Home>Discussions>EXTERIORS>Identifying Lime Mortar. Can it be repointed with Type N?
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Identifying Lime Mortar. Can it be repointed with Type N?

I have a chimney in Southern California from the early 1940s where mortar has been removed for repointing.

Efforts to identify the mortar at various professional masonry yards
were largely unsuccessful. Only one person (previously in the trade of buying old bricks)identified it as "lime mortar". Whether that fixes the formula to one certainty is beyond my saying.

Question one, is there a way to identify the mortar sample by a field test I can perform? I did put a drop of pool muriatic acid on it and it bubbled pretty well until the acid soaked in. Without expertise or comparative experience with how Portland cement mortars react I can't make an assessment. Any suggestions?

Is there a lab that could do an analysis on this quickly that anyone
can point me to? The job is scheduled to roll at the end of next week.

Question two, assuming that it is lime mortar, is repointing the chimney with Type N mortar a good option? The chimney brick has been identified as "Higgins brick" which was described to me as a softer brick.

I appreciate any experienced advice.

Re: Identifying Lime Mortar. Can it be repointed with Type N?

A structure constructed in 1940 would most likely have portland cement in the mortar.
You stated the brick are soft I would think you should have the brick tested for breaking point than adjust the mortar PSI to be lower than the brick PSI.
A type N mortar 28 day PSI is 750 but could reach 1500 / 2400 PSI.
You may want to use a Type O mortar 28 day PSI 350 but can reach 750 / 1200 PSI.

Research Estimators' Reference Mortar Mixes


Re: Identifying Lime Mortar. Can it be repointed with Type N?

Let me thank Clarence for his reply and everybody for continued input.

A test with 5% acid vinegar showed light bubbling on the old mortar. The reaction was neither vigorous or fizzy.

I called the people at Virginia Lime Works who were very genial. Because of the age, the gentleman there said an OPC mortar mix with lime was likely involved. Even though he couldn't see the brick, he advised Type N mortar. A visit to another masonry supply yard got a second opinion that the original mortar was lime.

I checked on testing. The cost is about $500 and getting results in time for the work to move as calendared was not likely.

Then I called the bricklayer's union local. The man there with plenty of local chimney experience in his working youth said Type S spec mix was a natural call.

Again, I appreciate all the time and continued consideration those who have responded have given this issue, even if there is a spread of uncertainties and opinions.

Re: Identifying Lime Mortar. Can it be repointed with Type N?

Let me make some additional comments on the brick and old mortar.

The old mortar is a whitish grey with prominent sand grains. Fragments
darken a bit when wet but dry quickly in the sun. When pieces break, they don't do so in a consistent way. Edges
are uneven, rough or bumpy. The material doesn't have any glossiness or glassiness about it. Overall, it appears very dry.

If you stroke a somewhat uneven edge on a cement step several times, particles are rapidly shed and the edge becomes wears pretty quickly to a pocked flatness. Strokes leave a light but detectable greyish streak on the cement.

Although it doesn't dig in, a rasping fingernail will dislodge grains of material from a rough surface.

I realize the above may offer no master key to identification.
Are there any other visible or working tests that can be used to make a differentiation?

Also, on the Higgins brick, I'm getting different opinions on its strength ranging from soft to medium soft.

Re: Identifying Lime Mortar. Can it be repointed with Type N?

I would stay away from the high PSI mortars my opinion based on working on old buildings dating bach from 1701 thru 1890's all ot these buildings that had repairs made using a very high an dense mortar have failed some have failed in 5 years to as long as 30 years the closer you can get to the existing mortar the better your results will be.
To check the existing mortar remove some mortar deep into the joint say like 2 inches and look for small pices of lime sometime these will be about the size of a ( B B shot ) mix the material with water as you would if mixing new mortar if it gets stickey the lime that has not recarbinated will turn into a paste. which would indicate a Lime mortar.
Check out these
Preservation Briefs # 2 Repointing Mortar Joints.
Lime's role in Masonry Construction / August 1996 page # 364
Bleaklow lime products pointing mortars for soft brick 1 cement 3 Lime 11 Sand.
www.oldhousejournal.com/magazine/1484 page 2/3/2009
www.historic-scotland.gov.uk ( loof for the use of lime & cement in traditional buildings )

Re: Identifying Lime Mortar. Can it be repointed with Type N?

Like Clarence stated, probably safest to go with type O, or buy some bags of Mix-n-go from VA Lime Works.

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