Exterior Painting: It’s All About Surface Prep

Cam Allen L.I.W. NHI

August 6, 2026

In this weekly Q&A column, retired builder/building inspector Cam Allen answers readers’ home renovation questions. Have a question? Enter it in the form below.

More years ago than I care to remember I spent a few months in between college semesters working for a paint manufacturer called the Glidden Company. It was an enjoyable, educational period for me. I was an intern of kind helping with new product testing. I remember one new paint called latex semi-gloss. I think back now chuckling how the adhesion of this new product was poor. If you did not fully sand or prime the surface, after about 2 to 3 days you could take your thumbnail and peel this semi gloss paint off the walls in nice clean strips, like cellophane wrapping. I understand it’s a lot better now. What I did learn from the lab techs and field reps was that the value of surface preparation cannot be underestimated and this still holds true today. While paint in general has vastly improved in coverage, durability and adhesion, the term I heard often in the test labs was “intercoatability”. This term means if the base you are applying your new coat of paint to is not stable, then your efforts
applying a new coat of paint is wasted.

I have not had any inquiries about painting for some time and just recently I have had two, both asking about painting the exterior of a home. Painting a room or two inside a home takes some effort, but generally within most homeowners’ capabilities. Painting the exterior of a home takes an extensive amount of planning, surface preparation and time along with some considerable costs.

The first step any exterior painting job requires is a safe, stable work area. Cover all vegetation with lightweight drop sheets. Along the first course of siding, staple the plastic tarps to the wall to catch all the chips and scrappings.

Every exterior paint job uses ladders or scaffolding. Safety is a must. The common setup for an extension ladder is ⅓ the height of the ladder is the distance the bottom should be away from the home. Most of the painting trades I knew staked their ladders and tied the base off with wire to the
stakes. The rule of thumb for working on a ladder, keep your hips between the rails. If you are leaning outside this, you are overextending yourself.

For the most part there are four main exterior sidings, wood, vinyl, aluminum and brick. They can all be painted, provided you use the proper paint. Vinyl, aluminum and brick are recommended to use a high quality 100 percent acrylic latex exterior paint. For vinyl and aluminum it is best if the surface is fully cleaned with trisodium phosphate, known as TSP. It’s best applied with a low pressure washer and a soft bristle brush for the real dirty spots. Then it
should be washed again with clear water, preferably warm. Allow it
to dry for 2-3 days, then you can paint it.

While you can use a roller or brush, for a professional looking finish it’s best sprayed on. Brick should be prepared by cleaning the brick with a pressure washer using a heavy-duty soap mix. Any brick with a white powdery deposit should be cleaned with a 50-50 mix of water and vinegar. Finally wash with clear water and allow to fully dry. If the brick is still raw, a primer is simply a must to ensure adhesion. Seal any porous areas or cracks with caulking in preparation for two coats of 100 percent acrylic latex paint. You will need two coats. Again brick can be brushed or rolled but a spray application will result in the most finished look.

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This is personal experience speaking, older bricks were clay and I always tried to talk our clients out of painting these bricks, they simply absorb water during the seasons and any rain storms. Most brick homes you see with failed paint jobs are clay bricks. Newer bricks are a blend of concrete and are not as susceptible to moisture.

Both the questions I had were related to heritage homes with wood siding and in these cases they require a significantly greater amount of surface preparation than vinyl, aluminium or brick. This is your opportunity to repair any damaged or rotted wood, remove any failed old paint and replace any siding that has reached its lifespan. I will cover a number of tips I heard over the years from pro painters we sub-contracted with.

Number one on the list is proper tools. If you have any amount of scraping to do spend the money on a pull style scraper with tungsten carbide blades – you will curse the steel blade ones as they dull quickly. Always scrape in the direction of the grain to reduce damage to the wood siding.

For the final cleaning before primer, sand the remaining old paint and take extra time to blend in the edges of the remaining paint. If you do this it will reduce the outline of patched areas once you paint. With the advent of battery pack tools, random orbital sanders are a blessing now. Use a 24 grit disk, working with the grain, do not over press the sander and keep it moving at all times as this grit will gouge the wood quickly. If at all possible, connect the dust port to a portable vacuum.

Today, there are electric infrared paint strippers. Hold the stripper in place for a minute and then immediately scrape off the paint. They work well for decorative mouldings and trim. You can expect to find some divots and dings along with larger cracks in the wood siding. A product called Ready Patch works well, sands smooth and is flexible and paintable. At all times during surface preparation use gloves, glasses and a good N95 mask. Some older
paints likely contain lead – get a sample tested so you can prepare for this contaminant. If lead is found, step up to P100 respirators and wear paint full type 5 coveralls.

If you encounter any mould you must address this before you paint as the mould will simply bleed through any paint coating you apply. Mix one cup of bleach to a gallon of water and scrub the area with a coarse brush, then rinse completely. Make sure you have proper gloves, mask and glasses on while doing this. Complete all your repairs, caulk any cracks and prime all new bare wood and areas where you have removed the old paint down to the original wood surface.

I have watched a number of good painting contractors over the years – nearly 75 percent of them used a brush application on a wood siding job, especially for the primer coat. To a trade they said the brush application worked the paint into the wood better than a spray application.

Our eastern provinces seem to have a greater percentage of wood-sided homes with amazing decorative paint finishes. If done right with a carefully chosen colour scheme applied, a fresh paint job can give a heritage home a classic, timeless look.

Lastly, painting the exterior of a home is a time consuming, skilled job. I would only recommend attempting this yourself if you are DIY experienced, prepared for strenuous, physical effort, the time to complete the job and are sure of your competency using ladders or scaffolds. The vast majority of exterior refinishing is done by professional painters with the equipment and experience.

Images from Depositphotos