How long since the brick has been laid? If it is over 2 months multiple your price times 1.5. If it is over 3 months old doulble it. The longer the mortar cures the harder to come off. Cleaners like SureKleen and NMD-80 work great and are safer but not on brick that is more than a few weeks old. The problem is you can't get enough dwell time to loosen the harder, older mortar before the chemicals either dry or soak in. Those chemicals are weaker and require longer dwell times.
That's where muratic acid comes in to play. Thats why most brick cleaners use it is because it is stronger and will do the job on older mortar with little dwell time. One caution, don't use it on white or light sand colored bricks. It will discolor them.
Like Bigboy said the main thing is you don't want it to soak into the brick. Wet the wall good before applying the acid. 2 ways to apply it. Either downstream or through an acid injector. An acid injector goes on the end of the wand just like an x-jet nozzle. Mix 20% muratic acid, 2 parts water-1 part acid, add a couple generous squirts of Joy dish detergent to a gallon of the acid and water mixture. Apply with the injector to the already wet wall and
let dwell about 5 minutes. Don't let it dry. if its drying, rinse it and start over doing smaller sections. If it doesnt loosen the mortar smears, cut back a little on water or let it dwell longer. If its not fizzing it isnt working. Also, the reason for the soap is to keep the acid on the wall long enough to do it's job. If it doesnt appear to be staying on the wall, add a little more soap.
If you downstream, use the acid straight from the bottle, add a couple squirts of Joy and apply the same way.
Rinsing is important! I always say, when you think you have it rinsed, rinse it again.
If you're worried about brass fixtures or windows, apply a sodium metasillicate truck soap to the windows and fixtures before appling the acid to neutralize any overspray that comes in contact.
To lessen your labor go around the house first thing with a long handle metal scraper and knock off all the mortar tags you can. The acid is for removing the smears left behind not the larger tags.
Remember, these methods, mixtures and dwell times are for a 20% baum of hydrocloric (muratic) acid. You can buy it at Home Depot in 4 gallon cases for around $8 a case. 2 cases should clean a fair sized house.
Les