Category: Painting Tips

A white, salt-like substance on the paint surface.  Frosting can occur on any paint color, but it is less noticeable on white paint or lighter tints. On masonry, it can be mistaken for efflorescence (see Efflorescence and Mottling).

Possible Causes:                                                                                              

• Forms mostly in protected areas (such as under eaves and on porch ceilings) that do not receive the cleansing action of rain, dew and other moisture.
• Use of dark-colored paints that have been formulated with calcium carbonate extender.
• Application of a dark-colored paint over a paint or primer containing calcium carbonate extender.

Solution:

• Frosting can be a stubborn problem. It often cannot be washed off readily. Moreover, the condition can recur even as a bleed-through when a new top coat is applied. In extreme cases, it can interfere with adhesion.
• The best remedy is to remove the frosting by wire brushing masonry or sanding wood surfaces; rinse, then apply an Rainbow Paints alkyd-based primer before applying a coat of Rainbow exterior paint.

Normally this is caused due to insufficient cement being mixed into the plaster. It can also been caused by too much moisture in the substrate that has not been allowed to escape.

   Solution:

• Ensure that the surface is dry.
• Brush the friable plastered areas with a soft bristle broom, to remove the bulk of the loose cement plaster.
• Apply two coats of Prominent Surface Restorer, the first coat diluted 15% with turps, allow to dry for 8 hours and apply the second coat undiluted,
• Allow drying for 24 hours.
• This system must not be used on floors. The topping will have to be redone.
• Apply the selected Rainbow Paints topcoat.

The most widespread cause of flaking is moisture, either in the surface or deposited during painting. If moisture is in the under-surface at the time of painting, heat will draw it out and the paint will blister or tend to crack or flake. Alternatively, moisture may have been introduced at a later stage through cracks or breaks in the paint film.

Painting wet or damp surfaces will also promote flaking because the adhesion of the initial coat is impaired by its inability to penetrate the moisture-laden surface.

Condensation on the surface may also leave a film of moisture that will impair adhesion. Painting should not be done under wet or frosty conditions.

Other reasons for flaking, which particularly applies to PVA’s are:

• • Powdering of severely chalking old paint or undercoat. This will cause poor adhesion between coats.
  • Likewise an old paint film that is still glossy provides poor adhesion for a subsequent coat of PVA finish.

Old paint that has deteriorated is never a satisfactory foundation for new paint. Whenever the old paint is suspect, it should be removed.

Another cause of poor adhesion is failure to clean off dirt, grease or salt and form release agents from the surface.

Flaking may be due to poor preparation or to the accumulation of many other coats of paint, some

of which may have been applied many years previously. The use of under-bound or unsuitable

primers can also give rise to flaking.

Substrate: Masonry, gypsum plaster, masonite/hardboard and woodwork

Solution:  Remove all the coating which is peeling; ensure that this is done to the point where a clean and sound surface is exposed.

• When exposed to raw substrate:
  • • Clean surface to remove all foreign debris.
    • Prime with Rainbow fresh plaster primer or Rainbow Wood Primer depending on the substrate, allow drying for 24 hours.

• • • Apply 2 coats of the selected Rainbow Paints topcoat.

• When is exposed to a sound coating:
  • • Abrade the surface with a GP Liquid Cleaner Solution and a Scotch rite pad, rinse off with clean water and allow 24 hours drying.

• • • Do a cross cut masking tape test to ensure good adhesion of the previous coating.
    • Apply 2 coats of the correct Rainbow Paints topcoat