B08_Attach_1_MORA_313019_331809_312439_Final_Specifications_App_B.pdf
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- Solicitation number
- 140P2024R0077
About this file
This document is a mortar analysis report prepared for a federal contract opportunity to rehabilitate comfort stations at Mount Rainier National Park. The report includes analysis of seven mortar samples and one chinking sample collected from various comfort stations, including aggregate size distribution, composition, and compressive strength. The results indicate the mortar contains Portland cement and is outside ASTM C144 standards for aggregate size, with larger aggregate sizes. The report recommends a Type O mortar mix ratio of 1 part Portland cement, 2 parts hydrated lime, and 9 parts sand, as well as a chinking mix of 1 part Portland cement, 4 parts lime, and 5 parts sand to match the historic materials. The report provides detailed information to assist masons in creating a historically appropriate mortar mix for the rehabilitation project.
The related federal contract opportunity is Solicitation Number 140P2024R0077 for the rehabilitation of the Ohanapecosh Campground at Mount Rainier National Park, issued by the National Park Service. The solicitation seeks proposals for the specified rehabilitation work.
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Mortar Analysis
Prepared For:
Anderson Hallas Architects
715 14th Street golden, co 80401
Project:
Mount Rainier National Park: rustic comfort stations
Packwood, Washington state
Prepared By:
Phillip Barlow, Historic Preservation specialist
Barlow CULTURAL RESOURCE CONSULTING, LLC
4576 Tanglewood Trail, Boulder, CO 80301
303-746-1602 : BARLOWPL@GMAIL.COM
December 19, 2021
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CONTENTS
EXECUTIVE SUMMARY
COMPOSITION ANALYSIS
AGGREGATE SIZE DISTRIBUTION
MICROSCOPIC ANALYSIS
COMPRESSION ANALYSIS
MORTAR MIX RATIOS
CHINKING MIX RATIOS
COLOR MATCHING
APPENDIX
MORTAR ANALYSIS FOR RATIO AND AGGREGATE DISTRIBUTION PROCEDURE
AGGREGATE DOCUMENTATION
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EXECUTIVE SUMMARY
Seven mortar samples and one chinking sample were collected from comfort stations throughout Mount Rainier National Park by Kristen Craig of Anderson Hallas Architects and Christine Britton of JVA consulting engineers. Locations and photographs of the comfort stations follow this summary. The eight samples were labeled as follows:
1: Narada Falls CS: Vertical stone wall on front elevation 2: Paradise CS: West wall 3: Panorama Point CS: South wall 4: Ohanapecosh CS 0302: Top surface of stone foundation wall 5: Ohanapecosh CS 0303: Under log sill atop foundation wall 6: Ohanapecosh CS 0304: Stone foundation wall 7: Ohanapecosh CS 0304: Under log sill atop foundation wall 8: Ohanapecosh CS 0304: Chinking between logs in wall
This intent of this report is to provide the necessary information that will allow a mason to create a mortar mix that will match the existing in a historically appropriate manner. The specifications include a mortar mix ratio, a detail of aggregate grain size and color, and a methodology for creating an accurate mortar color match.
Aggregate sieve analysis of each mortar sample was compared with ASTM C144, standard for masonry mortar aggregate. Results were as follows:
1: Outside of standard, skewing towards larger aggregate 2: Outside of standard, skewing towards larger aggregate 3: Outside of standard, slightly skewing towards larger aggregate 4: Outside of standard, skewing towards larger aggregate 5: Outside of standard, skewing towards larger aggregate 6: Outside of standard, skewing towards larger aggregate 7: Outside of standard, skewing towards larger aggregate 8: Within standard, but with a high percentage of very fine material
The high percentage of fine material present in sample 8 are likely indigestible components of the cement binder, clays, and pigments. The aggregate in all samples is very similar and appear to be native to the Mount Rainier region of Washington state. Aggregate is documented in the microscopy section and the appendix.
Aggregate shape is primarily sub-rounded.
Standards published by the American Society for Testing and Materials (ASTM C270) specifies that cement/lime/sand mortars should have a sand content of at least 2.25 times the lime/cement mix (31% binder), and not more than 3 times the binder mix (25% binder). Sample 6 is the only mortar sample that is well outside of this standard.
All of the sampled mortars appear to come from locations that are surrounded by granite. The samples all require significant effort to break indicating the presence of Portland cement in the mix. With the compressive strength of samples 1 (470 PSI) and 6 (229 PSI) in mind, the suggested mortar will be based on a type O profile as the closest match to the historic mortar.
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Sample
Sample Name % Dissolved
Portland Cement
Hydrated Lime
Sand Mortar Type
1 Narada Falls CS:
Vertical stone wall on front elevation
25% 1 2 9 O
2 Paradise CS: West wall
23% 1 2 9 O
3 Panorama Point CS: South wall
22% 1 2 9 O
4 Ohanapecosh CS 0302: Top surface of stone foundation wall
22% 1 2 9 O
5 Ohanapecosh CS 0303: Under log sill atop foundation wall
23% 1 2 9 O
6 Ohanapecosh CS 0304: Stone foundation wall
18% 1 2 9 O
7 Ohanapecosh CS 0304: Under log sill atop foundation wall
25% 1 2 9 O
Sample 8: Log Cabin Chinking.
The log structure is identified as Ohanapecosh Comfort Station 0304 in Mount Rainier National Park, constructed ca. 1950. The chinking sample was very hard, gray in color similar to Portland cement, and lost 48% of its bulk during acid digestion, indicating a 50/50 binder to aggregate ratio.
Considering the age of the structure and the characteristics of the sample, the following chinking mix is recommended:
1 part Portland Cement 4 parts Lime 5 parts sand.
The sand should match the aggregate size distribution identified earlier in this report to mimic the historic appearance as closely as possible. Please refer to the National Park Service's Preservation Brief 26 "The Preservation and Repair of Historic Log Buildings" for more information.
Available online at: https://www.nps.gov/tps/how-to-preserve/briefs/26-log-buildings.htm
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Image 1: Narada Falls Comfort Station. Photo courtesy of Anderson Hallas and JVA Inc.
Image 2: Ohanapecosh 0302 Comfort Station. Photo courtesy of Anderson Hallas and JVA Inc.
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Image 3: Ohanapecosh 0303 Comfort Station. Photo courtesy of Anderson Hallas and JVA Inc.
Image 4: Ohanapecosh 0304 Comfort Station. Photo courtesy of Anderson Hallas and JVA Inc.
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Image 5: Panorama Point Comfort Station. Photo courtesy of Anderson Hallas and JVA Inc.
Image 6: Panorama Point Comfort Station. Photo courtesy of Anderson Hallas and JVA Inc.
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Image 7: Paradise Comfort Station. Photo courtesy of Anderson Hallas and JVA Inc.
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COMPOSITION ANALYSIS
Before acid digestion a qualitative hardness test is performed to determine the presence of cement. A pure lime mortar, which is just lime and sand, will typically crush with minimal effort. If a significant effort is required to fracture the sample then it is safe to assume that Portland cement is part of the mortar mix.
Sample 1 Could not be broken easily with finger strength
Sample 2 Could not be broken easily with finger strength
Sample 3 Could not be broken easily with finger strength
Sample 4 Could not be broken easily with finger strength
Sample 5 Could not be broken easily with finger strength
Sample 6 Could not be broken easily with finger strength
Sample 7 Could not be broken easily with finger strength
Sample 8 Could not be broken easily with finger strength
A digestive mortar analysis was conducted on the material, the full procedure for which is available in the appendix. Acid digestion is the process of using acid to dissolve lime and cement. By measuring the weight of the sample before and after digestion it is possible to determine the ratio of binder to aggregate.
Following digestion the aggregate is washed, filtered, and sieved. This determines the gradation of aggregate sizes.
A U.S. Standard sieve set was used to calculate the proportion of grain sizes. The sieve sizes used were:
No. 4 – opening of .187” No. 8 – opening of .09” No. 16 – opening of .046” No. 30 – opening of .023” No. 60 – opening of .0098” No. 100 – opening of .0055” No. 200 – opening of .0029”
Pan - This is the material that was small enough to pass through the 200 sieve. Fines are generally clay or very fine aggregate material, including pigment that is smaller than .0029”.
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AGGREGATE SIZE DISTRIBUTION
Sample # 1
Sample Location Narada Falls CS: Vertical stone wall on front elevation
Name Mount Rainier NP, Rustic Comfort Stations
Date 12.09.2021
Sieve With Sand
Without
Sand Sand
Particle sizes % of total
4 60.8 60.65 0.15 >4.75mm 1% gravel
8 63.26 57.78 5.48 <4.75 mm 20% very coarse sand
16 63.16 56.92 6.24 <2.36 mm 23% coarse sand
30 59.32 54.4 4.92 <1.18 mm 18% medium coarse sand
60 60.61 53.66 6.95 <.60 mm 25% medium fine sand
100 54.47 53.05 1.42 <.3 mm 5% fine sand
200 53.14 52.66 0.48 <.15 mm 2% very fine sand
Pan 15.32 13.62 1.7 <.075 mm 6% silt
Total 430.08 402.74 27.34
Weight of sample
36.45 grams % dissolved 25%
Wt filter paper for sand 1.42 grams
Wt sand & paper
28.76 grams
Wt sand
27.34
% sand
75%
1%
20% 23%
18%
25%
5%
2%
6%
0%
5%
10%
15%
20%
25%
30%
% of total
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The following table compares this data to the ASTM C 144 standard for masonry mortar aggregate. Red indicates that the sample does not match the standard.
Sieve Size Percent Passing, SAMPLE #1
ASTM C 144, Natural Sand
No. 4 99 100%
No. 8 79 95-100%
No. 16 56 70-100%
No. 30 38 40-75%
No. 40 13 10-35%
No. 100 8 2-15%
No. 200 6 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, pigments, and indigestible portions of Portland cement and not considered part of the aggregate.
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Sample # 2
Sample Location Paradise CS: West wall
Sand Sand
Particle sizes % of total
4 61.25 60.65 0.6 >4.75mm 5% gravel
8 59.83 57.82 2.01 <4.75 mm 17% very coarse sand
16 59.01 56.94 2.07 <2.36 mm 18% coarse sand
30 56.57 54.41 2.16 <1.18 mm 19% medium coarse sand
60 57.23 53.7 3.53 <.60 mm 30% medium fine sand
100 53.51 53.05 0.46 <.3 mm 4% fine sand
200 52.83 52.68 0.15 <.15 mm 1% very fine sand
Pan 14.28 13.64 0.64 <.075 mm 6% silt
Total 414.51 402.89 11.62
15.05 grams % dissolved 23%
Wt filter paper for sand 1.41 grams
13.03 grams
11.62
77%
5%
17% 18% 19%
30%
4% 1%
6%
0%
5%
10%
15%
20%
25%
30%
35%
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SAMPLE #2
ASTM C 144, Natural Sand
No. 4 95 100%
No. 8 78 95-100%
No. 16 60 70-100%
No. 30 41 40-75%
No. 40 11 10-35%
No. 100 7 2-15%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 15
Sample # 3
Sample Location Panorama Point CS: South wall
Sand Sand
Particle sizes % of total
4 60.64 60.64 0 >4.75mm 0% gravel
8 58.5 57.79 0.71 <4.75 mm 12% very coarse sand
16 57.7 56.91 0.79 <2.36 mm 13% coarse sand
30 55.75 54.38 1.37 <1.18 mm 22% medium coarse sand
60 55.9 53.66 2.24 <.60 mm 36% medium fine sand
100 53.66 53.05 0.61 <.3 mm 10% fine sand
200 52.86 52.64 0.22 <.15 mm 4% very fine sand
Pan 13.81 13.6 0.21 <.075 mm 3% silt
Total 408.82 402.67 6.15
7.88 grams % dissolved 22%
Wt filter paper for sand 1.4 grams
7.55 grams
6.15
78%
0%
12% 13%
22%
36%
10%
4% 3% 0%
5%
10%
15%
20%
25%
30%
35%
40%
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SAMPLE #3
ASTM C 144, Natural Sand
No. 4 100 100%
No. 8 88 95-100%
No. 16 75 70-100%
No. 30 53 40-75%
No. 40 17 10-35%
No. 100 7 2-15%
No. 200 3 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 17
Sample # 4
Sample Location Ohanapecosh CS 0302: Top surface of stone foundation wall
Sand Sand
Particle sizes % of total
4 61.05 60.65 0.4 >4.75mm 5% gravel
8 59.62 57.79 1.83 <4.75 mm 22% very coarse sand
16 58.82 56.92 1.9 <2.36 mm 22% coarse sand
30 56.46 54.39 2.07 <1.18 mm 24% medium coarse sand
60 55.04 53.66 1.38 <.60 mm 16% medium fine sand
100 53.32 53.07 0.25 <.3 mm 3% fine sand
200 52.79 52.66 0.13 <.15 mm 2% very fine sand
Pan 14.12 13.62 0.5 <.075 mm 6% silt
Total 411.22 402.76 8.46
10.85 grams % dissolved 22%
Wt filter paper for sand 1.38 grams
9.84 grams
8.46
78%
5%
22% 22% 24%
16%
3% 2%
6%
0%
5%
10%
15%
20%
25%
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SAMPLE #4
ASTM C 144, Natural Sand
No. 4 95 100%
No. 8 73 95-100%
No. 16 51 70-100%
No. 30 27 40-75%
No. 40 11 10-35%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 19
Sample # 5
Sample Location Ohanapecosh CS 0303: Under log sill atop foundation wall
Sand Sand
Particle sizes % of total
4 60.65 60.65 0 >4.75mm 0% gravel
8 59.11 57.78 1.33 <4.75 mm 15% very coarse sand
16 58.94 56.94 2 <2.36 mm 22% coarse sand
30 57.31 54.37 2.94 <1.18 mm 32% medium coarse sand
60 55.71 53.67 2.04 <.60 mm 22% medium fine sand
100 53.3 53.06 0.24 <.3 mm 3% fine sand
200 52.84 52.66 0.18 <.15 mm 2% very fine sand
Pan 14.02 13.62 0.4 <.075 mm 4% silt
Total 411.88 402.75 9.13
11.83 grams % dissolved 23%
10.53 grams
9.13
77%
15%
22%
32%
22%
3% 2% 4%
0%
5%
10%
15%
20%
25%
30%
35%
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SAMPLE #5
ASTM C 144, Natural Sand
No. 4 100 100%
No. 8 85 95-100%
No. 16 63 70-100%
No. 30 31 40-75%
No. 40 9 10-35%
No. 100 6 2-15%
No. 200 4 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 21
Sample # 6
Sample Location Ohanapecosh CS 0304: Stone foundation wall
Sand Sand
Particle sizes % of total
4 60.78 60.64 0.14 >4.75mm 1% gravel
8 60.64 57.79 2.85 <4.75 mm 20% very coarse sand
16 59.8 56.93 2.87 <2.36 mm 20% coarse sand
30 58.39 54.39 4 <1.18 mm 28% medium coarse sand
60 57 53.64 3.36 <.60 mm 24% medium fine sand
100 53.47 53.06 0.41 <.3 mm 3% fine sand
200 52.86 52.68 0.18 <.15 mm 1% very fine sand
Pan 14.1 13.63 0.47 <.075 mm 3% silt
Total 417.04 402.76 14.28
17.32 grams % dissolved 18%
15.68 grams
14.28
82%
1%
20% 20%
28%
24%
3% 1%
3% 0%
5%
10%
15%
20%
25%
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SAMPLE #6
ASTM C 144, Natural Sand
No. 4 99 100%
No. 8 79 95-100%
No. 16 59 70-100%
No. 30 31 40-75%
No. 40 7 10-35%
No. 100 4 2-15%
No. 200 3 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 23
Sample # 7
Sample Location Ohanapecosh CS 0304: Under log sill atop foundation wall
Sand Sand
Particle sizes % of total
4 60.63 60.63 0 >4.75mm 0% gravel
8 60.01 57.8 2.21 <4.75 mm 17% very coarse sand
16 59.49 56.94 2.55 <2.36 mm 20% coarse sand
30 57.87 54.4 3.47 <1.18 mm 27% medium coarse sand
60 56.66 53.67 2.99 <.60 mm 23% medium fine sand
100 53.7 53.06 0.64 <.3 mm 5% fine sand
200 52.97 52.68 0.29 <.15 mm 2% very fine sand
Pan 14.31 13.65 0.66 <.075 mm 5% silt
Total 415.64 402.83 12.81
17.16 grams % dissolved 25%
14.21 grams
12.81
75%
17% 20%
27%
23%
5% 2%
5%
0%
5%
10%
15%
20%
25%
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SAMPLE #7
ASTM C 144, Natural Sand
No. 4 100 100%
No. 8 83 95-100%
No. 16 63 70-100%
No. 30 36 40-75%
No. 40 13 10-35%
No. 200 5 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 25
Sample # 8
Sample Location Ohanapecosh CS 0304: Chinking between logs in wall
Sand Sand
Particle sizes % of total
4 60.63 60.63 0 >4.75mm 0% gravel
8 57.96 57.78 0.18 <4.75 mm 3% very coarse sand
16 57.31 56.92 0.39 <2.36 mm 6% coarse sand
30 56.49 54.38 2.11 <1.18 mm 30% medium coarse sand
60 56.52 53.67 2.85 <.60 mm 40% medium fine sand
100 53.45 53.05 0.4 <.3 mm 6% fine sand
200 52.89 52.67 0.22 <.15 mm 3% very fine sand
Pan 14.5 13.6 0.9 <.075 mm 13% silt
Total 409.75 402.7 7.05
13.5 grams % dissolved 48%
Wt filter paper for sand 1.41 grams
8.46 grams 0.43 grams of paint
7.05
52%
3%
6%
30%
40%
6% 3%
13%
0% 5%
10% 15% 20% 25% 30% 35% 40% 45%
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SAMPLE #8
ASTM C 144, Natural Sand
No. 4 100 100%
No. 8 97 95-100%
No. 16 91 70-100%
No. 30 61 40-75%
No. 40 21 10-35%
No. 100 15 2-15%
No. 200 13 0%
While it is included here for accuracy, please note that the percentage that passes sieve 200 is primarily clays, Barlow Cultural Resource Consulting, LLC - 303-746-1602 - barlowpl@gmail.com Page 27
MICROSCOPIC ANALYSIS
Aggregate minerals Aggregate shape
Sample 1 Clear and cloudy quartz, Andesite, Basalt, Granite Sub-Rounded
Sample 2 Clear and cloudy quartz, Andesite, Basalt, Granite Sub-Rounded
Sample 3 Clear and cloudy quartz, Andesite, Basalt, Granite Sub-Rounded
Sample 4 Clear and cloudy quartz, Andesite, Basalt, Granite, Red/Black Granite Sub-Rounded
Sample 5 Clear and cloudy quartz, Andesite, Basalt, Granite, Red/Black Granite Sub-Rounded
Sample 6 Clear and cloudy quartz, Andesite, Basalt, Granite Sub-Rounded
Sample 7 Clear and cloudy quartz, Andesite, Basalt, Granite Sub-Rounded
Sample 8 Clear and cloudy quartz, Andesite, Basalt, Granite Sub-Rounded
All of the minerals are local to this region of Washington state. Aggregate appears to be similar across all samples. Images of the aggregate from each sample are included in the appendix for reference.
Image 8: Sample 6. Representative aggregate
Powers, M.C., 1953, Journal of Sedimentary Petrology, v.23, p. 116
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COMPRESSION ANALYSIS
Test procedure:
A portion of each supplied sample was selected for testing and the dimensions for each were recorded
The sample was placed on a 56Kn point load tester equipped with a ball-seated flat platen to allow for proper seating
The sample was compressed until failure and the peak pressure recorded
The compressive strength was determined and converted to the PSI standard
NOTE: Sample 1 and Sample 6 were the only two samples of adequate size to conduct compression testing
Sample # 1
Sample Location Narada Falls CS: Vertical stone wall on front elevation
Name Mount Rainier NP, Rustic
Comfort Stations
Sample Height
(mm) 28.09
Sample Width (mm) 22.01
Sample Depth (mm) 37.26
Max Kn at failure 3.944
Kn/sectional area 0.003244483
PSI 470.5725247
Mortar Type Per
ASTM C270 Min. Compressive Strength
M 2500 psi
S 1800 psi
N 750 psi
O 350 psi
K 75 psi
Sample # 6
Sample Location Ohanapecosh CS 0304: Stone foundation wall
Name Mount Rainier NP, Rustic
Comfort Stations
Sample Height
(mm) 17.63
Sample Width (mm) 31.4
Sample Depth (mm) 23.96
Max Kn at failure 1.102
Kn/sectional area 0.001582564
PSI 229.5314647
Mortar Type Per
ASTM C270 Min. Compressive Strength
M 2500 psi
S 1800 psi
N 750 psi
O 350 psi
K 75 psi
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MORTAR MIX RATIOS
Standards published by the American Society for Testing and Materials (ASTM C270) specifies that cement/lime/sand mortars should have a sand content of at least 2.25 times the lime/cement mix (31% binder), and not more than 3 times the binder mix (25% binder). Sample 6 is the only mortar sample that is well outside of this standard.
All of the sampled mortars appear to come from locations that are surrounded by granite. The samples all require significant effort to break indicating the presence of Portland cement in the mix. With the compressive strength of samples 1 and 6 in mind, the suggested mortar will be based on a type O profile as the closest match to the historic mortar.
Sampl e #
Sample Name % Dissolved
Portland Cement
Hydrated Lime
Sand Mortar Type
1 Narada Falls CS:
Vertical stone wall on front elevation
25% 1 2 9 O
2 Paradise CS: West wall
23% 1 2 9 O
3 Panorama Point CS: South wall
22% 1 2 9 O
4 Ohanapecosh CS 0302: Top surface of stone foundation wall
22% 1 2 9 O
5 Ohanapecosh CS 0303: Under log sill atop foundation wall
23% 1 2 9 O
6 Ohanapecosh CS 0304: Stone foundation wall
18% 1 2 9 O
7 Ohanapecosh CS 0304: Under log sill atop foundation wall
25% 1 2 9 O
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Mortar Types (Measured by volume)
Designation Cement Hydrated Lime or Lime Putty
Sand
M 1 1/4 3 - 3 ¾
S 1 1/2 4 - 4 ½
N 1 1 5 – 6
O 1 2 8 – 9
K 1 3 10 – 12
"L" 0 1 2 1/4 – 3
Suggested Mortar Types for Different Exposures
Exposure
Masonry Material Sheltered Moderate Severe
Very durable:
granite, hard-cored brick, etc.
O N S
Moderately durable:
limestone, durable stone, molded brick
K O N
Minimally durable:
soft hand-made brick
"L" K O
Technical Preservation Services, National Park Service. “Repointing Mortar Joints in Historic Masonry Buildings” 1980 http://www.cr.nps.gov/hps/tps/briefs/brief02.htm http://www.cr.nps.gov/hps/tps/briefs/brief02.htm
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CHINKING MIX RATIOS
Historically, chinking and daubing of log cabins was achieved with local materials with the goal of filling in the gaps between the hewn logs to keep out the weather. As this was a vernacular skill, there are a variety of suggested materials and methods to replicate this component. This section will investigate the composition of the chinking sample, compare it with the known parameters of the log structure, and make a recommendation that will replicate the original as closely as possible.
The log structure is identified as Ohanapecosh Comfort Station 0304 in Mount Rainier National Park, constructed ca. 1950. The chinking sample was very hard, gray in color similar to Portland cement, and lost 48% of its bulk during acid digestion, indicating a 50/50 binder to aggregate ratio.
Considering the age of the structure and the characteristics of the sample, the following chinking mix is recommended:
1 part Portland Cement 4 parts Lime 5 parts sand.
The sand should match the aggregate size distribution identified earlier in this report to mimic the historic appearance as closely as possible.
Please refer to the National Park Service's Preservation Brief 26 "The Preservation and Repair of Historic Log Buildings" for more information.
Available online at: https://www.nps.gov/tps/how-to-preserve/briefs/26-log-buildings.htm
COLOR MATCHING
Once an aggregate has been selected several small (roughly 1 cup) test batches should be mixed in the prescribed ratios. Matching the color as closely as possible with the aggregate is the best approach, but this testing period is when various pigments and additives can be tried to determine how best to match the existing color. Volcanic pumice, lamp black, and bone black are all chemically stable coloring agents that resist fading in the sun.
Using a masonry specific pigment, each test batch should be mixed with varying quantities and combinations of pigment to produce a palette of choices. It is important that each batch be labeled, and that precise notes are kept of the pigment recipe. Once allowed to dry the building owner or project manager should inspect the samples and select the one that best matches the remainder of the wall. The recipe for that sample should then become the master recipe for the project. It is important to note that mortar color can be different from one part of the wall to another, so if a discernible difference in color is noted as work progresses than the recipe should be altered to maintain uniformity.
Matching the new mortar to the existing will be a challenge because of the discoloration of the original mortar from dirt and plant growth. Options to address this include:
Match the new mortar to the original and let the discoloration occur naturally
Match the new mortar to the existing, keeping in mind that the pigments might weather differently
Clean the masonry to remove the discoloration
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APPENDIX
Mortar Analysis for Ratio and Aggregate Distribution Procedure
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AGGREGATE DOCUMENTATION
Image 9: Sample 1, representative aggregate
Image 10: Sample 1, , representative aggregate
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Image 11: Sample 2, representative aggregate
Image 12: Sample 2, representative aggregate
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Image 13: Sample 3, representative aggregate
Image 14: Sample 3, representative aggregate
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Image 15: Sample 4, representative aggregate
Image 16: Sample 4, representative aggregate
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Image 17: Sample 5, representative aggregate
Image 18: Sample 5, representative aggregate
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Image 19: Sample 6, representative aggregate
Image 20: Sample 6, representative aggregate
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Image 21: Sample 7, representative aggregate
Image 22: Sample 7, representative aggregate
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Image 23: Sample 8, representative aggregate
Image 24: Sample 8, representative aggregate
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