Kerdi Membrane Over Greenboard (Is It Recommended?)

A few years ago, greenboard was the best type of drywall to use in high-moisture areas such as showers and kitchens. That’s because it features a paper facing which is resistant to moisture and mildew.

However, it was discovered later that greenboard isn’t 100% water-resistant. After a while, it would experience water damage, leading to more problems.

If you have moved into a new home and discovered a greenboard in a high-moisture room, or you want to build a shower/kitchen and use a greenboard, you may also consider using a Kerdi membrane over it.

But is it advisable to use the Kerdi membrane over the greenboard? This is exactly what we will discuss in today’s post.

Greenboard drywall

Does Kerdi Membrane Stick to Greenboard?

Kerdi Membrane is a product of Schluter systems. It is a pliable waterproofing membrane that also doubles as a vapor retarder.

Kerdi membrane prevents water damage and mold development. Kerdi membrane can be used on cement board, drywall, and, as you may have guessed– greenboard.

Greenboard is the same as regular drywall. It’s only that greenboard has been designed for high moisture areas.

So, if you can stick the Kerdi membrane to regular drywall, you can be assured that it will stick to the greenboard.

If you were considering installing the Kerdi membrane over the greenboard, you don’t have to worry about the incompatibility of these two products.

What Benefits Can You Get from Installing Kerdi Membrane Over Greenboard?

Now that you know it’s okay to lay Kerdi membrane over greenboard let’s address why you would be interested in using these two products together.

Most people mainly apply the Kerdi membrane over the greenboard to enhance the system’s waterproofing capabilities.

Earlier, we mentioned that greenboard doesn’t do well in high moisture areas. Due to this problem, some expert contractors have sworn never to install greenboard in showers.

However, if you are building a shower and you have already installed a greenboard. Or you don’t have the resources to swap it out with cement board. Your best option is to lay a Kerdi membrane.

With Kerdi over the greenboard, no water or vapor will pass through. Therefore, your greenboard will remain intact and won’t experience water damage.

The purpose of using the Kerdi membrane over the greenboard is to create a more substantial waterproof barrier on your walls.

How to Install Kerdi Membrane over Greenboard?

Having figured out that the Kerdi membrane can stick to the greenboard and prevent water from passing through, it’s time we look at how to install it correctly.

Step 1 – Prepare the Greenboard

For the Kerdi membrane to stick, the drywall must be level, flat and clean. Therefore, get rid of any bulging spots. And clean the drywall to remove dirt.

Step 2 – Measure and Cut the Kerdi Membrane

Kerdi membrane is available in rolls of sheets. Therefore, before installation, you need to measure the size you will install and cut it using scissors or a utility knife.

In a shower setting, you will also need to make cuts for the tap areas and shower head arm. You need to be very keen to avoid making wrong cuts.

Step 3 – Apply the Schluter Set Mortar on the Greenboard

Schluter is very strict about the type of mortar you can use to stick their membrane to the greenboard. They have their mortar.

However, if you can’t get it, you can always use unmodified thin-set mortar. Do not use modified thinset mortar, which will likely lead to Kerdi failure.

You can apply this thinset using a notched trowel and drywall knives. You need to achieve a flat trim.

Step 4 – Fit the Kerdi Membrane to the Greenboard

After applying the thinset, you can now attach the Kerdi membrane to the greenboard. Start by pressing the membrane into the greenboard from the center. Then work your way toward the edges.

Press the Kerdi membrane firmly into the thinset so that it bonds well. Give the thinset time to dry before you add tiles or anything else on top of the Kerdi membrane.

Step 5 – Tape the Seams

If you are working on a large piece of greenboard, it’s a good idea to tape the seams. This ensures the greenboard is thoroughly waterproofed. Schluter makes their tape known as Kerdi Band. That’s what you should use to seal butt joints.

Is It Advisable to Install Kerdi Membrane over Greenboard?

On paper, it may not make sense why greenboard has to be waterproofed, yet it is a moisture-resistant drywall.

However, from the terrible experience homeowners have had with greenboard. It’s safer to waterproof it with a product such as Kerdi membrane to avoid water damage.

It is advisable to install the Kerdi membrane over the greenboard that has already been installed. It’s quicker and more cost-effective than pulling greenboard from the walls and replacing it with cement board or DensShield.

In case you are yet to buy and install a greenboard in your shower, I would advise you to consider a water-resistant alternative.

How Long Will Kerdi Membrane Last on Greenboard?

As long as the system is installed correctly, the Kerdi membrane can last for decades on the greenboard. Even the greenboard itself will last for years.

Because as we have discussed earlier, greenboard, after a while, its structure weakens when it’s exposed to moisture. But since water will be prevented from entering the greenboard by the Kerdi membrane, it should last for a long.

Are There Any Problems that Can Result from Using Kerdi Membrane over Greenboard?

You can expect zero problems when you use the Kerdi membrane over the greenboard. There are a lot of arguments online about the effectiveness of greenboard in barring moisture and water.

With the Kerdi membrane on top of your greenboard, this doesn’t even have to be a cause for concern. This is one of the few projects out there that has no downsides. But it must be installed correctly for it to work.

Do Local Building Codes Allow Kerdi Membrane to Be Used Over Greenboard?

The funny thing about the world we currently live in is that rules differ from one area to another.

There are certain places where the local building codes don’t allow the Kerdi membrane to be used on the greenboard. Most of the time, such areas recommend that Kerdi membrane be used on cement backer boards.

If you live in such an area, you have no option but to follow your local building guidelines.

What Alternatives Can I Use Instead of Installing Kerdi Membrane over Greenboard?

So far, you are well aware that greenboard is far from effective at preventing moisture and water from passing through.

If you want to build a shower and don’t want to perform the extra steps of adding a waterproofing membrane such as Kerdi, are there other options that don’t need to be waterproofed?

You are in luck because there are plenty of wall options that you can hang and proceed to tile directly without adding membranes. They include;

1. DensShield – This is the best backer board for high moisture areas. Unlike greenboard, DensShield won’t crumble when exposed to moisture.

2. Kerdi-Board – It is also another excellent alternative to the greenboard. They are very easy to install.

3. HardieBacker with HydroDefense Technology – HardieBacker is known to be one of the best cement boards for building showers. It is durable, and it’s a suitable tile substrate.

The regular HardieBacker wouldn’t have made it in this list of greenboard alternatives. But this particular one that features HydroDefense technology is waterproof and doesn’t need to be used with a membrane.

Was this article helpful?