I know a lot of you are DIY savvy but feel free to email me with any questions. Here's how I did it.
Since safety is number one, be sure and wear a face mask and eye protection. When you are scraping out the old grout there will be a lot of dust and debris.
Most grout can be removed using a sharp utility knife provided it is a smaller grout line. Larger grout lines, 1/4" or thicker, may require additional tools. You want to scrape the old grout out of the joints until you have most of the old stuff out. Grout only needs an 1/8" depth in between the tiles to adhere so keep that is mind when scraping.
Once you've gotten the grout out and swept and vacuumed the area its time to put in the new grout. I like to keep a bucket of water and a sponge nearby so I can keep my hands and tools clean. I used an unsanded bright white grout. The rule is 1/8" wide grout joint or smaller you used unsanded, anything over that you would use sanded grout. You like my pink sparkle bucket?
In this picture I am using a margin trowel to mix the grout. The best grout to buy is the kind you mix yourself with water. It comes in a powder form and you want to mix it so that it is the consistency of really thick pancake batter. You should be able to scoop a small mound on to the end of your trowel and the mound should stay on the trowel for a few seconds before falling back into the bucket.
Note: This type of consistency only works with unsanded grout, sanded grout is heavier and thicker so the mixture is slightly different.
This is my beat up grout float, I'll use this to put the new grout in. The edges of a grout float are hard rubber so it creates a squeegee effect.
Scoop a small amount (because a little will go a long way) on the edge of your grout float and press the grout firmly into the joints.
Sweet short video of the squeegee action. Use the grout float to get any excess grout off the face of the tile once you've gotten all you need into the joints. Also work in small sections so you do not get too far ahead of yourself.
Next you will use the sponge and water to clean any grout residue of the face of the tile.
Get your sponge wet and wring out excess water, then go in a circular motion to break up the grout on the surface of the tile. Then use the other side of your sponge to clean the tile off. You may need to change the water in your bucket a few times.
TIP: Do not pour the old grout water down the drain, pour it outside. Sometimes leftover grout can harden in your plumbing pipes and cause drainage issues down the road.
I use a white cloth towel to wipe the tile down lightly so I can ensure I have gotten all the grout haze off. If for whatever reason you notice a dusty haze on the tile once everything is dry, don't stress out, just use a dry white cloth and buff it off.
Be sure to give your grout 24 hours to dry before using the shower.
New grout made this 30 year old shower look brand new.