It's best to use caulk—specifically, silicone caulk—on shower corners. You'll also want to apply caulk to the area where the shower wall meets the shower pan or bathtub (and other places where two different materials meet). However, make sure to use grout between individual tiles on your shower wall or floor.
And you don't want tile/grout to connect to the shower pan because the shower pan shifts and flexes with heat and weight. So there needs to be a flexible connection between the two that will prevent water from pooling in there and keep mold from growing, but allows the pan to flex and tile to be rigid.
Caulk is a flexible sealant that is often used in areas where two different materials meet, such as where tile meets a shower pan. Its primary function is to prevent water from seeping into cracks and crevices, which can cause damage over time.
You should have a small 2mm gap to allow for expansion.
Your wall and tub or base will expand and contract at different rates – it will crack any cement-based product you place between the two. This includes thinset as well as grout. You do not need a solid backing behind your tile over this gap – it should be less than 1″ wide.
Leaving a 1/16″ gap between the tub and tile will prevent the tile from cracking when the tub expands. Plus, a 1/16″ gap allows the caulk to properly fill the space and waterproof the transition between the tile and tub or shower.
How To Seal A Large Gap Around A Shower Tray? Sealing a large gap around a shower tray demands a gap-filling sealant. Select a sealant designed for substantial gaps. Apply it generously to fill the space, ensuring complete coverage.
It is always better to fit tray first, siliconing to the wall and then tile down to the tray and seal again between the tray and the bottom row of tiles.
In general, silicone sealant is the best kind of sealant that is compatible with several different shower tray materials.
Installing a shower pan over an existing tile floor is a great way to refresh your bathroom, but proper waterproofing is crucial to prevent future water damage. Learn how to effectively waterproof between cement board and your shower pan to ensure a durable, leak-free shower.
There are some instances where a choice between grout and caulk may come up, such as the space between tile and a bathtub. A lot of contractors use grout in situations such as this, but for the most part, caulk should be used.
Should you grout shower corners or caulk? It's best to use caulk—specifically, silicone caulk—on shower corners. You'll also want to apply caulk to the area where the shower wall meets the shower pan or bathtub (and other places where two different materials meet).
Acrylic Grout: Acrylic grout is a great option for wet areas like decks and showers. It's intended to be mildew-resistant and retains its color well. Epoxy Grout: Epoxy grout is less do-it-yourself-friendly than other types.
If you prefer a material that is easier to apply and remove, grout is the better choice. Caulk takes a steady hand to apply, and it can be difficult to remove.
Grout isn't suitable for sealing around your bathtub or shower tray as it's not flexible and will crack as soon as any weight is placed on the tub or tray.
Step 10 - Fit the tiles leaving a gap (approx. 3mm) between the tray and tiles. Run a bead of sealant between the bottom of the tile and tray, ensuring it penetrates the gap. This secondary seal is important.
The flexible silicone sealant is a necessity in a bathroom. If you used standard grout between the course of tiles and the bathtub or tray, pressure when stepping on these will cause a hairline break in the grout where water can then ingress and blow out your tiles. And no one wants that!
If it's a huge gap, you can fill most of it with grout (leave a narrow gap against the tub), let it set, then caulk the remaining gap with silicone. I would try a pre mixed grout. They tend to stay put and crack less. Also easier to clean.
The first option for caulking large gaps is to use a backer rod to fill the gap and then caulk over it. The backer rod is a soft foam that goes inside the gap before you put the caulk on top. It helps keep the caulk from shrinking.
Secure the Shower Pan
If mounds of mortar are called for, mark the locations on the subfloor per the manufacturer's instructions. Then position mounds of mortar on the marks. Position the shower base in the area, placing it onto the adhesive or mortar, and press firmly in place.
Plan to extend the tile 2 or 3 in. beyond the tub and leave at least a half tile along the wall if possible. Don't stop tile even with the end of the tub. This leaves the walls along the front of the tub vulnerable to water damage and doesn't look as finished as tile that extends to the floor.
You should choose your shower or bath seal by determining the maximum gap 'X' that has to be spanned/bridged. Fig. 2 In this case we see a gap of 12mm has to be spanned between the shower tray/bath and the wall. For such a gap ShowerSealsDirect would recommend using either Sealux 25 or Trimlux 25 for such a gap.
The backer board should overlap the tub flange so the tile has a stable backing to attach to. This requires shimming the backer board out from the studs so the wall is plumb. There should be a 1/4" gap between the tub ledge and the backer board.