How to paint Masonry 

1. Potential problems with masonry surfaces

Masonry surfaces include bricks and cement plaster. In some instances gypsum-based plasters or skim coatings are also used. These surfaces provide specific challenges for the painter.

  1. Most masonry surfaces are weak, friable porous and sandy.
  2. Cement plasters are seldom aged long enough to allow the alkaline lime content to neutralise with carbon dioxide from the air. The surface is alkaline as a consequence.
  3. Moisture and damp are often present during and after application of paint. This can prevent good film formation as well as cause blistering in the dry paint. It is good practice to locate and remove all sources of water ingress into a structure before painting. A reputable waterproofing contractor should be capable of doing this. Fired Earth has a comprehensive range of waterproofing products. Contact Fired Earth for advice on 0860 builders (28453377) or contact us through our website by using our contact page.
  4. Efflorescence can be a problem on bricks. This is due to water carrying soluble salts from within the brick to the surface. The salts are due to poor or inadequate firing of the bricks resulting in the formation of soluble salts within the brick (usually sulphates from sulphur contamination).
  5. Fading and discoloration sometimes occurs when painting cement plaster as well as gypsum plaster. This is normally due to lime or alkali attack on the finishing coat in the case of cement plaster. The solution is to use Fired Earth Plaster Primer an alkali-resistant plaster primer as a barrier film between the plaster and the topcoat. On gypsum, a white patch often develops if the plaster is painted with a waterborne product before the gypsum has been adequately cured. The white effect is due to soluble sulphate being extracted into the wet paint. It tends to bleed through subsequent coatings as well. The solution is to ensure the plaster cures overnight before painting and that a sealer such as Fired Earth Bonding Liquid should be applied. This prevents extraction of soluble material into the finishing coating.

2. Standard surface preparation method:

This is the critical part of any painting project: poor preparation is the principal cause of coating failure. Cement plaster should be strong and hard. If it is not, this indicates a poor sand/cement/water mixture. Painting over poor plaster will usually result in flaking, blistering and efflorescence defects – which are not due to the quality of the paint system.

  1. Brush off all loosely bound sand particles
  2. Open out any cracks using a sharp knife
  3. Seal all cracks or surface imperfections using Fired Earth Bonding Liquid. Leave to dry for 2 hours.
  4. Fill cracks or surface imperfections using a quality ready for use acrylic crack & skim filler paste. Leave to dry for minimum of 4 hours or as per manufacturer’s instructions. Sand the surface smooth, wipe down with a slightly damp cloth.
  5. If surface is highly porous or friable, apply Fired Earth Bonding Liquid over the entire surface.

NB:

  1. Always use a penetrating sealer such as Fired Earth Bonding Liquid if the surface of the masonry (especially cement or gypsum plaster) is friable. This will strengthen the surface and reduce the possibility of coating failure.
  2. The use of gypsum-based fillers and skim coatings are generally very weak. These materials have inadequate flexibility and wet strength. Fired Earth recommends the use of a quality ready for use acrylic crack & skim filler paste for this application.
  3. For fibre-cement boards, or lower porosity surfaces, it is recommended that Fired Earth Bonding Liquid be applied.

3. Primer selection

  1. Top coat: Enamel
  2. Primer: Fired Earth Primer Plaster Alkali resistant barrier to protect enamel.
  3. Undercoat: Fired Earth Universal Undercoat aids overall coating integrity.
  4. Top coat: Acrylic (waterborne)
  5. Primer: Fired Earth Plaster Primer Water-resistant barrier to protect acrylic.

4. Finishing coatings

Use the highest quality that you can afford. It is well known that higher quality paints give the best durability and this results in the lowest cost in the long term. Fired Earth has a full range of finishing coats ranging from matt to medium sheen acrylics as well as enamels. Contact Fired Earth on 0860 builders (28453377)  for further information as well as details of your nearest store.

Fired Earth: GUIDE TO PRIMERS AND UNDERCOATS FOR MASONRY

Surface preparation:

This is the critical part of any painting project: poor preparation is the principal cause of coating failure. Cement plaster should be strong and hard. If it is not, this indicates a poor sand/cement/water mixture. Painting over poor plaster will usually result in flaking, blistering and efflorescence defects – which are not due to the quality of the paint system.

  1. Brush off all loosely bound sand particles
  2. Open out any cracks using a sharp knife
  3. Seal all cracks or surface imperfections using Fired Earth Bonding Liquid. Leave to dry 2 hours.
  4. Fill cracks or surface imperfections using a quality acrylic crack & skim filler paste. Leave to dry for 4h. Sand the surface smooth, wipe off dust the with a slightly damp cloth.
  5. If surface is highly porous or friable, apply Fired Earth Bonding Liquid over the entire surface.

NB:

  1. Always use a penetrating sealer such as Fired Earth Bonding Liquid if the surface of the masonry (especially cement or gypsum plaster) is friable. This will strengthen the surface and reduce the possibility of coating failure.
  2. The use of gypsum-based fillers and skim coatings are NOT recommended by Fired Earth. These materials have inadequate flexibility and wet strength and should not be used. Fired Earth recommends the use of acrylic crack & skim filler paste for this application.
  3. For fibre-cement boards, or lower porosity surfaces, it is recommended that Fired Earth Bonding Liquid.  

Primer selection

1.  Top coat:      Enamel
    Primer:           Fired Earth Plaster Primer alkali resistant barrier to protect enamel system.
    Undercoat:   Fired Earth Universal Undercoat aids overall coating integrity.

2. Top coat:       Acrylic (waterborne)
    Primer:           Fired Earth water-resistant barrier to protect acrylic system.
             
Homestead primer plaster typical coverage rates:

  • Non-stipple effects:  Synthetic / wool roller.
  • Floated Plaster:     (Fired Earth Plaster Primer)    7 m2/l
  • Scratch Plaster:     (Fired Earth Plaster Primer)    4 m2/l
  • Spanish Plaster:    (Fired Earth Plaster Primer)    3 m2/l            

Other important information

  1. NEVER apply paint if rain is forecast, or expected, during the day of application
  2. Apply paint after 8h00 (summer) or 10h00 (winter) to ensure the surface  is not too cold or damp.
  3. It is recommended that the paint is applied before 12h00 to avoid excessive temperatures and to allow the paint to harden sufficiently before any afternoon rain may occur.
  4. Always use the SAME batch number for touch-up work. This reduces colour/sheen variations, which otherwise may be visible on the surface being painted.