Let's talk first about Portland cement based grout since this is the most commonly used material. Once the grout is mixed per the Manufacturers instructions, it needs to be installed. ANSI recommendations for Portland cement based grouts used in tile work are described under ANSI 108.10. Be careful to allow the tiled installation to cure for the period prescribed by the adhesive Manufacturer prior to grouting. Some adhesives require longer curing time than the 24-72 hour normal Portland cement curing times.
This is a good time to carefully check the tiled installation for any adhesives that were left sticking out of the joints or left on the face of the tile. Thoroughly clean and inspect the tiled installation prior to starting the grout phase. Use a razor knife to scrape excess thin set or adhesive out of the joints.
Tile Doctor Tip: Always follow the manufacturer's instruction for the grout mixing and preparation.
For Portland cement grouts, it is a good idea to moisten the joints with water prior to applying the grout. This allows the grout to flow into the joint smoother and it prevents the tile from prematurely wicking too much water out of the grout. Do not leave puddled water in the joint prior to grouting. Check the Manufacturers instructions for the intended product for pre-moistening instructions.
Apply the grout to the tiled surface using a hard rubber grout float at a 45 degree angle to force the grout fully into the joint. Work in a small area applying enough grout to fill the joints. Do not work too large of an area. For beginners it is recommended to work a 2-3 square feet of area at a time to prevent grout from hardening too quickly. Use the grout float diagonally across the face of the tile finishing the grout flush with the face of the tile. In affect, you are "cutting" the grout excess off the tile.
The reason for working in a small area is simple. The grout will start to cure once it is applied. While it is still workable, it needs to be initially tooled into the joint. This means that the cutting off of excess and sponge finishing needs to be nearly complete before the curing begins.
Tile Doctor Tip: Remember to leave the necessary expansion joints open and clear of setting and grouting materials for the installation of sealant and backing material if necessary.
After the grout has been "cut off" the face, the next step is sponging the surface and tooling the joint. Tiles with a square edge need to have the grout finished flush with the tiled surface. Tiles with a cushion or radius edge should have the grout finished to the bottom of the cushion or radius.
This is accomplished by pulling the sponge across the face of the tile diagonally, exerting just enough pressure to move the sponge. The idea is to clean the excess grout off the face of the tile and give the joint a smooth finished look. This will take a little practice and the technique can be learned quickly. Do not dig out the grout with too much sponge pressure and try to keep the sponging to a minimum.
Per ANSI 108.10, "All grout joints shall be uniformly finished. Cushion edge tile shall be finished evenly to the depth of the cushion." "Uniformly finished" means that the joints should be smooth, uniform in color, and free from pinholes or voids.
The voids or pinholes can be filled and re-tooled with a sponge. Careful mixing of the grout combined with the lack of excess sponging should help make the joints uniform in color.
Note: Grouting is a technique that requires practice, this is the reason for grouting a small area at a time.
If the tile you have chosen is easily scratched; it may be necessary to apply the grout to the joint alone. This can be accomplished with care using the grout float. Just be careful to not exert too much pressure on the face of the tile when using "sanded" grouts. The other option when using easily scratched tile is to use a joint size that will accommodate non-sanded grout.
What if it is necessary to stop grouting and resume later on the same wall? This can be accomplished easily. It is always better to grout the entire installation at once. In this way, the chance of color variation and other problems are reduced. However, if it is mandatory to stop and resume later make sure that the grout in the finished joints is cut down to approximately 45 degrees to the substrate. Try to stop and start in an inconspicuous area as possible just in case a slight color variance does result.
In this way grouting can resume and the new grout can appear flush with the existing grout. The idea is to blend the new with the old. Of course, it is also important to make sure the area is clean and that no grout residue is left on the surface of any areas before ceasing work.
The grout work can then be polished using cheesecloth or towels to remove any grout haze after the grout has initially cured. If you were careful and thorough during the grouting process, the grout haze should be minimal. If there is stubborn residue, use a fiber abrasive pad, which normally does the trick.
In extreme cases of grout residue, the use of specific acids can be used like sulfamic or phosphoric. The acids should not be used prior to at least 10 days after the grouting was completed. Strictly follow the Manufacturers instructions for their use.
With few exceptions, Portland cement grouts should be "damp cured." In fact, ANSI a 108.10 recommends it. Use only 40-weight "Kraft" paper for this process. Do not use "poly" sheeting or roofing felt. The "poly" sheeting will accumulate water that will drip on the grouted joints and discolor them by uneven curing time. The roofing felt can have the same effect and can leave tar residue on the tile and joints.
The paper is placed over the newly grouted surface and helps the grout to cure uniformly. This reduces the chance of color variance and produces a harder/denser joint. The commonly recommended curing time for Portland cement grouts is 72 hours.
Let's talk now about a common problem associated most often with Portland cement based grouts in tile work. Efflorescence is a visible white powdery substance that is seen at times on the surface of grout joints. Efflorescence consists simply of dried salts that accumulate on the tiled surface, left there by evaporating water. This salt, alkali in content, can leach up from concrete or masonry substrates. When water moves up through the tile work, it brings the salts with it. When the water evaporates the salt is left.
Generally, efflorescence can be cleaned off the tile and joints by a good washing with pH balanced cleaners. In extreme cases, it can be cleaned with acid washing. As I said earlier, do not use any acids other than sulfamic or phosphoric. Absolutely use them according to the Manufacturers instructions. Remember that Portland cements are alkali based. Acid eats alkali, enough said.