The bathrooms are the main wet area in the house. Therefore, you need to waterproof the area so that water does not enter the substructure of the house and causes significant structural damage. Waterproofing is usually done by experts while the bathroom is being built. A moisture barrier is all you need to keep water out of the water cavity.
However, you'll need more extensive waterproofing for horizontal surfaces if you want to prevent a shower from leaking. You must waterproof all the walls of the shower before laying the tiles. A tile backing or cement board is usually not waterproof, although many are water resistant. The most effective and reliable solution is a separate waterproofing membrane on the primed shower walls before tiling.
The tile is mostly waterproof. Natural stones will not, but porcelain tiles for the most part will not absorb water. Ceramic tiles installed on walls will spill most of the water. Grout, on the other hand, stinks.
Grout is sand that is bonded with Portland cement (with some exceptions: epoxy grout, unsanded grout, etc.) Therefore, it acts like sand and absorbs water as it flows across the surface of the grout. This means that when building your shower, you need to consider what the water will do when it passes through the grout and reaches the back wall. The waterproof membrane prevents moisture and water from seeping into walls or floor. Failure to do so by a qualified professional can result in tens of thousands of dollars in costs later on.
Not to mention, it will save you the stress of having to rebuild an important part of your home. My contractor said he planned to do the same, about which I recently posted. I found an installation pdf on the Durock website that said Durock is waterproof, but for a waterproof installation, a different product is needed. It didn't mention adding a plastic liner, but rather referring to another Durock product.
If you need something to show the contractor, those installation documents can be useful. Waterproofing can serve as a moisture barrier, but a moisture barrier does not necessarily qualify as a waterproofing barrier. Custom Building Products requires two coats of its Redgard liquid waterproofing on all waterproof surfaces. If you have a shower niche that sits slightly higher than the minimum space for shower waterproofing, make sure it is fully waterproofed, as it is a common area where water can seep into the walls of your home.
Shower waterproofing is the process of coating the shower with a waterproof membrane to prevent moisture from seeping into your home structure. There are many rules surrounding the waterproofing of your shower; therefore, it is best to have a professional perform the waterproofing of your shower.