Rendering on the exterior walls of building is generally used as an alternative to brick or concrete blocks.

Note. While dry render is paintable care should be taken as to the quality and nature of the work.

If in doubt regarding the condition and product suitability of a coatings to applied advice from the manufacture should be obtained.

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Flaking 

Cause

The illustration is the result of the  finishing coat of plaster being over polished leaving little or no porosity for the waterbased coating to key onto. It can be seen that there is no latent plaster adhering to the reverse side of the paint flake.

This can also occur when the first coat of a heavy pigmented paint  is applied directly onto the surface without thinning to act as a sealer coat.

Remedy

Scrape back all loose material to a firm edge – dampen the exposed plaster with clean water and apply a fine plaster filler to the surrounding area. When dry,  lightly  rub down, dust off and apply a sealer coat of the waterbased paint followed by the required finishing coats.

Note : for face filling,  fine ready mixed plaster filler is suitable.

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Saponification

Cause

A paint defect as a result of an oil based paint coming in contact with an alkali surface which had a high moisture content at the time of painting and not completely sealed with an alkali resistant primer.

Solution

Remove the soft/sticky film, wash down with white spirit, and allow to dry then apply an alkali resistant primer followed by overcoating with an oil based system.

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Cause

Efflorescence can originate from any cementitious building products such as brick, concrete blocks, sand: cement rendering and plaster.  As moisture or moisture vapour passes through the materials to the surface it will bring any soluble salt deposits within the substrate  to the surface. Initially the deposits appear fluffy and can be brushed off.  If not removed this will crystalize, build up and damage the surface finish.   The salts can remain dormant for many years and efflorescence can appear if the building substrate is affected by water ingress due to water leaks, flooding  or a faulty damp proof  lining.

Remedy

Decorating should be left until salts cease to appear by constant dry brushing. If painting is necessary then it is best to apply water based coatings of a high pigment content which allow moisture vapour to pass through the paint film more readily than others, allowing further salts to come to the surface without causing any major problems.

Some suppliers recommend treating the area with an alkali resisting primer sealer and while this will reduce any moisture vapour coming to the surface  it is possible that any underlying salts could re-appear from the unsealed surrounding areas.

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Crows footing

Cause

Problems of this type occur when coatings, particularly water based paints are applied onto a surface which has a higher sheen level resulting in the adhesion quality of the newly applied paint being low, for example a matt emulsion being applied over a vinyl silk or an oil based coating.

It can also occur when water based paints are applied to new plaster without being thinned as a sealer coat.  This can result in the VOC’s (Volatile Organic Compound) being quickly absorbed into the surface resulting in poor adhesion of the coating.  Consequently, as the newly applied paint hardens the tensile strength of the newly applied paint film begins to shrink and cracks in the paint film appear.

Solution

After rubbing down and face filling with a fine plaster filler, applying a paint coating of a higher sheen level will in most cases overcome the problem.

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Cratering

Cause

Problems of this nature can be caused by rain falling onto the semi dried coating or  aeration/frothing of the paint during application usually by roller and not flowing out properly. Also referred to as pin holes

Solution

Once the coating is completely through dry, flatting down should take place using carborundum (wet or dry) abrasive paper preferably wet – using water/soap  or white spirit as a lubricant. Recoat with chosen paint finish.

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Cause

This colour variation is  highlighted where there is a difference in thermal conductivity i.e. the joists and the voids between. Or on internal walls of a timber frame construction highlighting the timber or steel upright studs.

Pattern staining has also occurred where cold water pipes have been chased into the wall before plastering.

Remedy

A paint coating can only improve the aesthetic appearance. To solve the problem the voids between the joists need to be filled with glass fibre or some other type of insulating material .

The illustration showing the pipework can only be rectified by re directing of lagging the pipe. 

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Cause

This defect mirrors that of an orange peel and is generally due to incorrect paint application by spray or roller.

Remedy

The dry paint film should be flatted down back to a  smooth and level surface.  Wet or dry carborundum paper, preferably wet, is generally used.

The post Orange Peel appeared first on Paint Check Plus.

Cause

This can occur not only in paint which has been stored for a long time but also in relatively new material, i.e. hard or soft settlement.

Remedy

Thoroughly stir the product and ensure the settled pigment/solids are fully dispersed into the material. Although stirring with a palette knife (broad knife) will generally suffice, mechanical mixing or high speed paint shakers. may be preferred.

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Cause

This defect is caused by a paint coating being applied to a surface which has been contaminated with oil, grease, or polish causing the wet film to creep back exposing the underlying surface. This type of problem can also occur when coatings are applied to surfaces which have previously been treated with a silicone based product, contaminated with body fats including hair sprays etc. In extreme cases where the coating flows back from a large area of the surface, the term crawling is sometime used.

Solution

Once the coating has completely dried and the general adhesion is satisfactory, thoroughly flat down to a smooth surface

using wet or dry carborundum paper wet. After rinsing and ensuring the surface is free from all contaminates re-paint as required.

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