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I'm just getting ready to lay down the grout after successfully tiling our master bathroom. I've been told in no uncertain terms that I must remove the spacers between tiles (or else grouting over them can result in cracking of the grout). That makes sense -- however, I'm also reading on the box that I should "clean the grout joints". They show a tool that appears to be scraping excess mortar from the joints.

Do I need to be worried about scraping down the hardened mortar so that the joints can be completely filled with grout or are they talking about simply removing any loose mortar? Although none of my joints have mortar that rises above the grout, many of the tiles have some sections where the mortar is higher than others. I'm reading elsewhere that it's ideal to get rid of all excess mortar between tiles before it hardens (whoops).

How important is this?

Update:

As of September, 2011, it's been 9 months since I completed this job and things have been solid. I scraped only the areas that were high (close to or slightly above the tile). From this purely anecdotal evidence, it seems logical to conclude that it isn't necessary to be too much of a purist about clearing out all mortar between tiles before laying down your grout.

Update 2:

As of April, 2012 I've found only one tile that may have a slight issue. On one of the center tiles that gets a lot of traffic, I must not have put down a perfectly smooth layer underneath because I can hear an occasional slight shift. The joints along the edge still look great though.

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Important tiling tip, spacers do not sit flat in the gap between the tiles where it would be possible to grout over. They should sit vertically with one side between the tiles, two other sides resting on top of each tile, and the last side pointing straight up so it's easy to remove. In this layout, you should have two spacers per side and nothing to dig out of the corners. –  BMitch Sep 25 '11 at 11:54
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2 Answers

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I wouldn't be too concerned unless there's mortar that is raised above the level of the grout - which you've already said there isn't.

Scraping the higher sections to give a reasonable depth of grout would be as far as I'd go.

A lot of adhesives these days are sold as tile cement and grout, though they do tend to be coarser than "pure" grout, so they are basically the same material. However, a pure grout does give a smoother, "cleaner" line.

Floor tile grout also tends to be coarser - I suspect to be able to cope with the higher degree of wear and tear it will receive compared to wall tile grout.

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Excellent -- thanks for the info. I examined it a little closer and there are some areas that have mortar awfully close to the grout line. I'll scrape it down a little. –  Andrew Flanagan Jan 4 '11 at 21:23
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There are several things to consider.

Unsanded grout (used with 1/8" tile spacing and less) is not as strong as the more commonly used sanded grouts. Given that fact, and the fact that the joints are narrower (making the grout more difficult to force into the joints), it going to more important to have the joints as free of excess mortar as possible.

Another consideration is the grout/tile color. When working with very light colored grout it's recommended that you use white mortar (which costs a little more) rather than gray to prevent the mortar from showing through. If the grout isn't very deep this is far more likely to be an issue if you used gray mortar and are using a lighter colored grout.

Finally, all cement based product need have a minimum thickness to achieve enough strength to hold up. Imagine a sidewalk poured in 2 layers with the first layer being 3 1/2" inches and the second layer being only 1/2". Unless special steps are taken to bond the second layer to the first the end result is not going to be anywhere near as durable as a sidewalk that was poured as a single 4" slab. Anywhere you have a significant amount of mortar built up between your tiles (more than half way up the side of the tile) it's like the 2 layered sidewalk. It's unlikely you'll have problems with the grout breaking out under normal traffic where it's thin, but if it takes heavy abuse it will be more susceptible to damage.

Clean joints are definitely preferable for a long lasting job. It's also worth mentioning that it's much easier to clean the mortar out while it's still soft. If you have a tool that is the exact same width as the grout lines it makes it easy to get them basically completely clean as you lay the tile. I recently completed a tile job using 1/8" spacing and used a "tile spacer remover" tool and it worked great for scraping out the excess mortar. alt text

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good detailed answer. you know your grout! –  shirlock homes Jan 7 '11 at 13:10
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