Can You Use AquaDefense Over Kerdi? (Explained)

Many professional and DIY enthusiasts are always reluctant to mix two waterproofing systems. There is always the fear that different waterproofing systems may be incompatible, resulting in total failure.

But then, if you have two waterproofing systems, you enjoy extra protection from water damage.

There are pros and cons to using two different waterproofing systems. Today, we will focus on two of the most popular waterproofing systems: AquaDefense, popularly known as AD, and Kerdi.

Is it okay to use AquaDefense over Kerdi? Keep on reading to find out.


A Brief Introduction of AquaDefense and Kerdi

Before I share with you whether AquaDefense can be used over Kerdi, it’s imperative that I introduce both products and what they are capable of.

What is AquaDefense?

AquaDefense is a crack-isolation and waterproofing membrane made by MAPEI. It is sold in a liquid, pasty form which dries into a waterproof membrane after application.

AquaDefense is the go-to waterproofing system for most DIY enthusiasts because it dries fast and is very easy to apply.

The new formula of AquaDefense features a lighter color that makes it easier to spot chalk lines when working in areas that aren’t well-ventilated.

This waterproofing system dries into a continuous rubber barrier that keeps the surface below from water damage.

You can install tiles over AquaDefense in less than an hour after application. It doesn’t have a strong odor, therefore ideal for use in confined spaces.

AquaDefense can be used as a shower-pan liner, and if you are worried about it not being strong enough, you can use it with MAPEI’s Reinforcing Fabric.

What is Kerdi?

Kerdi needs no introduction. It’s made by Schluter, a leading manufacturer of construction materials. Kerdi is a vapor-retardant and waterproofing membrane commonly used in shower installations.

It is a sheet-applied polyethylene barrier that prevents mold development and water damage. Kerdi is very easy to install thanks to the anchoring fleece that can be attached using thin-set mortar.

Since it’s a sheet membrane, you are assured of a uniform thickness. It is durable, and to ensure it prevents water from passing through, you can tape the seams with SCHLUTER Kerdi Band.


Will AquaDefense Bond to Kerdi?

Now that you know what these two waterproofing systems are, it’s time we look at whether they can be used together. Let’s start with the most important part – will AquaDefense bond to Kerdi?

AquaDefense will bond strongly over the Kerdi sheet. This will happen without the use of a bonding agent or additive. AquaDefense sticks like glue to Kerdi sheets.

Unless you pry it off using a knife or a sharp tool, AquaDefense will hold firmly onto Kerdi sheets. Therefore, you can paint AquaDefense over Kerdi, and it will stick.

Should You Use AquaDefense Over Kerdi?

Kerdi is a superior waterproofing system. Many people have used it, and it has worked well. At the same time, there are tons of Kerdi fail stories on the internet in popular forums. Therefore, it makes sense why you may want to use AquaDefense over Kerdi.

The main reason you may be interested in using these two together is to create a hybrid waterproofing system.

A layer of AquaDefense will add more waterproofing capabilities over Kerdi. Therefore, even if there are openings on the Kerdi seams, the AquaDefense will ensure water doesn’t seep through and damage the materials beneath the shower pan.

If you are a newbie in shower installations and you doubt whether you laid the Schluter system correctly, it’s a good idea to go with AquaDefense on top of it.

Therefore, there are valid reasons why you may be interested in using AquaDefense over Kerdi.

How Long Does AquaDefense Last Over Kerdi?

Because AquaDefense bonds well to Kerdi sheets, it often lasts a very long time after you have installed tiles over it.

Many DIY lovers have used AquaDefense over Kerdi and it has served them for a long time. With two waterproofing systems installed, there is a guarantee that if one fails, the other will continue to do its job.

This is why using these two isn’t such a bad idea. However, it will cost you more because you must buy both products.

Does Schluter Recommend Using AquaDefense Over Kerdi?

Let alone making recommendations, Schluter voids the warranty of Kerdi if you use it with another product such as AquaDefense.

Therefore, don’t bother reaching out to Schluter if you decide to use these two waterproofing systems, and they both fail. They will not honor their warranty.

It doesn’t come as a surprise that Schluter would not recommend using their product with that of another brand.

The thing is, Schluter has their kit containing Kerdi Fix and Kerdi Band. Therefore, if you need to seal the seams or corners, Kerdi recommends using the Kerdi Band.

Because they do make a product to reinforce the Kerdi sheets, they can’t promote another product from another brand.

Is AquaDefense Compatible with Kerdi?

Kerdi and AquaDefense are built using different materials. However, they are quite compatible. If they were incompatible, AquaDefense would not stick to Kerdi. It would either fall off once it dries. Or it would not dry at all in the first place.

Do Experts Recommend Using AquaDefense Over Kerdi?

In the construction world, there are two kinds of people; DIY enthusiasts and professionals who do everything by the book. DIY enthusiasts have no problem with using AquaDefense over Kerdi. But most professional tile installers do.

If you ask an expert, they will advise you to either stick to Kerdi or AquaDefense. After all, both products have been approved for use on shower pans.

Professionals will advise you to use Kerdi sheets with Kerdi Band or Kerdi Fix. They will also advise you to lay another Kerdi sheet if you think the one installed is punctured or perforated.

Does AquaDefense Affect the Bonding of Tiles to Kerdi?

Both Kerdi and AquaDefense are suitable substrates for tiles. That is, both waterproofing systems can easily be tiled over. When you paint AquaDefense over Kerdi, tiles will still adhere to it, but the bond won’t be very strong, and here is why.

Most sheet membranes, such as Kerdi and Ditra, bond to thinset by interlocking with it. Thinset crystals adhere to the sheet, and that’s why their bond to the tile is so strong that to remove the tile, you must also remove the sheet beneath.

Applying AquaDefense over Kerdi prevents the thinset from passing through or interlocking with the sheet membrane.

Therefore, the bond slightly weakens when there is AquaDefense on top. This is something you should know about when you consider applying AquaDefense over Kerdi.

Can You Install Kerdi Over AquaDefense?

We have already figured out that you can use AquaDefense over Kerdi. What about vice versa? Can you install the Kerdi sheet over AquaDefense?

It is possible to install Kerdi over AquaDefense. But you should use unmodified thinset mortar. The type of thinset mortar used to install Kerdi is of utmost importance because it determines whether the project will succeed or fail.

If possible, you should use the mortar made by Schluter as it’s the most recommended option.

If you use a modified thinset with Kerdi, it will fail, and the results will be catastrophic. Please note that when you install Kerdi over AquaDefense, Kerdi will not honor their warranty because they don’t recommend using their products with other brands.

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