Integrated Assignment 04

Restoration of historic monuments

“St. Michael’s Mount, in Cornwall, is one of the many places of historic interest in the National Trust’s care”.

The National Trust is a registered charity, founded in the 1890’s to look after places of historic interest. You may have visited a castle or old house which is in their care.

These old buildings are in need of constant upkeep not just inside, but outside too.

Imagine surveying the render that coats the walls of one of these ancient houses and finding that it needs to be replaced.

Render forms a protective finish to walls. Before 1900, it was made from lime, sand, hair and even dung. Nowadays render is made from Portland cement and sand. Modern cement is obviously much more advanced, but would it be right to use this on an old house?

The National Trust restores old buildings using traditional methods, and in this activity you are going to help the Trust’s restoration advisor, guiding the builders in the right choice of materials for the job.
You will be finding out which sand to use for the mixture to set properly and investigating the hairs used in render on old buildings.

Part A: Finding out if the sand you are using contains the inhibitor, sodium chloride.

The sand in render (or mortar) gives it a solid structure. However, the type of sand that is used is important. Smooth sand from the sea, which contains salt (sodium chloride), can be a problem. Too much sodium chloride is known to prevent the render from setting properly.

In this activity, you are going to test some samples of sand, to see if they contain salt.

What you have to do.

Weigh out 20 g of each of the sand samples that you have been provided with, and keep in a glass dish for later.
Set up the apparatus for filtering.
Place one of the weighed samples into the filter paper, and slowly add distilled water.
Allow the water to drip through for about 5 minutes.
Remove the filter funnel and paper, and discard the paper and its contents.
Pour the clear liquid from the flask into a labelled specimen tube or small glass container.
Repeat this with the other samples of sand.
Remember to label all your samples and the filtrates!
Take each sample and carry out the appropriate anion test in
SP 0006-1:2005.
Similarly, test a fresh (unwashed) sample of each sand for the expected cation using SP 0006-2:2005.

What you need to think about

Remind yourself what you are testing for. Which salt would you expect to find in sand that has been dredged from the sea?
In the above tests, make sure you only test for the cation and anion that you are looking for.
What should you be particularly careful about when collecting the samples that you are going to test?

Possible extension

You may wish to extend this assignment to find out how much salt (sodium chloride) is in the sand samples. How would you work this out accurately?

Hint: the chloride test involves a precipitate when you add silver nitrate solution. Is the quantity of precipitate proportional to the amount of chloride or salt present?

If so, how could you measure it accurately? You can express the answer as an actual amount per gram or as a percentage of the samples. You choose the best method to express your results.

You could also use a modified form of the method that is described in
SP 0008:2005 Determining the salt content of butter. Since the salt is already in solution, miss out the nitric acid step at the beginning.

Presenting your conclusions for part A

Present your findings in a short report, saying which samples you found to contain sea salt (NaCl) and if you managed to find out, state the quantity of ‘salt’ in each sample.

Part B: Comparing the strength of hair used in render

In the past, people have added other things to mortar to help give it extra strength when it sets. In particular they added straw or hair from goats, horses or oxen.
This tradition is carried out today, by the addition of steel mesh or plastic fibres inside the render mix. These give the render added tensile strength.

Testing the strength of hairs

Obtain a copy of SP 0012-1:2005.
Carry out the procedure on several varieties of animal hair.
Depending on the hair’s thickness and surface texture, you may need to change the methods of clamping the hair at the top and bottom. For example, you could try winding it around the dowel a few times before taping.
Some hairs may not be long enough to use 300 mm specimens as stated. Think about how this will affect your results, if at all.
Collect your results in a table or on a bar chart, so that you can draw conclusions.
To extend this investigation you could repeat the procedure with straw, sisal or even plastic fibres.

Part C: Comparing the surface of the hair or fibre used in render

The sand used in building needs to be angular so that the particles lock together. The same thing goes for any added material such as hair, which should have a rough surface.

What you have to do

Take new specimens from the samples of hair and fibre that you looked at in part B.
Using SP 0001:2005 Methods for setting up and adjusting a light microscope, and SP 0002-1:2005 Methods of preparing slides for microscopy, examine your specimens of hair or fibre.
Use both low and high magnification to examine the hairs.
Record the details of each hair sample so that you can easily compare their characteristics.

Presenting your conclusions for parts B and C

Draw up a table that shows the tensile strength and surface characteristics for each fibre sample. Devise a way of selecting fibres that have both good strength and good surface roughness.

Presenting your conclusions

You should be in a position to write a report on your findings informing the National Trust manager about the render for an old house they are renovating.
In your report, you should include:

your findings about the presence of salt (sodium chloride) in the sand samples;
details of your tensile strength test comparing different fibres to add to the mix;
your findings about the surface quality of the hair and fibre samples;

Recommend which sample of sand they should use in their render mix.

Make recommendations for the best fibre to add as reinforcement to the render.