It is important to remedy this situation quickly, especially in bathrooms where there is a risk of water penetrating into the joints and causing damage to the substrate or the building structure. Crumbly or powdery grout can be due to poor mixing and application.
When grout and water are mixed together, a chemical reaction called 'hydration' is started. It is this reaction that causes the grout to go from a thick paste to a hard tile joint. Powdery or crumbly grout is likely to occur if the tiler:
Before application, and especially on soft biscuit wall tiles, the tiler needs to wet the joints where he intends to grout. This extra moisture slows the hydration process. With soft biscuit tiles, the body of the tile soaks up the moisture in the grout. With incorrect hydration, the grout will not cure or dry correctly and the result is powdery or crumbly grout.
If the grout is not mixed thoroughly, patches of grouted areas on the wall or floor will end up powdery or crumbly.
The use of a rubber squeegee (trowel) and a firm sweeping action across the joints ensures that the grout is compressed into the joint and completely fills the joint without voids. Incorrectly applied grout will be unserviceable and is likely to crack and fall out over time.
Grout has a shelf life of about 12 months from date of manufacture. After this time it is likely to go powdery and is unsuitable for use. At Beaumont Tiles we turn our stock over continually and grout is not packed with the job until the day before delivery to ensure fresh stock is delivered.
The only way to rectify this problem is to scrape out the grout and replace it. This is done by using a grout rake (a small, cheap tool available at all Beaumont Tiles stores). Once the joints are clean, apply the correctly mixed grout.
If you are regrouting, Beaumont Tiles recommends using ABA Grout Additive in the mix. This enhances the grout to make it more flexible and more impervious and easier to clean than standard grout.
Note: Never grout the internal corners between two walls or the internal corner where a wall and floor meet. Movement and different rates of expansion and contraction will cause these joints to crack and fail. Silicone must be used in these places.