Cracks and peeling walls? 90% of the time, it’s because this step wasn’t done right.
When people renovate, one of their biggest fears is seeing cracks, peeling, or flaking after the latex paint goes on. In most cases, though, the paint itself isn’t the problem. The real issue is poor preparation of the wall substrate, which leaves hidden problems behind.
Today, we’ll break down the most important part of the process before latex paint is applied—wall surface preparation—step by step, so you can see what needs to be done and why.
The first step is removing the old skim coat, commonly called “scraping the wall.” Regular joint compound has weak adhesion and no water resistance, so it must be removed; otherwise, it can later become hollow and fall off. Water-resistant joint compound is stronger and holds up well against moisture, so it can stay, but removing it costs more, so the decision depends on the actual situation.
Next is applying a bonding primer, also called a wall primer or wall stabilizer. Its main job is to seal dust and improve adhesion so the new skim coat bonds firmly to the wall. As for timing, it can be applied right before the painter starts work; doing it too early makes it easy for dust to stick to it and weaken its effect. Apply it evenly and don’t miss any spots.
Filling seams and grooves is a key step in reducing cracks. If the channels left after electrical and plumbing work are filled directly with cement mortar, they can easily crack from expansion and contraction. The right approach is to use a dedicated joint compound to fill the channels, not cement mortar. After filling, place a layer of paper tape over the joint and apply wall primer again. This effectively prevents cracking. Where new and old walls meet, or where different materials meet—such as concrete and brick—mesh reinforcement must be installed.
If your home has a suspended ceiling or drywall features, pay special attention to drywall treatment. At screw heads, apply anti-rust paint first to keep rust from bleeding through as yellow spots later. At V-shaped joints, fill them flat with joint compound. Once the joint compound is completely dry, brush on white glue, apply paper joint tape, and then apply wall primer again. For curved drywall features, in addition to rust prevention, mesh should be installed over the entire surface to prevent cracks on the curved face.
Outside corners—the protruding wall corners—are the most prone to knocks and often aren’t straight, so corner bead needs to be attached to reinforce and straighten them. The corner bead should fit tightly against the wall; after pressing it down, let the compound squeeze out through the holes to ensure a strong bond. When skimming, only apply compound to the wall surfaces on both sides of the corner bead. Do not skim over the rounded part, or it may crack. Later, sand the rounded part. This also helps latex paint adhere better.
There are three main ways to level a wall. Follow-the-wall leveling, or basic flatness leveling, works along the original wall surface. It’s fast and cost-effective, and it’s the most common method for ordinary home renovations. Screed leveling is more precise and can level and square the wall at the same time, but it takes longer and costs more. It’s mostly used when cabinets have no adjustable panels or in minimalist-style renovations. Gypsum leveling is suitable for patching small, uneven areas. For follow-the-wall leveling, use a 2-meter straightedge together with an inside/outside corner square and scrape the wall flat along its surface. Try to level areas near doors, cabinets, and baseboards as precisely as possible. If wallpaper or wall cloth will be applied later, it’s best to level all inside and outside corners. For screed leveling, here’s a reference method: use a laser level to mark vertical lines and attach mortar dabs; set a screed every 1.2 to 1.5 meters; use vertical screeds when the wall height is less than 3.5 meters, and horizontal screeds when it is greater than 3.5 meters; the plastering thickness should be no less than 5 mm, and the maximum thickness depends on how much the wall leans.
When applying skim coat, it’s best to buy ready-mixed water-resistant joint compound. On a second renovation, it won’t need to be removed, which saves time and effort. Follow the manufacturer’s ratio for mixing with water, and never add glue. Adding glue actually makes later cracking more likely. Usually, two coats are applied, built up in layers: each layer should be about 1 mm thick, with a single layer not exceeding 2 mm, and the total thickness should not exceed 3 mm. After the first coat, wait 2 to 3 days for it to dry completely before applying the second. After scraping, the wall should be flat and smooth, with square corners and an even texture.
Once the compound is fully dry, sanding should ideally be done within a week after completion. You can use an electric sander or sand by hand, and a finer grit sandpaper is recommended. After sanding, the vertical deviation should be no more than 3 mm, the wall flatness deviation no more than 2 mm, and inside and outside corners should be square with straight lines. Why use bright light? Under ordinary lighting, bumps and dips in the wall are hard to see. Sanding with a bright light shining across the surface exposes every flaw, allowing you to create a finer wall finish. This is also a key test of a worker’s skill.
The whole wall preparation process can be summed up this way: remove the old skim coat, and regular joint compound must be removed; apply bonding primer, or wall primer; fill seams and grooves with joint compound, paper tape, and mesh; treat drywall for rust and joints; attach corner bead; level the wall, mainly with follow-the-wall leveling and screed leveling in special areas; apply water-resistant joint compound in two coats without adding glue; and sand under bright light until flat. If you complete these eight steps, your wall will truly have a solid base, and the latex paint applied afterward will be flat, attractive, and free of cracks.
