How to Remove Paint from Concrete, Wood, Metals, etc.? [PDF]

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The life span of a paint is around 10 to 15 years after which the paint wears out and does not serve its purpose. When the paint wears out, the surface must be repainted in order to protect the surface against deterioration and, at the same time, keep the appearance pleasant.

The purpose of repainting is not served if the painting work is carried out on old paint. The thorough and complete removal of old paint is a vital process in repainting to be effective and long-lasting.

In this article, we discuss the removal of old paint by the use of paint remover, caustic soda solution, and blowlamp. Further, we shall also discuss the preparation of the surface after the removal of old paint.

1. Removal of Old Paint using Paint Remover

The paint remover used in the removal of old paint shall consist of volatile organic liquids thickened with waxes and other ingredients to retard the evaporation of the liquid and to enable a substantial layer of remover to be applied to the surface.

It shall be free from alkaline matter and non-caustic so that it can be handled by workmen without injury.  It shall be of non-inflammable quality as far as possible.

This method of paint removal shall be used where burning off with blowlamp is not suitable.

1. The paint remover shall be applied on the paint coating to be removed thoroughly with a brush or applier and allowed to remain on the surface for a period depending on the particular brand of remover used. 
2. Under the action of paint remover, the paint film lifts and wrinkles, after which it shall be stripped with a sharp instrument.
3. If the film is not thoroughly removed, a second coat of remover may be applied if necessary over such patches, and then the film should be thoroughly scrapped.
4. After the surface has been stripped, it shall be washed down with mineral turpentine to remove all traces of paraffin wax, which forms one of the ingredients of paint remover and which, if left in place, will prevent the paint from drying.
5. The cleaned surface shall be suitably prepared for the application of paint or other finish, which is discussed in the latter segment of the article.

Precautions

In the case where the paint remover is inflammable, suitable precaution against the risk of fire shall be taken. The neighboring painted surfaces which are not to be treated should be properly protected from contact with paint remover.

2. Removal of Old Paint using Caustic Soda Solution

1. The caustic soda used for the removal of old paints shall be dissolved with 48 times its volume of water to prepare the solution.
2. The prepared caustic soda solution is applied to the old paint with a brush or applier. Due to the action of remover, the paint film lifts and wrinkles, after which it shall be thoroughly scraped off in the same way as described above.
3. After the surface has been stripped thoroughly, it shall be rinsed with clean water to remove all traces of alkali, which, if allowed to remain, are liable to spoil the new paint applied over it. 
4. A little acetic acid or vinegar added to the final change of rinsing water helps to neutralize any remaining alkali.

Precautions

1. Caustic soda, as its name implies, is a corrosive liquid, and care should be taken to see that no liquid spills over the skin or clothing.

3. Removal of Old Paint using Blow Lamp

1. The paint shall be removed either with a blowlamp or with air acetylene equipment.
2. The flame shall be allowed to play upon the paint just enough to soften it without charring either the paint or the background surface.
3. The softened paint shall then be removed with a stripping knife following the flame as it is moved up the surface.
4. The burning off shall begin at the bottom of the vertical surface and shall proceed upwards.

Precautions

The removal with blowlamp shall not be done on narrow or caved undercut surfaces or where there is a risk of damage to neighboring materials such as panes in glazed windows.

Preparation of Surfaces for Repainting

1. Wooden Surface

1. The woodwork to be printed shall be dry and free from moisture and cleaned thoroughly. 
2. All uneven surfaces shall be rubbed down smooth with sandpaper and shall be well dusted.
3. If required, appropriate filler material with the same shade as paint shall be used.
4. After the priming coat is applied, the closing of the holes and indentation on the surface shall be carried out with glazier’s putty or wood putty, respectively. 
5. Closing of the holes shall not be done before the priming coat is applied as the wood will absorb the oil in stopping, and the latter is, therefore, liable to crack.

2. Iron & Steel Surface

1. All rust and scales shall be removed by scraping or by brushing with steel wire brushes.
2. Hard skin of oxide formed on the surface of wrought iron during rolling, which becomes loose by rusting, shall be removed.
3. All dust and dirt shall be thoroughly wiped away from the surface.
4. If the surface is wet, it shall be dried before the priming coat is undertaken.

3. Plastered Surface

1. The surface shall ordinarily not be painted until it has dried completely. 
2. Trial patches of primer shall be laid at intervals, and where drying is satisfactory, painting shall then be taken in hand. 
3. Before primer is applied, holes and undulations shall be filled up with Plaster of paris and rubbed smooth.

FAQs on Removal of Old Paint

Read More:
1. Methods and Process of Painting on Different Surfaces
2. How to Paint Plastered Surfaces?