BUILT HERITAGE SERIES: AN INTRODUCTION TO SIMPLE ANALYSIS METHODS FOR: EVALUATING SURFACE QUALITY WITH THE SCOTCH TAPE TEST (PART 1 OF 1)

BUILT HERITAGE SERIES: AN INTRODUCTION TO SIMPLE ANALYSIS METHODS FOR: EVALUATING SURFACE QUALITY WITH THE SCOTCH TAPE TEST (PART 1 OF 1)

Mrs. Emilia Zambri, MSoc Sci Tangible Heritage Conservation.

PREFACE

Welcome to this series of techniques for managing change and assessing the condition of architectural heritage structures and historic heritage fabric. This newsletter aims to provide professionals, including Heritage Consultants, Architects, Archaeologists, and Conservators, with practical and effective methods to determine the most appropriate approaches to management, conservation, and restoration.

Inspired by the challenges encountered in safeguarding historic heritage, especially in under-resourced areas, particularly in Africa, this series has been developed to assist colleagues globally. The goal is to present simple and easy-to-use frameworks, case studies, and tests that can be employed to evaluate the preservation, conservation, and restoration needs of historic heritage, ensuring their safeguarding for future generations.

By utilising these techniques, the objective is to empower heritage professionals with the knowledge and tools necessary to make informed decisions about the preservation of our shared cultural heritage. Join us as we embark on a journey to protect and preserve the historical structures that define our shared identity..

1. INTRODUCTION

The preservation of architectural heritage is of utmost importance, and the conservation needs of historical structures must be assessed to ensure their continued existence. In this regard, simple and practical tests have been developed to evaluate the quality of plaster, stone and brick surfaces and the efficiency of interventions. The verified standard “Scotch Tape” test procedure is a low-cost, rapid, and easily applicable technique suitable for in situ investigations of historic mortar, brick and stone surfaces in conservation practice. The “Scotch Tape” tests presented here are shown to be reasonably reliable and useful for investigating historic surfaces. The success of the method requires that several repetitions of the “Scotch Tape” test are performed on the measured place to reduce the influence of surface degradation effects that are not bound to the real characteristics of the material. The method is sufficiently sensitive to demonstrate even rather subtle variations and differences in consolidation effects after the application of various treatment technologies. Despite its simplicity, the method has the potential for further development, such as specific tape quality recommendations and the refinement of the evaluation procedure. These tests can aid in the preservation of architectural heritage, ensuring the continued existence of these important historical structures.

2. BACKGROUND

The conservation of architectural heritage presents several challenges, particularly when assessing the condition of historic building materials. Traditional methods such as visual inspection, physical sampling, and laboratory analysis are often invasive, time-consuming, and expensive. Additionally, they may not always provide accurate information about the quality of the materials or the effectiveness of conservation interventions.

To overcome these challenges, researchers have developed the “Scotch Tape” test, a non-destructive, low-cost, and easy-to-use technique. This method is suitable for in situ investigations of historic plaster, stone or brick surfaces, and the efficacy of consolidation interventions.

The “Scotch Tape” test involves applying a strip of adhesive tape to the surface of the plaster, stone or brick and then removing it quickly. The strength and nature of the bond between the tape and the surface can then be used to infer information about the quality of the surface and the effectiveness of consolidation interventions.

Compared to traditional methods, the “Scotch Tape” test has several advantages. Firstly, it is relatively non-destructive, making it a suitable method for sensitive historic buildings. Secondly, it is low-cost and easy to use, making it accessible to conservation practitioners with limited resources. Finally, it provides reliable and reproducible data that can be used to assess the quality of the materials and the effectiveness of conservation interventions.

In the following sections, we will discuss the “Scotch Tape” test method in detail, including its strengths and limitations. We will also explore its potential for assessing the conservation needs of architectural heritage.

3. MATERIALS AND METHODS

The "Scotch Tape" test is a widely used method for evaluating the surface cohesion and deterioration of stone and brick materials. The method for measuring the amount of detached material that adheres to the tape is typically carried out before and after any conservation treatment or on weathered and sound stone/brick. This test follows the ASTM D3359-02 standard and the recommendations established by Drdácky et al. (2012). The main objective of this test is to evaluate the surface cohesion of stone or brick, which is important because surface cohesion provides an idea of the surface deterioration of the material in question.

To conduct this simple test, a strip of double-sided pressure-sensitive adhesive, such as Scotch brand tape, previously weighed, is applied to the surface to be evaluated, ensuring that the tape is totally adherent and then pulled off. Loose powder and grains of the surface will remain attached to the tape. The tape is then weighed again, and the result expressed as mg/cm2. Several strips of the tape need to be applied to different areas of the surface to obtain a useful number of data points. It is important to carry out the test in several different areas because if the same area is tested again, the released material will obviously decrease.

To analyze the results of the detached material, either the released material can be weighed following the ASTM D3359-02 standard, or visual examination can be carried out using a digital microscope or a stereomicroscope, following the ASTM 4214-97 standard to evaluate the number and type of particles detached. The visual evaluation will provide a good enough approximation regarding the deterioration condition or the effectiveness of a conservation treatment.

3.1. PERSONAL PROTECTIVE EQUIPMENT

Based on the information provided in the report, it does not seem that any personal protective wear is required for the Scotch Tape Test. The test is carried out in situ, which means it is performed on the building's surface and does not involve any hazardous chemicals or substances. The test procedure involves affixing double-sided tape to the material's surface, which does not pose any direct harm to the person conducting the test.

However, it is important to note that the test should be carried out in a dry and reasonably clean area of the building. If the building is in disrepair or has deteriorated significantly, it may be necessary to wear appropriate personal protective equipment, such as a respirator, gloves, or protective clothing, to protect oneself from potential hazards, such as dust or debris. But this is not related to the Scotch Tape Test procedure itself.

3.2. MATERIALS

In this study, the following materials and methods were used:

• Double-sided tape (2 cm width)
• Balance with a ±0.001 g sensitivity
• Graph paper
• Appropriate boxes or plastic sampling bags with a closing pressure zip to carry the tape with the attached powder and grains to a laboratory for weighing
• Note: If a balance is not available, the tapes can be examined with a digital microscope or stereomicroscope, and an approximate visual evaluation can be carried out.

3.3. TEST PREPARATION PROCEDURE

1. Cut nine strips from the roll of double-sided tape, measuring at least 8 cm2 (a strip of 4 x 2 cm) with exact same dimensions.
2. Press one side of each tape strip to a graph paper, leaving the protective sheet of the other adhesive side in place. Cut both the tape and graph paper to include an extra 1 cm of the graph paper at one end of the strip, which will be used to handle the sample strip. All free spaces must present the exact same dimensions, as the graph paper is scaled.
3. Put the nine strips together in a plastic bag or a box with a hermetical cover and weigh to the milligram. The weight is then divided by nine and by the strip surface (e.g., 8 cm2), since all strips should be exactly equal in size and weight. Note that other procedures and tape sizes have also been recommended (Drdácky et al., 2012, 2015; Drdácky and Slízková, 2015).

3.4. TEST PEELING

1. Select the area of the building where the test is to be carried out. Ensure the area is dry and reasonably clean before the test. Since measurements may be influenced by relative humidity, use similar environmental conditions to compare the results of different tape tests.
2. Affix the tape strip to the surface of the material. Once attached, apply even pressure with a finger and repeat this up to six times to ensure the tape's complete adhesion to the surface. It is crucial to apply similar pressure and an equal number of applications of pressure to all strips to have similar conditions.
3. After the specified duration, carefully remove the strip by pulling it off from the uncoated end tab at a steady rate of approximately 10 mm/s and at a 90° angle to prevent any loss of the attached grains. To ensure accuracy and consistency, it is important to adhere to this widely accepted method (Drdácky et al., 2015). Once the strip is completely released, immediately place it, along with its protective sheet, in a plastic bag or hermetically closed box. Repeat this process for all nine strips, and store them together in the same plastic bag or box.
4. Finally, weigh the bag or box containing all the tape strips, including the attached aggregates and protective sheets, on a balance, and compare the weight to that of the same strips before the test. The difference in weight between the initial and final weighings corresponds to the released surface material.

4. ETHICAL CONSIDERATIONS

When undertaking analysis on built heritage items using the Scotch Tape Test to evaluate the surface cohesion of stone or brick samples, there are several ethical considerations to keep in mind.

Firstly, the test should be conducted in a manner that does not damage or harm the heritage item in question. Care should be taken to select a dry and reasonably clean area of the building that is not likely to be contaminated or damaged during the testing process. Additionally, the test should be conducted in situ, and the Scotch Tape Test should be applied and removed with care to ensure that no additional damage is done to the surface of the material.

Secondly, the test should be carried out with respect for the heritage and cultural significance of the building or material being tested. The selection of a representative sample of the stone or brick material must be done with care, taking into account the importance of the building or material and the impact that the testing may have on its cultural value.

Finally, the results of the test should be reported and interpreted accurately and transparently, and any recommendations for conservation or remediation should be made with due consideration for the cultural and heritage value of the building or material being tested.

5. RESULTS

The results of the tape test applied to a weathered sandstone surface and repeated after a consolidation have been reported in Graph 1. When a balance with the required sensitivity is not available, the strips of tape can be examined by naked eye or under a digital or stereo microscope. Although the evaluation is only approximate, it provides a first estimation of the surface condition of the stone and is particularly useful to test areas that can be treated with different consolidants for comparison.

In this particular study, the sandstone samples treated with hydroxyapatite showed the highest reduction of released material, with an 88.3% reduction. Samples treated with TEOS (tetraethyl orthosilicate) showed a reduction of 71.79%, while samples treated with acrylic resin showed a reduction of 47.81%. These results serve to evaluate potential consolidation treatments and their effectiveness in providing surface cohesion to disintegrated areas. Additionally, the tape test can be useful to compare the level of weathering in a structure between more and less deteriorated areas.

The percent change in weight (ΔW) is calculated as follows: ΔW (%) = (initial value ? post-treatment value) × 100 /initial value.

Graph 2 summarizes the results of a tape test applied to an untreated sandstone surface and after consolidation treatments with three different products: tetraethyl orthosilicate (TEOS), an acrylic resin, and hydroxyapatite. The graph includes data on the weight of the plastic bag/box with the samples, weight difference (mg), and released material (mg/cm2) before and after peeling off the tape strips. Nine tape strips were applied, each measuring 4 × 2 cm (8 cm2), giving a total of 72 cm2 for all strips.

The results show that the untreated sandstone surface released the highest amount of material, with 6.84mg/cm2, compared to the treated samples. Among the treated samples, hydroxyapatite yielded the highest reduction of released material, with only 0.80 mg/cm2, indicating a reduction of 88.24%. TEOS and acrylic resin treatments also showed a significant reduction in released material, with values of 1.96 mg/cm2 and 3.57 mg/cm2, respectively.

It is important to note that the climatic conditions, including temperature, relative humidity, wind, and other factors, should be recorded for optimal evaluation of the tests. Additionally, other data such as the type of sandstone, its age, and its exposure to environmental factors may provide a more comprehensive understanding of the results.

Graph 3 presents the results of the tape test applied to a weathered sandstone surface before and after treatment with three different consolidation treatments. The released material from each sample was measured in milligrams per square centimeter, and the percentage change in weight (ΔW) was calculated by comparing the initial untreated value with the post-treatment value.

The results show that the untreated sandstone had the highest released material (6.84 mg/cm2) and was not applicable for calculating the percentage change in weight. The sample treated with tetraethyl orthosilicate (TEOS) had a significant reduction in released material, with only 1.96 mg/cm2, representing a 71.72% reduction in weight. The sample treated with an acrylic resin had a slightly higher released material of 3.57 mg/cm2, but still demonstrated a substantial reduction of 47.81% in weight. The most effective treatment was hydroxyapatite, which had the lowest released material of only 0.80 mg/cm2, indicating an impressive 88.30% reduction in weight.

The results of the tape test provide valuable information on the effectiveness of the different consolidation treatments in improving the cohesion and stability of the weathered sandstone surface. The lowest released material and the highest reduction in weight were achieved with hydroxyapatite, indicating that this treatment could be the most effective in providing surface cohesion to disintegrated areas. The data in Graph 3 also demonstrate that the tape test is a useful method for comparing the level of weathering and evaluating potential consolidation treatments.

6. IMPLICATIONS FOR CONSERVATION PRACTICE

The “Scotch Tape” test method provides a practical and cost-effective means of assessing the conservation needs of architectural heritage. The method has several advantages compared to traditional techniques, including its low cost, ease of application, and reasonable reliability. The test results obtained from this method can help conservation practitioners make informed decisions about the best treatment approach for a given building material. The “Scotch Tape” test is sufficiently sensitive to demonstrate even subtle variations and differences in consolidation effects, making it a powerful tool for assessing the quality of the plaster or brick surface and/or the efficiency of consolidation interventions. Despite its simplicity, the method has potential for further development and refinement.

Future research should focus on exploring the potential applications of the “Scotch Tape” test to other building materials and structures. Investigation of specific tape quality recommendations and further refinement of the evaluation procedure would also improve the sensitivity and accuracy of the test. These refinements would allow for more nuanced and detailed assessments of the cohesion and degradation characteristics of the tested materials. The “Scotch Tape” test is a promising tool for assessing the conservation needs of architectural heritage, and further research and methodological development will be needed to fully realize its potential.

6. CONCLUSION

In conclusion, the verified standard “Scotch Tape” test procedure is a simple, practical, and promising method for assessing the conservation needs of architectural heritage. The “Scotch Tape” test is a valuable addition to the conservationist's toolkit, providing a low-cost, rapid, and easily applicable technique suitable for in situ investigations of historic surfaces. The method has several advantages compared to traditional techniques, and its sensitivity makes it a powerful tool for evaluating the efficiency of various treatment technologies. While further development and refinement of the method are needed, the “Scotch Tape” test has significant implications for conservation practice and has the potential to help preserve our valuable cultural heritage for future generations.