When laying carpet, you need to prepare the concrete floor first. Use a broom to sweep away all debris and dust before vacuuming to ensure all dust has been removed. Mop the concrete floor using a bleach and water solution. Rinse the floor using a clean mop and fresh water. Make sure all the bleach has been removed.  Leave to dry completely, using fans if desired to speed up the drying process. Once dry, cover the floor with a commercial sealing product, using a paint roller for even distribution. Ensure the sealer is fully dry before installing the carpet