Why are there scratches on the putty after polishing?

Wall polishing, refers to the putty batch scraped on the wall, in order to make the wall more flat, the surface more detailed, uniform, and putty polishing.
you do wall polishing?
1, the main role of putty is to find flat, but only scrape putty words, only do half of the flat work, the other half, is also half of the final effect, to be solved by polishing. This is also the most important function of wall polishing
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2, putty scraping process, it is inevitable that there will be some small defects, such as putty junction of the pick-up, local batch scraping thin or too thick left traces, wall water absorption caused by pinholes, these defects can also be solved by wall polishing.
3, the overall polished putty surface structure is more uniform and consistent, can enhance the performance of latex paint, and avoid the differences in surface structure may cause some problems (such as color paint local color differences).
tools are used to polish the walls?
two tools are highlighted here: light bulbs and sandpaper.
01
light bulb
in order to be able to observe the flatness of the wall at any time, when grinding, day and night, workers generally have a light bulb in their hands. The wattage of the bulb is generally above 200 watts, so that the flattening of the walls can be observed well even during the day.
02
sandpaper
sandpaper selection is a matter of concern to everyone, here is the system to talk about.
number of sandpaper items commonly found in wall polishing (number of grains per inch) is 80, 120, 180, 240, 320, 400, 600. Among them, 80, 120 can be classified as coarse sandpaper, 180, 240 for medium, more than 320 for fine sandpaper.What is the number of
items, the so-called number of eyes, refers to the particle size of the material and the weight of sandpaper, refers to the area of 1 inch X 1 inch has how many mesh holes, the material can pass through the mesh hole is defined as how many eyes: for example, 150 eyes, that is, the material can pass through 1 inch x 1 inch inside the screen with 150 mesh holes. And so on, the smaller the number of items, the greater the material granularity. The larger the number of items, the finer the material granularity.
how do you self-test the number of sandpapers? Domestic standard list:
screen size: 4.75mm - standard number of eyes: 4 mesh
perforation size: 4.00mm - standard number of eyes: 5 mesh
sieve size: 3.35mm - standard number of eyes: 6 mesh
size: 2.80mm - Standard number: 7 mesh
perforation size: 2.36mm - Standard mesh: 8 mesh
sieve size: 2.00mm - Standard number: 10
Sieve size: 1.70mm - Standard number: 12 mesh
sieve size: 1.40mm - Standard mesh size: 14 mesh
sieve size: 1.18mm - standard number: 16 mesh
sieve size: 1.00mm - Standard number: 18 mesh
-perforation size: 0.850mm - Standard mesh: 20 mesh
-perforated size: 0.710mm - Standard number: 25 mesh
Perforated size: 0.600mm - Standard number of eyes: 30 mesh
-perforated size: 0.500mm - Standard mesh: 35 mesh
-perforated size: 0.425mm - Standard number: 40 mesh
sieve size:0.355mm - Standard number of eyes: 45 mesh
seeded size: 0.300mm - Standard number of mesh: 50 mesh
sieve size: 0.250mm - standard number of eyes: 60 mesh
perforation size: 0.212mm - Standard number of eyes: 70 mesh
seve size: 0.180mm - Standard number of eyes: 80 mesh
sieve size: 0.150mm - standard number: 100 mesh
perforation size: 0.125mm - Standard number: 120 mesh
-perforated size: 0.106mm - Standard eye size: 140 mesh
-screen size: 0.090mm - Standard mesh: 170
Sieve size: 0.0750mm - Standard number: 200 mesh
perforation size: 0.0630mm - Standard mesh: 230 mesh
perforation size: 0.0530mm - Standard number of eyes: 270 mesh
perforated size: 0.0450mm - standard number: 325 mesh
or more refers to the Sandpaper United States standard (the domestic use of this standard), if Taylor's size will be different should be measured.
Sandpaper is too thick, easy to lead to scratches, sandpaper is too fine, it is difficult to polish smooth, so the choice of wall sandpaper, is not the thicker the better, nor the finer the better, but with the wall putty match is appropriate.
In practice, first of all to be able to do a good job of flatness as the preferred goal, wall polishing with more than 240, 320 first try, if the polishing is not very hard, you can do a good job of flatness, then continue; Under the premise of ensuring the flatness of the wall, if the first use of coarse sandpaper, the general whole or local also need to be polished with fine sandpaper, in order to eliminate the scratches left by coarse sandpaper, and make the wall more detailed.
in terms of putty quality. Non-water-resistant putty because of the loose surface structure, so it is easier to polish, generally with 240, 320 or higher sandpaper to fight, but because most non-water-resistant putty quality is relatively poor, the powder itself is generally low, so even with high-purpose sandpaper sanding, it is difficult to play a very detailed feeling. Water-resistant putty surface structure is relatively strong, sanding than non-water-resistant putty labor is a lot, especially some high-strength type of water-resistant putty, if you wait until the putty is completely dry and then polished, it is very difficult, this time you need to use coarse sandpaper to do a good job of flatness, and then use fine sandpaper to hit the second time, in order to achieve better results.