Features of problem
It is when using your hand to rub the painted wall into chalk as fine powder which may be white or the same colour as the paint film. It often occurs with exterior paint exposed to outdoor weather condition or walls that have been used for a long time in high humidity. It is often found with fading problems.
Causes
The chalking surface problem can be found both inside and outside. However, it is often found with exterior paint due to the harsh weather condition. There are several reasons for the occurrence as follows:
1. Caused by the use of low-quality paint with less glue content. Over time, the exterior paint will be destroyed by sunlight causing the paint glue to deteriorate, cannot cover the paint powder and other elements of the paint turning into chalk-like dust.
2. Caused by not painting the primer or using the wrong type of paint, such as bringing paint for interior to paint outside which indoor paint is not resistant to weather condition.
3. Caused by painting the cement surface with high humidity. There is water seeping into the wall after painting. The water will dissolve the alkali in the cement. Alkali will react with the paint film causing the glue to deteriorate and make the colour fade and can deteriorate into chalk-like dust.
How to solve
1. All dust must be removed first using a plastic brush to clean or using Water Jet to spray the wall to be free of dirt, stains, grease and other foreign matters. Then, allow the wall to dry completely.
2. The surface must not have cracks. If any, cracks must be repaired with quality material prior to coating. Where cracks are less than 2 mm in size, cracks are repaired with Nippon Paint Vinilex Wall Putty. For cracks larger than 2 mm, fill with Terracryl.
3. For the areas with moss and fungi, scrub with Nippon Paint Vinilex Biowash fungicide and apply Nippon Paint Vinilex Biowash fungicide. Leave it overnight. The surface before painting must be clean and completely dry. If following Nippon Paint standards, the moisture content must not be more than 6% by Kett model HI-520 or not more than 14% by Protimeter Mini and not more than pH 8.
4. Apply 1 coat of old plaster primer (recommended paint system for exterior: 1 coat of Old Cement Primer, Nippon Paint Excel Primer, recommended paint system for interior: 1 coat of Nippon Paint Water-Based Primer Aqua Sealer) and 2 coats of Topcoat (Recommended colour system for exterior: 2 coats of Nippon Paint Weatherbond, recommended paint system for interior: 2 coats of Nippon Paint Aircare).
How to prevent
Paint work according to the correct steps must pay attention to the surface preparation process. The surface before painting must be clean free from dust, dirt, grease and other foreign matter and completely dry without cracks to prevent water and moisture from seeping into the wall and the cement wall should be allowed to fully curing.
The high-quality paint which is more resistant to weather conditions should be chosen. For heavily dusty surfaces, the clear primer system should be chosen to use with good infiltration, enhanced adhesion and strength to the wall before painting the next layer.
Oil-based primer: 1-2 coats of Nippon Paint Excel Primer.
Water-based primer: 1-2 coats of Nippon Paint Aqua Sealer
