Plaster non-structural cracks

Cementitious plasters are applied internally such as living rooms, bathrooms, kitchens, etc... And externally where they might be exposed to different environment conditions: sun light, wind…

Sodamco Weber offers a wide range of cementitious plaster that can be applied internally and externally and are suitable for different environment  conditions depending on the available substrate.

Common issues and queries you can face

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1-Reasons of plaster cracking or De-bonding

Many factors might affect the performance of an applied plaster.

Cracks in the plaster may result due to different reasons:

  • Evaporation if the wall is not protected from sun and wind which can cause map cracking or dry shrinkage cracks.
  • Suction into the walls if the blocks are absorbent and they have not been dampened which might cause drying shrinkage cracks.
  • Bad or badly applied rush coat
  • Bad plaster workmanship: high thicknesses, no curing...
  • Insufficient curing of rush coat or plaster which can cause de-bonding.
  • Bad preparation: leftover of dust, or loose particles on substrate
  • Excessive water in the plaster
  • Immature finishing

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2-Reasons of plaster cracking or De-bonding

Non-Structural cracks may occur in the following directions:

  • Crazing cracks: crazing is a network of fine cracks, usually in a hexagonal pattern. They are usually due to over-troweling a rich mix render.
  • Map crazing: is similar to crazing except that it is usually deeper (sometimes going through the plaster) and the hexagons of the pattern may measure up to 200 mm across.
  • Drying shrinkage cracks: are ther result of moisture loss after the plaster has hardened.
  • When water is not enough in the mix, then plaster cracks will also occur.

Non-structural cracks repair

Solution

 

    1. Non-structural cracks repair: crack without de-bonding

      In case of non-stuctural cracks, the method of repair depends on the assessment of the defect and the cause of its occurance:

      Plaster cracks without de-bonding:

      • Hair cracks without de-bonding are usually best left alone. If necessary they are repaired with weberep 360 FFR
      • Large cracks without de-bonding are repaired with weberep 350 NSG after the opening of the cracks and thoroughly cleaning and washing them.
    2. Plaster Non-structual cracks repair: Masonry block

      Plaster de-bonding on normal block or light weight blocks:

      De-bonded plaster is repaired after removal of the entire de-bonded surface and make the necessary substrate preparation for the new plaster as per below steps:

      1.     Substrate preparation

      • All bases should be sufficiently rigid, clean of any surface contamination that may prevent good suction.
      • Dampen the substrate before few hours from the plaster application
      • Fill the empty gaps in the joints of the block wall with block mortar weberbloc fix or weberbloc fix LW 

      Plaster application

      Depending on the type of substrate, plaster should be recommended:

      For normal and hollow blocks: use weberpremix hand or weberpremix SP-11 or weberpremix SP-1

      For light weight block: use weberpremix SP-33 or weberpremix SP3-FL

      • Spray the plaster on the dampened and prepared surface or apply it manually with a plastering trowel at a thickness between 10 and 20mm in one layer. For higher thicknesses kindly consult the technical department.
      • Follow the application method statement instructions
      • Finish the surface with a wooden or steel float as required
      • Let the product set properly on the surface before any curing
      • Cure for 3 days. 3 to 4 times a day
      • Protect the applied plaster from direct sun light and wind

       

      For more details kindly consult the product technical data sheet

    3. Non-structural cracks repair: Concrete substrate

      Plaster de-bonding on concrete with or without cracks:

      De-bonded plaster on concrete substrate is repaired after removal of the entire de-bonded surface and creating a grip key with well-adhered plaster.

      While removing the plaster, examine the rush coat for better repair:

      • if the rush coat is rough and strong, apply plaster to the rush coated surface
      • If the rush coat is rough and weak, remove it and apply a new rush coat
      • If the rush coat is smooth and strong, apply another layer of rush coat
      • If the rush coat is smooth and soft, remove and apply a new one according to the technical data sheet

      1.     Rush coat application:

      According to the type of concrete, the suitable rush coat is recommended

      For normal concrete: weberpremix key coat or weberpremix SRC-2

      For very dense concrete: weberpremix SRC-S is recommended.

      • Weak and failed rush coat should be removed properly. A new application with the convenient rush coat shall be executed on the prepared surface.
      • Substrate must be sound and clean. If cracks and defects are available, the substrate must be repaired before applying rush coat
      • In case of significant concrete defects, it is recommended to clean the defected area and fix wire/mesh after repairing with weberep 331 TX
      • If joints between concrete substrate and blocks are available, it is recommended to install a wire/ fiber mesh, in addition around openings and where needed.
      • Substrate must be wet before application. Free water on the substrate should be allowed to dry before any application. (For dense concrete, the substrate should left without curing for a minimum 24 hours before rush coat application)
      • Recommended rush coat (the proper rush coat must be chosen according to substrate) is re-applied on smooth surfaces and cured for 3 days, and 3 times a day.
      •  Make sure that the applied rush coat has a rough finish to secure the bonding of the plaster
      • Allow to harden depending on site conditions.
      • For more details, consult the technical department

            2.  Plaster application:

      • The convenient plaster should be used according to the type of substrate and the compatibility with the applied rush coat
      • In case of dense concrete, it is recommended that the rush coat to be left without curing before 24 hours from the plaster application.
      • Mix the plaster with a clean and cool water
      • Apply and press firmly the plaster over the rush coat. Each plaster coat should be applied between 10 to 20 mm. If more thicknesses are required, kindly consult the technical department.
      • Apply the plaster according to the application method statement and cure for 3 days and 3 to 4 times a day.
      • Protect the plaster from direct sun light and wind.

      For more details kindly consult the product technical data sheet