How To Grout Mosaic Tiles

How to Grout Mosaic Tiles

You need to know how to grout mosaic tiles if you’re going to benefit from the huge decorative and practical potential that they present. Even the most stunning looking tiles won’t work the way they should if you don’t apply them properly. 

There are various options when it comes to using grout and fixing tiles onto different surfaces. Here, we look at tile grouting, including techniques and materials.

What is Grout?

Grout is a type of mortar that fills in the gaps between tiles. This prevents moisture and dirt from getting between and behind the tiles. Grout also gives your entire tiled surface an attractive finish.

You can get grout in different colours and finishes, and this can make a big difference to how your tiles look dependant on if the required finish needs to compliment or contrast the tiles.

Grout colours include basics such as white, ivory, beige, grey and black. But there are also bolder finishes, such as grout that contains glitter, which will sparkle under lights. There are also specialist grout additives available, creating stain resistant as well as decorative grout finishes.

There are 3 main types of grout:

Norcros 4 into 1 Flexible Wall and Floor Tile Grout is the grout you’ll usually use when grouting ceramic, porcelain and stone tiles. It’s made from a combination of Portland cement, sand and other additives. You mix the sanded grout with water then apply it to the joints you wish to fill and usually dries in around 24 hours.


Norcros Stop Mould Flexible Wall Tile Grout , has the same basic mixture of Portland cement and additives but misses out the sand. Unlike sanded grout, it won’t scratch the surface of polished stone tiles when you apply it to them. Norcros Stop Mould Flexible Wall Tile Grout porous and therefore it would be best practice to apply a preparatory gout sealer to maintain the appearance of the grout once it has fully cured.

Norcros Super Epoxy grout is a water-free grout that’s made up of epoxy resin and hardener. You mix these elements just before you apply them. Once you’ve applied the epoxy grout and it has cured, you get a seamless finish that is resistant to both moisture and stains. Its disadvantage is that it is harder to apply than traditional grouts.

Do You Need to Grout Mosaic Tiles?

If you’re going to use mosaic tiles, then you will need to grout them. This will ensure that they stay clear of dirt and moisture, and it will also provide the kind of even finish you want to enhance the tiles’ decorative qualities.

However, you do need to choose your grout carefully. Mosaic tiles are smaller than other tiles, and they require a type of grout that won't damage their surface when you apply it.

The two types of grout best suited to mosaic tiles are:

  • Norcros Stop Mould Flexible Wall Tile Grout
  • Norcros Super Epoxy Grout.

Grouting mosaic tiles isn't essentially different to grouting any other type of tiles, and the techniques you should use are the same.


How Much Grout Do I Need for Mosaic Tiles?

You’ve got to look at various factors when working out how much grout you’ll need for your mosaic tiles:

  • The area of the mosaic
  • The thickness of the tiles
  • The gaps between the tiles.

First, calculate how much space you're tiling. If this space isn't straightforwardly rectangular then you should break it down into smaller rectangular components.

Measure the length and width of the area. The area you’re covering will be length x width. Where you’ve broken this down into smaller parts, calculate the area of each then add these together for your grand total. Next, measure the tiles themselves. Include both their size and thickness.

Now calculate the gaps between your tiles. The easiest way to do this before you start tiling is to measure the spacers you’re going to use. Spacers are small pieces of cross-shaped plastic that you use to ensure consistent spacing between your tiles.

Once you have all these figures, you can use them to calculate how much grout you’ll need.

For example, a 1kg bag of grout will cover approximately five square meters, using 750mm x 150mm tiles with a 2mm spacer.

The formula is: (tile length + tile width) x joint width x joint depth x 1.8 kg/m2 / (Tile length x tile width)

How to calculate the grout you need:

  1. Add length plus width of the tile
  2. Multiply this by the width of the grout joint
  3. Multiply this by the depth of the grout joint
  4. Multiply this by 1.8. This is the standard kg by m2coverage
  5. Multiply the length by the width of the tile
  6. Divide the figure in step 4 by the figure in step 5.

If you need any additional help calculating the amount of grout required for your project, you can use the handy Grout and Adhesive Calculator from Norcros.

If you need to know how many tiles you’ll need for your project, you can use our handy tile calculator

How to Grout Stone Mosaic Tiles

You must prepare your surface carefully. If you’re applying mosaic tiles to a wall then the wall must be level, clean and dry. Make sure it’s free of any grease, moisture or loose material.

The cumulative weight of tiles is heavy, so you must make sure the surface will be able to bear this weight. There’s also additional weight from the grout and tile adhesive, approximately and additional 3kgs/m2:

  • Walls that are plaster skimmed have a maximum weight loading of 20kg/m2
  • Bare plasterboard can take weights up to 32kg/m2.

If you have a newly plastered wall, you should allow it to dry for at least four weeks before tiling it.

Different surfaces will require different kinds of preparation for applying stone mosaic tiles:

  • You can apply tiles directly to a rendered wall, up to a maximum weight load of 40kg/m2
  • For an internal blockwork wall, the maximum loading weight is the same, providing the surface is sufficiently flat and fairfaced.
  • You should completely strip and clean wallpapered or painted walls before priming them in preparation for tiling
  • You can use a tile backer board to create a flat surface ready for tiling – these can take a maximum tile weight load of 80kg/m2.

In certain circumstances, you may be able to apply fresh tiles over existing tiles, but you should check the weight first. Generally, it’s best to remove the existing tiles first.

Some surfaces are NOT suitable for carrying tiles;

  • Pressed wood
  • Particle boards
  • Oriented strand board (OSB)
  • MDF
  • Engineered wood flooring
  • Solid wooden planks
  • Heavy stonework.

Always check your type of surface before attempting to tile it.

How to Set Your Tiles

You’ll need to set your tiles first, using an adhesive to fix them to the surface, before you grout them. Check that your surface is completely flat. Fill larger cracks by applying layers of filler, letting the filler dry between each layer. If necessary, sand the wall down to make it level. Vacuum clean the surface to remove any loose particles and then wipe it down. Prime the surface using Norcros Prime Bond and allow to dry before fixing your tiles.


Using your calculations (see above) you should have the right number of tiles and amount of grout to begin. If you’re tiling a wall that is going to get wet, such as a shower area, then you may want to consider the use of a tanking system, such as Norcros Wet Seal Tanking Kit to prevent moisture ingress in to the background and damaging the installation over a period of time. Wait for it to fully dry before installing your tiles.

Then you must apply an adhesive. This can be Norcros Ultim8+ Tile Adhesive or Norcros Standard Set Flexible White S1 Tile Adhesive. Consult with your supplier first to find the best option for your tiling project.

How much adhesive you need will depend on the size and type of tile. For mosaic tiles, you should apply adhesive using a 4/6mm trowel. This should ensure you have the right amount on the surface. Apply the adhesive using a notched trowel, dragging it down and across the wall at a 45-degree angle. Only cover around 1m2at a time, to prevent the adhesive from drying out before you apply the tiles.

Place the tile on the adhesive and twist and slide it into place. Repeat this process, using spacers to mark out the spaces between tiles evenly and consistently. Wash down the surface and clean the joint as you go. 

Grouting Your Tiles

Leave your tiles to set, approximately 24 hours, and make sure you’ve fixed them all firmly to the surface, and that they align evenly. Check for any risk of staining first by applying a small amount of grout to one area.

Once you're satisfied that the grout isn't causing any discolouration, you can mix the full amount required and begin the grouting process. The tool to do this is the grout float. This will apply the grout to the spaces in between your tiles. It's made of rubber to protect the tile surfaces as you move the float across them.

Press the grout firmly into the spaces between the tiles. Wait for the grout to begin to stiffen in the joints, then apply a grout sponge to a bucket of warm water, squeeze out excess water and wipe away the excess grout on the tiles.

Keep rinsing out the sponge in clean water, if required change the water regularly, and wiping away the grout until you’ve covered the entire tiled area. Leave the tiled area to dry overnight, then wipe over the tiles with a clean, soft cloth to remove any remaining grout residue.

How to Grout Mosaic Tile Art

Grouting mosaic tile art may require some adjustments to the grouting process. This is because the tiles are likely to be smaller and cut into intricate shapes. You can use the same grouts and sealants for mosaic tile art, and the same technique of applying the grout with a float, then sponging off the excess with warm water. Make sure you've filled all the joints. They may be less easy to spot if you're not using uniform tiles.

If your mosaic tile art isn’t large, you can grout and wipe in one go. Once you’ve wiped away the excess, you may find a thin haze of grout still on the surface. If you let this dry slightly it will be easier to see and clean off using a paper towel or a clean, dry cloth.

After this, check for any areas that need touching up and remove excess grout from the joints using a grout jointing tool, you want the grout to be flush with, or slightly lower than, the surrounding tiles.

Mosaic Tiles for Interior Design and Artwork

Have a look at our comprehensive range of mosaic tile brands and styles. They’re perfect for transforming your interiors or for decorative art projects.

For more information, please call us on 01727 839920 or email 

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