A word of caution regarding corrective action: before attempting to repair deficiencies, make certain that the repaired concrete will in fact look better than the original concrete. One common example of this type of mistake can be found in many attempts to patch areas of excessive blow holes- the blow holes are eliminated but every patched blow hole stands out. Corrective action should not be started until the architectural concrete finish has been completed. In the case of exposed aggregate finishes, the discrepancies that seem objectionable when the forms are stripped may not appear objectionable after the aggregate has been exposed. Patches applied before the abrasive blasting operation are frequently blown out when the finish is blasted. In designing patch mixes, when grey, buff, or tan cements are being used in the architectural concrete, a small amount of white cement should be introduced into the repair mix. In all other respects the patch mix proportions normally will be the same as in the architectural concrete. The proportion of white cement to be added must be determined by trial and error. This is best determined by applying trial patches to the project mockup and selecting the appropriate patch mix after the trial patches have been allowed to cure a minimum of seven days. The patch mix should be applied and packed to approximately the density of the surrounding concrete. For exposed aggregate finishes, the compacted patches are struck flush with the existing surface and the coarse aggregate is hand placed, if not already in the patch mix itself. As the concrete patch sets up, bristle brushes are used to expose the aggregate and texture the finish to blend with the surrounding concrete.