Think about undercoat (1)

Written by Archer. Posted in Professional Tips

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Published on May 02, 2016 with No Comments

Undercoat, just as its name implies, is a layer of paint on the surface before finish coat.
Official explanations from many websites and journals suggest that undercoat lies at the bottom of finish coat, functioning as a foundation, closing wall spaces (substrate), and increasing the adhesion of the finish coat. Generally, whenever it comes to finish coat, undercoat will be mentioned. It is definitely a fundamental base.
To be more detailed, we need to further distinguish the area requiring paint, is it a ceiling, a wall, a doorframe or a window? Is the doorframe made of wood or iron? When differentiated more detailed, it is required that different media should use different undercoat. Although most undercoat products currently on the market guarantee three-in-one or even five-in-one, saying that they can function well as a foundation on all kinds of media, it is still necessary for us to get started from traditional processes. It is because that, after all, the new characters are not known to everyone. When using, it will surely bring in some risks once skip the tradition ways.
When talking about undercoat, we should always start from the three attributes of the undercoat, namely, water-based, oil-based or alcohol-based. The explanation, however, is doomed to be lengthy. We will start from water-based undercoat. 80% of the products currently on the market are water-based, meaning that they can dissolve in water and diluted with water. In actual practice, although water will thin and reduce the coverage and adhesion of the undercoat, but if we blended it properly, it could make the surface of the paint smoother, avoiding too many marks and increasing the aesthetics greatly. Whether the undercoat has been applied evenly affects the decorative effect of the finish coat to a large extent. If the undercoat is applied roughly, it will certainly require large amount of manual work to sanding that even. The sanding process is indispensable since applying the undercoat to the surface is supposed to produce a few small particles. Therefore, there is another important indicator when evaluating the quality of the undercoat, which is whether it is easy to be sanding even.
We can see a few effects of the undercoat here using the most common product in the most common scenario as an example. We often build new houses or enhancement parts. Currently on the market, 80% walls and ceilings are made of plastered board. Customarily, we should first apply a coat of water-based undercoat to the plastered board (we usually choose Dulux Professional TotalPrep products before 2014). There are two reasons. 1. The imperfections on the plastered board are more easily to reveal, making it easy for us to fill the gray for the second time. It is hard to discover all the flaws with our first instinct only using naked eyes. When the undercoat is white, there will be slight reflection of light after drying out. So, it is much easier to find the imperfections when observing from the side. 2. Applying water-based undercoat on the surface of plastered board seals all the pores and particular areas like joints or nail patches, while provides a smooth and even surface for the finish coat. It is just like sealing the surface with a layer of plastic film.
In fact, most undercoat products are of the same purpose: sealing the surface and providing an even substrate. Why seal the substrate? What would happen if not sealed? Actually, surface seemed to be smooth has numerous pores, and are not evenly located. If the substrate is not sealed, after applying the finish coat, especially in wet, it is obvious to find that the abilities to absorb paint are different between parts of the substrate. Some areas dry out faster since the substrate has already absorbed some of the finish coat. While other areas dry out more slowly since seldom has been absorbed. What we are looking forward should be that: the substrate is perfectly even and the finish coat is hardly absorbed after applying, which means there is no loss, it is completely attached to the surface, and dry out naturally. In this way, it would be particularly aesthetic. If the substrate is not even, the gloss would be different, largely affecting the decorative effect of the finish coat.
It can be seen from the picture displayed on the right that it is easier for us to find which areas need repairs after applying a layer of the undercoat. The undercoat provides us with a quality flat surface, as a uniform tone.
Therefore, when reading the instructions of undercoat in English, we can often see instructions like, sealer, undercoat, and primer. Water-base undercoat currently on the market usually displayed with these three slogans. What are the differences? Do these have the same meaning? In fact, undercoat is a general term, while sealer is the genuine role of the undercoat. Primer is used in coloring in most cases, meaning the fundamental coloring before applying finish coat.
The sealing function is difficult to be seen simply on a new plastered board. The new plastered board itself is very smooth after all, so it is easier to find the flaws. However, when it comes to concrete walls, the undercoat layer is indispensable if they are new. This is because that it is difficult for finish coat to fill all the pores within 2 coats on bare concrete walls. For exterior walls, exposed to the weather, if the finish coat paint is not binding appropriately, peeling would be inevitable. What we have met many times are that interior walls in the condition of new plastered board, the quality is guaranteed throughout the year without undercoat as long as the room is not that humid, but that exterior walls would peel even a small area’s undercoat is not well applied. Of course, what I emphasis here is new panels or new concrete walls, which are media that have not been applied by any paint. Many painted old media will depend on their specific circumstances to decide whether undercoat is needed.
What displayed below are the good decorative effects achieved, given that the walls do not absorb paint anymore and the finish coat is applied evenly on the surface after the sealing of the undercoat. The liquid tiled effect is more obvious when in wet. (This is certainly a very high standard for walls. Some walls may even require twice sealing to achieve the effect.)
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About Archer

Archer is a full time painting contractor, specialize in research paint product, review milestones of painting industry, deliver the most effective way of project and fine finish. " I do painting, deal with the issues and fix the problems with the best solution and resources, sometimes write them down as an education material"

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