Masonry cement / Mortar Cement

Archive of Older Topics Archive - Specifications Discussions #3
1

We just had a Lunch & Learn today where a vendor was promoting masonry cement and mortat cement. His argument was that new testing has shown these products to perform better than portland cement / lime mortars for flexural strength and freeze thaw in cold climates. I see that there was a thread on this in 2004 without a whole lot of response.

We have continued to be in the portland cement / lime camp.

Two of the reasons being that the additives that the manufacturers place in these products are not disclosed (considered trade secrets) and considering the less dense (more air entrained) mortar to be detrimental to moisture penetration resistance.

Are you specifying these products?

2004 Thread:

Mitch Miller,AIA ,CSI,CCS
Senior Member
Username: m2architek

Post Number: 11
Registered: 02-2004
Posted on Wednesday, August 11, 2004 - 08:39 am:

I am interested in hearing comments concerning the pros and cons in the use of masonry cement.
John Bunzick, CCS, CCCA
Senior Member
Username: bunzick

Post Number: 251
Registered: 03-2002
Posted on Wednesday, August 11, 2004 - 08:45 am:

Though it’s been a while since I’ve reexamined this question, I have always avoided it for construction of masonry work. Reportedly, some have admixtures in them that improve their workability to the detriment of durability. Plus, there is inconsistancy of quality and mix design between manufacturers. Perhaps the industry has addressed these issues.
David Axt, AIA, CCS, CSI
Senior Member
Username: david_axt

Post Number: 331
Registered: 03-2002
Posted on Wednesday, August 11, 2004 - 03:38 pm:

We do NOT allow masonry cement (ASTM C91) and mortar cement (ASTM C1329) in our projects. There is a lack of quality control over the admixtures in these cements that causes a wide range of compressive strengths. In a seismic zone, we must have tight tolerances on our compressive strengths.

We only specify Portland lime cement mortars (ASTM C150).

Also, this is from The Masonry Designer’s Guide 4th Edition published by the Masonry Society.

“Masonry cement and mortar cement mortars, because of their entrained air, require less water than Portland cement-lime mortars. The lower water content is beneficial in cold weather construction with low absorption units. The lower water content because a detriment however, when using very absorptive masonry units on hot, dry days.”

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2

This is a very timely post. I was almost ready, after some recent conversations, to post the same question. There seems to be a concerted effort in the industry to push Masonry Cement. This has been confirmed to me by a masonry industry person. We have always been in the Portland-Lime camp and specify Masonry Cement only for small interior jobs or small exterior jobs where cavity wall is not involved. I assume that the push is due to economics, but you all know what assuming can do. Any new information on the subject? Other opinions?

3

I have this in my Notes to Specifier:

Because of seismic conditions and lack of quality control, following cements listed below are NOT accepted.
Masonry Cement, ASTM C91
Mortar Cement, ASTM C1329

4

We find very little use of masonry cements or mortar cements here in St. Louis. These products have a history of secret ingredients and spotty quality control, although perhaps tighter standards have helped minimize or eliminate those issues recently. Our sense of it here in the heartland is that masonry cement is used mainly on smaller projects, and is available from the local home improvement store. I never specify anything other than pc-lime mortars for architectural masonry, typically using ASTM C 270 proportion method. Our structural specifications sometimes use a property method.

The biggest change here in the last decade or so has been the dominance of factory prepared mortar mixes over jobsite prepared mortars, even for relatively small jobs. The pre-mix in this area, however, remains ASTM C150: portland cement, lime, and sand.

Because they are air entrained, masonry and mortar cements probably do “perform better” than non-air-entrained pc-lime mortars in cold climates, but we still don’t know exactly what else is in the mix. Why not just use our typical pc-lime mortar and add the required specific air entrainment and other additives; that way we know exactly what it is we are getting.

Dale, was the product rep forthcoming about revealing what was in the mixture? Or does it still rely on secret ingredients?

5

George -
He didn’t like it when I brought up that they identify everything that is in the mix - they couldn’t do that - it is what sets them apart (trade secret).
Dale

6

I see that I left out a key word (didn’t):

George -
He didn’t like it when I brought up that they didn’t identify everything that is in the mix - they couldn’t do that - it is what sets them apart (trade secret).
Dale

7

At one time masonry cement was not not considered appropriate for seismic conditions but it is my understanding that the thinking on this has changed and the proabition has been removed.

Regarding the concern that less water in the mortar causes problems with absorptive masonry units on hot, dry days, I believe that the real problem is that the workmen are not properly controlling the moisture in the masonry units. I have come to the belief that it does not make sense to try to compensate for poor workmanship. Address the workmanship issue directly. If the Contractor is out of control what you are doing to compensate likely won’t be effective.

8

I agree, Mark. Our engineers don’t design for buildings but I would think you’ll want spec similar QA methods as you would for a concrete or asphalt mix design, wouldn’t you?

I wonder what direction Caltrans is taking on this. If I have time later today I’ll check – I’ve got a committee meeting to get to & I know I won’t have any time once I get to the office on Monday!

:wink:

9

the west coast doesn’t typically use masonry cements for the reasons cited above, but they are very common in other parts of the country – the southeast is a strong user of them. if you are working in that part of the country, review your masonry submittals carefully – there are some contractors who simply use ONLY masonry cement and they will ignore any specification paragraphs that prohibit their use. I had one project where we specified portland cement and the contractor submitted masonry cement and he simply would not use anything else. we would have had to discharge him from the project if our structural engineer hadn’t accepted the product.

10

I would expect that Caltrans does not even think about brick masonry structurally and uses relatively little CMU.

I remember when the masonry industry was lobbying SEAOC (Structural Engineers Association of California) to relax their position on masonry cement. If there is a tendancy to require regular cement in mortar I believe that it is mostly a habit.

11

Our firm does not consider masonry cement to ever be acceptable for STRUCTURAL masonry such as CMU. However, the new kid on the block C 1329 mortar cement has better performance standards than masonry cement including bond strength, so for block work we have been allowing mortar cement, as well as port-lime.

We’ve recently been told that mortar cement does not come in factory-mixed colors, and so far my calls to cement manufacturers have not revealed otherwise. We strongly believe in factory-mixed colors to achieve greater consistency in the end result, so we have begun to consider ONE EXCEPTION to our previous position of not permitting masonry cement – ONLY FOR VENEERS, AND ONLY when colored mortar is required.

One structural engineer we are working with has independently come to the same conclusion, that masonry cement would be ok in this limited context. We have also heard the same from the Director of Technical Services of our regional brick association.

Has anyone else been asked about the concern of field-mixed colors when not allowing masonry cement for veneers? I’m trying to decipher whether this is a conscientious contractor question or a cost-cutting question. The further I go with this, it seems like it was an honest heads up.

12

After being transferred to several different people at Lafarge, and a total of about 2 days of waiting on calls back, they have indicated their Magnolia Superbond mortar cement product (one we specified) definitely DOES come in a good range of pre-mixed colors, and that several other mortar cement manufacturers also offer it. He mentioned Holcim, and CEMEX, and possibly SPEC MIX. Will have to do some more checking.