by Sarah Marie Jackson, Tye Botting, and Mary Striegel
NCPTT tested limewashed samples
using artificial weathering and adhesion
and abrasion tests that were based on
published standard methods. Samples
were photographed before and after
each test and monitored for color
change. A solids test was also performed
to determine how much limewash
was applied to the samples.
In 2004 the testing began after preparation
of samples of handmade brick,
modern brick, weathered wood, and
rough-sawn new wood provided by
CARI. The samples were cored with a
drill press using a saw bit with a 1 5⁄8-inch
hole so that they would fit in the sample
holders. NCPTT later purchased 105
Epoxy Resin, 207 Special Coating Hardener,
and 405 Filleting Blend, manufactured
by West Systems, the epoxy product
used at the historic site. The components
were mixed following the instructions
supplied by the manufacturer
and then cast and cored to the same
dimensions as the other materials. The
surfaces of the epoxy samples were
sanded to remove any remaining chemical
residue. Limewash was applied once
the samples were prepared.
The limewashes were prepared following
instructions shown in Table 1.
After the limewash was mixed and
screened, the viscosity was determined
by dipping a #4 Ford cup into the limewash
until overflowing and recording
the time for the limewash to run completely
through, a process that follows
ASTM D 1200-94. 9 After checking the
viscosity, the samples were dampened
and limewash was applied. They were
allowed to dry for a minimum of 24
hours before they were redampened and
the next coat of limewash was applied.
Quality Finish chose to apply two
coats of Edison Coatings Primer #342 to
consolidate brick surfaces and assist in
adhesion to wood samples for washes A
through K. 10 Washes A through I were
applied to the handmade brick, modern
brick, weathered wood, and rough-sawn
new wood. Wash K was applied to the
handmade and modern brick. An
NCPTT intern applied the primer and
the best performers from the wood test
— washes D, E, and G — to the epoxy
following the same instructions used
with the wood. NCPTT staff applied
washes L, M, and N to the handmade
brick and weathered wood without a
primer.
The tests were performed in triplicate
for each limewash on each sample material.
The samples were photographed
before and after each test to maintain a
visual record throughout the study. A
Minolta colorimeter was used to record
color data for all samples using the CIE
standard; results from before and after
the weathering, adhesion, and abrasion
tests were compared for color changes.
The solids test followed a simple
gravimetric method to determine the
total mass of the limewash applied to
the samples. Masses were taken of the
samples before limewash was applied
and after the final coat had dried. The
mass differences before initial and after
final application were averaged for each
sample, giving the amount of solids
deposited. Depending on the limewash
applied, the solids deposit would be
either lime or a mixture of lime and
additives, such as the salt additive in
washes A, B, and C.
Abrasion testing, based on ASTM D
968-93, was used to rank how a limewash
might stand up over time when
subjected to abrasion from wind- and
rain-borne particles.11 The testing apparatus
was a funnel fitted over a guide
tube and supported vertically. The samples
were mounted in a holder positioned
45 degrees from vertical exactly
1 inch below the outlet tube. Sand was loaded into the funnel in 1-liter increments
and discharged over the sample
until the limewash began to wear away
and the substrate was visible. As the
substrate became visible, the amount of
sand was decreased to 250-milliliter
increments until a patch 4 millimeters in
diameter was exposed. The amount of
sand needed to remove the limewash
was recorded. The test was performed
on three samples from each wash for
each sample material and the results
averaged. The best performers were
those samples that required the highest
amount of sand, indicating that they had
formed a harder, more cohesive finish.
Adhesion testing evaluated how
firmly the limewash bonded to the samples,
following ASTM D 3359-95. An
X cut was made with a sharp blade
through the limewash to the substrate
using a template with the smallest angle
of the intersection between 30 and 45
degrees. Pressure-sensitive tape was
applied over the cut and smoothed
down with a rubber eraser, and the tape
was removed in a quick, non-jerking
motion. Each limewash was rated on a
scale of 5A (best) to 0A (worst), and the
results were averaged. 12 The best performers
were the samples with the least
limewash loss, indicating the limewashes
that bonded most tightly to the material.
Artificial weathering was performed
on samples using a Q-Lab QUV Weathering
Tester following a procedure based
on ASTM D 4587-91. The controlled
conditions of this test cannot correlate
directly to outdoor exposure but do give
an idea of how the limewashes might
weather comparatively over time. The
samples were mounted in holders with
silicone adhesive and placed in the QUV.
They were subjected to four hours of
ultraviolet light at 140°F (60°C), followed
by four hours of condensation
and dark at 122°F (50°C) for 100 cycles,
for a total of 800 hours of exposure.
13 The sample locations within the
weatherometer were rotated daily to
ensure even exposure and eliminate any
instrumental irregularities. Artificially
weathered samples were rated on a scale
of 5A (best) to 0A (worst), similar to
that used in the adhesion-rating system.
The samples were evaluated visually
based on the overall appearance and the
amount of limewash remaining on the
samples. The results from each limewash
were averaged to determine the best
performers. Mass differences are commonly
used to determine loss from
weathering, but the final masses of this
test were affected by the silicone that
had been used to mount the samples and
adhered to the edges of the samples after
testing.
Originally published in APT BULLETIN: JOURNAL OF PRESERVATION TECHNOLOGY / 38:2-3, 2007
Notes
1. Laura Soulliere Gates, email to author, Aug.
17, 2006.
2. National Park Service Technical Information
Center, 'Class C' Cost Estimating Guide: Historic
Preservation and Stabilization (Denver:
Denver Service Center, 1993), 18.
3. Colin Mitchell Rose, Traditional Paints,
available from http://www.buildingconservation.com/articles/paint/paint.htm.
4. Abbott Lowell Cummings and Richard M.
Candee, "Colonial and Federal America:
Accounts of Early Painting Practices" in Paint
in America: The Colors of Historic Buildings
14 (New York: Wiley, 1994), 14.
5. Scottish Lime Centre, Technical Advice Note
15: External Lime Coatings on Traditional
Buildings (Edinburgh: Historic Scotland, 2001).
6. Ibid.
7. John Ashurst and Nicola Ashurst, Mortars,
Plasters, and Renders, vol. 3 of English Heritage
Technical Handbook (Great Britain:
Gower, 1995), 47.
8. Roger W. Moss, "Nineteenth-Century Paints:
A Documentary Approach" in Paint in America:
The Colors of Historic Buildings (New
York: Wiley, 1994), 55.
9. ASTM Subcommittee D01.24, Standard Test
Methods for Viscosity by Ford Viscosity Cup,
ASTM D 1200-94 (West Conshohocken, Pa.:
ASTM, 1996).
10. Marcy Frantom, email to author, Sept. 12,
2005.
11. ASTM Subcommittee D01.23, Standard
Test Methods for Abrasion Resistance of
Organic Coatings by Falling Abrasive, ASTM
D 968-93 (West Conshohocken, Pa.: ASTM,
1996).
12. ASTM Subcommittee D01.23, Standard
Test Methods for Measuring Adhesion by Tape
Test, ASTM D 3359-95 (West Conshohocken,
Pa.: ASTM, 1996).
13. ASTM Subcommittee D01.27, Standard
Practice for Conducting Tests on Paint and
Related Coatings and Materials Using a Fluorescent
UV-Condensation Light- and Water-
Exposure Apparatus, ASTM D 4587-91 (West
Conshohocken, Pa.: ASTM, 1996).
14. Pete Sotos, conversation with author, Nov.
15, 2006.
15. Ruth Johnston-Feller, Color Science in the
Examination of Museum Objects: Nondestructive
Procedures (Los Angeles: Getty Conservation
Institute, 2001), 35.
16. L. Franke and I. Schumann, "Causes and
Mechanisms of Decay of Historic Brick Buildings
in Northern Germany," in Conservation of
Historic Brick Structures, ed. N. S. Baer, S. Fitz,
and R. A. Livingston (Shaftsbury: Donhead,
1998), 26-34.
SARAH MARIE JACKSON joined NCPTT in
2005 as a graduate intern to continue the testing
for the limewash study. In 2006 she accepted
a permanent position with the Architecture
and Engineering Program at NCPTT. She
received a master’s degree in historic preservation
from the Savannah College of Art and
Design.
TYE BOTTING is a research staff member at
the Institute for Defense Analyses. He served as
the NCPTT/NSU joint faculty researcher for
three years. He holds a PhD in nuclear chemistry
from Texas A&M University, where he did
post-doctoral work in nuclear engineering.
MARY STRIEGEL is responsible for NCPTT’s
Materials Research Program, focusing on
evaluation of preservation treatments for
preventing damage to cultural resources. She
also directs investigation of preservation treatments
geared towards cemeteries and develops
seminars and workshops nationwide. She holds
a PhD in inorganic chemistry from Washington
University in St. Louis.