Painting Q & A

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Simple Tips & Solutions to answer the most common paint questions!

Q: Generally speaking, when do I need to use a primer?

A: A rule of thumb is to prime a surface that has not been painted before. Be sure to choose a primer recommended for the particular kind of surface you are painting, such as wall board (sheetrock), staining wood (mahogany, cedar, redwood), steel, etc. Most types of primers are available in both latex and oil based formulas. Sound repaint surfaces will benefit from priming as well, resulting in maximum adhesion and uniformity of appearance from the finish coat.,

paintQ: What are the reasons for priming?

A: Using an appropriate primer provides these benefits:

  • Maximum adhesion of the finish coat
  • Blocking of staining material from the surface being painted
  • Uniformity of appearance of finish coat, including gloss or sheen development and hiding

Q: Can we paint over wallpaper?

A: Technically, yes. Strategically, no. You’ll see the seams unless you skim coat with a special compound. And you have to use an oil-based primer to seal the paper. There isn’t a guarantee of a no show-through, and it makes it harder to remove the paper later. If you’re going to do all that work, it’s much better to just remove the paper now with a chemical wallpaper stripper.

Q: When should I use oil-based paint and when latex based?

A: For nearly all coating types, quality latex alternatives are available. Quality latex products offer superior resistance to yellowing, long term resistance to embrittlement, maximum colour retention and resistance to chalking and mildew. Areas where oil-based paint might be chosen over latex would be:

  • For wood varnish where a “warmer” appearance is desired
  • For enamels when the very highest glossiness is wanted
  • For semitransparent stains or wiping stains when lack of lap marks is essential
  • Where the coating is going over a chalky surface
  • When a primer with the very best stain blocking capability is required

Q: When would I choose a flat paint or a satin paint?

A: Flat paints are good for a muted, dull finish where dirt is not likely to get onto the paint. (Flat paints can absorb dirt, and be more difficult to clean). This could be for living room or bedroom walls, or a ceiling. Satin paints are better for walls of “high traffic” areas like hallways, playrooms and kitchens. However, a satin finish will show up unevenness of wall area more than will a flat finish.

Q: How can I figure out how much paint to buy?

A: For a smooth surface, most paints will apply at about 350 to 400 square feet per gallon. You need to measure the surface area of the job. Divide the area into rectangular areas and multiply the width times the height to get the area of each rectangle, and then add all the areas together. Divide the total area by 350 to see how many gallons will be needed for each coat. If the surface is rough or porous, the paint will cover at a lower spread rate, such as 175 to 250 square feet per gallon.

Q: What basic safety equipment should I have when painting?

A: In general, these are some of the thing you should have:

  • Goggles to protect the eyes when scraping, sanding and painting
  • Dust mask for scraping and sanding
  • An appropriate respirator to protect breathing when using any solvents indoors, like paint thinner, oil-based paint, primer or satin, paint remover, and brush cleaner, or when spray painting.
  • Chemical resistant gloves when using solvents like paint remover and paint thinner.
  • Leather or cloth gloves for scraping and sanding

**Note: Do not scrape, sand, heat-gun or otherwise attempt to remove paint if there may be lead in it. Please contact Environment Canada.

Q: What do I have to do to paint metal?

A: Remove any loose paint, using a scraper, wire brush or sand paper. Except with galvanized iron (do not scratch off the zinc coating). Use a stiff wire brush to remove all rust (on iron and steel) or white oxide (on aluminum). Then apply a metal primer. Use a quality acrylic latex flat, satin, semi-gloss or gloss paint. Alternatively, a direct-to-metal paint may be used without a primer.

Q: What are some main things to do when painting exterior wood?

A: It is best to thoroughly clean all the surfaces with a pressure cleaner and degreaser before prepping. Exterior bare wood should be primed before painting. Try to prime and paint the wood while it is new and has not weathered; any wood that has weathered more than a few weeks should be thoroughly sanded before being primed.

Q: What are the main things I should take into account when painting masonry, like stucco or brick?

A: In preparing the surface, first look for any “efflorescence”, which is an accumulation of white powder or salt-like material. This is brought to the surface by moisture coming from above or behind the masonry. Seek out and eliminate the source of moisture. Remove the efflorescence along with all loose sand, dirt, flaking paint, etc., by pressure cleaning it and using a strong degreaser or acid. Masonry less than a year old, very porous masonry and masonry with signs of efflorescence should be cleaned and once dry, apply a sealer or primer before painting.

Q: How do I get the best appearance when applying latex semi-gloss or gloss paint to interior trim?

A: Follow these points:

  • Clean and rinse the trim, and dull glossy areas with fine sandpaper
  • Apply a latex, alcohol-based or oil-based stain blocking primer
  • Use a top-of-the-line paint
  • If applying by brush, choose a top quality polyester brush. Pre-dampen the brush before using, and remove all excess water
  • Apply the paint in heavy coats. Do not brush the paint excessively and do not thin the paint unless necessary

Q: Can you paint over an oil-based paint with latex paint? Or use oil-based over latex?

A: Generally speaking, with proper surface preparation, for exterior use, you can apply quality 100% latex acrylic paints over oil-based, but not the reverse. However, if you have many layers of oil-based paint, stick to using oil on oil. For interior use, you can use 100% acrylic latex over the other but avoid using regular latex over oil base paint. Some manufacturers of latex products will recommend an oil base primer when going over oil-based paint. You can also use a super adherent acrylic primer or a new waterborne Alkyd primer.

Q: Can old, weathered aluminum siding be successfully painted?

A: Yes. Take into account these points:

  • The old finish is likely to be very chalky, so clean it thoroughly; power washing is effective for this
  • Apply a top quality exterior acrylic latex flat or satin paint
  • Spray application will provide the smoothest appearance, though brush or roller can be used
  • A flat finish will make dents and bends in the siding less noticeable than a satin finish

Q: What are some things to know about choosing paint rollers?

A: Generally, high quality roller covers are worth the added cost, vs. economy rollers, because they apply the paint more heavily and smoothly, which results in better hiding, appearance and durability. Use natural lamb’s wool and mohair for oil-based paints, primers, stains and varnishes. Use synthetic nap roller covers for water based coatings. Short nap rollers (1/8” nap) are for smooth surfaces like finished paneling, painted doors, etc. Medium length (3/8” nap) are for surfaces like flat paint, bare wood, etc. Long nap rollers (more than 1/2”) are best for rough surfaces like stucco, brick, etc.

Q: What are elastomeric coatings?

Elastomeric wall coatings are designed for exterior masonry surfaces like concrete, stucco and concrete block. They are generally acrylic latex masonry paints designed to be applied in very thick films (about 10 times as thick as regular paints). They are tough and flexible and stretch as cracks underneath open and close, thus bridging the cracks and keeping wind driven rain out while maintaining a nice appearance. These coatings are called EWCs for short. They can be tinted to a light colour. The EWC should be applied after cracks more than 1/16” are caulked with a quality acrylic or siliconized (not SILICONE) caulk. If the stucco is particularly porous, a masonry primer or paintable sealer should be applied first. An application of the EWC is usually about 50 to 60 square feet per gallon, and two coats should be applied.

Q: What is the difference between a paint and a stain?

A: The objective in applying a stain is usually to change the colour of the surface (typically bare wood or concrete) without hiding the texture of the material. Some stains, called semitransparent stains, also let the grain pattern of the wood be seen. With paint, we create a new appearance, that is, the surface takes on the appearance of the paint (which may be flat, satiny or glossy; smooth or textured), and the texture and grain of the surface is obscured. Stains are typically thinner (of lower viscosity) than paints, and the level of prime pigment (that provides colour and hiding) will vary with different types of stains. Interior stains are usually top coated with a clear coating, such as polyurethane varnish. Whereas exterior stains are often left uncoated. In exterior applications, a quality paint job will generally last longer than staining will.

Painting Solutions to Common Problems

Air bubbles under the paint

This usually happens in gloss paint and is caused by applying paint in bright sunlight, on a hard shiny surface or on water-based undercoats. Use a chalky-type undercoat (e.g. Crown) or non-wood surfaces such as MDF (Medium Density Fibreboard).

Bitumen and tar stains keep bleeding paint finishes

Prime with an aluminum primer, and then use a normal undercoat and topcoat.

Brushes: how to keep them soft when in use

Brushes that are being used in oil-based paints can be kept soft by storing in water. Place brushes in a container and fill with water up to the top of the bristles. Overfilling with water can result in water getting into the stock of the brushes and leaking out gradually while you are painting. Brushes can be kept soft for weeks at a time with this method (take care that the water does not evaporate in warm weather). Brushes used in emulsions and other water-based paints can be kept soft for several days by wrapping tightly in plastic bags ensuring that no air reaches the bristles.

Blistering paint

This is caused by moisture pressure when exposed to the sun. Scrape off, sand down and repaint.

Chipping paint

Chipping off paint is caused by the top coat not having a sufficient key. Commonly the result of applying gloss finish directly on top of previously glossed surfaces. To prevent this you must first apply a suitable undercoat or sand down the surface with a fine sandpaper.

Colour is not all the same shade

This is a result of not stirring the paint properly. Paint should be stirred thoroughly before use, especially strong and dark colours.

Cracking paint

This usually happens to old paint which hardens over time and is unable to expand and contract with changing weather conditions. With small cracks, sand down, fill, prime and repaint. With severe cracking, strip back to bare wood, prime and repaint.

Flaking paint

This is the advanced stage of blistering and all paint should be stripped back to bare wood, primed and repainted.

Flashing (uneven sheen or mat areas in gloss coat)

Caused when paint is applied in misty or humid conditions or when condensation is forming. Allow to dry thoroughly and recoat under better conditions.

Flies stuck on newly painted surface

Don’t try and pick the flies out of the wet paint. Leave the paint to dry overnight and the flies can be wiped away with a damp cloth the next day, often without any trace.

Hair/bristles coming out of the brush

If you get a bristle in your paintwork, don’t try to pick it out with your fingers. Turn the brush and gently pick up the bristle with the very edge of the brush. Even very small bits of hair and bristle can be picked up this way.

Metalwork: paint flaking off

This is a common complaint on galvanized metal which has been wrongly painted. Galvanized metal should be primed with a zinc plombate primer.

Mildew

Remove with a weak bleach mixture. Mildew needs moisture to survive so identify and fix moisture problem before re-painting.

Moulting brushes

Poor quality brushes often shed bristles. Over-thinned alkyd paint can also cause moulting.

Nail head stains showing through

Sand nail heads back to bare metal, touch up with a metal primer, fill if necessary and re-paint.

Paint is slow to dry

Emulsions and other water-based paints are normally quick to dry but can be dried even faster when required using a hot-air gun or a hair dryer. Do not hold too close to the painted surface and keep the gun moving in a horizontal figure-8 motion. Oil-based paints can be helped to dry quicker by adding about half a teaspoon of Terebene to each litre of paint. Do NOT try to dry oil-based paints using a hot-air gun.

Peeling paint

This is caused by moisture pressure when exposed to the sun. Scrape off, sand down and repaint. If stripped back to bare wood, prime and repaint.

Resin is bleeding through paint

Resin usually comes from knots in the wood. Prevent this by sealing the knots with a French polish or industrial shellac.

Running paint

Runs are normally caused by applying paint too heavily. Always try to brush out the runs before the paint sets. Leave off with an upward motion of the brush.

Uneven or poor coverage

This is caused by brushing out the paint too much. Apply another coat.

Water stains on ceilings and walls

To stop stains coming through emulsion, treat with a proper sealer such as Stainblock or coat the stain with gloss paint and allow to dry.

Wood pigment stains

Some wood extracts, usually brown in colour, bleed through some paint finishes. Wash with soapy water, prime and recoat.

Wrinkling

This is caused by applying a second coat before the first one is dry, or applying in strong direct sunlight. Sand down until smooth and repaint.