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How to Waterproof a Shower with Ardex 8+9

Easier Than Painting!

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How to Waterproof a Shower

Today you’ll learn how to waterproof a shower with Ardex 8+9.

This could be the inspiration you need to start a bathroom remodel.

Especially if you want a tiled shower surround.

Without proper waterproofing a tile job will fail BIG TIME.

And your beautiful shower will need to be gutted again.

Today’ we’re going to show you how to waterproof a shower using Ardex 8 + 9.

Let’s do this!!

Getting Started 

Here’s the deal, we used Ardex 8+9 to waterproof a cement board tub surround.

Cement board is one of the cheapest ways to install a shower or tub surround. It’s rock solid.

But you have to apply something over it to ensure water doesn’t get in the stud bays.

Here are the supplies you need

  • Ardex 8+9 (we recommend two boxes)
  • SK Mesh
  • Latex Gloves or
  • Nitrile Gloves
  • Protective Glasses
  • 1/2″ Drill (optional)
  • Paddle Mixer for Drill (optional)
  • Rags
  • Putty Knife
  • Paint Roller
  • Pan for Paint
  • Brush for 8+9
  • Painter’s Tape ( I used Frog Tape)
  • Garbage Bags
  • These affiliate links help support HRT, so thank you 😀


Addressing the Cement Board to Tub Transition

Should you mount cement board above the tub lip or on the tub deck?

Steve and I think you need to place the cement board above the tub lip.

Here’s why, if you mount it on the tub deck the cement board will be angled out.

Mount Cement Board Above Tub Lip

Not a big deal for the cement board.

However, your tile will look wonky in the corners.

But mounting the cement board above the tub lip creates a gap between the boards and tub.

This is where Ardex 8+9 can help.

Sure, you could fill this in with thin-set mortar then apply a mesh over it.

This adds a full day of work because you have to let the mortar harden overnight.

Ardex 8+9 is different.

You can mix it to a thick caulking consistency.

Steve shows you how in the video.

I almost forgot, it’s a good idea to add painter’s tape to the top of the tub.

That way any 8+9 that gets on the tub will be on the tape.

Painter's Tape on Tub

Fill in the tub to cement board gap with the 8+9 caulk.

Use a putty knife for this.

You should also fill in any gaps greater than 1/4″ with the same caulking.

If cement board panels are butted against each other with a 1/8″ gap or less you don’t need to caulk them with 8+9.

Tub and Cement Transition

The cool part is you don’t have to wait to waterproof, unlike with the mortar method.

We’ll show you the right way to paint the 8+9 on the cement board.


Waterproofing Cement Board with 8+9

Immediately mix one unit of Ardex 8 (liquid) with one unit of Ardex 9 (powder).

Add Ardex 8 (liquid) to the bucket first then Ardex 9.

Doing this cuts down on the dust and prevents the Ardex 8+9 from clumping.

Nobody likes clumping…it’s kind of a nasty word.

Mix this with a paddle mixer or margin trowel.

A mixer does a better job but it’s not totally necessary.

Just make sure the consistency is smooth and free of lumps.

Mix Ardex 8 + 9

Pour the 8+9 into a paint pan.

Paint it into the corners with a brush.

Then use the paint roller to apply it vertically on all panels.

Roll on Ardex 8+9

Roll the 8+9 up to the ceiling.

Before the 8+9 dries apply the SK Mesh over the tub to cement board transition.

You should also apply the mesh to the cement board and drywall transition.

Apply Mesh to Wet 8+9

Okay let’s jump into the video.

You’ll see step-by-step what to do.

Steve is an awesome teacher

Here are some key tips.

  • Let the first coat dry for 30-45 minutes.
  • Apply the second coat in the opposite direction.
  • Smooth out any wrinkles in the SK Mesh while 8+9 is still wet
  • Mix small batches of 8+9 since the pot life is about 60 minutes

If you follow all of Steve’s tips you’ll have a completely waterproofed cement surround.

And you can tile in in about 2 hours.

So technically you can apply 8+9 and start tiling in one day.

Now that’s cool stuff!


What’s Next

Ardex 8+9 is great for waterproofing cement board.

If you’d rather use wedi or KERDI-BOARD we have great tutorials on those systems.

If you’re building a custom bathroom or shower check out Bathroom Repair Tutor. The detailed video tutorials and professional tips are fantastic.

Here’s the link to Bathroom Repair Tutor


Jeff Patterson



  1. Sheila says:

    I wish I had come across your site a few weeks ago. I just knew something had to be put in the back wall when installing surround. We , my self and disabled husband hired a contractor to put in a tub & shower surround in our bathroom. I picked out the tub and surround sent him the pics the stuff was from Home Depot . He called me & said I would have to go with a different surround since I had a window. I was ok with that but, the next day when he was working in our bathroom I had an appointment & wasn’t home he only put plastic on the back wall then the surround and a tub so small it looks like a kiddie pool. I have never been so disgusted in my life. He wont change it and basically said tough luck. It’s so important to see a site like yours so people know what is suppose to be done the right way. I had to wait a lot of years to afford the job and I just got taken for something that will have to be redone in the future. Thanks for letting people know how things are really done.

    1. Sorry to hear about your experience Sheila, that really sucks.

      We hope to help more with our bathroom remodeling videos.

      Steve is the real hero. He’s honest with people and stays on top of the latest technologies.

      We’ll have a ton more videos like this one and are always here to answer questions.

  2. Char says:

    No way would I know about this product and so many others–including how to use without your information sharing and I am so grateful.
    However what I really need right now is help with an old shower stall. In the old part of the house the original shower stall has a leak. The ”pan”? To remove the tile and begin again would be almost impossible without removing all the tile in the stall [not matchable] around the separate bathtub, counter top and 1/2+ way up the walls. I am pretty satisfied with the tile, sort of arty. One reason too big to take on is that altho the tile work is from the late 50’s it was installed in the old way with cement and chicken wire and looks brand new. Do not wish to remove all that tile and create a huge and expensive job since it is satisfactory in every way except for the pan leak.
    Please please tell me you have some suggestions in your bag of tricks!
    Thanks Jeff, have a great day!

    1. That old tile is pretty tough to remove for obvious reasons.

      It’s solid as a rock because it sits on rock, lol.

      Maybe the leak is a pipe issue Char?

      Do you have access to the pipes from below?

      1. Deborah Harrell says:

        If it’s a hole in the pan, there is patching material for it

  3. Ingrid says:

    Great instruction. The previous homeowner of my home decided to overhaul the bath surround tile and installed the cement board OVER the lip of the tub. So, I have that “wonky” angled tile look. I never heard of Ardex 8+9. It sure looks like a terrific product.

    1. Yah, nobody notices the problem until the tile work Ingrid.

      Bummer to say the least.

      Ardex is pretty cool and their thin-set is fantastic, too. It’s X 77 and we like it for large tiles because it basically prevents the tile from sliding down the wall.

  4. dan says:

    Thanks Jeff and Steve for taking your time to show how it’s done. I appreciate it.
    Has Steve every put multiple tiled shelves instead of a nook? This is what I would like since I have 8 inches of play in front of tub. Can Steve send me some pics of how he does shelves? Maybe 3 or 4, one above the other separated by 2′ say? So one would be along knobs maybe and butt into the corners. The other ends would be where the curtain would “stick” to. Like nooks with an open side I guess? Is that messy to get all lines lined up. Will it look bad no matter how accurate I get lines? Will the end tiles falls of if I hit them since they will have a lot of corners exposed. But I think it will be a little more roomy than confining the space to dimensions of tub. Where can I put the shower bars? On the shelves or inbetween them “recessed”? Bad idea or is it doable? I can take my time all winter if I have to. Thanks Jeff and Steve.

  5. waykno says:

    I’ve never heard of Ardex 8+9 either but if it makes a shorter job, then I am for it.

    1. It’s a good choice for cement board 😀

  6. teresa says:

    i have a question.. instead of 8×9 i see other product at Lowes that is call Aquadefense what do you know about that product I see another video of a pro of 30 year experience using it can you tell me your opinion.

  7. Alex says:

    Hi Jeff,

    My husband and I are renovating our main bathroom right now. We have our tub all set in place and are ready to put the cement board up. My question is does the cement board go right on top of the tub lip above where we have screwed it in OR do we set it on top of the tub with shims. I have been reading a lot of different tutorials on your website and am just a little confused, with the Ardex 8+9 it says to set it on top of the tub lip, however in other posts it says to set it on shims and mount it below the tub lip. We plan on using the Red Guard to waterproof, before we tile. Thanks for your time. 🙂

    1. Hi Alex, I’d recommend installing the cement board on top of the tub lip then fill in the gap with extra thin-set, add alkali resistant mesh to that transition and RedGard it.

      The reason is this, if you pitch the cement board over the lip your tile will look wonky in the corner or where the tile meets the drywall. Hope that makes sense but let me know if you have any questions 😉

  8. David Beauchamp says:

    Hi Jeff – I purchased the Ardex product shortly after seeing the great step-by-step video. I was wondering a few things before applying. Should I put a vapor barrier behind the cement board prior to putting it up? Or can I skip the vapor barrier due to the waterproofing nature of the Ardex? In addition prior to applying the Ardex were the joints at the cement board taped with flex mesh & then sealed with thinset? Great website by the way best I could find online for waterproofing a shower 🙂

    1. Jeff Patterson says:

      Hey David, sorry if this is a late reply but we recommend consulting your local building code for vapor barriers. In addition, I’d call Ardex’s tech support and discuss it with them. They’re fantastic and will help a ton. Mark is a great guy over they, in case you get him on the phone. You don’t have to necessarily use the mesh at the joints with Ardex 8+9 but it does help with the sealing process. There are specific guidelines in the 8+9 instructions on this point. Feel free to email me any time.

  9. mitch says:

    As usual, a great video, thank you Jeff and Steve. I like the addition of the mesh at the tub to wall transition. I’m curious why this isn’t applied to the inside corners of the tub surround. I would have guessed that this would also be a critical area for waterproofing.

  10. Josh says:

    Hi Jeff, Is there any reason that the butts and corners can’t be Alkali-resistant mesh taped and then thinseted? After that dries then paint the 8+9 over all of it? I’m trying to avoid buying 2 kits of the 8+9. Thanks, Josh
    ps. Thanks for the great videos. They’ve been a big help with my recent bath reno.

  11. Trent says:

    Hi, and thank you for your videos. That are very very well done, informative and appreciate you show different cost and difficulty options.
    Questions of course for you;

    1) Like asked above do you need to do traditional thinset and tape the joints of the cement board before the Ardex? Or will the Ardex harden the joints like thinset and prevent movement? Can you do the same with Redgard?

    2) If using Redgard, and leaving the cement board above the lip very confused on options. Is tape and thinset down from cement board to tub deck okay? What about a gap for expansion between tub deck and thinset then? Of course then apply waterproof (i.e. Redgard in my case) over everything once dry. Is it worth siliconing a small bead between cement board and lip before the thinset?

    Thanks so much, and will be following your videos.

  12. Zachary says:

    Hey guys,

    Excellent video, I just used this stuff to waterproof my shower surround and I’m pretty impressed with the finished surface. I did exactly half and half of the product for each coat and had quite a bit of leftover in the second coat, which was really helpful in covering screw heads and working in some additional layers on the edges of the mesh.
    Anyway, question for you: how do you clean this off your tools? I haven’t found any reliable information on how to soften or dissolve it to get it off paintbrushes, roller handles, mixing paddle, etc.

  13. SVH says:

    Can I put this over Denshield? I’m aware denshield already has a waterproofing membrane however I would like to ensure that the edges and corners are 100% water tight

  14. Karen Breschi says:

    I want to use cement board with Ardex over it for the walls of my shower…Will that work? Do I need to seal it after I apply it? My interior looks like the plaster work on Greek islands and I want to continue that look in my new shower.

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