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1. Educational Linkage Approach In Cultural Heritage
E x e r c i s e 5.D
Advanced Course
Module 5 Monitoring & Maintenance
Topic 5.1 To Monitor or not to Monitor, that is the question!
Exercise 5.D
Hands on materials: What the contact angle can tell us
Authors: Prof. Guido Biscontin, Dr. Francesca Caterina Izzo, Prof. Elisabetta Zendri, Ms. Laura Falchi- Ca’
Foscari University of Venice
Objective
The aim of this exercise is to help students to understand what a contact angle is, how to measure it and its
importance as a monitoring parameter for the behaviour of the relation water/Cultural Heritage materials.
Introduction
“Monitoring means to carry out evaluation tests at the end of the conservation intervention and over time to
control the efficiency of the intervention and of the products in terms of water repellence”.
The application of a water repellent on the surface of a building material can change the behaviour in relation with
water. This difference can be seen also by measuring the contact angle which gives us the idea of the wettability of
the material, that is to say how much water can wet a material.
Guidelines
Exercise 5.D should be done after the Topic 5.1 of the Module 5
“Monitoring and Maintenance”.
Duration: 30 minutes on the first day to prepare samples and treat them
with water repellents, 30 minutes for the activity and 30 minutes for
writing the report.
Type of activity: it is a group activity that should be done in class. The
Fig. 1 example of mortar specimen
report could be written also as an homework.
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2. Educational Linkage Approach In Cultural Heritage
E x e r c i s e 5.D
Equipment
• Stone material samples, preferably regular specimen of:
pieces of bricks
local stone samples (marble, limestone,
sandstone)
pieces of mortars
• water
Fig. 2 applying the treatment
• water repellent products such as: linseed, walnut, Vaseline or olive
oils; natural wax; commercial water repellents…
• brush
• syringe without the needle
• block notes
• protractor
• camera
Fig. 3 spreading drops of water
Before the activity: prepare the equipment needed and copies of the on the treated surface
example report and of the data sheets.
During the activity:
st
1 day: treatment with water repellence products
• dry the samples
• label the samples and for each different material separate some
samples (which will be treated) from others (which will remain
untreated) Fig. 5 photo of a drop
• apply the oil or wax with a brush all over the surfaces of the chosen
samples 135°
• dry the treated samples
nd
2 day: determination of contact angle
• fill up the syringe with water
• gently spread some little water drops on the surface of the sample
• take orthogonal photos of the samples with the drops of water on
the surfaces
• measure the contact angle between the surface and the water drop Fig 4 measuring the contact
angle
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3. Educational Linkage Approach In Cultural Heritage
E x e r c i s e 5.D
WHAT IF…
“…the material absorbs the water drop immediately?!”
“Don’t worry! If the material absorb the drop immediately it means that the surface is completely
wettable and the contact angle is considered 0° ”
Remember!
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4. Educational Linkage Approach In Cultural Heritage
E x e r c i s e 5.D
Report writing:
Measure with the protractor the contact angles from the photos you have done. Note down the contact angles of
each sample.
Calculate the mean of the angles for each material after and before the treatment. Create an histogram of the
different contact angles.
Mean= (a1+a2+a3+a4+a5)/5
Look at the example:
sample nr 1 not treated sample nr 1 treated with
drop angle drop angle
1 20 1 120
2 0 2 110
3 15 3 85
4 5 4 98
5 10 5 100
mean 10 mean 102.6
Expected results
The samples treated with water-repellent products should have a higher contact angle (as in our examples
reported in the previous table).
If the contact angle is more than 90°, the surfaces are called hydro-repellent (the water cannot wet the material);
the treatment, therefore, is able to protect the materials against the possible damaging action of water.
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5. Educational Linkage Approach In Cultural Heritage
E x e r c i s e 5.D
Report writing:
Write the contact angle of different materials and calculate the mean:
sample nr not treated sample nr treated with
drop angle drop angle
1 1
2 2
3 3
4 4
5 5
mean mean
Answer the following questions:
1. What do you observe?
2. Do the different materials react in the same way in contact with water?
3. Do you think the treatments applied are good enough in order to prevent water to enter into on building
and/or historical materials?
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