How do you propose to make a window waterproof from the wrong side? How was the shower pan formed? Which is the worse hack here? Chicken or the egg?

That was brutal...I am using Redguard to waterproof AFTER I seal the seams and corners of the Durock with Thinset. Look at the picture, I am just asking if packing thinset into the 3/4 inch gap and then Redguarding over it will be enough for water proofing. When doing the Demo, I noticed that there was no gap there before, the backer board went all the way up and snug against the window...

The shower pan was formed with standard sand mix. Over a membrane, on top of a pre-sloped concrete pad. I am about ready for tile, just need to work out the gap from the Window.

The following technique is 10 years old and it’s still more current than what’s been done in your project. If I were you, I’d do—at minimum—the following around that window (notice that waterproofing membrane):

Just think how you’d want it done if it were your home... or your elderly grandmother’s home.

The reason this thread got brutal at the start was due to questions about the most basic requirements. Such as. "Also do I need to use mesh tape for the corners of the shower wall or is that just thinset only?" It appears to those of us reading along that you are in way over your head.You may say the base is done correctly but how would you know if you don't have the knowledge of whether to tape a corner.The one photo clearly shows there are not enough fasteners. It appears to be Philips head drive on those screws. Are they drywall screws that will get destroyed by the alkali in the mortar? Cement board screws are usually square or star drive. The advise I give to everyone is go directly to the manufacturer for installation instructions instead of an online forum or you tube where you run the risk of wrong information. You will always get the correct response without sarcasm. A window in a shower requires extreme care. You are risking thousands of dollars of damage. Hope all works out for the homeowner.

Okay, thank you Creative Tile. As I'm sure you were once, I am a Greenhorn. Most of my knowledge was passed down from Father to Son and as I have done this type of project more than a few times before, this is the first time I am going at it alone. Due to a bad illness, my father can't be here to help me this time around. And the Durock was not put in by me, it was put in by an outside company the homeowner chose to use. And I agree that they used the wrong screws, I have brought that to the homeowners attention and he is waiting for a call back. I have also informed him that I have never done this alone before. And after he got several quotes, he decided he didn't want to spend that much money. Experience is expensive, and he is fine with me learning along the way. The window is pre-existing and I suspected there was more to it than thinset, so thank you Sammy for the Diagram, I will start from there.

Hanndy Hubers- I currently have the exact same problem that you had in your original post: a gap between the window sill & cement board. I have no experience at all in waterproofing shower walls for tile but I’m trying to figure this out on my own. ANY advice is appreciated, especially since you had the same issue that I’m facing now.

Darlene:

I'm concerned that you don't have enough Do-it-yourself experience to pull this off.

@Darlene I understand your issue and having dealt with it I can tell you that you won't like the answer. The only thing you can do at this point is take the cement board down and re-measure and re-cut a new piece so that it's snug against the window sill. If the board was run horizontally and it's a whole piece instead of a cut piece as mine was, then you have to run the cement board vertically from bottom to top. And make your L shaped cuts so that each piece fits around and under the window sill nice and tight. Then you run your mesh tape down the seems and corners, thinset all of the tape and let it dry and then you're ready for waterproofing! And most importantly make sure when you get to tiling that you use trim tile ALL around the window frame! It's a crucial extra layer of protection against the constantly wet conditions and protecting the seams. Don't get discouraged if someone on here is rude or tells you you don't know what you're doing. Most of these people on here are probably the reason you are trying to do it yourself. They're arrogant and elitist, and they scoff at the idea that any normal person with a day job can do what they charge $8,000+ dollars to do. By the way, a year and 9 months later my customers shower is perfect. No leaks, no sagging tile, no problems. You can do it, just don't rush and there's no such thing as too many questions.

@Darlene. You may wish to start a new thread. There are several professionals here willing to help. Yes you can fill a small gap with setting mortar depending on the mortars limitations. Some form of backing or reinforcement will be needed. As I stated above always go directly to manufacturers for installation instructions. Yes showers have a high degree of difficulty with a lot of details that must be followed. If you choose to proceed please purchase a TCNA Handbook. A $35 investment well worth it.

You must use caution when seeking advise nowadays. I have found YouTube will have more bad info then good. Again go to the manufacturers videos!

Unfortunately Handy Huber with his 1 project experience has resorted to name calling while providing you with bad advice.

"then you have to run the cement board vertically from bottom to top."

FACT Cement board is installed horizontally with staggered seams. ANSI 108.11 page 57 A-4.8.5.1.4

Cement board recommendations such as "new piece so that it's snug" "nice and tight." FACT The manufacturer instructions state leave a gap.

https://www.usg.com/content/dam/USG_Marketing_Communications/united_states/product_promotional_materials/finished_assets/usg-durock-cement-board-with-edgeguard-installation-guide-en-CB237EG.pdf

"And most importantly make sure when you get to tiling that you use trim tile ALL around the window frame! It's a crucial extra layer of protection against the constantly wet conditions and protecting the seams."

FACT Tile has nothing to do with waterproofing. If you can't run the shower without tile it is not constructed properly.

Many feel as I that showers are not a DIY project. Can it be done? Certainly. It's all in the details.

Good luck with your project.