Here are some important tips on how to prep metal for paint and how to paint metal surfaces. Metal designs in private houses and apartments, too, must have reliable weather protection. Before you paint any metal product, it is necessary to make the metal preparation for painting. It is also necessary to pay special attention to the choice of primers and paints. If you want you metal structure to serve you for a long time, you should remember some following rules on how to paint metal.
Metal Paint Preparation
Before painting metal products, you need to prepare the surface properly. Preparing metal for paint may be carried with the help of different technologies. But all of them are removing the rust, essentially.
According to the degree of destruction corrosion is classified into several levels
- corrosion spots (small penetration depth)
- pitting (little dots, penetrated deep into the body of the material)
- rust (loss of the part of the material)
- deep corrosion (rust lesions are formed under the surface of the coating)
Preparing metal for paint can be carried out by the following methods:
The Main Stages and Ways How to Prep Metal for Paint
Removing old paint
The metal coating process should be started with removing old paint and rust. First of all, it is necessary to remove old paint. There are several technologies that can be used separately and to be combined:
Remove rust with a wire brush and then treat the surface with putty (corrosion inhibitor).
Take a sharp scraper and push it – with equal force – while moving in one direction, and then in the other. Then do some grinding work – treat the surface with sandpaper with a medium grain to obtain it.
Apply special washing chemicals with a thick layer on small areas using a cheap brush with natural bristles. Leave it on the metal surface for the time specified by the manufacturer. Carefully remove the softened paint with a wooden spatula. Apply washing chemicals again, if required, then clean the surface with a crumpled paper napkin. The wool is not suitable, since it can change the color of the processed product or structure.
Preparation of metal surfaces for painting
The new paint has poor adhesion with metal, so it is recommended to be sanded. It is possible to provide good primer to the surface. For the most of the products, especially for structures exploited in the open air, use sandpaper with an average grain. To ensure the best quality at the most critical areas, such as decorative elements, take a fine sandpaper. After sanding remove the dust with a cloth.
The mechanical method of removing corrosion has established itself as the most effective one. It is done with your own hands using a power tool.
There are several ways to remove rust mechanically:
- Cleaning the surface with wire brushes to remove small pockets of corrosion, to clean the welds and for the primary treatment of surfaces coated with a thick layer of rust.
- Abrasive processing of metal by means of grinding discs. It is used for small areas of corrosion. If you use high-quality discs, the result will be quite good.
The method has two serious drawbacks in terms of handmade work:
- consumption of high-quality materials
- requirements for certain skills of work
- Sandblasting installation: the bombing of the centers of the sand jet corrosion filed under pressure. It is the so-called metal sandblasting. The main elements of sand plants are a container with sand and sandblasting gun. For sandblasting installation use a small compressor.
Removing the rust with sand
Before the use, sand must be thoroughly dried. The sand can be recycled after sifting – the cleaning efficiency decreases in this case, but, of course, it will take you much more time. Sandblasting removes not only all rust, but also the layers of the old paint. In the treatment of the joints, for example, this method is the only one possible.
- Waterjet machining metal provides the rust removal under the action of the water jet and abrasive mixture.
The intensity of distinguished waterjetting:
- under super high pressure – completely removes all corrosion coatings applied previously to the work surface;
- under high pressure – removes most of the old coating and corrosion, but there may be areas of highly durable coating and black oxides;
- under low pressure – the most economical way against the abrasive flow, but after the drying the secondary rust traces usually remain.
This method is based on the removal of rust under the influence of chemically active substances. A related species is an electrical-chemical treatment. The formulations are applied to the surface using a brush or a spray.
Means for removing rust are divided into two main categories:
A disadvantage of such compositions is that while contacted with water there can be new sources of corrosion on the treated surface. So, after the washing the materials should be quickly and thoroughly dried and treated with high quality anti-corrosion agents. It is 21st century, but there is still no ways to save the metal from water!
5% aqueous solution of sulfuric or hydrochloric acid also removes rust in a very effective way. But it is definitely added to a corrosion inhibitor – a substance that slows the chemical reaction. Most often it is used as an inhibitor of methylamine. It is necessary to add it in an amount of 0.5 g per liter of solution. Without an inhibitor you can not use acid solutions – otherwise it will dissolve not only corrosion, but also the material.
Quite an interesting result is provided by means of phosphoric acid. Apply 15-30% solution of phosphoric acid onto the treated surface, it will become a durable coating. This is possible because the chemical reaction produces iron orthophosphate, which creates a protective film on the surface. For the best effect an alcohol solution may be added (4 ml per liter of solution) or tartaric acid (15 ml per liter of solution).
Surfaces with the deep corrosion must be treated with a mixture of:
- lactic acid – 50 g
- paraffin oil (100 ml)
This solution converts rust into a soluble salt inside of vaseline oil – the iron lactate.
For the heat treatment you should used oxy-acetylene torch. As a result of exposure of flame, the rust is removed virtually all mill scale. Unfortunately, not all types of rust areas burns well, so this method is almost never used in modern paint systems.
Galvanized surfaces should be prepared correctly: carefully wash away the dirt, grease, debris. Use alkaline solutions (for example, usual washing powder) to wash salts, dirt and grease. Remnants of detergent are thoroughly rinsed with clean water – preferably under pressure – and then well dried. After careful preparation of the surface of the surface you may start painting.
We will be glad if you were able to get all the necessary information on preparing rusty metal for paint and preparing galvanized sheet for paint right here!
Choosing the coating
The primer must be used on the smooth metal surfaces to improve adhesion of the new paint layer, and to ensure uniformity of gloss finish. According to the rules, any unpainted metal surface must first be primed. For some coatings you may need a special resistant to staining primer. In most cases the organic water-borne materials are suitable. In order to prevent leakage of substances from the substrate in the dye layer, it is better to take organic primer. Remember that for metal surfaces you should use primer designed for outdoor use. Moreover, it must have information on the package on how necessary the second layer of the primer is.
Choosing the color and texture
For the painting of metal products and structures you may use various types of paints. In particular, it is possible to use spray paints. However, they need to be put on a well-prepared and primed surface. Glossy paints create strong and durable protective coating and may be applied in one layer. They really resist dirt and mildew. Some of the gloss paints need to be applied over the primer, which is usually said on the package.
There are some special paints for metal designed specially to create the protective coating on metal. They are produced in different versions – with satin or gloss texture.
The most important ‘mustfollows’:
- If you use spray paints, make sure that everything located next to the painted surface is covered with film properly;
- For the painting of metal gutters the waterproof paint containing bitumen should be used;
- Remember that you CAN NOT apply the usual oil paint on the metal.
- goggles or a mask;
- clothes completely covering the body;
- thick rubber gloves.
Important! In too dusty rooms use a dust mask and a respirator to protect the lungs against ingress of chemicals.
We hope this article helped you to learn how to paint metal surfaces with your own hands in a proper way.
How to paint galvanized metal
In modern construction galvanized sheets of paper become more and more popular. It is a very reliable material – it is easy in use, and installation in the construction of various structures, it has resistance to weathering and durability. This choice is truly common in the private and civil construction nowadays. So, more and more customers and house owners want to prolong the life of this material. To achieve this you should perform a simple step – to paint it with special compositions. So, how to paint galvanized metal in a proper way?
The paint must provide:
- increasing the strength parameters of the product;
- improving the product’s aesthetic appearance;
- protection from sudden changes in temperature (it is proved that the correct coloring on galvanized sheet does not change its positive characteristics at temperatures from – 120 – + 300 ?);
- increasing the service life of the material.
According to experts, painting of galvanized sheet with high quality paints manufactured by well-known brands gives a guarantee for increasing the service life of this product for 10-30 years.
Option #1 – powder paints
They are used for coating the entire surface of galvanized structures (for example, the roof of an apartment house or an administrative building). Such paints include fine particles of polymer powder, hardeners, pigments, and various specialty resins. They provide a maximum strength and a high level of adhesion.
- safety application (fire safety, the lack of any kind of allergies and irritations for a man who works with such compositions);
- excellent resistance to weather events and UV radiation;
- unique mechanical properties, such as flexibility and hardness;
- providing the perfect thickness of the coating in a single application layer;
- stability to chemicals (for example, petroleum products, some solvents with organic structure, most of the known acids and alkalis).
In addition, powder coatings do not require use of the additional solvents – they are completely implemented and ready for use just after buying.
Option #2 – alkyd enamels
For some indicators they are comparable powdered paints. In particular, they have similar surface, they resist changes in temperature during the day and different seasons without changing their properties, they are sufficiently stable to UV rays. The only uncomfortable moment – the painting should be carried out on perfectly clean and dry surface ONLY!
It is also allowed to use other kinds of paints. They should ensure the following qualities:
- the ability to exploit the structure of the buildings is galvanized at high temperatures (during the heat of summer) and winter when the cold tangible;
- stability and strength to the service conditions, which are known as adverse (to those already mentioned, including temperature changes, UV radiation, etc.);
- the aesthetic appearance of the coating – unattractive stains and streaks will not appear after the first rain;
- security while application and other operations with the paint (high flammability, emission of harmful toxins elements are not allowed);
- a high level of corrosion protection.
How to paint over galvanized metal: the procedures
There are the following methods of painting galvanized sheet:
- air painting;
- airless painting;
- combined type.
Air method involves the use of a special pneumatic spray gun which uses compressed air for its work. If you correctly pick the speed of ink supply, the shape of the spray plume, the ratio of air flow rate and the composition of the coloring, you can achieve a perfect surface. In addition, air method is considered as very economical and environmentally friendly. Nowadays there is a variety of spray guns for paint – choose the one you like.
Airless technique may be even more favorable – minimum consumption of material, the coefficient of performance is high enough, the paint is applied to the surface evenly thanks to the actions of the painter’s hands. But this option is only suitable for the construction of a flat type. If it is necessary to paint a complex surface, it is better to resort to the combined procedure, carried out under high pressure. This type fits better for the structures that have some peculiarities in the design, sharp angles, etc.
We hope this article helped you to get proper information on the useful information on how to paint galvanized sheet of metal.
Related: How to paint a garage door.