Water-based wood paint is a wood paint with water-based resin (emulsion) as raw material and water as the dispersion and operation medium. It has the most incredible technical difficulty and technological content in wood paint.
1. About water-based wood paint
1.1. Classification of water-based wood paints (according to different components)
1.1.1. The main feature of water-based wood paint with acrylic acid as the main component is good adhesion and will not deepen the colour of the wood.
1.1.2. The water-based wood paint with the composite of acrylic acid and polyurethane as the main component, in addition to having the characteristics of acrylic paint, also has the attributes of strong wear resistance and chemical resistance.
1.1.3. Polyurethane water-based paint has superior comprehensive performance and high fullness. Its paint film hardness can reach 1.5-2H. Its wear resistance can be even better than oil-based paint. It has longer service life and better colour matching. It is a Premium product in water-based paints.
1.1.4. Pseudo-water-based paints need to be added with curing agents or chemicals, such as “hardeners,” “paint film enhancers,” “special dilution water,” etc. Some can also be diluted with water. But the solvent content is very high and harmful to the human body. Some are even more toxic than oil-based paint.
1.2. Characteristics of water-based wood paint
1.2.1. Water-soluble paint is non-toxic and environmentally friendly. It does not contain harmful solvents such as benzene and free TDI.
1.2.2. The operation is simple and convenient. It is not prone to bubbles, particles and other common defects like oil-based paint. And the paint film feels good.
1.2. 3. solid content is high, and the paint film is full and tough.
1.2. 4. It is no yellowing, non-combustible and has excellent water resistance.
1.2. 5. Anti-rust, high-temperature resistance.
1.2. 6. It can be applied simultaneously with other paints, such as latex paint
1.2.7. Some water-based paints have low hardness and are prone to scratches. So we need to pay special attention to this.
1.3. Is water-based wood paint poisonous?
1.3.1. Toxicity: Since the water-based paint is made of an advanced polyurethane system, it has an ultra-low VOC content (below the national mandatory standard of 200 mg/L). It is a genuinely non-toxic, odourless, high-tech and environmentally friendly product. Nitro paint and polyester paint need to add organic solvents and thus contain benzene, toluene, xylene and their derivatives. So polyester paint is the most toxic, while nitro paint is the second.
1.3.2. Stimulant odour: water-based wood lacquer uses water instead of organic solvents, and it will not produce any irritating odour when painting. Nitro and polyester paint contain organic solvents, which will volatilize into the air during the painting and drying. And it will directly stimulate the sensory organs of the human body.
1.3.3. Moving in time after painting: Water-based wood paint has fewer brushing times, quick drying, and easy application. You can move into the apartment soon after painting.
Yet the organic solvents of Nitro lacquer and polyester paint will volatilize harmful gases during the drying process. So we can’t move into houses decorated with nitro lacquer and polyester paint soon after painting. We will need to wait for a period.
2. Operation technology of water-based wood paint
2.1. Preparation before operating water-based wood paint:
2.2. Preparation of tools: brushes, spray guns, air power equipment, scrapers, rags, filters, sandpaper, etc.
2.3. Environmental inspection: Check whether the operating temperature and humidity are suitable, whether the dust is too much, whether there is exhaust ventilation, etc.
2.4. Inspection and treatment of base materials: inspecting the moisture content of base materials ≤ 14%, flatness, suitable operation method, surface cleanliness (whether residual glue, stains, etc.), and treatment of wood joints, etc.
2.5. Product inspection: whether the water-based wood lacquer used is sufficient, whether the variety is correct, whether there is any abnormality in appearance, etc.
Water-based wood paint includes three major products: wood decoration, furniture, and floor paint. Water-based wood paint is only a semi-finished product. It must undergo an operation process until it forms a film on the substrate, produces a decorative effect and creates a perfect wooden life.
2.6. operation technology: base material treatment – scraping putty (this step can be missed if the substrate is flat) – brushing the primer – brushing the top coat.
2.7. Precautions for operation
2.7.1. Substrate treatment: if wooden materials have a moisture content higher than 12% and we can feel damp when we touch the wooden material by hand, we should not do painting on the wooden material.
The wood substrate must be clean and flat, and there should be no oil, glue or other impurities. If there is oil, we can use thinner to remove it.
2.7.2. Substrate treatment before woodworking: use a universal primer or clear primer for sealing (remove surface dust, stains, especially glue before sealing with primer.) and then do woodworking.
2.7.3. Scrape putty: on the treated substrate with a rough surface, we need to scrape 1-3 times of transparent putty, with an interval of 2-3 hours. Suppose the scraping is even and smooth. Then no need to sand and dry thoroughly. The scraping putty can be done before or after the woodworking. The putty does not need to be diluted, and it is generally better to scrape it after one coat of primer.
2.7.4. Apply primer: apply 2-3 times of primer at an interval of 4-5 hours. After each layer is dry (depending on humidity and climate conditions), sand with 800# sandpaper. The primer should be diluted with 10-20% water.
2.7.5. Apply topcoat: Apply topcoat 2-3 times with an interval of 4-5 hours, and lightly sand with sandpaper ≥800# after each layer is dry.
2.7.6. With oil-based primer: Before the wood is painted with water-based paint, if the oil-based primer has been painted, the oil-based primer must be sanded with 360# sandpaper. And only after the dust is removed the water-based primer can be painted. Otherwise, it will affect the adhesion of the paint film.
2.7.7. Rough base material: When applying primer during operation, the rough base material should first be polished with 360-400# sandpaper. And the primer can only be painted after removing the grinding dust. Otherwise, it will affect the operation in the future. The dust that has entered the wood grain can be removed with a brush or sucked out with a clean towel or cloth with humidity.
3. Commonly used water-based wood paint operation schemes
3.1. operation process of water-based wood varnish:
3.1.1. Substrate treatment: remove dust, sand the substrate with 400# sandpaper along the wood grain direction, and remove surface stains, especially glue.
3.1.2. Apply the first primer: (most boards have been painted with oil-based, universal or clear primer). Add about 15% water to the clear primer.
3.1.3. Filling the nail holes: mix the nail hole putty slightly darker than the board. If you are not sure, try it first. After the nail holes are polished, they must be cleaned with a brown brush.
3.1.4. Apply the primer for the second time: After drying, consider whether to scrape the putty one or two times, depending on the depth of the wood grain, and do not need to polish in the middle.
3.1.5. Apply the 3rd primer: use 600# sandpaper to smooth the scraped putty, and dry it until it is not sticky to the sandpaper.
3.1.6. Apply the 1st top coat: (mix with 15% water, mix thoroughly with a 300-mesh filter cloth, let it stand for 20 minutes before use, and clean the surrounding environment).
3.1.7. Brush the top coat for the last time: (sand with 800-1000# sandpaper and then remove the surface particles).
3.2. operation of transparent paint
3.2.1. Substrate treatment of water-based wood lacquer: first, do a sealing primer
Primer: scrap one or two coats of transparent putty according to the thickness of the wood grain of the board and polish it smoothly. Generally, the 2-3 times primer is mainly sprayed thinly until it is the same colour as the samples. Sanding should be avoided.
Topcoat: Do clear topcoat twice. If there are particles, lightly grind them.
Special note: For the boards whose colour is not very deep, generally use high-solid primer done after filling the nail holes and add about 25% water. And it must be dry before proceeding to the following process. Dry sanding should be at 25°C. After 3 hours, the sanding should be powdery and non-stick to the sandpaper.
3.3. operation process of water-based white paint:
3.3.1. Substrate treatment: apply white primer once (add 10-15% of water to seal the substrate to prevent the colour of the plate from coming back through. if necessary, we can do one primer on the substrate to seal). If the primer is not applied first, the self-adjusting putty in the wooden pores is easy to bulge when exposed to water.
3.3.2. Scrape the self-adjusting putty twice: (the first time is thick, the second time is thin). Levelling shall prevail. Please do not use the pig’s blood ash as the base because the pig’s blood ash itself will swell in water.
Methods of making self-adjusting putty:
①cooked glue + a small amount of white latex + double-flying powder or putty powder
②transparent putty + double-flying powder + a small amount of water. When adjusting the putty, the hardness and polishing depend on the amount of white latex added.
The method of scraping self-adjusting putty:
①Scrape evenly to fill the solid wood seams and pores, and sand with 400# sandpaper after drying. Do the scraping 3 times.
②scrape thinly and not too thick to prevent cracking. (The thinner, the better).
3.3.3. After the putty is dry, sand it with 600# sandpaper: add no more than 10-15% water for the first time when applying the white primer. Sand with 600# sandpaper after drying and then scrape the 2nd primer. The drying time depends on the actual temperature, and it must dry well.
3.3.4. Spray and brush the top coat for the first time: (mix with water 10-15%. the top coat must be sprayed thinly). After drying, polish it with 800-1000# sandpaper.
3.3.5. Spray the top coat for the last time: (add 15% water and filter with 100# filter cloth and spray one cross.) we can do one more top coat before the last coat.
4. Matters needing attention in the operation of water-based wood paint
4.1. The temperature at the operation site must be higher than 8°C. The relative humidity should be lower than 85%, and the moisture content of the wood should be lower than 15%.
4.2. The wool brush should be soaked in clean water to remove foreign matter and electrolytes before use. Otherwise, the brush and water-based paint will easily agglomerate. After use, the wool brush should be cleaned immediately and cannot be left in the prepared paint.
4.3. Please use pure water or distilled water to dilute. If you want to use tap water, you should be careful. It can be used only after 15 minutes when there is no abnormality after mixing the paint.
4.4. Stir evenly before mixing the paint. After mixing the stain, let it stay for 10 minutes and filter it before use. Please seal the mouth of the tank immediately after use to avoid the entry of harmful substances.
4.5. If the finished paint is not used up or the operation interval is too long, it should be covered immediately so as not to affect the operation effect.
4.6. Water-based wood lacquers are sensitive to salt. If sweat and other salt substances contaminate the substrates, we should clean them in time. Otherwise, the adhesion and appearance will be affected.
4.7. Water-based wood lacquer can be painted on nitro-lacquer, and PU paints after fully polished. But nitro-lacquer and PU paint cannot be painted on water-based wood lacquer (the older paints may contain wax and silicon components. We suggest applying a small scale of thin sealing primer first for test and then doing large-scale primer.)
4.8. When painting water-based wood paint, do not drag the brush back and forth, but brush thinly and lightly along the wood grain in the same upward or downward direction.
4.9. When mixing nail hole putty, the colour of the dry putty should be the same as the base material.
5. Several critical issues in the operation of water-based wood paint
5.1. About water-based filling soil, atomic ash, pig blood ash, white latex and putty powder: Generally, when making white primer and white topcoat, a filling soil will be applied on the first layer to increase its filling performance. And It will also be used in the gap of wood bonding.
Water-based wood lacquers will crack if unsuitable filling soil is used and the film-forming strength is insufficient. If the gap is too large, it must be filled with sawdust and then filled with soil, so it is not easy to break.
5.2. Regarding patch holes: fill the nail holes on the substrate with the nail hole ointment directly. The ointment can completely cover the nail holes without unique colour adjustments.
5.3. Regarding the sealing primer: the sealing primer plays a vital role in the white series of water-based wood lacquers. For example, in some materials such as MDF and veneered solid wood, if the sealing primer is not used, the material is easy to bleed, and the paint film turns yellow. Not all materials need to be sealed. It is recommended to do a small board test first.
6. Common operation problems and solutions of water-based wood paint
6.1. Brush marks
Analyze the reasons:
(1) The water-based wood paint is not diluted enough, and the viscosity of the paint is too high;
(2) The tool brush for painting is too hard, and the bristles are too short;
(3) Repeated brushing or re-brushing too many times;
(4) Repaint when the paint film is drying;
(5) Improper operation techniques.
(1) According to the provisions of the product operation manual, add water and dilute in a reasonable proportion;
(2) Be sure to use a delicate wool brush for painting;
(3) Do not repeatedly brush or lightly brush;
(4) Do not repaint when the paint film is drying;
(5) During operation, pay attention to brushing up and down to make the coating even lightly.
Analyze the reasons:
(1) Brushing too thick;
(2) Too much water diluted in the water-based wood paint;
(3) The operation humidity is too high;
(4) The nozzle hole of the spray gun is too large
(1) It is recommended to choose a light and thin wool tool brush to brush thinly and lightly.
(2) When adding water and diluting, pay attention to the ratio, and the paint cannot be adjusted too thin;
(3) Ensure the ventilation of the operating environment and control the indoor humidity;
(4) Adjust the nozzle hole of the spray gun;
6.3. there are cracks
Analyze the reasons:
(1) The temperature during operation is lower than 5°C.
(2) The operation paint film is too thick.
(3) The quality of the substrate is not good and shrinks.
(1) Ensure that the operation problem is above 5°C;
(2) Spray thinly to ensure that the thickness of the paint film is moderate;
(3) Choose good quality substrate to ensure stability.
6.4 Shrinkage cavity of a paint film
Reason: there is an organic solvent or other oily substances mixed.
Solution: paint it after re-sanding the wood.
6.5. Whitening of the paint film
(1) The humidity of the operating environment is too high, and the indoor temperature is lower than 5°C;
(2) During the painting process, the paint film is too thick to dry completely;
(1) Adjust the humidity and temperature of the operating environment;
(2) Be careful not to apply thickly and ensure that the paint film can dry completely.
6.6. Poor adhesion
(1) There is an oily substance on the surface of the wood, or the polished dust has not been swept away;
(2) The interval between recoating should be shorter.
(1) Grinding to remove oily substances and impurities on the wood surface;
(2) Control the recoating time well and recoat after thorough grinding
7. Frequently asked questions about water-based wood paint
7.1. What is water-based wood paint?
As the name suggests, water-based wood lacquer is a paint diluted with water instead of organic solvents. It is painted on wood products for decoration and protection.
7.2. What are the characteristics of water-based wood paint?
Water-based wood paint does not contain harmful substances such as toluene, xylene, CAC, formaldehyde and free TDI. The paint film has or is close to solvent-based paint’s general characteristics and surface effects.
7.3. Why are solvent-based paints (paints) toxic? What are the harms to the human body?
General solvent-based (paint) inevitably uses a large amount of thinner during operation. The thinner contains harmful solvents such as benzene, toluene, xylene and their derivatives, which can accumulate in the human body and cause Respiratory system, and liver disease may also cause leukemia.
Free TDI (toluene diisocyanate) can cause respiratory and reproductive lesions in the curing agent. Even long-term low-dose exposure to these harmful substances can lead to various cases of leukemia, male and female infertility, cancer, and even death.
7.4. Why does the water-based wood paint not yellow latex paint during operation?
During solvent-based polyester paint, the volatilized free TDI monomer reacts with specific chemical substances in the latex paint to produce coloured substances, turning the latex paint yellow. However, water-based wood paint only evaporates water, and there is no free TDI, so it will not make the latex paint yellow.
7.5. Why is water-based wood paint better in abrasion and impact resistance than solvent-based polyester paint?
This is related to the resin used. Solvent-based polyester paint is hard and brittle, cannot withstand the impact of hard objects, and is easy to crack and peel off. And we choose the water-based acrylate system. The latex particles have a three-layer core-shell structure, which makes the strength and toughness of the product reach a perfect combination point, so it is hard but not brittle and has good wear resistance and impact resistance.
7.6. Why use a special wool brush?
Commonly used wool brushes very easy to react with water-based wood paint, harden and produce particles. The matching special wool brush has been treated so that the above phenomena will not occur. If other wool brushes are used, they must be cleaned with detergent or washing powder or soaked in water for more than 12 hours before use.
7.7. Why should the storage temperature of water-based wood paint be between 5°C and 35°C?
Because the freezing point of water is 0°C, water-based wood paint uses water as a diluent. Although antifreeze is added to the product, the water may freeze when the temperature is lower than 0°C. When the temperature is higher than 35°C, various additives in water-based wood lacquers may change, and some even fail to hydrolyze, resulting in product quality problems.
7.8. Why should the operation temperature not be lower than 5°C?
The film-forming and drying of water-based wood paint are based on water volatilization. If the temperature is lower than 5°C, the water volatilization is too slow, causing the paint film not to dry and become white. If the temperature is lower than 0°C, the paint film may be Icing and cracking.
7.9. Can water-based wood lacquer be waxed?
Yes. But since the drying of water-based wood paint is closely related to temperature and humidity, it is recommended to wax after one day of operation.
7.10. Can water-based wood lacquer paint film be polished with water?
Yes, the paint film of water-based wood lacquer can be dry sanded with sandpaper and polished with water. But we should pay attention to the dryness of the paint film when sanding. If the paint film is not dried thoroughly, the whole film may be sanded off or become whitening.
7.11. How long can we stick stickers to protect the paint after painting?
Sticker protection mainly depends on the drying degree of the paint film. Generally, we can stick stickers in 12 hours after the surface is dry. But when tearing off the sticker, pay special attention to whether the paint film is completely dry. If the paint film is not fully dry, it is easy to tear off the whole piece. The correct way is to use a blade to cut the edge of the sticker and then tear it off the sticker.
8. Water-based wood paint acceptance skills
8.1. Clear varnish
(1) Check whether the paint surface is smooth and whether there are cracks, scratches and dirt;
(2) Touch the paint surface with your hands to see if it is smooth and whether there are roughness and particles;
(3) Check whether the thickness of the paint surface is consistent, whether the paint surface is saturated, and whether the fullness is good;
(4) Check the glossiness of the paint surface and whether the reflection is uniform;
(5) Check whether the hardness of the paint surface is up to standard, but it is recommended that you do not use hard force to scratch so as not to cause “mishaps” if the hardness of the paint film is not reached.
(6) Check whether the bottom of the paint surface is thorough and whether there is any whitening.
8.2. Wipe colour paint
(1) Check whether the colour at the bottom of the paint surface is evenly rubbed and whether there is any inconsistency in colour depth;
(2) Check the corners of the wood to see if there is any missing colouring;
(3) Check the position of the water chestnut of the wooden furniture to see if there is any “colour loss” caused by uneven polishing;
(4) Check whether the paint surface is smooth and whether there are cracks, scratches and dirt;
(5) Touch the paint surface with your hands to see if it is smooth and whether there are roughness and particles;
(6) Check whether the thickness of the paint surface is consistent, whether the paint surface is saturated, and whether the fullness is good;
(7) Check the glossiness of the paint surface and whether the reflection is uniform;
(8) Check whether the hardness of the paint surface is up to standard, but it is recommended that you do not use hard force to scratch so as not to cause “mishaps” if the hardness of the paint film is not reached.
(9) Check whether the bottom of the paint surface is thorough and whether there is any whitening.