After you have done a great job tiling your projects, you may find out that the grout has cracked the next day, this is quite a common problem and there can be many reasons why this is happening
Here are a few reasons why grout cracks
1. The grout joint is too wide, as the grout dries it shrinks as the water is displaced. If you are using a big spacer between your tiles make sure you buy a wide joint grout
2. You may have filled the gap between the tiles but it is important to make sure the grout has filled the whole joint down to the background otherwise the grout is not supported, pockets of air below the grout can cause this cracking
3. Deflection or movement is the substrate surface, like wood which may be expanding or contracting with changing of temperatures, make sure the grout is flexible or has a polymer latex additive to stop this happening.
4. Tiles that have not been bonded correctly, failure in the adhesive will result in the grout moving, therefore, leaving the crack
5. Grouting before the adhesive has had time to fully cure. Some tub adhesives can take up to 4 days to fully cure, rapid set cement can be dry in as little as 3 hours.
6. The substrate the tiles are sticking to is not strengthened, any movement in the substrate will be transferred into the tile and grout lines.
By making sure all the above points are covered you will find there will be no more problems with grout cracking between your tiles.