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close this bookProduction Guide - Fibre or Micro Concrete Tiles (SKAT, 1992, 67 p.)
close this folder3. Production process
View the document(introduction...)
View the documentMortar preparation
View the documentVibrating and molding
View the documentMold curing
View the documentDemolding
View the documentTank curing
View the documentAir curing, storage
View the documentTransport

(introduction...)

Besides the quality of the raw materials, a careful production procedure is the other important guarantee for a product of a high standard.

The steps of the production process are:

3.1 Mortar preparation
3.2 Vibrating and molding
3.3 Mold curing
3.4 Demolding
3.5 Tank curing (in water tanks or vapor atmosphere)
3.6 Air curing, storage
3.7 Transport

Mortar preparation

Proportion of Components

The proportion of cement, sand, water and fibre or fine aggregate in a mix is based on the properties of the actual raw materials and can vary from place to place. It should be defined during the prototype production and again when the properties of the raw materials change.

Cement / Sand / Aggregate Ratio

For FCR, the cement to sand ratio is normally between 1:2 and 1:3. For MCR, the cement to sand to aggregate ratio is around 1:2:1. The proportions are measured by volume.

Too much cement results in fine cracks in the tile and also in high costs. Too little cement results in a weak and porous product.

Ratio of Fibre

The ratio of fibre is usually between 0.3 and 1.2 % of the wet mortar by weight.
Too much fibre results in a low strength and high porosity. Omitting fibre may result in cracks during molding.

Workability

A good workability of the mix is important so as to obtain a good production result. The following indicators show if the right workability has been chosen:

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A practical instant method is to squeeze the mortar by hand. No water drops should come out and the mortar should not crumble.

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Water appearing on the surface after a short vibration period is a clear sign that too much water is being used.

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An easy test to maintain the correct ratio is the workability test (see Quality Control Guidelines).

Water / Cement Ratio

The water to cement ratio of the mortar (as well as curing, especially during the first 24 hours before demolding) is a major factor governing tile quality.

The correct ratio:
A good quality mix has a water to cement ratio of 0.5 by weight (1 l water = 1 kg) and results in a mortar which hardens in the correct time, is easy to demold and does not have to be cured in water for more than 5 to 7 days.

The strength and watertightness of FCR/MCR products are sufficient if the water to cement ratio is below 0.65, but the risk of breakages during demolding is greater and longer water curing times may be required compared to products made of mortar with a water to cement ratio of 0.5.

A water to cement ratio higher than 0.65 will result in low quality products, and if the water to cement ratio of the mortar exceeds 0.7, the watertightness and durability of the FCR/MCR products are not ensured. Products with a water to cement ratio exceeding 0.65 should not be used as roofing material. Such products may ruin the good reputation of cement-based roofing products.

When calculating the water to cement ratio, the moisture content of the sand also has to be taken into account. When using wet sand, less water should be added.

The water to cement ratio also varies according to the sand quality. A mix with porous sand requires more water than a mix with non-porous sand.

The following rule is generally valid:

Suitable water to cement ratio: 0.5 - 0.65 ( by weight )
Never use a water to cement ratio above 0.65
Mixing

The mortar has to be mixed well, so that no lumps of fibre, aggregate and cement remain.

First mix sand, fibre and aggregate; then add cement and colorant and mix again thoroughly. Add water.

Use Fresh Wet Mix

Every hour fresh mix has to be prepared.

The mortar mix has to be fresh when cast. The acceptable maximum time between mixing with water and casting depends somewhat on the properties of the cement and also on the temperature and air humidity. However, it should not exceed one hour.

(see also Production Management Guide)

Stiff Mix

If the mix stiffens during the production process, do not add water. Prepare a new, smaller quantity of mix instead.

The method of mixing a large quantity of cement, sand and aggregate at a time and then adding water to a small portion of that dry mix should be practiced only in areas with low humidity or with very dry sand and aggregate. Moisture in the mix will cause the setting process to start.

The rules and the range of possible mixes as given above should be understood as general guidelines. Testing of different mix proportions would tell you what the best mix for your material is.

Vibrating and molding

Placing the Mortar

Put a clean plastic interface sheet on the vibrating table, close the frame and put the accurate quantity of mortar on the table by the use of a measuring scoop. Spread the mortar roughly with a trowel before vibrating.

Cleanness

The equipment used (especially the plastic interface sheets) must be clean. The vibrating table and the frame must be free of any old mortar.

Free from Defects

The interface sheet must not have any holes.

Fresh Mix

The mortar has to be used within one hour after water is added to the mix.

Accurate Vibration Time

The vibration time depends on the equipment used and the workability of the mortar. It varies between 20 and 50 seconds.

Vibration is sufficient when water starts to appear on the surface, provided the water to cement ratio is correct. At the end of the vibration, there should be:

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no water film on the surface;

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no cracks, holes or air bubbles in the matrix;

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no lumps of fibre;

and the matrix should have:

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an even thickness and

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a uniform surface.

Too long a vibration leads to a reduction in the quality of the tiles due to the segregation of the mix components.

Nib Molding and Placing of Fixing Device

When the vibration is stopped, the nib is mounted. The nib mold is filled with mortar which is then tightly connected to the tile by another short vibration.

Hereafter the fixing device is inserted and the tile is again vibrated for a few seconds; then the mortar flush to the nib is cut off with a trowel.

When opening the nib frame, the nib has to be kept down by pressing with a finger.

Molding

After vibration the matrix is moved to the mold, where it must be placed exactly in the correct position, otherwise the shape of the tile will not be correct and this could result in a leaking roof. To ensure the correct positioning the molds should have marks.

During this process no cracks should appear on the surface. Fine hair cracks that may appear are closed by a trowel or a brush.

(The photos show the method using the equipment of J.P. M. Parry & Associates).

Mold curing

Cure Immediately

The proper setting of the mortar is only possible if the tiles are cured correctly. The curing procedure should start immediately after the product has been cast. The tiles have to be stacked in an airtight manner or covered within 5 minutes after casting. Neglecting this would result in drastically weakened tiles and cracking.

Curing Method

During this period the tiles are cured in a horizontal position while still on the mold, by covering their surface with a plastic sheet or by stacking with molds that guarantee airtight and dampproof stacking.

If during this step cracks develop on the surface, it is a sign of too much air circulation.

Curing Period

The most important curing period is during the first 24 hours.

For organizational reasons it is difficult to keep the tiles on the stack for exactly 24 hours. However, a minimum of 20 hours must be allowed.
(See also Production Management Guide)

Demolding

Time of Demolding

After 24 hours the strength of the tiles is sufficient for demolding. Do not demold earlier than 20 hours after vibrating.

Demolding

This operation can be done by tilting the mold with the tile over a jig (method using the equipment of J.P.M. Parry). Instead of the jig a mold specially made for this purpose may also be used.

Demolding can also be done by sliding the tile and the interface sheet from the mold and holding the tile gently in the palm of the hand. Care should be taken to avoid holding the tile by the corners or between two fingers only.

Remove the interface sheet by pulling it across the tile (short dimension) and remove any fresh mortar. Then place the tile on the test mold.

Testing

Check if the demolded roofing product fits on the jig or test mold without wobbling and with all the edges in the right position. The size and shape should also be checked.
(See also Quality Control Guidelines)

Cleaning of the Molds and the Interface Sheet

So that good quality tiles can be produced later, it is most important to immediately clean the molds and plastic interface sheets with a brush and water. They should be checked for holes and stored properly (see also 5.1).

Tile Marking

The tiles should be marked with

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the production date,

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the name of the company and

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the name of the worker.

This helps to observe the correct curing time, determine the right time for the end control and to relate the service performance of installed tiles to the production data and the producer.

Marking can also be done during the vibrating process.

Tank curing

Curing Time

After tiles have been cured for 24 hours in a horizontal position, they are carefully moved to the curing tank where they are kept completely under water in a vertical position for at least 5 days, provided the water temperature is above 20°C.

Mark the date on the curing tank to avoid confusion. (See also Production Management Guide)

Immediate Curing

After demolding, the tiles must immediately be moved to the curing tank. Never allow the tiles to dry in the sun or wind before water curing.

Water Level

The water level in the curing tank should be checked daily. The tiles should be covered by at least 20 mm.

Curing at Low Temperature

If the water temperature is below 20°C, the curing time must be increased.

For a temperature of 15°C, the curing time must be at least 7 days.
For a temperature of 10°C, the curing time must be at least 11 days.

Make sure that the water temperature is measured because it is lower than the average daytime air temperature.

Curing Time for Tiles Cast with a high Water to Cement Ratio

If the water to cement ratio is higher than 0.5, the curing time must be increased as well.

Change of Water

If the water becomes too aggressive on the skin, it should be changed, this may be once a week, but at least every two months. At the same time the tank should be cleaned.

Curing in clean water is especially important when producing colored tiles. Old water may cause white stains.

Storing Method
There are different possibilities for storing the tiles in the tank:

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Stacking the tiles in a row

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Stacking the tiles in sets of three tiles.

Stacking in sets is a space and time saving method, but is only possible with tiles that have a nib at the top. It involves a certain risk of damage to the nibs.


Storing method

Vapor Curing

Another method is to cure the tiles above water in air saturated with water vapor.

This can be achieved by placing only a little water in the curing tank. The tiles are stored above the water level. The tank is then made airtight by covering it with a black plastic sheet. As the tank is exposed to the sun, the enclosed air becomes saturated with humidity and the temperature rises, thus accelerating the setting process.

The water level must be checked at least every morning.

This environment, where the curing temperature is higher, favors the curing process. The result is a strong product with a smooth and clean surface.

The method is especially advantageous for colored tiles, giving a proper coloring without white stains.


Vapor curing

Batch Marking

Properly mark the daily batches with the date of production and product number so that the curing time can be checked.

(See also Production Management Guide)

Air curing, storage

Curing Time

After the water curing period the cement setting process is not yet completed. 28 days after casting only 80% of the final strength of the tiles has been reached.

After the tank curing, another 20 days must be allowed for air curing.

Shaded and Wind-protected Storing

During this time the tiles must be protected from direct sun radiation and air circulation, which would result in too fast a moisture evaporation.

Water Sprinkling

In dry climates the tiles should also be sprinkled with water twice a day to avoid complete evaporation of moisture.

Protection from Mechanical Damage

To avoid mechanical damage the tiles are stored in a vertical position on properly built racks or on sand.

Batch Marking

Properly mark the daily batches with the date of production and product number so that the curing time can be checked.
(See also Production Management Guide)

Transport

Careful Shipment

The last step in the production process is the shipment.

The means of transport varies from a lorry, a bullock cart, a ricksha to people carrying the tiles on their backs. The roads are often extremely rough.

To avoid damage during transportation, careful handling is required. Proper packing methods adapted to the means of transport have to be used.

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The tiles have to be transported in a vertical position, preferably in packages of three pieces.

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They must be tightly stacked, with no scope for knocking each other during transportation.

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Proper racks should be used when carrying tiles.

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When transporting in a vehicle, sand, sawdust or fibre rejects should be used at the bottom to cushion the tiles. The direction of stacking must be the same as the direction of movement of the vehicle.

Instruction of Customers

Often the tiles are transported by the customer. He must be properly instructed how to handle and transport the tiles.

A simple leaflet can be designed for this purpose and distributed to the customer.

Transport by Lorry

Transport by Pick-up