in that area.

It was about 80 degrees / 80% RH the day these readings were taken.

I didn't go in the basement or open the meter channel but it looks like PVC was used where it went through the stone.

There is a 1" PVC conduit coming out of the ground and goes into the bottom of the meter channel that I'm guessing has the ground wires in it (I didnít install the service).

The ground wires wouldn't be terminated in the meter channel (that's not permited here), they must have been routed to the panel.

The owner wants to have the motar repaired but needs to solve the route cause first.

Could the deterioration of the motar be caused by electrolysis?

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#206411 - 06/29/12 01:06 PM Re: Deteriorated mortar caused by electrolysis? [Re: WNYJim]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1280
Loc: Sacramento, CA
Inferior materials for the patch...

52mV is too low for electro chemistry...

Any such would necessarily cause massive metallic corrosion, too.
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#206412 - 06/29/12 03:44 PM Re: Deteriorated mortar caused by electrolysis? [Re: WNYJim]
mikesh Offline
Member

Registered: 06/07/06
Posts: 614
Loc: Victoria, BC, Canada
Some chemical reaction to the galvanizing materials? Maybe. Galvanic corrosion would show on the metal first I would think and if the brick or rock is mettalic maybe some reaction to that but the morter? I don't think it is an electrical cause.

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#206416 - 06/30/12 03:06 PM Re: Deteriorated mortar caused by electrolysis? [Re: WNYJim]
WNYJim Offline
Member

Registered: 06/06/02
Posts: 39
Loc: Rochester, NY, USA
Thanks for reviewing this and sharing your ideas.

Glad to know it's doesn't apear to be a problem with the service.

I think the next step for me is to ask a local mason what he thinks the problem could be.

The building is over 175 years old but the mortar was redone in 2004.

It had been an abandon house for several years but now is an upscale office building.

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#206417 - 06/30/12 03:52 PM Re: Deteriorated mortar caused by electrolysis? [Re: WNYJim]
Alan Belson Offline
Member

Registered: 03/23/05
Posts: 1801
Loc: Mayenne N. France
Common Portland cement [ now almost universal ] was invented in about 1825. I believe Edison had a cement works in about 1899 - and his usual famous 'backdated patents', no doubt! I'd guess that the original mortar was thus lime based, often with added straw, or animal hair, or wood ash and sand for economy. That stuff took months to set, but nobody was in a hurry in those days. The biggest problem with pointing up old masonary in patches is that there is a tendency to make the mortar too strong- this can crack the masonary- or to use up an old bag of cement in the truck that's gone off - mortar then crumbles. Mortar should be 1:5 [unless flaunching roof ridges, chimneys and the like when 1:3 can be employed], no stronger for brick/stone and made with fresh cement, clean water and clean sand. Small areas of pointing often dry too fast and need damping down for a day or so- or worse, they get frosted and don't gel properly and crumble as a weak mortar. There will be a local voltage around metal parts- cements are alkaline and thus form electrolytes. Damage is usually minimal if iron is galvanised or painted. Bare iron will swell alarmingly in contact with mortar, to the extent that it can fracture structural beams. A tar coat usually suffices to prevent surface corrosion- deep embedded stuff like rebar is susceptible unless there is at least 2" of 'cover'.
ps; My pa was a 'brickie', old school. He used to bore us kids rigid for hours with talk of frogs, sharp-sand, slate damp-courses, soldiers etc! Some of it must have sunk in! sleep
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#206429 - 07/01/12 07:50 PM Re: Deteriorated mortar caused by electrolysis? [Re: WNYJim]
WNYJim Offline
Member

Registered: 06/06/02
Posts: 39
Loc: Rochester, NY, USA
I sure have a lot of information to share with the owner of this place.
It looks like the mason will have some work to do.
Thanks for the help, somebody on here always has the answer.

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