‘Perfection’ is the word. ‘Smoothness’ is the feeling. ‘Mortar’ is the item. The wall is the receiver and we are the admirers. Everybody wants a perfectly smooth wall for their interiors but we sometimes get more than what we bargained for. Rough, uneven and not properly detailed wall plastering or rendering are some end results that stares us in the face because we somehow engaged the wrong hands. But that’s not the end of the road.
Rendering (or plastering) action on wall usually precede painting. It is the process of applying mortar made from a mix of cement, fine aggregates (or smooth sand) or Plaster of Paris and water to cover the surfaces of block, brick or concrete walls. This process if not properly handled can lead to a bad output.
For instance there is often the problem of unevenness in the texture of the finish, flaking-off, breaking edges, cracking, etc. which hitherto affect overall aesthetics and durability. But not all cracks on walls are as a result of poor mortar or rendering work; sometimes it is a consequence of structural defects in the building. Sometimes when this happens, there is a temptation to simply cover it with paints or other finishing material; but that really doesn’t work. The effect of a bad plastering will still resurface with time. Talking about getting the job done properly; it is important that the mason team understands the mix ratio for mortar in order to get the right output. They must also know how to use the trowel (or application device) and smoothing devices well. A cement-sand mix ratio of 1:6 -12mm thick is generally acceptable for walls; corresponding to about 3 wheelbarrows of smooth sand to 1 bag of cement. 12mm specified here represents the thickness of the layer on the wall after application.
The nature of sand is also important. The suitable grade of smooth sand for wall rendering is one that contains a good proportion of clay which gives it a tacky or gummy feel. This does not imply the use of pure laterite. The use of sharp sand for rendering should be avoided because overtime pores are generated within the layer that affects the surface texture of the wall. The moisture content in your mortar should be adequate; just enough to make the mix workable. There are special cements used to achieve quality rendering; they were produced with the required functional requirements of good mortar/plaster in mind. It is good to make use of them rather than the general purpose cement so as to obtain great results. It is wrong to use mortar made for setting blocks or bricks to also render your walls because the composition are naturally different. Naturally if you make a bad mortar, you can only expect a bad rendering.
Once there is a noticeable defect on a rendered wall, even if it has been painted; it is better to simply chip-off, prepare the surface and reapply properly so that it cures without cracks. Although it may cost more to chip-off old rendered layers before re-applying mortar or P.O.P, the durability potential often override the cost burden, hence making it a cost-effective approach to the alternatives. The use of filling materials to close-up voids in walls to create even texture without chipping off in walls is a welcome development but it is not often the best option; especially if the defect is on a large scale. If you must use filling materials some Experts advice that you drill tiny holes into sections of the wall (using a simple drilling device) to allow for a good grip to the wall; the hole is such as extends beyond the plastering layer well into the wall fabric. Special gums are sometimes used to fill the hole to enhance firmer grip; thereby improving stability in the face of shocks.