Of course, you can! However, there are some things that should be kept in mind before starting this job. First of all it is better to have the right tools for the job as they will guarantee a good result and secondly knowing what materials to use is an important aspect of the job. For example, you need to know that mortar repair can result in different outcomes depending on whether it is non-hydraulic or hydraulic and also if the original material was lime based or gypsum. This means that knowing what kind of mortar was used will help determine which type of mortar mix should be used for mortar repair.