Preparing the surface before painting

The type of preparation you will need to undertake is determined by two key factors:

1.    the nature of the surface itself, i.e. wood, metal, plaster
2.    whether it is a bare, new surface or it has been painted before


Previously Painted Surfaces
Wash to remove all dirt dust grease and grime. Fill holes and cracks with a suitable filler and sand smooth. Surfaces must always be clean, dry and free from any contamination. Prepare and spot seal bare substrates as per new work instructions below. Always read and follow any additional instructions on the paint can for specific surface types.

Preparing large unpainted Surfaces
Exterior Timber:
All sharp edges should be slightly rounded by planing, scraping or sanding. If timber has been exposed for some time or damaged it must be sanded before painting. All sanding should be carried out with the grain. Wash, or dust off as necessary before painting. Cracks and holes in the timber should be scraped clean of any soft material, and filled with an appropriate filler. Undercoat with White Knight Acrylic Primer Undercoat.
New/green timber should be seasoned.

Interior Timber:
Sand smooth before painting. Timber should be sanded along the grain to prevent fibres being raised. Remove all dust and dirt before painting. Undercoat with White Knight Acrylic Primer Undercoat.

Paperfaced gypsum Board (Plasterboard):
Ensure joints are smooth and surface is dust free. Seal with White Knight Acrylic Undercoat Sealer.

Particleboard, MDF:
Dirt and grease should be removed, edges should be filled or fitted with an edge strip and holes filled before sanding. Seal with MDF Primer White Knight Acrylic Undercoat Sealer. Do not use oil based undercoats on fibre board.

Galvanised Steel and Zincalume:
New metal should be thoroughly degreased by wiping with mineral turpentine. Structural galvanised steel (pipes, beams, hand rails etc) must be thoroughly abraded by sanding or grinding to remove chemical treatments from the surface and ensure adhesion of coatings. Prime with White Knight True Bite or S.L.S. Etch Primer.

Iron and Steel:
If no rust is present, the surface should be thoroughly degreased by wiping with mineral turpentine. Loose rust can be removed with a wire brush or power tool. Prime with White Knight Metal Primer.

Claybricks:
Remove loose particles by dry brushing the surface down. Fill holes and cracks with a suitable filler. Wash the surface if necessary with a solution of water and household detergent. Rinse with water and allow to dry.

Concrete walls:
Paint will serve best if concrete is cured and dry when painted. New concrete may be wet under the surface and this moisture may later cause blistering and peeling of coatings. Aging is a reliable surface treatment for concrete. With age, moisture and alkalinity are reduced. Concrete should be allowed to dry for at least 4 weeks. (12 weeks if painting with oil based coating)  Fill all unwanted holes with suitable filler. Wash if necessary with a solution of water and household detergent to achieve a clean surface before painting.

Concrete floors:  
The surface should be left at least 12 weeks before painting with oil based PP or 4 weeks with Ultrapave. Use concrete etcher. and must be acid etched for good adhesion of the paint to the concrete. Mix 1 part Spirit of Salts (Hydrochloric acid) to 9 parts water. Pour the solution over the concrete and follow with stiff bristle broom. Allow acid to fully react with concrete and continue etching until no fizzing reaction is seen. A properly etched surface feels like rough sandpaper. Wash thoroughly with clean, fresh water and allow to dry completely before painting.

Cement Render:
Surfaces must be cured and dry prior to painting, at least 6 weeks for oil based paints and 4 weeks for acrylic paints. Treat any mould with a suitable mould wash solution.