Grout does not shrink, but it is prone to forming voids and bubbles if it is not rubbed thoroughly into the grout gaps. These holes are easily repaired.
My friend Fredrik reported a problem while grouting his mosaic portraits of famous rock icons. He described the grout as having shrank in the grout gap.Shrinking Grout Detail shows voids and bubbles at the intersection of groutlines. This is a classic problem and indicates that the grout was inadequately rubbed and pressed into the gaps. Real Grout Doesn’t Shrink
The grout didn’t actually shrink, which isn’t possible with traditional grout made from portland cement, sand, and water. (I can’t speak for the newer epoxy-based grouts because we haven’t used them.) What actually happened was that voids were left in the intersections of the groutlines, and these voids got covered with a thin film of grout that then dried out without curing.Press Grout DOWN Into The Gaps
When you grout a mosaic, it is important to press the grout down between the tiles, and to rub and press the grout thoroughly. Otherwise, voids and bubbles will be left down in the gaps and get covered over with a superficial layer grout similar to how a thin layer of wind-driven snow and ice will sometimes form over a crevasse in a glacier. That is why pressing down is important, and you shouldn’t just rub tangentially across the surface.
You can also “pull” voids into grout by rubbing it repeatedly in the same direction. That is why it is best to rub in circles and to vary the direction of the rubbing randomly.Avoid Dry Air: Use Humidifiers
Fredrik reported that he wasn’t able to able to spend very long pressing the grout into the gaps because it started to harden almost immediately. It takes grout a while to harden, and this hardening happens by binding water not by drying out, but grout can become prematurely stiff and difficult to manipulate if it starts drying out. Since Fredrik was working in Sweden in February, I suspect the air was very dry due to the heat running, not to mention the already low humidity of the winter air. You can avoid this problem by running a humidifier near your mosaic and by doing the grouting away from heater vents. You can also cover the grouted mosaic with plastic kitchen wrap such as the Saranwrap brand.How To Fix Holes In A Groutline
The good news is that it is possible to grout voids and holes and bubbles in a mosaic that is already grouted. The only caveat is that the old grout can suck the moisture out of the new grout before it can properly cure and harden. To prevent this, mist the mosaic thoroughly with water before you begin so that the old grout is saturated with water. Note that the mosaic should not be coated with water because droplets of water or a thin layer of water could interfere with intimate bonding. It really helps to have a humidifier running near the mosaic, and you should start the humidifier an hour or so before you grout so that the old grout isn’t bone dry.
Before you regrout, you need to expose all the hidden voids and bubbles. You can do this by pressing on the grout with a small screwdriver and vacuuming out all the loose crumbles. Of course, you need to do this in places that look like there is a problem, and but you also need to press in places that look deceptively fine. You don’t want to have to grout a third time.
I prefer to press straight down instead of dragging the screwdriver because I want to avoid scratching up grout that is fine. If you do get some scratched up grout from your probing, use a stiff bristle brush and a little water on the finished mosaic to buff out the scratches and make them less noticeable.
If you notice that your grout is crumbly in general, you should scrape it all out and regrout. In that case, you might want to use the grout removal tool.Mixing Up Small Amounts of Grout
One objection to fixing small grout problems is that people don’t want to mix up a whole container of grout and end up wasting almost all of it. The good news is that you don’t have to waste any or at least very much, and you don’t have to be paranoid about whether or not you are adding the right amount of water. You can easily mix up a small amount using a few rules of thumb:If you have a small postal or kitchen scale, use 1 part water by weight to every 4 parts dry grout. If you don’t have a small scale, add a little water and mix thoroughly. Stop adding water when the grout has the consistency of dough. Once you have enough water in the grout, mix it thoroughly to ensure even consistency with no tiny lumps of dry material. These can sabotage the grout hardening process.
Fredrik Tigerstrom (“T29ART” on Instagram) has made some impressive mosaic portraits of rock icons David Bowie, Bruce Springsteen, Joe Strummer, and Tom Waits. These mosaics are worth sharing for several reasons, and not merely because they are faithful renderings of famous people. Yes, these mosaics are “accurate” in terms of capturing individual likeness, and that is an accomplishment most any artist would be proud of, but what makes them noteworthy is that the artist was able to achieve this verisimilitude in spite of using arbitrary colors (not flesh tones) and using whole uncut tiles in a rigid grid pattern. Also, the total number of tiles in each mosaic is relatively low (29 x 29)! To fully appreciate how successful these mosaics are, look at them at a distance or at low resolution.David Bowie Aladdin Sane Mosaic David Bowie Aladdin Sane Mosaic Portrait by Fredrik Tigerstrom is shown uninstalled and still in the black plastic mounting grid used to lay up the design.
A mosaic design laid up in a plastic mounting grid can be picked up using mounting paper or mounting tape (or clear packing tape if you are on a budget). All of these portraits were made with 10mm (3/8 inch) glass mosaic tile.Joe Strummer Mosaic Joe Strummer Mosaic Portrait was made without a grout gap, but note the white shining through from the backer which illustrates an important point: Tiles cannot be placed so closely that no gap exists. That is why you should leave a usable gap that can be grouted if you need to seal out water. Yes, this mosaic could be grouted to eliminate the white backer from shining through, but the places where the tiles touch will not seal out water because grout can’t fit between them.
The gridded patterns used in Fredrik’s mosaics are the exact opposite of the flowing contours I like to use in my artwork, but they are successful, and there is plenty of visual interest. The gridded patterns are also very hip because they resemble the pixels of digital images, and this calls attention to the fact that these are contemporary interpretations of an ancient medium.Bruce Springsteen Mosaic Bruce Springsteen Mosaic is still in the mounting grid used to lay out the design, and you can see the mounting tape or contact paper that Fredrik is using to pick up the design and mount it.
Note how the black plastic grid lines between the tiles make the colors more vibrant. That is why we recommend medium gray and black grouts instead of white and lighter colors. If you do make a dry indoor mosaic and use a light color grout and are unhappy with it, you can rub artists acrylic paint on the mosaic, which will stick to the porous grout and wipe off the glass tile. Using acrylic paint, you can go from white grout, which makes colors look bleached out, to a dark umber or black, which makes colors look more rich.Tom Waits Mosaic Tom Waits Mosaic Flesh Tones Required?
The mosaics above are successful in spite of not using skin tones, but most portraiture is rendered using natural colors. For that reason, we get many emails from people asking which tile is our best light pink or coffee color for making skin tones, depending on which ethnicity they are trying to portray. My answer usually vexes people because it is not the simple one-color solution they were expecting.
Even if you are trying to work as photorealistically as possible, you don’t need (or want) one color that best approximates a particular person’s skin tone or even their ethnicity in general. The reason you want multiple colors is that uniform color fields are boring, and you want to vary the color to create visual interest and to render light and shadow. The best example we have of this on our website is Harjeet Singh Sandhu’s work at the bottom of our mosaic portraits page. Harjeet’s portraits on that page really are worth studying if you are planning to make a mosaic portrait yourself and have concerns about color accuracy.
This method for altering a mosaic can be used before grouting, or grout can first be removed by scraping it out with a grout removal tool or screwdriver.Why Remove Tiles?
Even experienced artists modify their designs as they work on them, and beginners can’t help but use a trial and error approach. After all. it’s hard to plan exactly what you will do when you are just learning a new medium.
With drawing and painting, revision is easy, but what about mosaic? How do you remove and replace tiles after the glue is dry?Prancing Horse Mosaic Before Versus After shows the changes made by prying up and replacing tiles. The purpose of the change was to make the head more horse shaped. I think the mosaic could be further improved by making the mane and tail from the same umber tile used in the hooves and outlines. How To Remove Tiles SELECTIVELY From A Mosaic
The following method assumes the tile is attached to a plywood backer using a white PVA glue such as Weldbond. You could use the same techniques on an outdoor mosaic made with thinset mortar, but it would be very difficult if the mortar has cured for more than a few days. Mostly this method is used while you are working and see obvious mistakes, and the glue or mortar is not very hard.Soften The Glue If Needed
OPTIONAL: If needed, apply a few drops of water around the tiles in question to soften the glue. If the surrounding tiles get wet and unexpectedly come up or look like they might, you can pull them up and reglue them too.
Cotton swabs are useful for applying drops of water to precise locations. Dry cotton swabs are useful for soaking up excess water and containing the spread.Use A Metal Tool To Pry
VERY IMPORTANT: Use a ruler as a fulcrum to lean the metal tool on when you pry. If you lean the tool on the surrounding tile, you can split or crack the tile VERY EASILY without applying much pressure at all.Prying Up Mosaic Tile can very easily crack surrounding tile if you lean your tool on surrounding tile as a fulcrum. Instead, hold a ruler firmly in place and lean your prying tool on that. Scrape Off Broken Pieces
If the tile breaks into pieces, and some pieces are still glued down, you can scrape that off, but take care because the tool can slip, and then you can jam your hand into the razor sharp pieces before you are aware what is happening. Wear leather work gloves to avoid skinning your knuckles or cutting your fingertips open on broken tile.Repairing Holes In Backers
If you gouge a hole in the backer while scraping or prying, it can be repaired with Weldbond glue or glue mixed with sawdust if the hole is deep. If a layer of plywood gets snagged and sticks up like a flap of loose skin, squirt glue under it and apply a heavy weight on that precise location to hold it down until the glue is dry.Safety
Wear safety glasses with side shields RELIGIOUSLY when doing this work. Prying tile with a metal tool can shoot tiny splinters right at your face. Wear leather work gloves when scraping in case your tool slips.Mosaic Art In Progress. Sometimes you don’t see your art objectively until you start working on another mosaic. Thus, it is better to wait instead of grouting a mosaic right away.