What Is The Thickness Control Standard For The Terrazzo Surface Layer Of Prefabricated Panels? What Problems Can Occur If The Terrazzo Of Prefabricated Panels Is Too Thick Or Too Thin?

Control standard and problem analysis of thickness of prefabricated panel terrazzo surface layer
1, Thickness control standard
According to the "Code for Acceptance of Construction Quality of Building Ground Engineering" (GB 50209-2010) and industry practice, the thickness of the precast slab terrazzo surface layer (excluding the bonding layer) should be controlled between 12mm and 18mm, which needs to be determined according to the stone particle size. For example:

Ordinary terrazzo: The stone particle size is small, and the surface layer thickness can be taken as 12mm to 15mm;
Advanced terrazzo (such as colored and large-sized stones): In order to ensure uniform distribution of stone particles and surface smoothness, the thickness of the surface layer needs to be increased to 15mm~18mm, and even up to 25mm~30mm (such as when using the "seed" construction method to lay large-sized stones).
2, Problems caused by excessively thick or thin surface layer
1. The surface layer is too thick (>18mm)
Increased risk of cracking:
Excessive thickness of the surface layer can lead to an increase in cement shrinkage stress, especially when the base settlement is uneven or temperature changes occur, which can easily cause cracks. For example, if the backfill soil at the grassroots level is not compacted properly or there is a large difference in settlement at the pipeline trench, the excessively thick surface layer will crack due to stress concentration.
Hollow drum and detachment:
When the surface layer is too thick, the cement slurry bonding layer may not fully penetrate to the base layer, resulting in weak bonding. If the grid strip is not firmly embedded or the surface layer cement slurry is laid too high, the grid strip will not be exposed clearly, further weakening the connection between the surface layer and the base layer, which can easily cause hollowing.
Rising construction costs:
The increase in material usage directly drives up costs, and the excessively thick surface layer requires longer curing time, prolonging the construction period.

2. The surface layer is too thin (＜ 12mm)
Decreased wear resistance:
The wear resistance of terrazzo depends on the bonding thickness between the stone particles and cement. When the surface layer is too thin, the stone particles are not exposed enough, and the surface is prone to wear, especially in high flow areas such as industrial workshops and hospital corridors. After wear, the base layer is easily exposed, which affects the service life.
Uneven exposure of stone particles:
A thin surface layer can lead to uneven distribution of stone particles, with some areas having too many exposed stone particles and others having insufficient exposure, affecting the decorative effect. For example, if the surface layer of colored terrazzo is too thin and the pigment distribution is uneven, color difference is prone to occur.
Difficulty in ensuring flatness:
When the surface layer is too thin, the small unevenness of the base layer will be directly reflected in the surface layer, resulting in an uneven surface. If the joints or end joints of prefabricated panels are not poured tightly and the surface layer is too thin, it will exacerbate the height difference of the panel joints and affect the comfort of use.

3, Key construction control points
Grassroots treatment:
Remove the floating slurry and oil stains from the base layer, and use a wire brush or chisel to clean it to a solid base layer;
Backfill soil should be compacted layer by layer, with the moisture content controlled within the optimal range to avoid mixing frozen soil or ice cubes.
Grid strip inlay:
The dividing strip is fixed with cement slurry, with the top 4mm to 6mm lower than the surface layer, to ensure even distribution of stone particles;
Leave a gap of 15mm to 20mm at the intersection of the dividing bars to prevent the accumulation of stone particles during polishing.
Surface layer laying:
The volume ratio of cement to stone particles should be controlled at 1:1.5 to 1:2.5, and the viscosity should be based on the standard cone sinking degree of 30mm to 35mm;
The thickness of the surface layer should be uniform, avoiding local areas that are too high or too low. After laying, it should be compacted by rolling with a roller.
Polishing process:
Adopting the "two slurry and three grinding" method, namely rough grinding (60 #~80 # grinding wheel), medium grinding (120 #~180 # grinding wheel), and fine grinding (240 #~320 # grinding wheel), with each polishing process followed by additional slurry and grinding;
When polishing, the specifications of the grinding stone should be complete to avoid using too many large grinding stones, which may cause insufficient exposure of the dividing bars.