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Edition 07: 11 October, 2007.

Edition 08 : 31 August, 2011.



There is no single form, shape, appearance, colour, hardness, resistance, or surface for gypsum composite products. A sample of à gypsum composite product  is therefore meaningless unless it is a given product, designed for a specific purpose, for use in a specific area, using cheap gypsum or anhydrite from a specific deposit.

Each product has to be individually developed, and its development typically requires about six months of research. Some important aspects are:


Description of the products needed?
What are they needed for?
How users are accustomed to meeting the needs
Physical conditions in which they will be used
Specifications : size and volume, preferred shape, resistances, type of finish, colour, weight limits


Clear list of priorities : which items are to be first
Quantities required
Rate of production required
Territorial distribution of the consumers
The degree of automation (if any) required.


Which waste materials are usually available locally? Examples : discarded coconut fibres; flax fibres.


Where the deposits are situated.
The project coordinator or his appointees will be led through a series of tests to check the specific characteristics of the locally available cheap gypsum or anhydrite deposits to be used to make the products. This work must be done scientifically and the instructions exactly followed.


On the basis of the raw material test results, the product specifications, and the local waste materials available, a number of different recipes are developed. These are used to make product samples for testing and approval by the users.


The moulds to be used are finalised, preferably in the gypsum composite production units which in the meantime will have been designed and built. The first moulds can be quite expensive to make, which is why the number of products each production unit can make to start with may be rather limited. Successive copies of the moulds are, however, easy and cheap to make.


This varies according to the nature of the product. A water container (=jug) will normally be made in two halves, joined together, the internal pores first filled, and an epoxy coating given to the inner surface to make it impermeable and hygienic. Tanks will normally be made in hexagonal segments.


Here are the procedures to be followed for the development of "more or less waterproof" material with transpiration for the external covering (not strengthening) of mud houses. To reach a solution efficiently it is important that all work be extremely systematically executed. Every development has to be "scientifically" recorded. Every sample must always be carefully coded and labelled. Failure to do so will just cause extra work for everyone, especially for the local partner, as there is quite a lot of paper work to be done. For the same reason systematic cross-checking of data is of vital importance, as will be seen from the following description.


Phase One

a) Collect samples of the following basic raw materials from various sites in the project area. Each sample must be carefully coded dated and labelled. As a general rule, the less the water in the chemical structure the longer the hardening time.

The two basic types of interest are:

Anhydrite : CaSO4 + 1/2 H2O. Has a lower water content, hardens in 1 1/2 hours. For your guidance, this costs between 2 1/2 - 3 US cents per kg in Europe.
"Cheap" gypsum : CaSO4 + H2O. Has higher water content, hardens in less than 30 minutes. This is what is discarded during gypsum production. It costs between 4 and 5 1/2 US cents per kg in Europe. (The price of top quality gypsum is between 9-10 US cents in Europe)

Conserve three sets of the carefully coded dated and labelled samples in sealed plastic bags. Keep the bags in darkness at about 18 degrees C.

b) Collect two samples each of about 300 grams taken from the walls of existing houses, at least 5 houses from each of 5 areas. The samples must be carefully coded dated and labelled with location, age, type of mixture used (e.g. % straw, % clay, %dung) plus a careful description with percentages of any other extra materials (additives etc) included in the mixture, description of the building method used.

c) Send one set of the samples under b) to the Consultant.

d) Test one set of the samples under a) for their hardening time. Record the date and hardening time on the labels OF THE HARDENED SAMPLES ONLY.

e) Collect samples of fine milled sand and/or desert sand (the sand on the leeward side of hills is finer than that on the windward side). You may use several types of sand, in which case the procedure under phase two is to be conducted with each type of sand.

Phase two

Prepare b) following before proceeding with a)

a) For each raw anhydrite or cheap gypsum collected under a) above make sample blends each blend containing 50% of sand and 50% of the raw material concerned. Each such blend must be carefully coded, dated and labelled. Use EXACTLY the same quantity for every such mixture.

b) The following must be conducted exactly. Hold in reserve before proceeding with point a) a reserve container with EXACTLY one third of the amount of water used in a), and a second reserve container with EXACTLY one third of the amount of anhydrite or cheap gypsum used in a)

The blend in a) must be just pourable, so that the mixture is just able to flow. If it is too liquid add some more anhydrite/gypsum, if it is too thick add some more water.

c) Carefully record hardening time, the EXACT percentage of extra water or raw material added, and code, label, and store the new composite products.

d) Copy to us all a full documentation on everything done on raw materials, sand and material mixtures, wall samples to date.

Phase 3

a) An analysis is now made of the materials most suitable for the application in question and a set of 5-7 recipes will be formulated according to the wall materials to be protected.

b) You then prepare two sets of each mixture according to the recipes given, and carefully code and label them. One set is tested for ageing. The second set is to be kept in a labelled plastic bag in a dark place at a temperature of around 18 degrees Centigrade, preferably without air.

c) From your own recorded observations and from your paper-work, we can then assume which material(s) are likely to give the best results.

d) The UNTESTED examples of the best material(s) are then sent to us so that we can conduct mirror tests for counterchecking purposes.

Phase 4

a) This is the most important phase. We discuss the final (presumable) recipes and the financial consequences of choosing various possible additives.

b) A simulation project is then set up with, say, 5 houses in each of say 5 regions, each house with 5-10 check points. Ideally the houses should be the ones the samples under 1 b) come from. If other houses are involved, then collect samples for them as set out in 1 b) above, code them, label them and pack them well.

c) Apply the recommended mixtures to the walls of the chosen houses, carefully recording:
-code of mixture and code of wall sample
-date and time of day
-weather conditions
-humidity at the moment of application
-details of mixing
-size of mix
-number of people working
-ease (feel) of application
-comments of workers (seems too thick, seems too thin)
-hardening time
-ALWAYS with exact measurements of quantities etc

c)Every week thereafter at exactly the same time, check the control points:
- is the material still strong
- description of climatic events over the week
- tears or signs of tears with description of length and width of tears indicating whether they are on the North, South, East or West side of the house
- if the moisture feels uniform to the touch at the top and at the bottom of the walls and around the doors
- check uniformity of colour
- check if little black spots appear, especially towards the bottom of the wall
- check carefully what happens at the bottom of the wall in contact with the soil, by tapping the wall with a stick and listening for "empty" sounds.

Phase five

After about six months a decision will be taken on what the final recipe will be from the point of view of cost, storage, handling, preferred colour etc.




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