Porous surfaces should be treated with special sealer and cracks larger than 3mm (1/8in) should be filled with wall filler: a special caulking tool is available to make this job easier. Filled cracks and joints between new plasterboard should be taped over with joint tape (tape should also be used on the edges of filled areas). If any parts of the wall are powdery or 'chalky', use a solution before applying the coating.Mix up powder, following the manufacturer's instructions. To speed up this process, whisk attachments are available for both hand and powered drills.