Conservation mortar mix

[88v8]

Conversation with a chap yesterday. I'm going to employ him + two labour to hand-shift several tons of earth behind the cottage, lower the levels, land drain, dry-stone retaining walls. He's been 20 years in this line.
He also does brickwork, mortared stonework.
Naturally, the subject of lime came up.
He's never heard of limecrete, or NHL.
He knows about the damage done by cement pointing. His pointing mix would be 9/2/1 soft sand, hydrated lime, and... cement. At least it's weak enough that it will probably do no damage.
Good illustration of what one is up against when trying to find someone to work on a period house.
Some repointing will be needed no doubt when the lower walls are exposed, I think I'll be doing that myself.

Whilst googling 'hydrated lime' found this hair-raising lime discussion, btw
Moto... :shock:
http://cr4.globalspec.com/thread/13932/Breathable-Walls

Ivor

 

[Flyfisher]

Looks like we're all doomed then:

"Many of these older structures are not healthy, because of the composition of the old wall and roofing treatments. In fact they are carcinogenic and respirators and over-clothes should be used to eliminate any inhalation of the dust. Much of the dust can contain rodent urine. Disposal of the broken plaster is considered hazardous wast and should be disposed of properly. Many times asbestos was included into the mixture. Ask your client if the "health and breath ability of the building", includes cancer or lung infection prevention."

There's only one answer: "Spray it all with plastic and be done with it."


Not sure if I should be laughing or crying.

 

[tobydog]

I read this all the way through and realised that for 10 minutes I had been sitting there with my mouth open. At least I've got a more pressing reason to remove the gypsum plaster from my timber frame - it's radioactive :shock:

 

[skier-hughes]

He knows about the damage done by cement pointing. His pointing mix would be 9/2/1 soft sand, hydrated lime, and... cement. At least it's weak enough that it will probably do no damage.
Good illustration of what one is up against when trying to find someone to work on a period house.

Ivor

Surely it's whatever you want it to be?

 

[stuart45]

9/2/1 is a mix that was used years ago on older brickwork. Nowadays research suggests that less than an even amount of cement in a lime mix will actually weaken the mix. Lime should used in equal amount to cement as in a 1/1/6 mix, producing a cement mortar. Lime mortars should contain no cement.

 

[88v8]

He knows about the damage done by cement pointing. His pointing mix would be 9/2/1 soft sand, hydrated lime, and... cement. At least it's weak enough that it will probably do no damage.
Good illustration of what one is up against when trying to find someone to work on a period house.

Ivor

Surely it's whatever you want it to be?

Yes, but if someone's not used to working with NHL, I don't want them learning on my house!

Ivor

 

[88v8]

9/2/1 is a mix that was used years ago on older brickwork. Nowadays research suggests that less than an even amount of cement in a lime mix will actually weaken the mix. Lime should used in equal amount to cement as in a 1/1/6 mix, producing a cement mortar. Lime mortars should contain no cement.

Quite so.
For the builder, the 9/2/1 has the advantage that it doesn't need tending, and they can tell the client 'it's a lime mortar, guv'.
For the building's benefit, it has a modicum of breathability compared to the usual cement-rich mix, and is so weak that it will have a degree of flexibility.
But as you observe, it's not right.

I had the inside of the wall repointed in NHL5 so ideally the outside will be 3.5. That will make the outside more breathable than the inside, so rising damp (if it exists) will tend to evaporate outwards rather than inwards. OTOH, that wall gets most of the weather, and NHL3.5 will be more absorbent, so perhaps I should use NHL 5. Errrm.

On a west flank wall which is more protected, we used NHL 2 for maximum breathability. But, as I say, that's more protected.

I already have a bag of NHL 5 so the temptation to use that is strong, especially as I'm not sure about using NHL 3.5.
Hmmm.

Ivor

 

[plasticpigeon]

I used NHL 3.5 mortar for some area of brickwork, both pointing and building. After a year it is incredibly hard, just like cement. I bet it is harder than my bricks. I now use a composite mortar 1:1:6 NHL, hydrated, sand which is easier to work with and seems softer and is hopefully weaker than the masonry.

 

[skier-hughes]

My mortar is incredibly hard, it has been there hundreds of years in places!!! But I don't think it is just the physical hardness that matters, obviously it is the way in which it allows moisture to penetrate in and out that matters. Of course I may be wrong. We sent a sample of our mortar for testing and it came back with a 1 - 2.5 (NHL) mix as having been used, but then again, there are also a lot of small stones in the mix which weren't included in my sample!!

 

[88v8]

....a 1 - 2.5 (NHL) mix as having been used...

Wow. That's pretty fierce. I use about 4 sharp :1 NHL.
Probably there was less uniformity back in them days.

Ivor

 

[skier-hughes]

I think the rest may have been made up with the aggregate!!

 

[DJH]

Anything that was handy was swept up and mixed in with mortar. I've heard that chippings were swept from the road along with horse and cow manure.

Doug

 

[Flyfisher]

Indeed, and sand/mud out of rivers, chalk out of the ground (depending on the subsoil) or almost anything they could find in the absence of being able to order a lorry load of washed, graded, sorted, certified materials from Jewson.

These days it's all about standards and repeatability (and speed of course), little of which existed in the good old days. This meant a huge variability in building quality and longevity but we only see the best examples today because all the bad stuff has fallen down and rotted away.