Can You Put RedGard Over Kerdi Seams? (Explained)

When setting up a shower or bathtub, you must be 100% sure there won’t be leaks. Some of the products you can use to waterproof your shower system are RedGard and Kerdi.

These two are different systems that should be used separately. You either use Kerdi or RedGard to waterproof your shower. And the good news is that both can be tiled over. However, when using Kerdi, there will be seams since it’s a pliable sheet.

Kerdi provides a solution to ensure the seams are waterproof. However, as a contractor or DIY enthusiast, you may be interested in ensuring the seams don’t let water through.

And you may consider applying RedGard over the seams. Today, we will discuss whether RedGard should be applied over Kerdi seams and whether it will work.

Kerdi board

What are RedGard and Kerdi?

To better understand whether these two products are compatible, we need to define both of them. Starting with Kerdi, these are pliable sheets that create a waterproofing membrane.

Kerdi sheets create an excellent moisture protection barrier, and that’s why they are popularly used in showers, bathtubs, steam showers, and any application that may require waterproofing.

These sheets prevent mold development by keeping water at bay. Kerdi adheres well to tiles and thinset. All Kerdi sheets have a uniform thickness and are 2 meters wide which fits most bathrooms.

On the other hand, RedGard is a liquid-applied waterproofing membrane. It is popularly used in commercial and residential buildings.

RedGard can be applied on a wide range of surfaces, from concrete to cement backer boards. Besides creating a waterproofing membrane, RedGard also prevents cracking.

It does that by ensuring water doesn’t seep into the substrates beneath. Many contractors and DIY builders love RedGard since it’s easy to use.

You only need a roller brush to apply it. It’s also very durable and will prevent mold growth behind your shower walls.

Is It Okay to Put RedGard Over Kerdi Seams?

As mentioned earlier, Kerdi comprises pliable sheets attached to the walls using thinset mortar. These sheets have to be joined using seams.

You can either use lapping seams or butt-joined seams. The option you go with depends on your personal preference.

If you doubt whether the seams will prevent leaks, you can apply some RedGard over the Kerdi seams. RedGard will stick to Kerdi sheets if that’s what you are worried about.

It’s something a good number of people have done in the past. However, should you RedGard over Kerdi seams? Probably not!

RedGard and Kerdi are two different waterproofing membranes. One’s a liquid, and the other is a sheet. But they both do the same job.

When Kerdi introduced their waterproofing sheets, they knew there would be a challenge when it came to joining the sheets together. It’s why they also make Kerdi band waterproofing strips which should be layered over butted Kerdi sheets.

Using the Kerdi band waterproofing strips is pretty straightforward. Butt-join two Kerdi sheets together, apply some thinset over the butted area, and layer with the Kerdi band waterproofing strips.

Remove any excess bubbles or air, and the installation should be done. The seams will have been layered with the Kerdi band waterproofing strips.

In case you don’t want to use the Kerdi band waterproofing strips, another option entails creating overlapping seams.

A lap seam allows you to layer one end of a Kerdi sheet over another. It’s pretty simple. Once lapped, the Kerdi seams won’t let in water or moisture.

There are two methods, not even one for dealing with Kerdi seams. It doesn’t make sense for you to bring in RedGard into the picture.

Yes, RedGard will stick to Kerdi seams and create a waterproof barrier. But it won’t make sense for you to bring it into the picture in the first place. If you are using Kerdi waterproofing sheets, stick to that; the same applies to RedGard.

Does RedGard Add Any Waterproofing Benefits When Used on Kerdi Seams?

As long as you have installed Kerdi seams as recommended by the manufacturer, there is no added benefit when you apply RedGard. It’s probably a waste of money and time.

It doesn’t make sense for you to use two waterproofing membranes on the same surface. You should either choose RedGard or install the Kerdi seams as recommended.

Don’t forget that Kerdi is also a waterproof membrane. Therefore, it doesn’t need any help or support.

Applying RedGard Over Kerdi Seams Voids the Warranty

Besides the fact that RedGard won’t add any waterproofing benefits to properly installed Kerdi seams, it also voids the warranty.

Kerdi, made by Schluter, comes with a ten-year warranty. This warranty will be honored if you don’t abuse Kerdi or mix it with systems not recommended by the manufacturer, such as RedGard.

If you are not interested in compensation in case the Kerdi fails, you can go ahead and use RedGard. Considering that no advantages are added, it’s not worth using RedGard over Kerdi seams.

Can You Use RedGard If Kerdi Fails?

There have been reports about Kerdi failing a few months after installation. When Kerdi fails, you will spot leaks all over the shower system.

Before advising on whether you can use RedGard when Kerdi fails, we need to look into why it would fail in the first place.

Overall, Kerdi is an excellent waterproofing membrane. Very many people have had success with it. Most of the fails associated with Kerdi are due to incorrect installation.

Most leaks occur on the seams, which doesn’t come as a surprise because seams can be pretty complicated. When you don’t overlap the seams or cover butt joints with weatherproofing strips, there is a chance that water will pass through.

Therefore, before you start descending on how Kerdi fails, make sure that you have installed it correctly. Follow the instructions provided by the manufacturer and also do more research. There are plenty of resources on YouTube.

If you have a terrible experience with Kerdi, you can always use RedGard. The funny thing about these two waterproofing membranes is that they appeal to different kinds of people.

Some prefer to layer Kerdi on shower walls, and others like applying RedGard with a roller brush. It’s up to you to choose which preference suits you the most.

Anyway, should Kerdi fail, you can result to switching to RedGard. But don’t brush RedGard over Kerdi seams, yet you have installed them correctly. You would be wasting product.

The other scenario where you may consider using RedGard is if your bathroom has a lot of corners. Layering sheets of Kerdi on corners requires precision. However, since RedGard comes in the form of liquid.

All you need is a brush for the corners. And on the straight wall surfaces, you can use a roller since it covers more ground in a shorter duration. Please note that this scenario only applies to a bathroom that is yet to be waterproofed.

Can You Lay Kerdi Over RedGard?

The vice versa also doesn’t offer any benefits if the RedGard is relatively new. Because both are waterproofing products, they shouldn’t be used together.

The only time you can lay Kerdi over RedGard is if you are renovating the shower and the RedGard is pretty worn out.

In such a scenario, you can decide to try another waterproofing product which would be Kerdi, and you can lay it over. Don’t forget to install the seams as we have recommended above.

Should Kerdi Seams Be Left Uncovered?

By uncovered, we will assume that you are talking about Kerdi sheets that have been butt-jointed. Moisture can be pretty sneaky and penetrate even through the smallest spaces.

Because of this reason, Kerdi seams shouldn’t be left uncovered. You should cover them with the Kerdi band waterproofing strips.

These should cover any openings and ensure there is no risk of leaks. You don’t have to worry about seams if you overlap the sheets of Kerdi.

Is RedGard Compatible with Kerdi?

We have already mentioned that RedGard will stick to Kerdi. However, when it comes to RedGard being compatible with Kerdi, that’s a different story.

You must understand that RedGard and Kerdi are made using different materials. Therefore, when used together, they may not be compatible.

There is a possibility that RedGard may hinder the effectiveness of Kerdi. Hence, it’s not an experiment worth trying.

Other than being incompatible, there is absolutely no reason why you should use these two products at once. If you are using Kerdi, stick to it.

If you are worried about the seams, cover them with a waterproof brand made by Kerdi. Or, you can overlap the Kerdi sheets. Either of the options should work sufficiently.

On a head-to-head comparison, Kerdi and RedGard are both excellent waterproofing products. Each has its highlights, but you shouldn’t waste money using both together, irrespective of which you settle on.

While we are still on compatibility, Schluter recommends that Kerdi should be used with an unmodified thinset mortar. It’s advisable to use the mortar sold by Schluter. That will ensure there aren’t any compatibility issues.

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