Grodan Expert Slab 20/75 36 x 8 x 3 in | Case of 12, Vertical Fiber

Reading the Numbers on a Grodan Expert Slab

The 20/75 in the name is the metric section: 20 cm across by 7.5 cm deep. In inches that is 8 wide by 3 deep, over a 36 in length, or 91.4 x 20.3 x 7.6 cm. The item number is 320565, with twelve slabs to a bundle. Fiber runs vertically through the wool, so water travels down to the drain line rather than tracking along the slab. The wrap is a printed foil that excludes light and carries the handling labels. Wool in this line is built around an advanced wetting agent and a reworked structure. The effect is that water content and EC read the same at both ends of a 36 in slab. Nothing in the wool binds nutrient, so the solution at the dripper is the solution at the root. No pre-plant flush is required. Twelve slabs cover thirty-six plant positions at the usual three to a slab.

How a Wider Stone Wool Slab Behaves Under a Root Plate

Extra width changes where the roots go rather than how much water is on hand. A plate spreading sideways finds wool instead of foil, and that tends to show up as a flatter, wider root mass by mid-flower. It also means the dry edge is further from the stem, so a missed irrigation is less immediately felt at the crown. Drainage still has to be set up properly for any of that to hold. Cut the slit at the lowest point beneath the seam and give the bench enough fall that the slit is genuinely the low spot. On a dead level bench the water pools at the far end and the readings diverge within a week. Keep the foil intact everywhere except the openings you cut, because exposed wool in the light grows algae within days. Cut plant holes to the block footprint and no larger. The honest cost of a case is handling, because twelve saturated slabs are heavy and awkward. Wet them in place on the bench rather than filling them and then carrying them.

Key Features

• 20 cm by 7.5 cm section: The 20/75 designation is the metric cross-section, 8 by 3 in in imperial.
• 36 in length: Fits a standard bench run end to end without cutting the slab down.
• Twelve slabs a case: Thirty-six plant positions at the usual three plants to a slab.
• Vertical fiber: Sends water down to the drain slit instead of tracking it along the slab.
• Advanced wetting agent: Holds content and EC level from one end to the other, so irrigation steers evenly.
• Printed light-excluding foil: Keeps light off the wool, which is what stops algae taking hold.

Technical Specifications