My outbound e-mail has been messed up for the past few days, so excuse
me if I already answered this. My take on this issue is that the
primary reason masonry cement is used is because it is cheaper/lower
energy to produce, as Steve S. has suggested. It is not necessarily
air-entrained, and there are those who adhere to the belief that air
entrainment significantly reduces bond strength.
We have been partial to using lime-cement because of the greater
plastic deformation cited by Eric. I'm not very sure how efficiently
or reliably autogeneous healing occurs as a practical matter, but in
theory, this can happen.
The great overlooked point in my mind is that although lime
theoretically reacts with carbon dioxide to form calcite (calcium
carbonate) which is the same as the main component in limestone, lime
never really converts completely, even after a century or more. The
remaining calcium hydroxide readily forms a soft paste when wet, hence
the greater plastic deformation.
Mike E.
> Thanks for the responses so far, but it seams to me, clumping issues
aside,
> that PCL makes a much better mortar - better plastic deformation and
> autogeneous healing of cracks. What purpose does the pulverized
limestone
> have (powdered aggregate?) and isn't hydrated lime better?
>
> Also the technical notes from the Brick Institute of America and the
> Portland Cement Association "qualify" the heck out of describing what
> masonry cement is - there is no good info provided. The primary
aspects
> mentioned are job site ease - one bag for cement, a pile of sand and
water.
> How is one supposed to confidently specify mortar when you can't
find out
> what is in it?
>
> Mike E, can you shed some of your wisdom?
>
> Thanks,
>
> Eric Hammarberg
> Director of Preservation
> Associate
> LZA Technology
> 641 Avenue of the Americas
> New York, NY 10011-2014
> Telephone: 917.661.8160 (Direct)
> Mobile: 917.439.3537
> Fax: 917.661.8161 (Direct)
> email: [log in to unmask]
>
>
>
> -----Original Message-----
> From: S. Stokowski [mailto:[log in to unmask]]
> Sent: Tuesday, February 04, 2003 10:52 PM
> To: [log in to unmask]
> Subject: Re: Masonry Cement or PCL
>
>
> Eric:
>
> Masonry cement is a mixture of Portland cement, mineral filler, and
other
> components. The mineral filler is usually limestone powder. It can
be
> other things, such as diatomaceous earth, ground basalt, ground
feldspar,
> ground quartz, etc. The "other components" that I allude to, if
included,
> are usually hydrated lime, an air-entraining agent, and in some
situations
> an anti-cake agent. Calcined bentonite and calcined kaolin clays
have also
> been used. During the manufacture of masonry cement the Portland
cement and
> the limestone powder are usually mixed and interground in a ball
mill. The
> Portland cement becomes finer, more reactive, and more effective.
Limestone
> is the usual mineral filler because it does not cause excessive wear
on the
> ball mill. The approximate proportions for Type N masonry cement
are 45%
> Portland cement, 45% pulverized limestone, and 10% hydrated lime. In
> manufacturing practice, the proportions are adjusted to a happy
medium
> between workability, ASTM C-270 strength, and RMC (raw materials
cost).
>
> It has not been my experience that the manufacturers will not
divulge the
> composition of their product. However, the sales force usually does
not
> have this information in their memory, although if you read the MSDS
you can
> get a good qualitative idea. The MSDS usually doesn't tell you the
> admixtures, but they really aren't that difficult to identify with
$10 worth
> of labor and $20,000 worth of knowledge. The quantitative
proportions are
> usually only known to the lab and production guys. And to guys like
me who
> reverse engineer and develop these products.
>
> Masonry cement is on the market because it is a profitable product
that
> performs well. It is primarily a bagged product. As such, it has a
major
> advantage over bagged Portland cement/hydrated lime mixtures; it
cakes less.
> That is primarily because of the interground mineral filler.
Masonry cement
> is also less expensive and has a couple of purely technical
advantages. If
> an air entrainer is used, the resulting mortar has enhanced frost
> resistance. If the mineral filler is limestone, the masonry-cement
mortar
> also has more acid resistance because of the reactivity of the
pulverized
> limestone with acids. There are also more nebulous advantages
related to
> masonry cement being a relatively "Green" product.
>
> Steve Stokowski
> Stone Products Consultants
> Building Products Microscopy
> 10 Clark St., Ste. A
> Ashland, Mass. 01721-2145
> 508-881-6364 (ph. & fax)
> http://members.aol.com/crushstone/petro.htm
> <http://members.aol.com/crushstone/petro.htm>
>
> ******************************************************
> In a message dated 2/4/03 4:41:31 PM Eastern Standard Time,
> [log in to unmask] writes:
>
>
>
> I am trying to find out why masonry cement (MC) is on the market when
> portland cement / lime (PCL) mortars appear, at least to me, to
perform
> better and more reliably?
>
> As many of us know, MC is typically a mix of portland cement,
pulverized
> limestone and "proprietary admixtures" which manufacturers seldom
(never)
> will divulge. PCL is portland cement and lime, period.
>
> Can anybody shed light on this for me?
>
>
>
>
>
>
>
>
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> --
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>
>
Edison Coatings, Inc.
M. P. Edison
President
3 Northwest Drive
Plainville, CT 06062 USA
Phone: (860)747-2220
Fax: (860)747-2280
email: [log in to unmask]
Internet: www.edisoncoatings.com
--
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