There are three main types of maintenance paints currently used on ships, namely alkyd paint, green rubber paint, and epoxy paint.
The following is an introduction to the properties of paints, problems encountered in crew maintenance, and their uses:
1. Properties of alkyd paint, chlorinated rubber paint, and epoxy paint; advantages and disadvantages and applicable areas are compared as follows:
(1) Alkyd paint
This type of paint has a thin film, generally 40-50 microns. It has a low solid content, a large coating rate, dries slowly, and generally has a drying time interval of 8-15 hours. The paint will not dry below 5 degrees. The paint film is brittle and will crack when the temperature difference changes greatly. Alkyd paint is generally used for cargo holds, decks, hatch covers, and living area buildings. This paint cannot be used for ballast water tanks and freshwater tanks.
(2) Chlorinated rubber paint
The paint film thickness can generally reach 60-100 microns, with a high solid content, a soft, elastic, and resilient film, and is not affected by temperature. The anti-rust performance is better than that of alkyd paint. It dries quickly and the drying interval of each coat of paint is 4-6 hours. It does not affect drying below 0 degrees. Chlorinated rubber paint can be used on hulls, decks, etc. (3) Epoxy paint
The paint film thickness should be at least 70-80 microns and cannot be too thin. The paint thickness can reach 300 microns. It has a high solid content, a low coating rate, and is difficult to apply. It dries quickly and is not affected by weather. Generally, it can be applied normally above -10 degrees. The drying interval is 3-6 hours. Epoxy paint can prevent rust, collision, and wear. This paint can be used for maintenance in various parts of the ship. However, the metal surface needs to be sandblasted to level 25 before using this paint.
2. In actual work, crew members often use the wrong paint because they do not know the nature of the original paint. How to test the type of paint that has been applied?
First, soak a piece of cotton yarn or rag in the paint mixing water of chlorinated rubber, then place the soaked cotton yarn or rag on the surface of the topcoat to be identified. After 5 minutes, use this wet cotton yarn or rag to wipe the soaked paint surface. If the paint surface is melted and wiped off, it means that the topcoat is chlorinated rubber topcoat. On the contrary, if it does not melt and cannot be wiped off, it means that the topcoat is alkyd paint or epoxy paint. So how to distinguish between alkyd paint and epoxy paint? This is very simple. Use a rusted hammer to tap the paint's surface. The painted skin falls off from alkyd paint; the hard surface is epoxy paint.
3. Storage of paint and identification of whether the paint can be used
Usually, the temperature of the storage place is high and the paint has a short storage time and is easy to deteriorate. On the contrary, the storage time is long. Generally, the paint bucket needs to be turned over every six months for storage. After the paint bucket is opened, if there is no block in the paint and it can be fully stirred (WeChat public account: Shipping Elite Circle), the paint can be used.
4. As for whether alkyd paint, chlorinated rubber, and epoxy paint can cover each other, the crew is usually not very clear. Here is the explanation:
A. Alkyd paint is used as the base, and chlorinated rubber topcoat can be applied on the surface (but it is best not to do so). Epoxy paint cannot be applied on the surface of alkyd paint, otherwise the paint will fall off or curl up.
B. Chlorinated rubber paint is used as the base, and alkyd paint cannot be applied on the surface, otherwise cracking will occur. Epoxy paint cannot be applied on the surface of chlorinated rubber paint, otherwise cracks or wrinkles will occur.
Epoxy paint is used as the base, and alkyd paint and chlorinated rubber paint can be applied on the surface, but the surface must be polished and roughened. Otherwise, the two paints will not adhere.
5. What will happen if the interval between repainting of alkyd paint, chlorinated rubber paint, and epoxy paint and the incorrect time interval for repainting?
Usually based on 20℃, the time interval for repainting of alkyd paint is 8-15 hours; the time interval for repainting of chlorinated rubber paint is 4-6 hours; and the time interval for repainting of epoxy paint is 3-6 hours. Alkyd paint and chlorinated rubber paint can be repainted later, but it is best to repaint within the drying time.
6. Paint coating thickness and coating rate
Alkyd paint coating thickness is about 40 microns, and the coating rate is 8-9 square meters per liter. 2. Chlorinated rubber paint coating thickness is about 50 microns, and the coating rate is 6-7 square meters per liter. 3. Epoxy paint coating thickness is about 75 microns, and the coating rate is 5-6 square meters per liter.
7. Usage and dosage of paint mixing water for various paints
(1) Pay special attention to the fact that the paint mixing water of various paints cannot be mixed, and it must not be used incorrectly.
(2) The amount of paint mixing water used for alkyd paint is 0-5% (WeChat public account: Shipping Elite Circle). The amount of paint mixing water used for different storage times is different. Usually, the amount of paint stored for a long time is slightly larger.
(3) The amount of paint mixing water used for chlorinated rubber paint is 4-8%, and it cannot be used too much.
(4) The amount of water used for epoxy paint is 8-12%. Add more when the temperature is low and add less when the temperature is high.
8. Use of curing agent for epoxy paint
Epoxy paint is a two-component paint that is divided into large barrels and small barrels. The small barrel of paint is the curing agent and the large barrel is the paint. When using, match a small barrel of curing agent to each large barrel of paint. Mix thoroughly and use it all at once, otherwise, the remaining paint will become as hard as stone and cannot be used. If the area to be painted does not take up a whole barrel, mix the amount in proportion to avoid waste. The proportion of curing agents must be appropriate. Too much paint will dry quickly, resulting in the paintwork not being completed, and the paint in the barrel will be dry and cannot be used; too little curing agent will not dry the paint. Therefore, the key to the use of epoxy paint is the correct ratio of curing agent to paint. After the work is completed, the painting tools must be cleaned in time, otherwise they cannot be used next time.
9. The influence of temperature and humidity on paint during construction
(1) Alkyd paint is above 5℃ and humidity is below 85%. The paint will not dry below 5℃.
(2) Chlorinated rubber paint: above 0℃, humidity below 85%.
(3) Epoxy paint: above -15℃, humidity below 95%.
10. Deck surface pretreatment before painting
(1) Before painting alkyd paint and chlorinated rubber paint, the surface must be cleaned with fresh water to remove salt, and rust and wipe clean. Generally, two coats of primer and one coat of topcoat or one coat of primer and two coats of topcoat are used. Pay special attention to cleaning the surface salt, because salt will absorb water and cause the steel plate to rust quickly.
(2) Before painting epoxy paint, the surface needs to be sandblasted at level 2.5.
11. Antifouling paint below the waterline
Currently, self-polishing antifouling paint is used below the waterline of ships. Its antifouling performance is that the paint film is constantly polished and worn during the voyage of the ship, and toxins are released to prevent marine organisms from surviving on the hull. The slower the ship speed, the slower the polishing speed of the paint film, and the less toxins are released. When the ship is not sailing, the paint film is not polished and worn, and no toxins are released. Therefore, marine organisms may live on the hull of the ship during the period when the ship is at rest.