Terrazzo floor laying is a technical work that require a lot of care and consideration right from the beginning.The various processes required can be summarized as follows:
Design stage is where various factors are considered before the actual work starts. Terrazzo is mainly used in the following areas;
1. Wet areas like Bathrooms,Toilets and kitchens.
2.Areas with heavy human traffic like Staircases and Corridors
3.Areas where heavy duty works is carried out like Garages and Warehouses.
So the above considerations will help in determining the areas where terrazzo will be used.
Once the area has been identified the next stage is to choose the colours that will be used. Colours mainly depends on the client taste or the intended use of the rooms. There are many factors that determine the colours to be used mainly;
1.The colours that the end user intends to use on the walls ( Matching ).
2.The kind of activity that the area will be used for. For example you may be tempted to use dark colours in garages and bright colours in kitchens.
3.Personal choice of colours. Some people are more biased on certain colours.
The main colours available locally as oxides are Red, Yellow, Black Green and Blue. By carefully mixing various colours , one can obtain various other colours like Grey, orange,pink cream etc.
The next stage in the design to choose the patterns . The most common form is the square or rectangular boxes. However one can become creative by making triangular, octagons , pentagons, flowers or even drawing objects like logos,animals , letters.
Floor preparation is very important before terrazzo laying commences.A stable concrete floor is required in order to achieve a durable crack free terrazzo floor.
If it is a new floor , ample time is needed for the concrete to cure. After curing the floor is teethed (hacking) to produce a rough surface.The floor is then thoroughly cleaned to remove all the dust.
For an old floor, it is important to remove the old screed completely , do the hacking and clean all the dust and debris.
If a crack appears on the concrete, it will definitely appear on the terrazzo. So ensure the concrete floor is firm.
Once the floor is clean, the next step is laying the cement screed. This is a combination of sand and ordinary cement. The most common ratio for sand and ordinary cement is 3 wheelbarrow sand to 1 bag cement. However this ratio varies depending on the strength of the screed required.
Before laying the screed, the previously prepared floor is sprinkled with water. Ordinary cement is poured with a trough and then evenly smeared on the floor with a hard brush. This acts as an adhesive.
The cement screed is then evenly spread on the floor taking into consideration the levels required. In some case the floor may need to have some gentle slope to direct water in certain directions like gully traps and floor traps.
The dividing strips serves two main purposes:
1.Divide between various colours.
2.Limit the spread of cracks on the terrazzo floor should a failure occur on the foundation.
The dividing strips are either made of PVC,Aluminum or even Brass. The Standard size has a the size of 20mm x 2mm x 7ft long. Another common size available size is 32mm x 3mm x7 ft long which are mainly used in warehouses with heavy moving equipments.
The dividing strips are put in place before the cement screed hardens. The required patterns are drawn on the wet floor using nylon string , squares and straight edges. The dividing strips are then carefully put in place as per the designed pattens.This stage is very critical in laying of terrazzo. Any mistake made at this stage cannot be corrected once the next stage starts.
One critical point to note is that all the dividing strips needs to completely flash at all the intersections so that they will all appear uniform after grinding.
Before proceeding to the next stage, it is recommended to give the floor approximately three days of curing.
This stage involves the following;
1.Mixing the terrazzo chippings.
The main colours for terrazzo chippings are White, Cream and Black.Other colours available are Red and Yellow. For the floor area it is recommended to use size 1/4" or 3/8". For the skirting,walls,staircases, table tops etc is is recommendable to use size 3/16".
For most ordinary floors using bright colours, the chippings are mixed in the ratio White:Cream:Black=10:2:1 . However for Granolithic (Grano) floors the ratio changes to White:Cream:Black=1:2:10 . However this acts only as a guide and the ratios can change to any custom values.
Once the required ratio has been identified, the chippings are thoroughly mixed to give a uniform mixture.
2. Mixing the Premixed Chippings with Cement and Colouring Oxides
The premixed terrazzo chippings are then mixed with cement and the colouring oxides. The most common ratios for Terrazzo Chippings:Cement=2:1 . Depending on the colour required , oxides are added and the mixture is thoroughly mixed to make a uniform mixture without adding water.
Water is slowly added as the mixing continues. At this point one can be able to see the colour of the terrazzo mixture. More colouring oxide can be added to attain the required colour. It is recommended to measure the oxides in a particular way by either a spoon or any other container or a weighing scale.This will help in replicating the same colour should the mixture fail to cover the predetermined area.
3.Laying the terrazzo mixture in the patterns.
The floor in which the dividing strips have been put is thoroughly swept to remove dust and foreign objects.Water is then poured to soak the floor.
The mixture is then spread into the patterns that requires that particular colour using a trough. As a precaution to avoid two colours mixing in a pattern, different colours needs to be separated by at least one day.
After one hour curing, a roller is passed over to compact the mixture.After another two hours a second roller is passed while sprinkling the mixed aggregates until the floor is uniform.
The excess cement mixture is swept with a soft brush. Using a trough, the floor is evenly leveled.
4.Laying the Skirting
Once terrazzo has been laid on the floor , the next to follow is the skirting. The 3/16" size terrazzo chippings are mixed in the required as above. Cement and coloring oxides are added to produce the required shade.
A timber of size 3mm thick by 20mm wide commonly referred to as Skirting Timber is nailed on the wall using Steel Needles at a height of approximately 4-5" above the floor. This helps in shaping a clear cut line for terrazzo on the wall.
Where tiles are used on the wall, the tiles are normally fixed 4-5" above the floor just as the skirting timber to act as the cut line.
If the wall had been plastered smoothly, teething is required so as to make a rough surface. A thick mixture of cement and water is applied to act as adhesive.
Using a trough the terrazzo is evenly applied . The smothering is repeated until it holds on to the wall. After curing for about three hours the excess cement is removed with a soft brush.It is later smothered using the trough.
Grinding is done using Electric or Kerosine terrazzo machine.
For the grinding to start, the floor needs to be given at least seven days to cure. White cement cures faster than ordinary cement and works done using white cement can be grinded in four days.
Grinding is done in two phases. The first phase involves rough grinding using Block-stones 8x2x2 rough.Diamond grinding pads can also be used. River sand is occasionally used to help in grinding.Once rough grinding is completed, a mixture of cement and colouring oxide matching the floor colouring is spread evenly using a rubber squeezer.This is given one to two days to cure but can be extended longer.
The second phase of grinding then follows using Block stone 8x2x2 smooth. This is the final grinding though there are several grades of smothering Blocks tones which can be applied to make the floor even smoother.
The skirting,staircase,walls or table tops can be gridded by hand using Handstones 6x2x1. It is done using the rough stone first, filling it with mixture of cement and oxide matching it's colour and finally smothering with smooth stone.
Another method of grinding skirting is using a power grinder fitted with Diamond or Stone Cup Wheels.This works faster and can produces a much more smoother surface.
Cleaning and applying Polish
Once the grinding has been done, the next stage is cleaning and polishing.
The floor is thoroughly washed with detergents, steel wools and plenty of water to remove all the dust and dirt that may have remained during grinding.
If there are stains of any kind on the floor, this are removed with HCL acid.
Once the floor is clean and completely dry, a floor polish is applied .
Various types of floor polish are available and should be applied as per the manufacturers advice.
This Notes are prepared by: