Preparing a surface for painting


General Ship Maintenance:

Preparing a surface for painting Removing rust and scale by chipping hammers. Paint brushes. Painting defects and their Prevention, Cleaning of wooden decks, Cleaning and polishing of brass and copper.



Preparing a surface for painting:

Cleaning: Clean all surfaces using water soluble detergent and high pressure fresh water. Remove salt, oil, grease, loose coating, dirt and detergent prior to de-rusting.

De-rusting: When de-rusting, turn smaller patches of rust into one larger area by removing the paint between the rust patches. Remove rust manually or mechanically by use of power tools. Mechanical removal is recommended as it offers higher efficiency and better results. Work to limit edges as these are often a weak spot. Edges are recommended to be feathered. This is done by grinding or sanding the edges to create a diagonal shape. Avoid smooth surfaces to secure adhesion.



Preparation and Priming: Generally, Sound preparation is essential to successful painting. Dirt, moisture, rust, salt deposits, grease and oil prevent the paint from adhering properly and additionally may cause slow drying and other defects.

Paint does not adhere well to smooth, shiny surfaces, e.g. glossy paint which has aged and hardened but not weathered. Adhesion to certain metals, e.g. zinc and aluminium, is poor also, unless the surface is pretreated.

The methods normally available for the cleaning of Steelwork are:-

  • Mechanical or manual wirebrushing, chipping, etc.
  • Flame cleaning.
  • Grit or wet sand blasting.





Of these, grit or wet sand blasting is probably the most effective

but it is expensive and often not practicable because of difficulties of access, inconvenience caused by residues of grit or sand, etc.

By force of circumstances, most steelwork is prepared for painting by manual or mechanical chipping, scraping and wirebrushing. This method will not remove tightly adherent scale but, if conscientiously done, is reasonably effective in removing loose scale and rust. When metal is to be chipped especially with mechanical tools, it should be ensured that the metal itself is not excessively chipped, indented or “burred”, thus producing high spots & sharp edges which protrude through the paint film.

Oil & grease must be removed by washing with white spirit or other suitable solvent (not paraffin).Where contamination is heavy,repeated washing, with repeated changes of solvent and rag or waste,will be necessary.


Salt and similar deposited material must be removed. Usually,

this can be done by washing with clean water, preferably before the surface is wirebrushed so that any rusting induced by wetting the surface is removed.

In all cases, the steelwork must be primed as soon as possible after preparation and the work should be so planned that prepared surfaces

are primed the same day. With flame cleaning, the metal should be primed whilst still warm.

Whenever possible, at least two coats of primer should be applied to ensure that sharp edges and “holidays” in the first coat are properly covered.





Primers for Iron and Steel. Iron and steel rust rapidly if not protected, especially in marine conditions. Complete exclusion of air and moisture from perfectly cleaned steel would prevent rusting, but, in practice, complete removal of rust is rarely possible and most paint films will not exclude air and moisture altogether. Primers for iron and steel must, therefore, help to stifle or “inhibit” rust and they usually contain “rust inhibitive” pigments in a suitable vehicle. Rust inhibitive pigments include:

Red and white lead.

Basic lead sulphate.

Chromates of lead and zinc. Metallic (dust) lead and zinc.



Lead based paints should not be applied to surfaces in refrigerated spaces and spaces used for foodstuffs and drinking water. They are also unsuitable for use on galvanised metal.

Aluminium, Copper, etc. The adhesion of paint to these surfaces

is usually poor. Aluminium should be pretreated or wash primed if possible; if not, the surface should be abraded with glasspaper or wire wool, using white spirit as a lubricant. Lead-containing primers must not be used; zinc chromate primers are suitable.

Copper, brass, lead, etc., give adhesion troubles; abrasion, followed by priming with a zinc chromate primer or direct application

of gloss finish, gives best results but some flaking must always be expected.





Preparing a surface for painting: (i) Steelwork

Before a structure is painted, a number of operations must be performed on the substrate. The initial work required is generally known as “steelwork”. Steelwork is a very important part of the surface treatment and must be carried out before cleaning and priming of the steel. Good steelwork will ensure that the life time of the paint system meets expectations.




Preparing a surface for painting:

Steelwork : Steelwork involves the following stages before cleaning and priming:

  • All sharp edges are rounded to a radius of at least 2 mm by grinding.
  • All welding beads and slag are grinded off.
  • Surface defects such as lamination, etc. are removed by grinding.
  • Undercutting in the weld is repaired before priming.
  • Rough manual welds to be grinded.
  • Gas-cut edges are to be grinded before priming.





Preparing a surface for painting:

  • Pre- Treatment

I has been completed, pre-treatment can begin. The purpose of preparation is to ensure that the substrate is suitable for application of the paint, i.e. the steel is sufficiently clean and rough.

Contaminants such as of I, grease and salts for example cannot be removed by blast-cleaning. Before preparation begins, the steel must be properly cleaned. Cleaning removes contamination and impurities such as oil, grease, salt, dust and dirt. Salts from a marine atmosphere which are deposited on the structure, and welding fumes from manual welding are examples of salts which should be washed off before preparation. Salts can cause osmotic blistering and oil will reduce the adhesion of the paint. Saltsmust be removed with plenty of fresh water. Oil and grease cannot be removed with water alone; strong alkali washing agents and solvents must be used. Once the substrate is clean  pre-treatment can begin


(a)  Blast-Cleaning: To ensure maximum paint adhesion, a rough surface is required. In view of this, blast-cleaning is the best preparation method. Blast cleaning removes old paint, rust and scales and gives a clean rough surface. Possible blast-cleaning methods are dry blast-cleaning, slurry blast-cleaning (addition of water) and wet blast-cleaning (water with addition of abrasives). Dry blast-cleaning gives a clean dry surface and the required roughness but causes considerable dust which contaminates the immediate environment. Slurry and wet blast-cleaning give a rough, clean surface without dust, but create flash rust. It has been found that much of the abrasives remain on the substrate after blast-cleaning. Such contaminants may on some alloys cause a risk of corrosion at these points. For preparation of stainless steel, aluminium and galvanised steel, it is important to use non metallic abrasives.


  • Ultra High-Pressure Water Cleaning: This preparation method is becoming increasingly common. The method consists of removing contamination, corrosion products and old paint by applying water to the substrate under extremely high water pressure (up to 2500 bar). The method has two essential advantages: no cloud of blasting dust is created to contaminate the immediate environment as in traditional blast-cleaning, and water-soluble salts are removed from the substrate. It is important to use clean water so that the substrate is not contaminated by the water used. The method gives a clean surface but will not give any extra roughness to steel. The original roughness of the steel is retained where intact paint is removed, but the corrosion pattern on corroded areas will be considered as roughness where corrosion has occurred. One disadvantage with water cleaning is that the tendency to form flash rust on the steel will increase as moisture is added to the substrate. The degree of flash rust depends on the relative humidity, the temperature of the steel and atmosphere, and the cleanliness of the surface.



(iii)     Mechanical Cleaning: Use of mechanical cleaning tools such as steel brush grinding equipment or machining, does not achieve the same degree of cleanliness and roughness as blast-cleaning and the adhesion between substrate and the paint system will therefore be reduced. Needle guns for example often cause excessive roughness or break-up of the substrate. Mechanical rotating wire brush
  • Needle gun
  • Hand Wire brush

The method to be used will be described in the paint specification and is primarily selected on the basis of:

  • Purpose of the structure Exposure conditions Required life time

Restrictions related to environmental requirements and safety.