Every time you take a shower, the grout will soak up water. In an older bathroom, there likely are cracks in the grout that allow in even more moisture. Some of this water will evaporate throughout the day, but some will penetrate behind the wall - leading to mould, mildew and rotting of the structure. In this regard, does grout sealer keep water out?
Why you need grout sealer As a result, if you don't seal your grout, it will absorb water, bacteria and stains. Adding a grout sealer protects your grout so it's water resistant and will repel moisture and germs.
Likewise, should grout darken when wet? It is very normal for unsealed grout to change to a darker color when wet. This will happen even with fully cured grout. Sealing the surface of the grout will stop the wetting of the grout and end the color changes. You may find you need to reapply some sealer every year or so in a shower surround.
Hereof, what happens when grout gets wet?
You can turn a fan on it and just let it air out for a few days, see if that does it. It should return to its normal color once it dries out. You can hasten the drying process by running a fan. Kind of strange that the wet grout is lighter than the rest, it usually darkens when wet.
Why is my grout wet?
Grout discoloration is often the first sign that there is a moisture problem on a tile floor. It is caused by moisture entering the grout, either from above or below. Moisture can soften the grout, making it more prone to crumbling or damage, or it can result in efflorescence as moisture evaporates away.
Related Question Answers
How many coats of grout sealer is needed?
Two coats
What happens if you don't seal grout?
As a result, if you don't seal your grout, it will absorb water, bacteria and stains. Sealing the grout helps prolong the look, texture and consistency of your grout and it prevents mildew and mold. Your grout will look better and last longer. The one exception to the rule is if you have epoxy grout. Can shower water leak through grout?
Cracks in grout can be source of water leaks: The Weekly Fix. If you see stains on the ceiling below your bathroom, don't assume it's from a leaking water or drain pipe. This tile needs periodic maintenance; cracks can develop in the grout between the tiles, allowing moisture to seep through. What happens if water gets under tiles?
If your home has been flooded, floor tiles may come loose. Standing water does not damage ceramic floor tiles. However, it damages the grout between the tiles, loosens tile adhesive and saturates the subfloor. The wood soaks up the water and expands, causing the tile floor to buckle or tiles to become loose. Can you put new grout over old grout?
ANSWER. ANSWER - It is possible to grout over existing grout if there is enough depth to do so. 1/8 inch depth may or may not be adequate depending on the type of grout used. A latex modified grout may work, but you have to properly clean the existing grout to ensure the new grout adequately bonds. What type of grout does not need to be sealed?
grout epoxy grout
How often should you Regrout your shower?
Luckily, regrouting tile is a practice you shouldn't have to do often. If you take care of and clean your tile grout regularly, you should only have to replace it every 12 to 15 years. Lesser quality jobs or failure to care for the grout may lead to the need for replacement every eight to 10 years. Can water get through cracked grout?
In my opinion, grout needs to be able to breathe, so that any moisture that gets in behind your tile is able to escape. If you seal the grout, that can't happen. No matter what, moisture - steam and water - eventually will get through the grout, or through a crack in your tile. How long does wet grout take to dry?
Consider Damp Curing Most grout jobs will dry within two or three days. However, many homeowners and contractors use a longer drying method to strengthen the grout on their floors. How long does grout need to dry before getting wet?
24 hours
How do you dry out wet grout?
If your grout is runny or too wet, add additional dry grout to the mixture until it reaches the proper consistency for use. Although much less common, it is possible to mix grout too dry. Overly dry grout is difficult to stir and crumbles. Simply add a bit of water to fix the consistency of dry grout. How long does grout need to dry before showering?
48 to 72 hours
Should sealed grout change color when wet?
It is very normal for unsealed grout to change to a darker color when wet. This will happen even with fully cured grout. Sealing the surface of the grout will stop the wetting of the grout and end the color changes. You may find you need to reapply some sealer every year or so in a shower surround. Does grout change color when sealed?
Darkening Action Adding grout sealer may very well darken, but not change the color of your grout. As you apply the seal, you may notice your grout change 1 or 2 shades. How long does grout need to cure?
Grout Cure Times Most cement-based grouts require a cure time of 48 to 72 hours before applying a penetrating sealer. After sealing, wait a minimum of 24 hours before using the shower; some products may recommend three days instead. Can I touch up grout the next day?
If you want to be sure, yes, you have to dig all the grout out first. Grout bonds mostly to the tiles, less so to itself. Typically grout takes a few weeks to fully cure, but is ready to seal after 2 or 3 days. That says to me that you might still get the new grout to bond to the old. Can you dry grout with a hair dryer?
Dry the area with a hair dryer or heat gun, and make sure the grout is thoroughly dry. Apply a small amount of grout coloring with a paintbrush to the cleaned area. Dry the grout coloring with the hair dryer, and leave overnight if time permits. Will grout sealer darken my grout?
Adding grout sealer may very well darken, but not change the color of your grout. As you apply the seal, you may notice your grout change 1 or 2 shades. Can you seal wet grout?
Sealing Damp Grout You cannot effectively seal grout before it is hard and dry. You can apply the seal, yes, but the sealer will soon peel or flake, leaving your grout vulnerable to stains and dirt. What happens if grout is too wet?
Adding too much water when mixing the grout can cause it to cure incorrectly and eventually crumble or crack. This is the result of the excess water evaporating as the grout sets, leaving microscopic holes in the structure of the grout and leaving it prone to premature deterioration. Why does my shower grout stay wet?
It probably plugged the weep holes, too, preventing any of that moisture from eventually draining, and requiring it to evaporate instead. Tile and grout is not fully waterproof, a little bit will get under the tile with each shower. It should hit the sloped membrane and slowly flow to the weep holes in the drain. 
