Wednesday, 29 June 2016

How to prepare the work area before plastering

For a good bond, the prepared surface should be rough, hard and clean. We follow these steps when preparing the work area for plastering:
Remove all dust, dirt and oily substance from the walls by high-pressure hosing with water, vacuum cleaning and blowing with oil-free compressed air.
Remove all protrusions like metal studs, nails or rivets.
Check that the substrate is plane (flat and even) and vertical. There should be no areas that protrude or are depressed.
If necessary, roughen the substrate to allow the plaster to bond properly with it. We will use one of the following methods to do this:
  • Wire brushing
  • Hacking/chopping
  • Abrasive grit blasting
  • Application of a splatter-dash layer
  • Application of bonding liquids
  • Application of mechanical supports
Ensuring that the wall is strong enough as plaster will break away from the brittle substrate.
Testing the area for water absorbency. If it is too dry it will absorb the moisture from the plaster. The plaster will then dry out too quickly and will not bond properly with the substrate and will flake off.
On the day before plastering, wet the area well.
Clear the surrounding area of all materials and tools that you do not need for the job. This is to ensure that the area is safe and suitable for the work.

Tuesday, 21 June 2016

When to start plastering your walls

Once the masonry walls have been built they need to harden before you can start plastering. You should wait 28 days from the completion of the wall until you can plaster it. The cement used in plaster or mortar needs time to hydrate before it reaches its full strength and hardness.
Adding water to cement to form a water-cement paste starts a chemical reaction that makes the paste into a bonding agent. This hydration produces a stone-like substance or the hardened cement paste as we all know. The quality of hydration determines the strength of the bond in masonry and the lower permeability risks of the wall.
This hydration process is also called curing during which the mortar in the masonry wall becomes hard or solid by crystallization.
When the plaster or masonry surface drys out excessively, the structure may be under undue stress ,which the still-hydrating interior cannot withstand. This will eventually course cracks in the plaster.