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I just tried an oscillating tool with a carbide blade to remove grout from between wall tiles in a less visible bathroom area, and despite starting very carefully I'm chipping tiles all up and down their length.

The grout line is between 1.9 (5/64") and 4 mm (5/32") wide, usually 3 mm (1/8"). The area I tried has around 2.9 mm wide grout at narrowest. The blade, including the carbide grit coating, is 2.6 mm (7/64") thick at maximum. I aimed for 2 mm reduction in grout depth. It went OK for the first couple of passes, then the next pass I chipped the tile all along its length, even though I didn't slip that I could notice, presumably because of the very narrow clearance between blade and tile.

Few web stores mention blade thickess and the thinnest I've found on the web or locally is only 2.3 mm (3/32"), so not much different.

I don't see this going well, does everybody who has success with these tools have wider grout, or a narrower blade?

Another problem is that some of the grout is level with or even slightly above the tile (maybe 10% of the grout line, but maybe 1/3 of tiles have some grout like this). Where it's not, it often fills the gap fairly high - it's 1 mm below the tile surface at most. It's hard to see how I can grind that out without chipping tiles.

Is it a good idea to regrout this at all, or is it a fool's errand?

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  • I can't vouch for this because I never did this myself, but this guy had the same problem with a standard carbide multi-tool blade... so instead he attached an angle-grinder metal cutting disk to his multi-tool. It seems the problem with chipping comes from side-coating of the carbide blade.
    – Fizz
    Sep 3, 2017 at 23:19

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It can be done but it will take time and patience.

Where delicacy is a must, power tools are not used as my preference. You could use a grout saw, But I usually use a heavy duty razor knife and change the blades often. You may use a dozen blades perhaps doing a 3'X3' shower.

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  • I found that in my case a hand grout saw was not up to the task -- very hard grout in my bathroom. I eventually found a sufficiently thin carbide blade at a local shop, although some sections were even then too thin to access. I found that key to avoiding chipping was to be patient in not applying ANY lateral force (i.e. apply gentle pressure into the wall, and no force towards the tiles). It's tempting to "help along" the blade break through remaining grout by applying lateral pressure, but whenever I did this I eventually found myself scratching the tile!
    – Croad Langshan
    Aug 10, 2018 at 20:37

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