1 Prepare the surface

This is key to the success of your project. Although you may not notice on a day to day basis, interior surfaces accumulate dirt, fingerprints, and a variety of stains and contamination that can dull your home's appearance. It is therefore important that you address them before you paint or they'll undermine the quality, look and longevity of your paint job.

Correct surface preparation may take much longer than the actual application of paint so be sure to allow for this important step in your budget and schedule.

Clean the area

Before priming you should remove any dirt, chalk or treated fungus or algae. Scrub the surface area with a household detergent, water and a stiff bristle brush and/or cloth. Rinse the surface thoroughly, and allow it to dry completely before priming. Never use harsh cleansers since they can infiltrate the substrate and inhibit paint performance. If using bleach or fungicidal solution to remove the fungus or algae, be sure to wash the area thoroughly and allow to dry before applying paint.

Prepare glossy surfaces

New coatings do not adhere well to high-gloss surfaces, so it is recommended that all glossy areas be dulled using a fine grade sand paper. After sanding, remove any dust with a damp cloth.

Chemical deglossers are also available, but require care and caution. Leaving the product on the surface too long can soften and wrinkle the old coating. Make sure there is plenty ventilation, open windows and doors to keep the fumes from building up in the room. Follow all manufacturers’ instructions and treat these products as strong solvents, exercising safety precautions with protective goggles, gloves, respirator, and clothing.

Prepare other unpainted surfaces

New Plasterboard

Before painting new plasterboard, be sure all joints and patches are sanded smooth, and dusted with a cloth. Next apply an appropriate water based primer sealer. Pay attention to the manufacturer's instructions and spread rates. As an alternative, a general purpose stain-blocking interior sealer can be used. If staining occurs with a wallboard sealer, apply a stain-blocking sealer.

New Plaster

Allow plaster to dry thoroughly. With a simple patch job, this will take one to two days, for larger areas like walls and ceilings it can require up to several weeks depending on the weather and interior humidity conditions. Thick plaster applied in extremely humid conditions can take a month to dry adequately. Once dry, all rough areas must be sanded smooth with medium grade paper followed by a second treatment with fine grade paper. Clean surface of all dust with a dry cloth and then apply a stain-blocking interior water-based sealer recommended for plaster surfaces. Be sure to wear a mask and protective eyewear when sanding.

Tile

Inspect grout joints and repair them as necessary. Next wash the entire surface with a detergent and an abrasive nylon scouring pad. Rinse and dry thoroughly. As an option to guarantee maximum adhesion, sand the tile surface with a fine aluminium oxide sand paper. Clean area off with a damp cloth. Use a high-adhesion interior water-based bonding primer. This type of primer requires the use of a respirator and ample ventilation. Allow it to dry thoroughly before applying a finish coat.

MDF

This type, Medium Density Fibreboard, is a manufactured wood made from sheets of compressed fibres and requires a specific primer prior to painting.

Prepare previously painted surfaces

Inspect the surface for cracking, peeling, flaking, loose paint. Following are several methods that could be used in preparation.

Scraping

This is a traditional effective approach for most flat surfaces from plaster and wallboard to wood and ferrous metal. Use shaped scrapers like triangle or oval shapes to get into corners and on rounded profiles. Feather sand all rough edges with a medium, then fine grade sand paper.

Wire Brushing

This is mostly used on Wrought Iron or masonry. Use a stiff wire brush, being careful not to damage the substrate. Once all loose paint has been removed sand the surface with a medium then fine grade sand paper.

Sanding

If the surface is just flaking slightly you can simply sand the area with progressively finer grade sand papers starting with coarse, then medium, then fine.

Chemical removers

Choose a paint remover that is recommended for the coating and substrate you're preparing. Apply a heavy coat of the remover with an old or a low-end natural bristle paint brush since the remover will likely ruin the brush.

Give the product plenty of time to work as recommended by the manufacturer, usually 15 to 20 minutes or longer depending on the thickness of the old paint. Carefully remove the softened paint using a putty knife or wooden blade and scrape the material into doubled paper bags inside a cardboard box. If subsequent coats are required, reapply and remove using newspaper or rags.

Before using these products, clear the area of children and pets; cover floors and steps and remove plants, rugs and furniture.

Dispose of all waste after the job carefully following manufacturer instructions. Wear goggles or face mask for eye protection; use chemical resistant gloves, long sleeve shirt and trousers to protect the skin; and protect breathing with a respirator designed for use with chemical solvents.

There are low odour alternatives to the strong solvent removers, but they may take several hours to accomplish the same job. Once the remover has done it's work, sand the surface thoroughly with fine sand paper and dust before applying primer, stain or varnish.

Prepare stained and discoloured surfaces

Water stains

The first step to covering water stains is to make sure that their source has been eliminated. Once you are assured that no more damage will occur, begin the preparation process. Clean as much of the stain as possible from the surface and rinse. Allow the surface to dry and apply a suitable stain-blocking primer. If there is still evidence of stain-through, apply a second coat. Once the primer or sealer has thoroughly dried, you may apply the top coat(s).

Tobacco, fire damage, soot, grease

Clean the stained area as much as possible with a detergent and rinse thoroughly. Allow the surface to dry and apply a  stain-blocking solvent-based or shellac-based primer or sealer. If there is still evidence of stain-through, apply a second coat.  Once the primer has thoroughly dried, you may apply the top coat(s).

Prepare wallpapered surfaces

It is far better to remove wallpaper and residual adhesives before painting. If not you risk a variety of problems from lifting and curling to staining and uneven textures. It is sometimes however necessary to paint over it. Here is how to handle either situation. Wallpaper can be removed by peeling, soaking and scraping, or steaming and scraping. There are some excellent wallpaper strippers available that dissolve the old paste making it the ideal choice when painting over. Scrub off any glue and rinse thoroughly. Any gouges or scratches can be patched with plaster or filler, then sanded and dusted with a damp cloth.

When painting over wallpaper begin by checking for loose areas of paper and poorly adhering seams. Re-glue these problem areas by using an overlap and repair adhesive and then try a paint test in an inconspicuous area of the room to make sure it will look acceptable, making sure there is a seam included in the test area. Apply a stain blocking sealer. Allow it to dry thoroughly and inspect it to ensure there is no discoloration and apply a second coat if necessary. Apply a finish coat to the test area and allow it to dry. Matt finish paints will minimise the texture of the underlying paper. Consider applying a second coat and then evaluate the test area to see if you will proceed with the entire room.

Prepare bare wood

If the wood surface is rough it should be sanded smooth with a medium grade sand paper. Be sure to sand with the grain, never against it, diagonally or across the grain. Wipe away any dust with a cloth. To achieve the smoothest appearance, apply a coat of water to the wood with a wet but not soaking cloth. Allow it to dry 30 minutes to raise the grain of the wood. Sand with fine paper to remove the raised grain. This will avoid grain raising when applying primer, paint or other coatings. Use a stain-blocking primer applied in a heavy coat and allow it to dry overnight. A second coat can be applied if staining is evident. Solvent-based stain-blocking primers are most effective over high-staining woods such as mahogany and redwood. Light sanding may be required before a finish coat is applied. Follow manufacturer's recommendations for best results. When using solvent-based primers, proper ventilation is required along with use of a respirator.

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