I'm not an expert. I hope others will post.

Remove grout and put in 100% silicone. Custom, the maker of Polyblend has a product that I will link below. It comes in colors.

Removing the grout is always recommended, but I don't know how. would a dremel tool help? When I put in the caulk I always tape up both planes to project the tile and surfaces from the silicone. I use 70% isopropyl alcohol to help with finishing the line and cleanup. I put a bit on my finger to run along the caulk line to make a smooth seal. I put some on a paper towel to help cut any residue that smears onto the tile when I am cleaning up. I don't know if that is recommended but I have not had a problem with this.

Here is a link that might be useful: polyblend commercial 100% silicone caulk.

We just bought a home with travertine in the shower and the corner grout lines on the floor are cracked. It looks like they used a sanded grout. Is the silicone superior and does it last longer than the sanded grout? I noticed that the specs say it can discolor stone.
Also, do you have any tips for maintaining the travertine. It looked to be in good shape and the previous owner is no longer around to ask.

Enduring, I like your method of applying caulk!

Pretty much what enduring wrote. Polyblend has color-matching caulks that come in 100% silicone and in a siliconized-latex version.

To remove grout, you can use a manual grout saw and remove it with elbow grease. I've also use a diamond bit in a dremel tool. Some bits are listed as tile cutting bits, so they can be aggressive. You need to control the bit when using it:

Or a cutting tool in a multi-master type of tool.

You want to remove the grout deeper than the grout joint is wide.

An elbow grease powered tool will be a bit of work. Anything electric powered will generate a lot of dust.

Thanks for everyone's comments/suggestions thus far. Looks like I'll be removing the old grout, cleaning, and the caulking!

In regards to removing, I'm planning on getting a hand grout saw. Perhaps maybe this http://www.amazon.com/Dremel-568-Grout-Removal-Kit/dp/B0000302ZX/ref=sr_1_1?ie=UTF8&qid=1373470698&sr=8-1&keywords=dremel+grout but I need to see if this attachment fits on my dremel. If not, I can get a multi-tool. But I am afraid of damaging the tiles! Does anyone have comments/opinions on using powered tools to do this?

I'll be doing this for our bathrooms and kitchen as well. Changing planes! Should have caulked it to begin with!

I need to dig out my old grout boxes to see what colors I need in the caulk. Hopefully my local home depot has it in stock!

That dremel adapter my not be the perfect solution for you. You seem to need to get the grout out of inside corners, that adapter looks like it's mostly for cleaning out grout on flat surfaces.

FWIW? I freehand with a dremel. Grout is softer than tile, so the bit will usually self-guide through the grout as long as you provide a bit of hand pressure to guide the bit in the direction you want it to go.

There are blade kits that get mounted in a sawzall type of tool, but they can be a bit unwieldy.

Or you can go full manual with something like the Marshalltown Hand Saw, about $15.

Hmmm, upon further thought, you're right, that Dremel tool may not work for me since I'm trying to get the grout out of "inside corners" and not flat areas.

I just want to make sure I have all the tools ahead of time so I'm not wasting time going back and forth or waiting.

I think I'll get a couple of hand saws (Is the Marshalltown what you're recommending?) and possible have a multi-tool on standby if the grease in the elbow starts to dry out!

Biggest thing is not to damage the tiles (or stone on the kitchen counters) or my wife will kill me!

You can still use the dremel with a diamond bit without that adapter. I angle the body of the dremel towards me as I draw it towards me across the wall. I angle it so the edge of the dremel's base is riding on the face of the tile, and angle it enough so that bottom of the bit is at the depth I want it inside the grout line.

Tough to describe, but pretty simple once you start cutting.

But certainly, you do need to be careful. And I might have written this before, but with the Dremel, you can create a dust cloud. Unsanded grout creates more dust than sanded grout. The Marshalltown hand saw will pretty much eliminate fine airborne dust.

If you go with the Marshaltown (or equivalent), one saw handle will do you. But get a few extra blades. If you have a wide grout line, with some of the "hand saws" you can double up the blades for added cutting thickness.

So doing more research on this, it seems that Polyblend offers two types of caulks.

One is Ceramic Tile caulk $7.27 a tube: http://www.homedepot.com/p/Polyblend-10-Antique-White-10-5-oz-Non-Sanded-Ceramic-Tile-Caulk-PC1010N/100678074#.UeQldlPeb-k

The other is Silicon caulk $11.97 a tube: http://www.homedepot.com/p/Custom-Building-Products-101-Quartz-10-1-fl-oz-Silicone-Caulk-CCSC101/202753926#.UeQjzVPeb-l

I'm not so much concerned about the difference in pricing at all. I just want the superior product.

Having read thru various forums, etc, it seems like I want to use the silicon caulk. Is there a reason i should not use the silicon caulk? (Looks like the colored caulking selection is the same for both the regular and silicon caulk)

Also, for the regular caulk, they have sanded and non-sanded. But both are for gaps 1/4" or less (I don't have lines that are wider than 1/4"). I suspect that the sand vs. non-sanded in this case is strictly for looks and not for bonding. Is that correct?

thanks!

I have always heard that 100% silicone is the way to go for the tile in the shower and wet areas.

Correct, around water you'll get your best performance with silicone.

Latex caulk is fine, but not around water. At least not as much water found in a shower or tub surround. But latex caulk is very easy to apply, tool, and clean up.

On the other end of the spectrum, 100% silicon will give you your best performance in a watery environment. It can be more difficult to apply, tool and clean up though, as it's not really water soluble.

In between are the silicon-latex hybrids. More durable than a 100% latex, and easier to tool and clean up than 100% silicon.

Sanded versus unsanded in caulk is not a real performance thing, it's simply to give a textural match when used in conjunction with sanded or unsanded grout.

Okay ordered all the stuff:
-silicon caulk (various colors to match the grout -- hopefully)
-grout saw and blades
-dremel multi tool with blade (if handsaw progress is slow)

So my plan is to remove the grout. When I'm cleaning/prepping the area for the silicon, what/how should I clean it? Alcohol rub down and wait for that to completely dry and I'm good to apply the silicon?

I also plan to use one of those "caulking tools" to smooth the silicon over instead of my finger. Hoping to be able to get a more consistent bead/look.

Thanks!

When I'm cleaning/prepping the area for the silicon, what/how should I clean it? Alcohol rub down and wait for that to completely dry and I'm good to apply the silicon?

Correct. Scrap/scrub all surfaces clean. Final cleaning is with alcohol.

Dry the area, then caulk.

Biggest mistake you can make is applying too much caulk. When you tool it, you'll get a big mess.

@mongoct, when you say "big mess when toolling" do you mean the extra caulking will be on the tool and I'll need to clean the tool often? Or do you mean the tool will spread the unwanted caulk everwhere?

Okay, I just did one of the bathrooms this weekend.

Some notes:
-I did not use the grout removal saw, the seams/gaps were too small and I did not want to damage the tiles. I did this by hand with a small flat blade screwdriver (lots of scrapping!)
-Filling up the tub with water makes a difference! Some of the cracked grout was pushed inside and i could not get it out. I put water in the tub and vacuumed one more time and viola, more stuff made it out!
-Considering it's silicon, the fumes were basically non-existent from the caulk (100% silicon caulk)
-3 corners are a pain in the butt to smooth out! You smooth out two corners and the 3rd gets messed up! Rinse and repeat! OCD doesn't help here either.
-My legs/arms hurt due to the funky positions I had to get into to remove grout and caulk! (ugh)
-I'm surprised I did not fall into the tub when it had water in it!

I have a question in regards to applying caulking around fixtures (what I'll need to do with the other bathroom and kitchen).

What's the best (maybe easiest) way to caulk around fixtures that are in your way? Obviously when they first grouted the fixtures weren't there so it easy. I don't want to remove the fixtures, any suggestions? Put caulk on my fingers and goop it in?

Thanks!