HOW TO REMOVE MILDEW:
To remove mildew from a painted surface, wash the surface with the following mixture: 2/3 cup trisodium phosphate (t.s.p), 1/3 cup detergent, 1 quart chlorine bleach and 3 quarts of warm water. Rinse the surface well with clean water after washing. Please wear appropriate safety equipment (rubber gloves and eye protection). Also protect shrubbery and plants with plastic sheeting.
The maximum moisture content for any surface that is to be painted is 12-14%. Painting a surface that contains a higher level of moisture can lead to peeling problems. The only accurate way of determining moisture content is with an electronic moisture meter.
TOO MANY COATS:
There is a limit of the number of coats of paint that a surface can support. As the paint thickness builds up over time and the coatings get older, they lose their flexibility. As the substrate (surface) expands and contracts because of temperature fluctuations or moisture, the paint film is no longer flexible enough to move with the surface, cracking or flaking of the coating usually results. It is not uncommon to put a coat of paint on a surface that appears sound only to have many layers of paint peel away. At this point, the surface must be stripped.
100% silicone caulking is not compatible with paint. Painting over silicone caulking will cause the paint to separate or crack, leaving the film full of craters. Once a painted surface has been contaminated with silicone, it is very difficult to get the surface clean enough to re-coat in the future. Use only latex caulking if the caulking is going to be painted over.
Wood decks are commonly painted or stained after they have been constructed. After construction, the sides and bottom of the wood cannot be coated properly. Many failures on decks are caused by moisture entering the wood through the sides and bottom. Moisture seldom leaves these surfaces the way it entered. The sun shines on the coated surface and the moisture tries to come out through the paint or stain which causes peeling. To improve the resistance to moisture, the coating should be applied to all surfaces prior to construction.
PAINTING OVER VARNISH:
Adhesion of most paints to varnish is poor. Although de-glossing by sanding with #120 grit sandpaper can help adhesion, paints applied over varnish usually chip easily. For best results, strip off the varnish with paint remover and then prime with an alkyd primer before top coating with alkyd or latex.
Because water doesn’t freeze until the temperature drops to 32F (0C), some painters feel that latex paints can be applied down to that temperature. This is not true, because the minimum temperature required for latex paint to dry properly is 50F (10C). Latex paints applied to surfaces below 50F will form films that are weak and will result in early failure of exterior products and poor washability of interior products.
Chalking is part of the aging process of paint. The binder (resin) breaks down with exposure to the sun, leaving unbound pigment (chalk) on the surface. Repainting should be done before the chalking becomes excessive. In the early stages of surface chalking (in most cases, five years’ exposure), the film integrity is still good and all that is usually necessary before repainting, is to wash off the surface dirt and chalk.
Dark colours can cause wood surfaces to become very hot. In the extreme, blacks and dark browns can cause cracking and/or cupping of wood in indirect exposure to summer sun. Dark colours can also cause natural resin or sap in wood to migrate or be drawn out, which can in turn cause paint to peel.
PAINTING IN OLD BUILDINGS:
In older buildings where the insulation is poor, shadows appear at stud locations on the inside of exterior walls. The difference in temperatures causes dirt to collect at these areas. This is not related to the type of paint used and must be rectified by repainting. These shadows will not bleed through the next coat of paint, but will likely reappear if the lack of insulating is not rectified.
LATEX OR ALKYD?:
To establish if paint on a surface is an alkyd or latex, rub the surface with a cloth wet with xylon (or nail polish remover). Latex paint has very poor solvent resistance and will come off on a cloth. Alkyd paint will not be disturbed by either solvent.
Most paint manufacturers produce their colour chips in a low sheen and often the architect or owner is surprised when they see the colour in an eggshell or semi-gloss finish because it looks different. To see what a colour will look like in an eggshell or semi-gloss, wet the colour chip with water.
LIGHT REFLECTANCE VALUE:
The light reflectance value of a colour is a function of colour only. The gloss or sheen of a product does not influence the light reflectance.