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Subject: Jahn products

Jahn products

From: N. J. Bud Goldstone <as768>
Date: Wednesday, November 3, 1999
Elizabeth Goins <goinses [at] shore__intercom__net> writes

>Can anyone tell me anything about Jahn products. Specifically,
>what's in them (stone patching and re-pointing compounds).

I am not sure what Jahn mortars are made from but we were not able
to apply them and develop the advertised strength. My article in the
WAAC Newsletter
has data on that deficiency. Copied from Newsletter

    Volume 16, Number 3, Sept 1994, p.11
    Technical Exchange
    by Dean Yoder, Column Editor

    Watts Towers Mortars

    In our work on the Watts Towers of Simon Rodia in Los Angeles,
    we use about 1 1/2 bags per month but have had several problems
    with Jahn mortar: inconsistency in the color of M70-18A and
    disbelief in the wide variation in compression values published
    for the Jahn injection mortars, M30/40, which we do not use. In
    a series of commercial lab tests on specimens made at our site,
    we were only able to achieve 64% of the published compression
    values for mortars M70-11, M70-18A and M90. The response from
    the distributor was that we did not use the proper amount of
    water. I do not agree with that explanation.

    In 1990 and 1991, a local testing lab ran compression tests on
    three each, standard specimens of the Jahn M70-11, M70-18A, M90
    and on a special cement mortar mixture. See the specs, below.
    The average compression values of the Jahn specimens were 2,280
    psi, 36% lower than the value listed in the literature. (The
    artist's 40-70 year-old mortar, taken from a few selected areas
    tested at 3,000 psi, 4,000 psi and 9,000 psi, in the base area
    of one sculpture.) Because of the low value and to reduce
    unwanted failures in higher stresses repair areas, we have
    restricted use of Jahn mortar to non-structural members and
    those carrying low loads and stress levels. We use a cement
    mortar mix which has tested in compression at 2,700 psi (above
    Jahn but below Rodia's mortar) in structurally stressed members.
    This mortar is as follows: 1 pt. cement, 3 pt. sand, .1 to .25
    pt lime

    Aggregate: clean sharp natural sand conforming to the following
    size gradations and the requirements of ASTM C144

         Sieve Size           percent passing
         #4                   100
         #8                   95 to 100
         #16                  70 to 100
         #30                  40 to 75
         #50                  20 to 35
         #100                 2 to 15
         #200                 0 to 2

    Water: Potable, free of oils, acids, alkalies and organic matter

N.J. Bud Goldstone, conservation engineer
Watts Towers, Las Pozas, Nitt Witt Ridge;
Bottle Village; The Orange Show; co-author
The Los Angeles Watts Towers - a Getty Publication

                  Conservation DistList Instance 13:29
                 Distributed: Friday, November 12, 1999
                       Message Id: cdl-13-29-007
Received on Wednesday, 3 November, 1999

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