How to Stop Backer Board and Start Drywall the Right Way

Hey guys — Isaac here, your Tile Coach. Today we’re diving into a question that pops up constantly on the TileCoach.com forum:

“Where exactly do you stop your backer board and start your drywall when transitioning out of a shower?”

It might sound like a small detail, but this one decision can have a huge impact on both how your shower looks and how well it performs over time.

If you stop the backer board too early, you risk water damage and weak transitions. If you run it too far, you might complicate your finishing work and create visible humps or mismatched surfaces.

So today, we’re breaking it all down:

• Where exactly to stop your cement board

• How to frame and block for support

• How to waterproof the transition

• How to finish the joint cleanly for a seamless, professional look

This is a short section of a much bigger shower project I’m building. If you want to see the full process — from demo to plumbing, framing, waterproofing, and tile — I’ve linked the complete series on TileCoach.com.

Let’s get into it.

Key Takeaways (TLDR for Pros & DIYers)

If you’re short on time, here’s the quick version before we get into the deep dive:

• Stop your backer board about halfway across the shower curb or framing nailer (usually a 2x4 or 2x6 turned flat).

• Use that same nailer as solid blocking so both the backer board and drywall can fasten securely.

• Mark a transition line vertically using the outside edge of the shower curb as your reference.

• To waterproof, either:

  • Use a sheet membrane (like Schluter Kerdi or RSS) over the transition, or

  • Use alkali-resistant mesh tape and liquid waterproofing.

• Always use blue painter’s tape to protect the drywall edge when applying thinset — and remove it early before it pulls drywall paper off.

• Use MultiMax Lite thinset (smooth and sand-free) for embedding tape and membranes.

Let your tile overlap the transition by about ½ inch for a clean visual finish.

Understanding the Setup

Picture your shower layout: you’ve got a curb or threshold where the wet area ends and the dry area begins. Everything inside the curb is waterproofed; everything outside is part of your regular finished wall.

This is where the materials change — cement board (like PermaBase) inside the wet zone and drywall outside.

The question is, where exactly should those two meet?

The Goal: A Clean, Waterproof Transition

You want a joint that’s strong, flat, and sealed. The backer board handles the moisture side of things, while the drywall blends into your standard wall finish. If you get this transition right, it becomes invisible once tiled and painted.

Step 1: Install Solid Blocking (the “Nailer”)

This is one of those behind-the-scenes steps that make all the difference.

When you frame your shower, install a 2x4 or 2x6 horizontally on its side between the studs — right around the height of your shower curb. This acts as a nailer or blocking point.

That nailer gives both the backer board and drywall a common fastening surface. Without it, one side can flex independently and cause cracks at the joint later on.

In my setup, I have a 2x6 laid flat, and I stop the backer board roughly in the middle of that 2x6. That gives me about 1½ inches of fastening space for each material — perfect balance.

Step 2: Stopping the Backer Board

Now that the framing is ready, let’s determine where the cement board should stop.

Here’s the rule of thumb:

Stop the backer board about halfway across the curb or nailer.

That means the drywall will start halfway across the same piece of blocking.

This location marks the exact point where your waterproofed tile area transitions into standard wall finish — just outside the wet zone.

It’s okay if you extend the cement board a little farther out (I did on this job). The key is that both materials stay anchored solidly to that nailer and don’t “float.”

Step 3: Marking the Transition Line

Next, grab your level and a Sharpie. Line up the level with the outside edge of the shower curb and draw a clean vertical line.

That line marks where your waterproofing and tile will end — the transition boundary.

Everything inside that line gets waterproofed; everything outside it stays part of your painted drywall wall.

You’ll also use this line later to guide your membrane application and tile layout.

Step 4: Waterproofing Options

Now that the boards are up and the transition is defined, let’s waterproof the joint.

There are two main methods pros use — both work great, depending on your waterproofing system of choice.

Option 1: Sheet Membrane Method

If you’re using a sheet membrane system like RedGard RSS or Schluter Kerdi, here’s what to do:

• Cut a strip of membrane wide enough to cover the joint, extending about 3 inches onto each side.

• Apply thinset to the wall and embed the membrane so it bridges the gap between the backer board and drywall.

• Press firmly to eliminate bubbles.

• Let the thinset cure before applying tile.

• This gives you a continuous waterproof layer from the shower side out past the curb.

When you install your tile, it should overlap that transition line by about ½ inch, creating a neat edge that protects the drywall and hides the joint.

Option 2: Liquid Waterproofing Method

If you’re using liquid waterproofing (like Hydro Ban or AquaDefense), the process is even simpler.

• Apply alkali-resistant fiberglass mesh tape over the joint between the two boards.

• Use a smooth, sand-free thinset (I recommend MultiMax Lite) to embed the tape.

• Once dry, roll or brush your liquid waterproofing membrane up to — and slightly past — the transition line.

This creates a flexible, paint-on barrier that seals the seam and bonds perfectly to both surfaces.

Why MultiMax Lite?

MultiMax Lite is ideal for this step because it spreads like drywall compound. It’s creamy, holds its shape, and doesn’t contain coarse sand that would scratch or rough up your finish.

In my own testing, it held water under sheet membranes for 14 days with zero penetration — super impressive.

Step 5: Protecting the Drywall Edge

Here’s a big pro tip:

When working near drywall, always use blue painter’s tape along the drywall edge before you start applying thinset.

This protects the paper surface from getting stained or softened by moisture.

But here’s the trick — don’t leave the tape on too long.

If the drywall paper absorbs water from the thinset, the tape can pull the paper right off when you remove it.

So as soon as the thinset is firm (not wet, but not fully cured), peel that tape off. You’ll get a perfect, crisp line every time.

Step 6: Finishing and Overlapping Tile

After the thinset and membrane are dry, your transition is ready for tile.

When setting tile, always overlap the transition line by about ½ inch.

This overlap ensures:

• No water can seep behind the tile.

• The drywall edge is completely covered.

• You get a clean, finished visual break between tile and paint.

• If your tile layout allows, use a Schluter trim or bullnose piece for a polished edge finish.

Step 7: Final Waterproofing Check

Once everything’s in place, give your transition one final inspection:

• Is the joint sealed smoothly?

• Any pinholes in the waterproofing?

• Tile coverage extending beyond the curb line?

• Fix any missed spots now — it’s a lot easier before paint and trim go on.

Common Mistakes to Avoid

1. Skipping the Blocking:

Without that horizontal 2x4 or 2x6, your drywall edge will flex and eventually crack.

2. Forgetting to Mark the Line:

You’ll end up guessing where to stop waterproofing, which often leads to over- or under-coverage.

3. Using the Wrong Thinset:

Regular mortars with sand can tear mesh tape or create uneven texture under the membrane.

4. Leaving Painter’s Tape Too Long:

Pulling off drywall paper is a nightmare to repair — remove the tape as soon as the thinset sets.

5. Stopping Tile Flush at the Curb:

Always let tile hang over by about half an inch. It looks better and sheds water properly.

Recommended Materials

Here’s what I used on this job and what I recommend:

• PermaBase cement board for the shower walls

• Moisture-resistant drywall for the exterior

• MultiMax Lite thinset (for tape and waterproofing)

• Hydro Ban liquid membrane or Kerdi/RSS sheet membrane

• Blue painter’s tape for edge protection

• Schluter trim (optional for finishing the tile edge)

Frequently Asked Questions (FAQ)

Q1: Can I extend the backer board past the shower curb?

A: You can, but you don’t need to. Stopping around the middle of the curb is ideal. It keeps drywall out of the wet zone and maintains a flat transition.

Q2: Is liquid waterproofing better than sheet membrane?

A: Both are effective if done right. Liquid is faster and easier to apply; sheet gives a thicker, uniform layer. Choose whichever matches your workflow.

Q3: How do I prevent drywall damage when using thinset?

A: Use painter’s tape on the drywall edge and remove it promptly — don’t let thinset moisture soak in.

Q4: What’s the best thinset for this area?

A: MultiMax Lite by Laticrete. It’s smooth like drywall mud, bonds great, and holds waterproof membranes perfectly.

Q5: Should I waterproof the drywall too?

A: You can extend waterproofing slightly past the transition line, but full waterproofing of drywall isn’t necessary — just ensure proper overlap.

Summary

Let’s recap the key points:

• Stop your backer board halfway across the framing nailer at the shower curb.

• Use solid blocking to support both materials.

• Mark your transition line at the curb’s outside edge.

• Bridge the gap with mesh tape and thinset or a waterproofing membrane.

• Protect drywall with painter’s tape during application.

• Overlap tile by ½ inch for a professional, waterproof finish.

Closing Thoughts

Transitioning from backer board to drywall might sound simple, but it’s one of those steps that separates an amateur job from a professional installation.

By taking the time to frame correctly, seal that joint properly, and overlap your finishes, you’ll end up with a shower that not only looks great but also lasts for years without water damage or cracking.

If you have more questions like this or want to share your own shower projects, join the TileCoach.com community. We’ve got an amazing group of pros and DIYers sharing ideas, photos, and solutions every day.

Thanks for reading — I love being your Tile Coach.

Until next time, stay safe, stay precise, and as always — happy tiling!