19th century brick joint thickness 3

[ajk1]

The brick masonry mortar joint thickness in buildings built in the 19th century is generally relatively relatively thin, compared to buildings built in most of the 20th century, at least in my area of practise in Ontario. I believe this is related to the lime mortar that was generally used at that time. They seem to have aged well, without masonry deterioration, as long as there are no unusual adverse conditions (such as broken downspout or flashing which concentrating water on the masonry). Does anyone know why this type of thin joint was abandoned and not used anymore, and how it is related to the line type mortar in use in those days? I am just curious.

 

[dik]

Early brick and stone mortar joints were often 1/4", but practice varied widely, and 1/2 joints are not uncommon. It had nothing to do with the high lime mortar. Lime relied on the impurities to give it hydraulic properties else over time the lime would 'wash out' leaving sand. I've encountered that occasionally. Often stonework, even today uses 1/4" mortar joints. One of the functions of the mortar was to allow moisture (humidity, etc.) to 'wick' out from within.

SRE should have a copy of a paper I prepared on Historic Brickwork.

Dik

 

[SlideRuleEra]

Dik's paper "Historic Brickwork - Revised 2017"

http://www.SlideRuleEra.net

 

[dik]

Thanks SRE...

Dik

 

[ajk1]

Does anyone know why this type of thin joint was abandoned and not used anymore, and how it is related to the lime type mortar in use in those days? I am just curious.

Thanks dik. I will read your paper and may have some questions. Interesting is your comment that often 1/2" joints were used. I have looked at a fair number of 19th century brick buildings in Toronto and have never seen them with 1/2" brick joints. Did your comment refer to brick joints, and if so can you tell me where? In Toronto, or elsewhere?If in Toronto, can you tell me which 19th century building has 1/2" joints. Thanks again. Much appreciated.

 

[ajk1]

I have so far had only a quick read through this very interesting paper, but see no answer to my basic question of why such thin mortar joints were generally used in 19th brick walls. Do you perhaps have an answer to that? I believe that I had been told by masonry specialist many decades ago that it was due to the lime mortar used in the 19th century (I assumed that the lime mortar was too squishy to support the weight of the brick when the mortar was wet, and this squeezing out was less an issue with the thinner joints...maybe I am way off), but you say that is incorrect and has nothing to do with the lime mortar.
So my question is why such thin brick joints were used in 19th century, and modern brick joints are thicker. I wonder if modern mortars make the thinner joints harder to construct??

 

[dik]

It takes less skill to use a thicker joint... the greater tolerance provided by the increased joint thickness makes construction faster and requires less skill.

I've seen stonework where the joints were consistently 3/16"... no room for error. The thinner joint does provide containment for the mortar and allows a higher load carrying capacity.

The old stonemasons were real experts... in particular with the mortar. They had to source the right lime to ensure that the mortar had proper hydraulic properties so it wouldn't wash away in a decade. I've worked on old buildings where the mortar was reduced to confined sand... the Lindsay, Ontario town hall was one of them.

I missed that in the paper... I'll have to update it...

Dik

 

[ajk1]

It takes less skill to use a thicker joint... the greater tolerance provided by the increased joint thickness makes construction faster and requires less skill.

That makes sense. The old masons I was told long ago were often of European and Scottish background, really skilled craftsmen. Thanks for the answer.

The thinner joint does provide containment for the mortar and allows a higher load carrying capacity.

I am not aware of any code provision or recognized published Standard provisions allowing for higher permissible bearing stresses for thinner joints. Are you?

 

[IRstuff]

Paper looks great, but didn't get all the way through. Some additional pictures would really help.

TTFN (ta ta for now)
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[kipfoot]

I think it may have been a local preference. Thin joints I've seen in buildings from the 1800's/early 1900's were for aesthetics. Thin joints were the style and look good. My house, in the mid Atlantic US, was built in the early 20th century and has thin joints on the front and cheaper brick with thick joints on the side. (photo attached)

A lot of early construction can be explained with idea that labor was cheap and materials were expensive, but I don't think anyone was trying to save money with thin joints. I also don't think that anyone was worried about higher compressive strengths in low rise masonry buildings. It might be that the consistency of a lime mortar is more pasty and suited to thinner joints, but as the 20th century came around, the masonry sizes became more standardized.

In the US, three courses with 3/8" joints were always 8". I think this standardization is why it's mostly like that now. You could specify a 3/16" joint and tell us what happens.

 

[dik]

I'm not aware of any codes that permit an increase due to the mortar joint thickness... I don't think there are... There are numerous test results that bear this out. Some work done in the 70s at the U of Manitoba show this.

I've got up update the paper to include mortar joint thicknesses... missed it somehow.

When I was a kid, the old guy (about80) on the corner was a master stone mason and he had some great pictures (tinplate)... likely gone forever. When he passed, my dad received all his tools... don't know whatever happened to them... I recall there were lots of dividers, squares, and hammers and chisels.

Dik

 

[dik]

kipfoot... it wasn't until the late 1700s when they started standardising brick dimensions... and it took several decades to catch on.

Dik

 

[dik]

I just received an email from Peter Foley with a lot of added information on joint thicknesses and have asked him to post it here. If it doesn't show up here in a couple of days, I'll send him an email to post it.

Dik

 

[OldBldgGuy]

ajk1: plain and simple, it's exactly as dik says: skill. It is much more difficult to lay bricks (or cut stone) straight, level, and plumb with tight joints. Yes, there are old buildings with fat-ish joints, but there are far more with 1/4" joints than >3/8". The joints weather less, are stronger, last longer, and look better to boot, so the benefits are many.

 

[ajk1]

ajk1: plain and simple, it's exactly as dik says: skill. It is much more difficult to lay bricks (or cut stone) straight, level, and plumb with tight joints. Yes, there are old buildings with fat-ish joints, but there are far more with 1/4" joints than >3/8". The joints weather less, are stronger, last longer, and look better to boot, so the benefits are many.

I am unclear. Is it the thicker joints that weather less, are stronger, etc.?

 

[dik]

OBG and ajk... what I posted is correct, but Peter Foley provided a lot of useful information and detail about constructability (Sp?) and tolerances... I'll post him an email tomorrow to see if he will copy the forum or if he will let me copy it.

Dik

 

[dik]

ajk "I am unclear. Is it the thicker joints that weather less, are stronger, etc.?"

Thinner joints weather better and are stronger. As Peter Foley pointed out in his eMail, they are also more difficult to construct and are affected by tolerance with variable masonry unit dimensions. If a brick may vary by an 1/8", then a 1/4" joint is more difficult to maintain.

OBG is correct...

Dik

 

[ajk1]

ok, thanks. Why was lime mortar generally used in old brickwork, but today is generally not?

 

[phamENG]

Lime was a more readily available resource (here on the coast, a lot of the lime in historic structures came from burning oyster shells). Advancements in cementitious material technology (namely Portland cement) has made lime mostly obsolete.

 

[dik]

A bit of a history... Early masonry mortars used sand and lime. The master mason had to know where to source the lime because the hydraulic properties of a mortar joint depend on the impurities in the lime. If there were insufficient impurities, over time the lime would wash away and the mortar would 'disappear' leaving only the sand. Master masons also had their own 'additives' that would often be mixed into the batch. Pure lime does not make a durable mortar joint.

Over time lime became more 'pure' and lacked hydraulic impurities. It was also in greater demand. Pozzolans had to be introduced. In the late 1800s, Portland cement became the #1 pozzolan. This was added to the lime sand mixture to provide a workable and durable mortar.

I'm not positive, but I think the current trend is to 'bag mortar cement' a single product to mix with sand and water to create a mortar mix. This can be done on site or off site. This can have various admixtures to improve the workability and durability, including air entrainment, plasticity, etc. I also understand that the lime has largely been replaced with powdered limestone, or other products. Lime used to be produced by 'burning' limestone, or as noted... oyster shells.

Care has to be taken in mortar mixes for historic brickwork to ensure the replacement mortar has similar properties and strength as the mortar it is replacing. Portland cement and lime mixes often produce a mortar that is too hard and not as breathable. This causes future distress to occur through the brickwork and not be generally constrained to the mortar joints, which can be 'repointed'.

Dik