What condition must the surface be in before applying grout to a concrete slab?

Before applying grout to a concrete slab, it is critical that all specified conditions are met to ensure proper adhesion and performance of the grout.

Having the surface roughened with a needle scaler improves mechanical bonding by increasing the surface area for the grout to adhere to, which is especially important for achieving strong and durable joints. A roughened surface helps reduce the chances of cracking and enhances overall stability.

Dampening the surface for cementitious grouts is also essential because it prevents the substrate from absorbing too much water from the grout too quickly. This allows for better hydration of the grout and contributes to its strength and setting properties. However, it's important to note that the surface should not be saturated; just damp.

Additionally, keeping the surface free of oil and chemicals is vital. Contaminants like grease, oil, dust, or any chemicals can act as a barrier and impede the bonding process. A clean surface ensures that the grout properly bonds to the concrete slab, which is crucial for the long-term integrity of the installation.

Thus, all the listed conditions are necessary to prepare the surface adequately for grouting, making 'All the above' the correct answer.