Types of concrete surface finishes and how to do it
Top's of slabs , pavements, canal linings, and floors are unformed surfaces i.e. the finish is obtained by working the surface of the concrete before final set to provide the type of surface required.
Unformed surfaces are finished by one or more of the operations of screeding , floating , troweling and brooming
Screeding
Screeding is the process of striking off the surplus concrete immediately after compaction to bring the top surface to its proper contour and level.
This type of finish is suitable for surface to be backfilled, construction joints and rough exposed slabs. In most cases
screeding is followed by either floating or trowelling or both.
Screeding is done by moving a straight edge or a template back and forth over the wet concrete surface and advancing it a short distance with each movement.
There should be surplus of concrete against the front face of the template as the concrete will then be forced into the lower areas as the template passes over.
Floating
Floating is the process of bringing to true line and level the concrete , which had just been screeded, by working it with a wooden float.
While , “floating” , take care not to over work the concrete. This will bring an excess of water and mortar to the surface. If this happens, the excess water should be allowed to evaporate or removed by soaking with a cloth.
After the surface moisture film or ‘shine’ has disappeared, a second floating may be done if a coarse-textured finish is desired.
Floated finish is usually specified for outdoor concrete such as tops of bridge piers, canals and reservoirs.
Trowelling
Trowelling is done where smooth and dense finish is required. As the name implies, this is done using a steel trowel.
Before trowelling is done, the water brought to the surface by floating should be allowed to evaporate.
If excess water is found on the surface , it should be removed by soaking the water with cloth or jute bag.
Trowelling should be delayed as long as possible at least till the concrete has hardened sufficiently, to prevent fine material from being worked to the surface. So, during early finishing operations , the surface should be worked as little as possible.
Dry cement or a dry mixture of cement and sand of the same proportion as in concrete may be sprinkled over the surface of the concrete in floor finishing and pavement construction so as to improve the quality of finished surface. But, then, care should be taken to see that the mixture is floated well into the surface.
However, avoid sprinkling of dry cement on wet spots to take up excess moisture since this may lead to surface cracking. As far as possible , wet spots should be avoided by adjustments in the grading proportions and slump of concrete.
The final trowelling should be delayed till the surface has hardened such that the surface can no longer be dented with a finger.
During final finishing , till the (steel) trowel at a slight angle and exert heavy pressure to compact the paste and form a dense, hard surface.
If cracks are formed when the concrete is still sufficiently plastic, rework the surface to close the cracks.
Trowelling should leave the surface smooth, even and free of trowel marks and ripples.
Protect the freshly finished surface from rain by covering with tarpaulin.
Provide sufficient slope for the drainage for surfaces which would be exposed to weather.
This type of finish is suitable for all inside floors where further floor finishes are not specified, roof slabs, sidewalks and pools.
Brooming
Brooming is done using a steel wire broom or ordinary broom stick, when a scoured surface is desired. A scour surface is provided as a key when other finishes like tiles, mosaic or marble are desired over the concrete surface.
Brooming is done after floating and when the concrete is hard enough to retain the scouring.
Top's of slabs , pavements, canal linings, and floors are unformed surfaces i.e. the finish is obtained by working the surface of the concrete before final set to provide the type of surface required.
Unformed surfaces are finished by one or more of the operations of screeding , floating , troweling and brooming
Screeding
Screeding is the process of striking off the surplus concrete immediately after compaction to bring the top surface to its proper contour and level.
This type of finish is suitable for surface to be backfilled, construction joints and rough exposed slabs. In most cases
screeding is followed by either floating or trowelling or both.
Screeding is done by moving a straight edge or a template back and forth over the wet concrete surface and advancing it a short distance with each movement.
There should be surplus of concrete against the front face of the template as the concrete will then be forced into the lower areas as the template passes over.
Floating
Floating is the process of bringing to true line and level the concrete , which had just been screeded, by working it with a wooden float.
While , “floating” , take care not to over work the concrete. This will bring an excess of water and mortar to the surface. If this happens, the excess water should be allowed to evaporate or removed by soaking with a cloth.
After the surface moisture film or ‘shine’ has disappeared, a second floating may be done if a coarse-textured finish is desired.
Floated finish is usually specified for outdoor concrete such as tops of bridge piers, canals and reservoirs.
Trowelling
Trowelling is done where smooth and dense finish is required. As the name implies, this is done using a steel trowel.
Before trowelling is done, the water brought to the surface by floating should be allowed to evaporate.
If excess water is found on the surface , it should be removed by soaking the water with cloth or jute bag.
Trowelling should be delayed as long as possible at least till the concrete has hardened sufficiently, to prevent fine material from being worked to the surface. So, during early finishing operations , the surface should be worked as little as possible.
Dry cement or a dry mixture of cement and sand of the same proportion as in concrete may be sprinkled over the surface of the concrete in floor finishing and pavement construction so as to improve the quality of finished surface. But, then, care should be taken to see that the mixture is floated well into the surface.
However, avoid sprinkling of dry cement on wet spots to take up excess moisture since this may lead to surface cracking. As far as possible , wet spots should be avoided by adjustments in the grading proportions and slump of concrete.
The final trowelling should be delayed till the surface has hardened such that the surface can no longer be dented with a finger.
During final finishing , till the (steel) trowel at a slight angle and exert heavy pressure to compact the paste and form a dense, hard surface.
If cracks are formed when the concrete is still sufficiently plastic, rework the surface to close the cracks.
Trowelling should leave the surface smooth, even and free of trowel marks and ripples.
Protect the freshly finished surface from rain by covering with tarpaulin.
Provide sufficient slope for the drainage for surfaces which would be exposed to weather.
This type of finish is suitable for all inside floors where further floor finishes are not specified, roof slabs, sidewalks and pools.
Brooming
Brooming is done using a steel wire broom or ordinary broom stick, when a scoured surface is desired. A scour surface is provided as a key when other finishes like tiles, mosaic or marble are desired over the concrete surface.
Brooming is done after floating and when the concrete is hard enough to retain the scouring.
