How to paint exterior walls

Posted by Michael Boyle on

When people tell us at Donegal Town Hardware that they want to paint the exterior walls of their homes, we direct them to our range of Dulux, Crown Weathercoat, and Sandtex exterior paints.

Specialist exterior paints such as these will provide your home with ultimate protection against the weather. They can cope with anything the Irish climate throws at it, from the wind and rain we get all too often to the sun we don’t see enough, and we stock a massive range of paints and other exterior protection products in our dedicated Paint Centre.

We’ve put together this ‘how to’ guide to choosing exterior paints and getting the job itself done, based on the questions that our Paint Centre team members are most commonly asked. Hopefully you’ll find the answer to any questions you may have here, but don’t be shy about asking us too if you wondering about anything else – we’re always glad to help!

How to choose a colour

We’d say there are several factors to think about:

  • The size of the house. Light colours can make a home look larger, while warm colours can make it look smaller.
  • The aspect of the house. Sunny settings can take cool colours, but north-facing houses need warmer hues.
  • Neighbouring buildings. A stand-alone house can take strong, bold, colours, while a terraced house in a town can do the same. A semi-detached house, however, should complement its neighbour.

Depending on the design of the house, you may need to consider up to three different colours: one for the walls, a complementary colour for sills and plinths, and a gloss or wood-stain for doors, frames, and facades.

How to paint brickwork

Most brickwork can be painted, with the only real exception being Fletton bricks, which are uncommon in Ireland. Prepare the bricks as you would with any other masonry, ensuring it is clean and sound. Treat any sign of organic growth with fungicide or a weak bleach solution. Prepare chalky or powdery surfaces with stabilising solution.

How to know if the weather is right

Temperature under 8°C or above 20°C can bring challenges for exterior painting, with paint either not drying quickly enough, or else drying too quickly. It’s a good idea to have a look at the weather forecast for the week ahead before you start – and hope that things work out the way they’re predicted!

How to choose a colour scheme of two or more exterior paints

First, select your main wall colour from the colour brochure. The colours available in Smooth masonry have all been laid out in complementary palettes to make it easy to select colours to go on sills, plinths and quoins.

To choose a contrasting or complementary trim paint for wood, metal or PVC-u, cut out the colour chips from the brochure and lay them next to your chosen wall colours.

You could also create a mood board by cutting out images you like from magazines and brochures.

Compare these images to the colours available in the various paint brochures and choose from there.

How to know how much paint you will need

All our exterior paints have their spreading rate on the back of pack or summarised in the colour brochure. Alternatively, there are several handy online paint calculator tools to do the sums for you.

How to check for problems before you start

Always check your walls for the following and take the appropriate action:

  • Old flaking or blistering paint
  • Worn or damaged surfaces
  • Cracks
  • Damp and fungal growth
  • Unstable chalky surfaces

You should also consider how you will access hard-to-reach areas and what ladders, etc., will be needed. Also think about dust sheets and masking tape, and purchase them if you don’t have them already.

How to get rid of flaking old paint

Complete all stripping and rubbing down before you start painting, so that dust and flakes will not fall on wet surfaces. Start from the top and work down, and clean out gutters and paint if necessary.

When removing old flaking masonry paint, use a scraper where possible, then for small flakes, a stiff bristle brush will remove residual flakes. It is important NOT to use a wire brush on the masonry surfaces as metal particles can become embedded on the surface. These will react to the water based masonry paint thus resulting in potential rust spots that will make the walls look unsightly. When removing old paint, it is recommended that you wear safety goggles or glasses, gloves and a mask.This will reduce the risk of damaging your eyes or breathing in dust particles.

How to deal with mould or algae

Do not just paint over it! It is important to thoroughly treat contaminated areas of mould, or other organic growth, as otherwise it will come through newly painted areas.

Initially remove any surface contamination with a scraper, then use a stiff bristle brush. Once the surface is sound you must apply a fungicide solution, diluted with water according to the pack instructions. Use gloves and goggles or safety glasses for protection while doing so.

Exterior Paints Img2

Apply the fungicide solution to the affected area plus an overlap to ensure the solution penetrates the surface and kills the organic growth. Again check the pack instructions as to the recommended time prior to painting over the fungicide solution – this is usually 24 hours.

This will ensure a clean surface for a better adhesion of the masonry paint.

Mould tends to grow in damp conditions so it is important to deal with not just the mould problem but also the cause of the problem, as this could be a leaking gutter concentrating water on the wall creating a damp area.

How to deal with ‘powdery’ walls

One of the problems that can occur when painting an exterior wall is that you can come across a chalky and unstable surface. If you apply paint without effectively treating this problem, the paint will dry and stick to the loose dust particles instead of getting a sound adhesion to the wall. This will result in the paint blistering and failing.

A stabilising solution can fix the problem. Apply it directly to the surface with a brush, and allow to dry for 24 hours before painting. It will not only stabilize the surface to allow for good paint adhesion – it also allows the same amount of paint to cover more surface area.

How to deal with old paint bubbling and lifting away

This is a problem known as blistering. It results from localised loss of adhesion, and lifting of the paint film from the underlying surface. There are a number of causes, but primarily underlying moisture is the issue. Moisture escaping through the exterior walls is less likely to affect water-based paint, but more so with solvent-based. Other causes can be painting a warm surface in direct sunlight or an under bound / powdery substrate beneath older paint coatings.

Exterior Paints Img3

To fix the problem, first scrape off the blisters. If you can see the substrate, the problem is due to moisture. To resolve the issue off blisters originating at the substrate, try to remove the source of moisture. Ensure any underlying chalky/powdery surfaces are fully stabilised.

If you find paint, then it could be a solvent blister and is probably caused by painting with an oil base or alkyd-base coating in hot weather.

If blisters do not go all the way down to the substrate, remove them by scraping, and identify and cure any underlying defects.

How to prevent and correct cracks in the paint surface

Cracking is caused by the splitting of a dry paint film through at least one coat, and it will lead to complete failure of the paint over time. Causes include over-thinning of the paint (or spreading it too thinly) and painting under excessively cool or windy conditions that make water-based paint dry too fast.

It may be possible to correct cracking that does not go down to the substrate by removing the loose or flaking paint with a scraper or stiff bristle brush (not wire), sanding to feather the edges, priming any bare spots and repainting. If the cracking goes down to the substrate remove all of the paint by scraping, sanding and/or use of a heat gun. Then prime and repaint with a quality exterior water-based paint.

How to deal with white powder under spots that the paint is coming away from

This is normally caused by efflorescence, where salts originating from the bricks, concrete blocks, concrete, etc. are brought to the surface by water drying out or excess moisture escaping through the exterior masonry walls from behind.

Active efflorescence is likely to push off any type of sealer or paint coating. Other likely causes are ground salts contamination due to a broken or missing damp proof course.

To resolve, if excess moisture is the cause, eliminate the source of the moisture. If moist air is originating inside the building, consider installing vents or exhaust fans, especially in kitchen, bathroom and laundry areas. Then remove the efflorescence and all other loose material with a stiff bristle brush. Allow to completely dry out and continue brushing and removing the salts until they cease to appear. The substrate may be washed using a dilute vinegar solution in order to neutralise the alkalinity. Once dry, repaint.


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