ARDEX 8+9 Over Kerdi (Is It Recommended?)

When building a shower, steam room, or anything else that will be constantly exposed to moisture, you have to be careful when waterproofing the walls and floors.

In such a setup, there is a considerable risk of water seeping through the walls and floors, thus damaging other materials such as sheathing.

In an attempt to create a complete waterproof system, you may consider using two waterproofing products such as Ardex 8+9 and Kerdi.

There are a lot of varying opinions regarding the use of two waterproofing products in one project. That is why in today’s article, we will evaluate whether it’s advisable to install ARDEX 8+9 over Kerdi.


Can You Use ARDEX 8+9 Over Kerdi?

ARDEX 8+9 can be used over the Kerdi membrane. But this heavily depends on what you intend to achieve with these two waterproofing products.

There are two main reasons why you can use ARDEX 8+9 over Kerdi which include;

• ARDEX 8+9 can be used as an adhesive to attach Kerdi seams

In other parts of the world, such as Germany, Schluter recommends that Kerdi membrane be installed using Kerdi-Coll-L, a waterproof adhesive. Most of us are accustomed to using unmodified thinset mortar.

Suppose you would like to follow the above method of Kerdi installation using an adhesive instead of mortar. You can use ARDEX 8+9 instead of Kerdi Coll-L because the latter is only available in Europe.

In this case, the ARDEX 8+9 will enhance the adhesion of Kerdi seams and create a complete waterproof system.

• ARDEX 8+9 is ideal for waterproofing corners and areas where its difficult to install Kerdi membrane

The other reason you may consider using Ardex 8+9 is when you want to waterproof corners and areas that are hard to reach for the Kerdi membrane. Ardex 8+9 is a liquid membrane. Therefore, it’s much easier to install than the Kerdi membrane.

Therefore, if you are struggling to fit the Kerdi membrane on specific areas, instead of leaving these parts exposed to moisture, you can waterproof them with ARDEX 8+9.

These two are the only valid reasons why you may want to install ARDEX 8+9 over Kerdi. Anything else that falls out of this framework is unreasonable.

Does Using ARDEX 8+9 Over Kerdi Make Your Project More Waterproof?

It’s normal to be cautious of water damage when engaging in any construction project. But using two waterproofing products together doesn’t usually make much sense.

If you want to use ARDEX 8 over Kerdi to make your walls or floor more waterproof, there is no need to use these two waterproofing products together. The thing is, installing Ardex 8+9 over Kerdi will not interfere with the performance of the latter or affect it.

The product that’s below will continue doing its job of waterproofing the surface. There won’t be any added value. On the contrary, you will have spent more money and effort using two waterproofing products.

The best approach here would be to weigh out which of these two is the best waterproofing product. And the one you settle for is the only product you should install.

Never be misled that using two waterproofing products will make your surface more resistant to water penetration.

Will Using ARDEX 8+9 Over Kerdi Void the Warranty?

Manufacturers are always looking for the simplest reasons not to honor warranties. Can you imagine what the Schluter reps will tell you when they find out that you added ARDEX 8+9 over their product?

When you use these two products together, you can forget any warranties from both companies. It’s one of the risks you will be taking. And it’s wise to avoid engaging in such a practice because it is against your manufacturer’s guidelines.

If you want an adhesive for the Kerdi membrane, look for the Kerdi Coll-L. On the other hand, if you want the polyethylene membrane version of ARDEX 8+9, they have the SK-175.

When you use waterproofing products from the same company, you are guaranteed a warranty and don’t have to worry about incompatibility issues.

Do ARDEX 8+9 and Kerdi Use the Same Formula?

Absolutely not. These products are made by different companies. Even though they do the same job, the formulas are quite different.

You should also know that Kerdi is a pliable sheet waterproofing membrane. ARDEX 8+9, on the other hand, is a two-component liquid-based waterproofing and crack isolation product.

They are two different waterproofing products that shouldn’t be used together unless it’s very necessary. I have already listed the two scenarios where you may consider using ARDEX 8+9 over Kerdi. But any reasons apart from these two don’t make sense.

ARDEX 8+9 vs. Kerdi

Since you can’t use ARDEX 8+9 and Kerdi in the same project, you will need to pick one of these waterproofing products.

Both are popular waterproofing options that do a great job of preventing moisture from passing through a surface. But each has its unique features.

ARDEX 8+9 stands out as a waterproofing compound because it can resist the penetration of wind-driven water. It’s also a crack isolation product that allows tile installation in less than two hours.

ARDEX 8+9 comes in liquid form, which is solvent free. That makes the application relatively straightforward.

You can apply ARDEX 8+9 using a brush or roller. And the best part is that you can use this compound to create a shower pan.

You can get ARDEX 8+9 is either white or gray. It can be used in kitchens, bathrooms, and other high-moisture areas. It is highly resistant to efflorescence and will waterproof your surfaces for a long time.

Moving on to Kerdi, this is one of the most popular waterproof membranes. It comes as a pliable sheet that also doubles as a vapor retardant.

Kerdi membrane is a bit more complex to install because you have to cut the sheets into pieces and attach them using mortar. There is an anchoring fleece on the bottom part that facilitates adhesion.

You can install Kerdi in bathtubs, showers, steam rooms, or saunas. With Kerdi on your wall and floor, you never have to worry about mold growth. Kerdi membranes are suitable tile substrates, and it creates uniform thickness.

It is widely available in stores such as Home Depot. You can also order it online. Kerdi is made by Schluter, which is a renowned brand in the construction industry. Therefore, it’s a product with an excellent reputation.

From the description of these two waterproofing products, you can see that each option excels in various scenarios. For instance, ARDEX 8+9 is easier to apply. On the other hand, Kerdi is a vapor retardant.

Is It Advisable to Install ARDEX 8+9 Over Kerdi?

Many experts would not approve the use of ARDEX 8+9 and Kerdi in the same project. The best solution is to choose either Kerdi or ARDEX 8+9.

Most people don’t know that ARDEX has a pliable sheet membrane version of Kerdi. Therefore, if that’s what you prefer, go for the one made by ARDEX. As for Kerdi, you can use their Kerdi Coll-L adhesive, which functions like the ARDEX 8+9.

Mixing these two products won’t reinforce your waterproof system. It’s even disadvantageous because it will void the warranty.

Except for the two reasons I shared with you earlier, you don’t need to install ARDEX 8+9 over Kerdi and vice versa. Weigh the pros and cons of each, then choose the one that seems ideal for your project.

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