1. First, Check How Severe the Mortar Sanding Is

A mortar wall that sheds dust or sand does not always need to be completely removed and replastered. The first step is to determine how serious the problem is. You can lightly scratch the surface with a key, screwdriver, or another hard object, or rub the wall firmly by hand. If only a small amount of dust or fine sand comes off while the mortar remains solid, with no obvious peeling, detachment, or hollow areas, it is usually mild surface sanding. However, if a large amount of sand comes off easily, or the wall shows loose mortar, peeling, large-scale material loss, or hollow sounds when tapped, the problem is more serious and may indicate significant loss of strength or bonding performance.

For mild surface sanding, a suitable penetrating wall consolidator or mortar hardener can usually be used to strengthen the surface. First, thoroughly remove loose dust, sand, and weak particles to ensure a clean substrate. Then apply the treatment evenly with a roller, brush, or spray equipment and allow it to penetrate into the weak mortar layer. If the wall absorbs the material very quickly, an additional coat may be applied when necessary. After the material has fully dried and cured, the surface strength can be significantly improved. However, if the wall has extensive sand loss, loose mortar, peeling, or hollow areas, a simple surface treatment is usually not enough. The damaged mortar should be completely removed until a sound and stable substrate is reached before replastering.

Before applying new mortar, clean the substrate thoroughly and pre-wet it when necessary, depending on its water absorption. For smooth or unevenly absorbent surfaces, suitable bonding or interface treatment may be required to improve adhesion between the new mortar and the substrate. During replastering, use stable and suitable raw materials, maintain a proper mix design, and avoid adding excessive water during application. Proper curing is also essential, especially in hot, dry, or windy conditions where moisture can evaporate too quickly and affect mortar strength development. In short, mild surface sanding can often be repaired through surface strengthening, while moderate to severe damage usually requires removal and replastering. Choosing the right solution based on the actual condition of the wall is the key to improving long-term strength and durability.