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  • Interior Project Guide 1 - Surface Preparation

Interior Project Guide

Surface Preparation

Your ultimate guide to interior projects

We love paint projects like a Labrador loves a chop. And no matter how big or small your next project is, we want to arm you with the best tools, tips and tricks to ensure your DIY project goes smoothly.

Whether it be a full room makeover or upcycling some well-loved furniture, an interior paint project will give you home a new lease on life - so check out the below guide to help you with your next interior project.

SURFACE PREPARATION

Preparation is key! Ensuring your surface is properly prepared will prevent paint problems from popping up in the future.

Unpainted Surfaces:

No two unpainted surfaces are the same – different surfaces need different preparation to allow for the best end result. Plus, the appropriate prepcoat and topcoat will also differ depending on the surface. These processes are suitable for unpainted (bare) surfaces.

Plasterboard

  1. Lightly sand the final coat of plaster with 180-360 grit sandpaper to create a smooth, flat surface.
  2. Wipe the surface with a damp rag to remove any dust particles.
  3. Apply one coat of acrylic sealer undercoat to the surface. Apply the prepcoat as soon as the plasterboard joints are set so moisture can’t penetrate the joints.
  4. For a premium finish, lightly sand the prepcoat with 180-360 grit sandpaper (this is optional).
  5. Wipe away any dust particles with a damp rag.
  6. Apply two coats of acrylic topcoat to the surface.

Brick

Note - When mortar (the “glue” between bricks) has been used on a new brick surface, you will need to allow 4-6 weeks curing time before painting.

  1. Thoroughly clean the surface with sugar soap and a wire brush. Clean the solution off with a wet cloth.
  2. Once dry, brush the surface down with a hard bristled brush to remove dust particles.
  3. Apply one coat of non-alkyd masonry primer.
  4. Apply two coats of acrylic top coat.

Hard Set Plaster

Newly applied hard set plaster needs to be left for roughly 12 weeks to cure before applying any paint.

  1. Fill any imperfections with an interior filler
  2. Sand the surface smooth with 180-240 grit sandpaper. Brush down to remove excess dust.
  3. Apply one coat of quality sealer binder.
  4. Apply two coats of acrylic top coat.

Bare Timber

  1. Sand the surface with a 120-240 grit sandpaper.
  2. If there are any nails present, punch them to 3mm below the surface.
  3. Fill nail holes, cracks and any imperfections with a filler.
  4. Wipe down surface with a cloth to remove all dust particles.
  5. Apply one coat of quality stain-blocking primer sealer undercoat on your surface to inhibit the timber absorbing any moisture, and to stop tannins and natural oils from leaching through to the topcoat.
  6. Apply two coats of acrylic or oil based enamel.

Pre-primed timber

  1. Lightly sand the surface with 120-240 grit sandpaper to remove any loose and chalky pre-primed finish.
  2. If there are any nails present, punch them to 3mm below the surface.
  3. Fill nail holes, cracks and any imperfections with a filler.
  4. Wipe down surface with a cloth to remove all dust particles.
  5. Apply one coat of primer sealer undercoat to the surface.
  6. Apply two coats of acrylic or oil-based topcoat to the surface.

Pre-primed doors

  1. Sand the surface with 180-240 grit sandpaper to remove any loose and chalky pre-primed finish.
  2. Wipe down the surface with a damp cloth to wipe away any residual dust particles.
  3. Apply one coat of Dulux Precision Max Adhesion Strength Primer to the door.
  4. Apply two coats of top coat to the surface. Both oil-based and water-based top coats are suitable for use on interior pre-primed doors, however a water-based paint is recommended for exterior settings.

Melamine

  1. Clean the surface with a scourer and Sugar Soap to remove any grease from the surface.
  2. Sand with 180 grit sandpaper until the surface is dull or matte, with no shine or gloss.
  3. Wipe the surface with a damp cloth to remove any dust particles.
  4. Apply one coat of high-adhesion prepcoat.
  5. Apply two coats of hard-wearing acrylic enamel top coat.
  6. Let the surface to cure for a few days prior to use.

Particle Board

  1. Sand with 180-240 grit sandpaper.
  2. If there are any nails present, punch them to 3mm below the surface and fill with a filler
  3. Wipe the surface with a damp cloth to remove any dust particles.
  4. Apply one coat of high-adhesion undercoat.
  5. For an expert finish, apply two coats of prepcoat to the edges of the particle board for better long-term performance and moisture resistance.
  6. Apply two coats of hard-wearing acrylic or oil-based enamel top coat.

Glass and Ceramic Tiles

These steps are not suitable for walk-on surfaces and are only recommended for hard and glossy surfaces.

  1. Clean with sugar soap and a scourer.
  2. Wipe the surface with a damp cloth to remove any cleaning residue.
  3. Apply one coat of Dulux Precision Max Adhesion Strength Primer to the tiles.
  4. Apply two coats of hard-wearing acrylic or oil-based enamel top coat.

Pre-painted Surface Testing:

Before repainting a surface that is currently painted, you should perform a few checks to ensure the coating and surface can be painted over. Painting over an unsound surface can cause more problems in the future, so it’s better to take the time to perform these easy checks so your project can be completed without hiccups and will last without problems.

Chalking Check:

To determine the degree of chalking, rub your finger or a dark cloth over the surface. Dampen the area and scrub with Sugar Soap. Clean off and dry, and then repeat the process to ensure all chalking has been removed.

Cross-Hatch Adhesion Test:

Check the condition of the previous coating of paint to confirm it’s in good condition. If the current coat is not in good condition, your new coating may not adhere to the surface and will cause future paint problems. Check the condition of your surface by following these steps:

  1. Use a sharp blade to cut an X into the existing paint coatings.
  2. Place a piece of sticky tape over the X and press down firmly.
  3. Quickly peel the tape off the surface.
  4. Repeat the process in different areas to check the entire surface.

If flakes of paint are stuck to the sticky tape, or have flaked away from the test surface, the current coating should not be painted over. The paint should be removed by sanding or stripping the surface back and treating the area as a new, unpainted surface.

If there is no paint on the tape, and no paint has flaked from the test areas, your surface can be repainted.

Contaminant Clean:

Contaminants will sit on the surface of the substrate and previous coating, and the residue of these contaminants can affect the adhesion of the new paint. Contaminants can include dirt, dust, salt, oil, grease, mould, surface moisture and residual cleaning products.

To ensure the surface is free from any residue;

  1. Clean the surface with Selley’s Sugar Soap to remove all contaminants
  2. Thoroughly wipe down the surface with a water-soaked rag free of any chemicals to wash away traces of Sugar Soap
  3. Make sure your surface is completely dry before painting.
Lead Testing:

Before 1970, house paint contained high levels of lead, as white lead was used as the main white pigment. In 1970, due the health impacts of lead paint, Australia limited the amount of lead in paint 1%, which was further reduced to 0.1% in 1997.

When painting in an older house, it’s important to test to see if there is lead present in the paint, particularly if your surface is flaking or chalking.

Lead tests can be purchased from Inspirations Paint and are easy to conduct. Follow the instructions on the packaging of your Lead Test Kit to determine if there is lead present.

Previous Paint / Metho Test:

Knowing whether oil-based or water-based (acrylic) paint was used on the existing surface will determine what type of paint and processes need to be followed when repainting.

  1. Apply methylated spirits to a clean rag so the rag is moist
  2. Rub the painted surface with the metho-soaked rag
  3. Check the surface and rag to see what effect the metho has had

If the paint on the surface has slightly dissolved, or the paint has rubbed off onto the rag, the coating used is water-based (acrylic).

If there has been no effect on the painted surface, and there is no paint on the rag, the surface has been painted with an oil-based paint.

UNSOUND SURFACES: DIAGNOSING SURFACE PROBLEMS

Surface issues on a pre-painted surface are often caused by poor preparation. Poor preparation can result in different problems all requiring different fixes and solutions.

Mould

Mould is a fungus that grows when moisture is present, there isn’t enough sunlight or fresh air/poor ventilation. It usually forms a dark stain on surfaces.

If dealing with minor surface mould, spray a mould removal product (remember to always use protective equipment when removing mould), let the solution soak into the surface and wipe away with a damp rag. Repeat if necessary. If repainting, use a mould and stain blocking prepcoat to and a mould and bacteria resistant topcoat.

If you have more than surface mould, or the mould is growing back, moisture is possibly affecting the structure of the building. Speak with a professional to ensure there is no structural damage and complete any required waterproofing before painting.

Efflorescence

Efflorescence is a crusty white mineral salt that appears on masonry substrates (brick, render, concrete, etc.) when excess moisture causes minerals to leach.  If caused by residual moisture, efflorescence will naturally disappear as the surface cures. If this does not happen, the moisture is coming from an external source that requires attention.

If efflorescence is present on a bare surface, brush the substrate with a stiff brush to remove the leached minerals, then sponge the surface with a diluted vinegar mixture. Only paint the surface when it is fully dried and the moisture leak has been fixed.

If the surface is painted, remove the paint by mechanical or chemical stripping. Wash the surface with a diluted vinegar mixture, then allow to fully dry. 

You should not repaint until the surface is clean, dry and water-damaged surfaces are repaired.

Wrinkling

Wrinkling is a rough, crinkled paint surface that develops on a painted surface and is caused by the paint being applied too thick, second coat of paint was applied too quickly, surface not properly prepared, not painting in ideal weather conditions or the surface was exposed to moisture too early.
If your surface has started to wrinkle, you’ll need to scrape or sand back the existing coatings and reapply the paint. Prevent wrinkling from occurring again by ensuring you thoroughly prepare the surface, paint in ideal weather conditions and follow the advised dry, recoat and cure times (allow extra dry time if the weather conditions are not ideal).

Cracking & Flaking

Cracking is the splitting of dried, brittle paint which can affect multiple coats of paint, including the prepcoat. If left, cracked paint can eventually flake.

Cracking paint can be caused by poor surface preparation, incorrect or no prepcoat used, the prepcoat was exposed to the weather, the wrong topcoat was used or applied incorrectly, or the coatings were exposed to high humidity or moisture during application or drying. Sometimes, the paint will crack or flake because the paint system is old and needs replacing.

To repair cracking or flaking paint, remove the paint by scraping or sanding. Once the cracking/flaking paint has been removed, apply a quality and suitable prepcoat and topcoat depending on your surface type. Ensure you follow the recommended drying, recoating and curing times, as well as painting in ideal weather conditions.

Blistering

Blistering is when bubbles of gas or moisture form under a coat of paint, usually when a coating has lost adhesion with the previous coat or substrate. 

Blistering can occur when moisture has travelled through a surface and cannot escape. This is more common with an oil-based paint which seals the surface after painting, unlike water-based paints which allow the coating to “breathe”. Blistering can also be a result of painting a warm surface in direct sunlight, moisture was present on the surface during application and not allowing enough drying time between coats.

If blistering becomes a problem, you will need to strip the surface of existing paint, dry the surface and repaint with a quality prepcoat and topcoat following the recommended times for drying, recoating and curing, as well as painting in the ideal weather conditions.

Peeling

Peeling occurs when the paint coat had lost adhesion to the previous coating or surface. Unlike flaking paint, peeling paint retains its cohesion and remains intact. Peeling is commonly cause by a poorly prepared substrate, no prepcoat or the wrong prepcoat was used, the wrong topcoat was used, the topcoat or prepcoat was applied incorrectly, there was moisture present in in the substrate or the surface temperature was too hot.

Peeling paint will need to be completely removed by stripping, sanding or scraping the paint away before recoating with a quality prepcoat and topcoat. Ensure the topcoat and prepcoat are compatible, and that recommended times for drying, recoating and curing, as well as completing the project in the ideal weather conditions are followed.

Alligatoring

Alligatoring is the patterned cracking of brittle paint that looks a bit like alligator skin when cracking. Alligatoring happens when the paint loses its flexibility, so is more common in oil-based paints as they are less flexible. This problem can also occur if an oil-based paint is used to paint over a water-based paint, there was insufficient drying time between applications, or the coating was applied too thick.

Paint that is starting to “alligator” needs to be stripped, sanded or scraped off before recoating with a suitable topcoat and prepcoat. Ensure the surface is properly prepared, and that the drying times are followed.

Surfactant Leaching

Surfactant Leaching is the appearance of watermark-like streaks on a painted surface. It generally occurs in rooms where there is a lot of moisture (bathroom or laundry) but can also affect your exterior due to rain or overnight dew. It occurs when the painted surface is exposed to moisture during the curing process.

Surfactant leaching only effects the appearance of the paint and doesn’t affect the paint’s performance. To remove surfactant leaching, wait until the paint has fully cured and then scrub the surface with sugar soap. If the surfactant leaching has left permanent marks, you can repaint the surface making sure you allow the paint to cure before being exposed moisture.

Flaking Lead Paint

If you have flaking lead paint, it should be dealt with carefully so any excess paint flakes are not spread around, setting into furniture and carpet.

If you’re looking to remove the lead paint as a DIY project, we recommend using a product like Dumond Peel Away Heavy Duty Paint Remover to safely strip the lead paint away. Make sure the appropriate safety equipment is worn at all times, and the instructions on the manufacturer’s label are followed to a tee.

REPAINTING SOUND SURFACES:

If your surface is in good condition to be painted over, check to see what your existing coating is before starting your next project.

Acrylic based
  1. Scrub the surface with Sugar Soap to remove any stains, dirt or grease.
  2. Lightly sand the surface with 180-240 grit sandpaper, wiping away excess dust particles.
  3. For walls, apply two coats of acrylic topcoat. For doors and trims, apply two coats of acrylic enamel topcoat.
Oil based
  1. Scrub the surface with sugar soap to remove any stains, dirt or grease.
  2. Lightly sand the surface with 180-240 grit sandpaper, wiping away excess dust particles.
  3. Apply one coat of acrylic or oil-based primer sealer undercoat.
  4. For walls, apply two coats of acrylic or oil-based topcoat. For doors and trims, apply two coats of acrylic or oil-based enamel topcoat
Stained / clear timber coat
  1. Scrub the surface with Sugar Soap to remove any stains or dirt.
  2. Lightly sand the surface with 80-120 or 180-240 grit sandpaper, wiping away excess dust particles.
  3. Apply one coat of acrylic or oil-based primer sealer undercoat.
  4. For walls, apply two coats of acrylic or oil-based topcoat. For doors and trims, apply two coats of acrylic or oil-based enamel topcoat
Lead paint

Surfaces painted with lead paint should only be painted over if the topcoat is in good condition (i.e not chalking, flaking, peeling, etc.). If the topcoat is damaged, it will need to be stripped before painting

  1. Scrub the surface down with Sugar Soap to remove any grease or dirt.
  2. Apply one coat of acrylic or oil-based sealer.
  3. For walls, apply two coats of acrylic or oil-based topcoat. For doors and trims, apply two coats of acrylic or oil-based enamel topcoat
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