Removing old grout between bathroom floor tiles

[MissDIY]

Hi all,

I’ve got a nice tile floor in the bathroom, but the grout is old (probably as old as the floor, i.e. from 1970) and needs freshening up.

What is the easiest way to remove the old grout between floor tiles? I’ve seen someone recommend a patio cleaner – does this work? What tools should I use to remove the grout between the files? How much of the grout should be removed before a new layer is be applied?

Anything else that I should know about doing this?

Many thanks in advance

J

 

[Nestor_Kelebay]

Instead of removing that grout, I'd try cleaning it first. You may be quite surprised at how well you can clean it. The following is the process I use to clean mildew discoloured wall tile grout. If you follow a similar process on your floor tile grout, you may get it a lot cleaner than you expect. (Then, just replace any grout you can't get clean.)

Clean it with ordinary soap and water and a stiff scrub brush first, just to remove any loose dirt that can easily be removed. Allow to dry.

Now, get some phosphoric acid based toilet bowl cleaner and scrub the grout lines with that stuff and an old tooth brush. Don't bother with anything less than 10 percent phosphoric acid, and try to get one that's at least 15 percent phosphoric acid. Don't use a hydrochloric acid based toilet bowl cleaner on the grout, they're too aggressive and will probably damage the tile, too.

You just want to use the phosphoric acid to dissolve the very surface layer of grout which will probably be plugged up with dirt, soap scum, mildew and whatever else. Once you dissolve that dirt clogged surface layer, rinse the acid off with clean water and allow to dry. (If phosphoric acid is left for TOO long on grout, it will dissolve enough of it to become noticable, so don't leave it on for a long time.) Once it's diluted with rinse water when you're cleaning it up, it'll be too weak to dissolve anything.

Then, after letting the grout dry thoroughly (for several days, even) if there is any mildew growing inside the grout and discoloring it, you can apply bleach straight out of the jug with a small paint brush to the grout lines. The bleach will wick into the grout and kill any mildew inside it. Sometimes, you have to leave the bleach on for hours (or even overnight) for it to penetrate in deep enough.

Finally, apply several coats of an acrylic grout sealer to your grout lines to prevent history from repeating itself. The clear film of sealer over the grout will keep the grout lines easy to clean up with a damp sponge.

And, if there are still spots that you're not happy with, I'd use an inexpensive plastic laminate knife (the kind with the single tungsten carbide tooth at the end of the "blade") to scratch the grout out in those areas you couldn't get clean. I'd scratch the grout out to about the same depth as the grout joint is wide to ensure that the joint is deep enough for the new grout to hold well.

 

[MissDIY]

Thanks Nestor for your very thorough instructions.

I posted my desperate cry for help before reading other posts about removing old grout and after reading them I realised what an uneasy task I had set up myself to do…!

I have used grout pen before but the result was very superficial and didn’t last very long.

You say that at the end I should apply acrylic grout sealer to the grout lines. What about those lines where the grout has already come off partially? Will I then apply new grout on the top of the sealer and then cover this again with a sealer?

Thanks
J

 

[DarrenSL]

How about simply using a Dremel to just drill out the old grout and replace. Never done it myself but sounds easy enough.

 

[Moz]

DarrenSL
an you can get diamond blade grout scribes too that really whizz the grout out

 

[Nestor_Kelebay]

You need to have a reasonably deep crevice for the grout to hold well. That's why I suggested that the grout be removed to a depth equal to the width of the grout joint. If the grout is just a bit shallow in some areas, and you don't want to cut it out, then I'd apply the grout sealer and leave it like that. If you cut out the old grout, let the new grout dry for a minimum of 10 days before painting the grout sealer on top of it.

A Dremel would make a pretty good tool to cut the grout out with, although the only complaint I have about Dremel is that they're kinda underpowered. Although, if it's only a few areas that need to be cut out, that wouldn't be much of a problem. If she buys a Dremel Mototool, I'd suggest also getting the flex-shaft accessory cuz the handle on it is only 1/2 inch thick. Dremel's #426 cut-off wheel (that's not the diamond one, only the fiberglass reinforced one) is 1 3/8 inch in diameter, so the two together would allow a maximum cut depth of 7/16 of an inch, which is more than enough.

Wear a dust mask, too, and maybe have a vaccuum cleaner and the ceiling fan going to blow the dust laden air outside.

Another option would be a hand grinder fitted with a diamond blade, but it would sure kick up a lot more dust than the Dremel. Would get the work done a lot faster, too, tho.

(I use worn down 7 1/2 inch masonary blades from my circular saw in my hand grinder. Once they wear down to about 5 inches and become too small to use in the circular saw, I use them in my hand grinder. They're only rated to about 7,000 rpm, but that rating is when they're still 7 1/2 inches in diameter. They'll take the higher speed of the hand grinder once they're worn down to a smaller diameter. I ain't telling anyone else to do that, tho.)