Looking for Advice on Plan to Lay Tile over Tile for Shower Floor

Hello,

Just joined the forum and am hoping to get some advice on a project. I live in San Diego, CA - hope this is OK (just noticed you are UK based). My wife and I have been unhappy with our master bath walk-in shower floor since we bought the house 25 years ago. We do not like the aesthetics and the floor always looks dirty. For the last 10 years I have kept a deck scrub brush in the shower to scrub it every now and then to keep it presentable. Several years ago I tried to solve the always dirty problem by sealing the entire floor. This was a multi-day project where we acid-washed the floor and then applied an industrial sealer (I could look up the name of the product if needed). The floor did look better for a while, but it still did not look great.

I am now motivated to finally solve this issue. We found a ceramic tile mosaic at Home Depot that we both like. Rather than demo and replace, we want to lay the new mosaic directly over the existing floor. I have done some research online (YouTube videos) but would love to get confirmation from experienced people in this forum that my plan is sound. I will be doing this project with a handyman I have worked with for over 15 years. He is experienced with tile but is not a tiling expert.

I have uploaded a picture of the shower floor as it is today (after I spent a solid 30 minutes scrubbing very vigorously) that also shows two sheets of the mosaic we picked out. Structurally, the floor is in excellent shape. We have no cracked tiles and no leaks. There are a few cracked tiles in the shower wall along the floor (which I may replace during this project or at least seal). From what I read, the tile on tile should work as long as the original tile is structurally sound and does not have any problems.

Step 1: Prep floor. I am scrapping off the sealer I applied several years ago and will scrub to remove the small amount of mold along the edges. I may also use a hand sander to rough up the floor and speed up the removal of the sealant.
Step 2: Apply two coats of MAPEI ECO Prim Grip directly on the tile as a bond-promoting primer. I wanted to remove/strip the sealer before applying this so it is directly on the current tile.
Step 3: Raise the current drain. Carefully pry up the existing 4" square drain plate. Then use either an Extend-O-Drain product or a homemade 1/4" thick piece of 3" ABS that is glued using marine glue on top of the existing drain.
Step 4: Lay a new mosaic over the existing floor like any other project using a modified thin-set. Use a 17" manual tile cutter to cut the new 6mm thick ceramic mosaic tile. Install a 4" square drain plate.
Step 5: Grout the floor with grout that has built-in sealant.

Q1. How does this plan look? Do you see any red flags? Any recommendations?

Q2. At the local Floor&Decor where I bought the ECO Prim Grip, the technician asked if I wanted to get the Mapelastic AquaDefense t apply first before using the ECO Prim Grip. Is this necessary since the shower does not currently leak and we are not removing the existing floor? Am also thinking I would want the Prim Grip to be applied directly to the tile, not to a waterproof shield.

Q3. My wife is wondering how much it would cost to hire a professional tileer to come in, demo the existing floor, and install the new. My estimated cost for this project, excluding the cost of the tiles which I would buy either way, is $500 for materials and labor. I am also putting in 8-10 hours of my time in prep and installation assistance which I do not mind at all. I assume it would be far more expensive to have a tiler come in and demo/install. Am I correct? I also must admit I enjoy these DIY projects. So as long as I am not creating a headache down the road, I would prefer to do it this way even if a tiler would cost about the same (which I cannot imagine).

Q4. One of the problems with the existing floor is that a small amount of water pooled in a few spots after the shower was turned off. Not a lot but enough for a layer of soap scum to form. I would like to eliminate this by increasing the slope to the drain. Is this something that we can do with the modified thinset or would we need to use something like dry-pack mud? I am not talking about a huge increase in slope. The distance from the drain to the furthest wall is about 2 feet. I was thinking of increasing the existing slope by adding about 1/2" of height at the walls to facilitate a more complete drain.

Thanks for reading this long post and providing any insight!

Your plan seems well thought out, and it's excellent that you're addressing the existing issues methodically. Scrapping off the sealer, using MAPEI ECO Prim Grip, and raising the drain all sound like appropriate steps. Just ensure the surface is clean and free of any contaminants before applying the primer.

Adding Mapelastic AquaDefense as an extra waterproofing layer is a good precaution, especially if you want to ensure long-term durability. While the existing shower may not leak now, adding an additional layer of protection can provide peace of mind and prevent future issues.
Hiring a professional tiler to demo the existing floor and install the new one may indeed be more expensive than your DIY approach. However, your enjoyment of DIY projects and the potential cost savings make your choice valid. Just ensure you follow the steps carefully, as you're doing, to avoid headaches down the road.

Hi gamer1. thanks so much for the feedback. A few updates. I think I finally finished stripping the sealer I used a few years ago. It took many hours of scraping with a raxor blade (I broke the blade maybe 10 times) and sanding by hand and with a small black and decker hand sander with 60 grit paper. The old floor looks pretty nice now that it is all clean and white, haha. My handyman came down with Covid and is now out of commission for at leats a week. I have been talking with tech support from Mapei several times. After the first call, they are now saying I should use Mapelastic AquaDefense as well (Floor and Decor said it was unnecessary). My main contact at Mapei is checking with some people, but he thinks I should use Aqua Defense on the bare tile first (3 coats) to prevent moisture from coming up from the mud, then apply the Eco prim grip (2 coats). He is checking with other people to see if I should then apply another layer of Aqua Defense on top of the Eco Prim Grip before laying the tile in modified thinset.

My contact then shocked me by saying if it was him he would pull the existing tile and skip the tile on tile. He said He could remove the existing tile in just an hour or two with a steel chisel and hammer. Any small holes in the mud could be repaired using their Quick Patch or 330 Fast products. I could also enhance the pitch of the floor so it drains better. Then I could keep the existing drain. He disagreed with the local tiler I contacted and said I would not need to pull 12" of wall tile as well. He said I would only need to do that if my shower was leaking. Since my shower was built in 1997, he said I likely have a rubber liner or p[possibly some kind of tar paper that was popular in California. He said it is easy to pull the tile and not disturb the waterproofing. Then I would not need to use the Eco Prim Grip or the Aqua Defense or the Extend-O-Drain.

I am going to get my handyman's opinion on this. I like the idea of doing it the right way, but only if I am sure I will not create a monster headache and expense. If we somehow damage the waterproof membrane, it could end up costing me an extra $1,500+ to fix the shower and I may be without it for 8 weeks. How easy/safe is it to chisel out the existing floor? Again it is 1" square tiles (95% sure porcelain) with 1/4" grout lines.

I think it all comes down to your appetite for risk!

If you lay the new tile on tile, it may be ok, you've thought it through and done your homework, put in the labour and are ready to buy the correct materials.
BUT
It's not how I would do it for a customer as IF it did fail, you are back at square one, having spent time trouble and money, and then you are back to ripping it out.
I would try and get your contact to do the job of ripping up, if it takes ages, you have the argument that he said a couple of hours!
Then, when the new floor is laid properly, you know it's not going to fail!