Port spacing in the case of crack injection has nothing to do with the distance between a port in Miami and a port in Jamaica. In this case, we are simply discussing how far apart to place your injection ports. This is not a fixed distance, as proper port spacing varies depending on site conditions.
For estimating, 1’ on center is the standard and will cover you pretty well with the exception of hairline cracks. Typically, the tighter the cracks the closer the spacing.
I am not a big fan of predrilling the ports as you never know when you are going to hit that sweet spot and get 3’-6’ of travel. Or on the other hand when you have numerous dead holes or very little grout travel. So I start from the bottom, work my port, and then observe how far the grout travels. I then place next port to pick up where the grout left off.
I see predrilling done on shutdown jobs where time is of the essence. This may lead to some extra holes and wasted ports but can speed up the injection process. If it is not shutdown work, I prefer to be more methodical and drill as I go.
Lastly, whenever possible, stitch grout. This is the practice of alternating the sides of the crack to install your port. This helps prevent cracking and spalling of the concrete.
Crack injection is a thoughtful and methodical practice which is not for the impatient.