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Last edited 16 May 2018
Grout is fluid, viscous material that is used to fill and seal gaps. It is similar to mortar, but the water concentration is greater and it is less stiff which makes it more suitable for filling complex, inaccessible or small spaces.
It is commonly used for tiling, but is also used in structural and civil engineering applications.
 Tiling grout
Tiling grout is used to fill spaces between tiles, helping secure the tile to its base and acting as a sealant, preventing moisture from penetrating joints:
- Smaller tile joints tend to use non-sanded grout, which is cement-based and designed for use on tile surfaces that are dry when the grout is applied.
- Larger joints tend to use sanded grout, which is a cement-based mortar with small sand grains added to assist setting and provide a stronger grout. It should be tested first to make sure the sand will not scratch the tile surface.
- Epoxy grout has water-resistant properties and does not require additional sealing. It also prevents bacteria growth and limits cracking. This type of grout is ideal where tiles may be exposed to large amounts of water, chemicals or grease. It can be produced in sanded and unsanded varieties.
- Furan grout is similar to epoxy but is composed of polymers of fortified alcohols which give it highly chemical-resistance properties. It is typically used for brick pavers and quarry tiles, and is particularly suited to areas that are exposed to chemicals and grease.
The colour of grout should be carefully selected as this will determine how the eye perceives the tiles. Light grout tends to become ‘invisible’ and accentuates the individual tiles whereas dark grout tends to accentuate the tile pattern. However, lighter colours are more likely to noticeably discolour.
The thinset mortar, which is used to fix the tiles during installation, must have cured before grouting can proceed. Grouting should be mixed according to the directions. A float should be used to spread the grout over joints, moving it at a diagonal angle to the grout lines for a smooth finish.
Some 15-30 minutes after applying the grout, use a large sponge with water to remove excess grout from the tile surfaces. This should be repeated again after a few hours until the grout lines are smooth.
Refer to the manufacturer’s directions in terms of how long to wait for the grout to cure before sealing it. Make sure the room has good ventilation. Pour a small amount of sealant on the grout and, with small circular motions, work it in using a sponge. After 5-10 minutes this can be wiped off. It is generally recommended that the grout is regularly re-sealed.
Some of the tools that are commonly used for groutwork include:
- Grout saw or scraper: A manual tool used to remove old and discoloured grout from joints.
- Grout float: A trowel-like tool made of rubber, used for smoothing the grout line surface.
- Grout sealer: Water or solvent-based sealant applied over dried grout.
- Pointing trowel: Used for applying grout in stone works such as flagstones.
 Structural grout
Structural grout cab be used to fill voids in masonry that contains reinforcement steel, helping to secure the steel in pace and bond it to the masonry. It is a particularly strong grout that can withstand vibration and dynamic load shock, and tends not to shrink.
 Non-shrink grout
Non-shrink grout is a hydraulic cement grout that hardens at a volume that is greater or equal to its original volume. It sets rapidly and includes ingredients to compensate against cement stone shrinkage. It is often used between load-bearing members as a transfer medium.
Grouting in civil engineering refers to the injection of pumpable materials into a soil or rock formation to alter its physical characteristics. Different materials may be used for grouting depending upon soil type, the size of fissures and so on, however, the basic process is the same: the soil or rock is injected with grout which sets and reduces or acts as a sealant on the material’s permeability.
For more information, see Grouting in civil engineering
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