The traditional use of external rendering is two-fold, namely to weatherproof the property facade and to provide pleasing finishes of various textures. Plastering is a skilled trade and a trained craftsman should be employed as often as possible the reason being there are several skills that can only known to experienced tradesmen. Although, if skilled help is not available it is necessary to know the fundamental principles involved, that is how to ensure the preparation is correct, choose the mix, proportion the materials and apply the plaster.
The proportions of cement,lime and sand to use depends upon the purpose of the plaster and the composition of the building surface to which it is to be applied. A pure lime plaster is comparatively soft and is slow setting, so it is usually gauged with cement to increase its strength and resistance and to shorten the period of hardening.
the strength improves and the setting time reduces as the amount of portland rises. A 100% portland render with no lime, the mix is the optimum and the curing time the shortest. But, as the volume of portland is raised the render starts to thicken and harder to plaster. The amount of sand should not be more than three times the total volume of lime and portland. A harder render must not be trowelled on a weak wall neither should a hard plaster coat be applied to a less strong base coat.
When external rendering on such as hard clay bricks of low porosity, the perfect proportions to use are 1 part cement, 1 part hydrated lime and 6 parts sand by volume. In exposed house walls subject to driving rains the proportion of lime may be decreased and the cement increased to enable a heavier mixture and less permeable but ensure the mix is still workable.
On masonry house walls of low strength and high porosity such as lesser quality breeze concrete blocks the external stucco should not be stronger than a 1:1:6 mix as a strong cement mix with little or no lime should not be used as it will crack.
If internal plastering the optimum combination is 1 cement, 1 pure lime and 6 sand; or 1 cement, 2 pure lime and 9 sand; or a pure lime mix only. Bear in mind that the more cement you use will increases the hardness and also decreases the the length of setting. For water structures such as fishponds only 100% cement plasters should be mixed to guarantee complete water proofing.
The conditions when plastering and screeding can have considerable on the final outcome. External rendering should be begun on the West facing side of the structure to keep it protected from the sun's rays as long as is practical. Do not consider rendering in frosty weather. In freezing conditions render sets slowly and a longer period of time between coats should be allowed. In unusually humid conditions the successive coats need to kept wet and shielded from drying out for at least two days after application. In addition to keeping direct sunshine off the wall a moderate draught from an open door will prevent the stucco from drying too quickly.
The proportions of cement,lime and sand to use depends upon the purpose of the plaster and the composition of the building surface to which it is to be applied. A pure lime plaster is comparatively soft and is slow setting, so it is usually gauged with cement to increase its strength and resistance and to shorten the period of hardening.
the strength improves and the setting time reduces as the amount of portland rises. A 100% portland render with no lime, the mix is the optimum and the curing time the shortest. But, as the volume of portland is raised the render starts to thicken and harder to plaster. The amount of sand should not be more than three times the total volume of lime and portland. A harder render must not be trowelled on a weak wall neither should a hard plaster coat be applied to a less strong base coat.
When external rendering on such as hard clay bricks of low porosity, the perfect proportions to use are 1 part cement, 1 part hydrated lime and 6 parts sand by volume. In exposed house walls subject to driving rains the proportion of lime may be decreased and the cement increased to enable a heavier mixture and less permeable but ensure the mix is still workable.
On masonry house walls of low strength and high porosity such as lesser quality breeze concrete blocks the external stucco should not be stronger than a 1:1:6 mix as a strong cement mix with little or no lime should not be used as it will crack.
If internal plastering the optimum combination is 1 cement, 1 pure lime and 6 sand; or 1 cement, 2 pure lime and 9 sand; or a pure lime mix only. Bear in mind that the more cement you use will increases the hardness and also decreases the the length of setting. For water structures such as fishponds only 100% cement plasters should be mixed to guarantee complete water proofing.
The conditions when plastering and screeding can have considerable on the final outcome. External rendering should be begun on the West facing side of the structure to keep it protected from the sun's rays as long as is practical. Do not consider rendering in frosty weather. In freezing conditions render sets slowly and a longer period of time between coats should be allowed. In unusually humid conditions the successive coats need to kept wet and shielded from drying out for at least two days after application. In addition to keeping direct sunshine off the wall a moderate draught from an open door will prevent the stucco from drying too quickly.
About the Author:
Joe Smith has a website and Blog featuring tips and advice about
external rendering and render painting. It explains what is best practice for rendering
walls
external rendering and render painting. It explains what is best practice for rendering
walls
1 comments:
Hey Joe,
Very interesting topic & writing too. Thanks for sharing.
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