For accurate slump test results, the mold should be what?

For accurate slump test results, ensuring that the mold is placed on a stable surface is crucial. A stable surface guarantees that the mold does not shift or settle during the process of filling and removing it, which could lead to inconsistencies in the slump measurements. The integrity of the test relies on the mold maintaining its position and not being affected by any external movements or vibrations that might occur on an unstable surface.

While greasing the mold may make removal easier, it is not a standard practice recommended for accurate slump tests as it could affect how the concrete behaves when the mold is removed. Filling the mold with dry aggregate is not appropriate, as the slump test is intended to measure the consistency of a fresh concrete mix, not dry materials. Heating the mold is also not relevant, as the temperature of the mold does not influence the direct measurement of slump and could alter the workability of the concrete.