Kerdi membrane is one of the best products you can use to waterproof drywall. With a Kerdi membrane, you can prevent the effects of water damage on drywall.
Even though drywall is an ideal substrate for Kerdi membrane, will it stick if the drywall is painted? This is going to be our main focus in today’s discussion.
I will also be highlighting other issues that surround the installation of the Kerdi membrane over painted drywall.
Can You Put Kerdi Membrane Over Painted Drywall?
Kerdi membrane should never be applied to freshly painted drywall. The presence of fresh paint will affect the adhesion between the drywall and the Kerdi membrane.
When it comes to the installation of drywall, you are required by Schluter, the manufacturer, to use thinset. When the thinset encounters fresh paint, a reaction occurs that reduces the adhesive strength of the former product.
Therefore, if you directly apply Kerdi membrane over painted drywall, it won’t take long before the pliable sheet fails and comes out of your walls.
But before you give up on the idea of applying Kerdi membrane over painted drywall, I have some good news for you.
There is a way you can cover painted drywall with Kerdi membrane. This process entails the use of a primer and a high grit sandpaper.
How to Apply Kerdi Membrane Over Painted Drywall?
Step 1: Score the Paint with a High-Grit Sandpaper
As mentioned earlier, the Kerdi membrane won’t last long over painted drywall. Therefore, if you want to enjoy the waterproofing capabilities of Kerdi membrane for a long time, you must score a good amount of the paint.
One of the perks of using sandpaper is that it can scuff up both fresh and old paint. You can also use an orbital sander but I am not a big fan of it because it may tear through drywall.
Unlike other surfaces, drywall is pretty delicate. Therefore, sandpaper should be enough for this task. Your goal here should be to try and remove as much paint from the drywall as possible. Make sure that you wear a dust mask.
Step 2: Cover the Drywall with Some Primer
A layer of primer can help prepare the surface for thinset which is used to bond the Kerdi membrane. The primer will also cover any paint that was left behind.
Some people usually skip this step but I think it’s very important to layer drywall with primer if it was recently painted.
Do not apply the Kerdi membrane immediately after covering it with primer. Give the primer enough time to cure. If it’s wet it will be ineffective.
Step 3: Install Your Kerdi Membrane with Thinset
Your painted drywall will now be ready for the Kerdi membrane. You can proceed to install it with thinset. Make sure that you follow Schluter’s instructions.
This may seem like a lot of work. But it’s better than risking installing Kerdi membrane over painted drywall.
Do You Have to Remove the Paint on Drywall Before Installing Kerdi Membrane?
You need to remove the paint on the drywall before installing a Kerdi membrane over it. Even if you won’t remove all of the paint, make sure that a substantial amount of it is removed.
Feel free to use any method of paint removal other than sanding. There are plenty of paint removers out there. Chemical strippers are a great example.
If you go ahead and install the Kerdi membrane over painted drywall, you will most likely run into adhesion problems.
Will Kerdi Membrane Stick to a Glossy Painted Drywall?
It will even be more difficult for Kerdi membrane to stick to a glossy painted drywall. High gloss paint usually has a smooth finish over it. This smooth finish makes it impossible for the thinset to adhere to it.
If your drywall has high gloss paint, you need to be more thorough with the sanding. The rougher the surface of your high gloss painted drywall is, the easier it will stick to the Kerdi membrane.
Does Schluter Allow Their Kerdi Membrane to Be Installed Over Painted Drywall?
Schluter only mentions that the Kerdi membrane can be used to waterproof drywall. They do not specify whether the drywall should be painted or not.
To ensure you don’t void Schluter’s warranty, I would recommend getting one of their reps to sign off on your project. This way you will have peace of mind knowing that your Kerdi membrane is covered by Schluter’s warranty.
Do You Need to Hire an Expert for Kerdi Membrane Installation Over Drywall?
That depends on how you approach this issue. If you hire an expert contractor, they will most likely follow the steps I have shared with you.
However, the advantage is that they will do all the heavy work which entails sanding and installing the Kerdi membrane. But these services will come with an added cost.
If you are a DIY enthusiast who doesn’t mind getting your hands dirty, this is a project that you can pull off by yourself.
But if you have a busy schedule and minimal experience with waterproofing drywall, it’s a great idea to have an expert do it for you. This option ensures you don’t make silly mistakes.
Do You Need to Perform an Adhesion Test Before Installing Kerdi Membrane Over Painted Drywall?
Considering that this isn’t the typical method of waterproofing drywall with a Kerdi membrane, it’s a good idea to perform an adhesion test.
This entails sticking a small piece of Kerdi membrane over the painted drywall and waiting for it to cure. After it dries, try to remove it.
If it sticks, then you can proceed to waterproof the entire drywall. However, if it fails, you need to re-evaluate your application technique.
One of the benefits of adhesion tests is that they can inform you about the compatibility of painted drywall and Kerdi membrane.
What Challenges Can You Face When Installing Kerdi Membrane Over Painted Drywall?
Many things can go wrong when installing Kerdi membrane over painted drywall. Familiarizing yourself with these obstacles is important as you will know what mistakes to avoid. Some of these challenges include;
• Peeling of the Kerdi membrane due to poor adhesion – If you don’t scratch or remove the paint on drywall, the Kerdi membrane won’t adhere firmly to it. As a result, the membrane may start peeling prematurely.
• Kerdi membrane being incompatible with some paints – Kerdi membrane is usually incompatible with some types of paint. High-gloss paint is an excellent example.
Before installing the Kerdi membrane over the painted drywall, you have to check its compatibility with the paint on the drywall.
• Flaking paint can affect drywall adhesion to Kerdi membrane – One of the reasons I am advising you to scuff up the paint is to prevent such scenarios. Chipping or flaking paint can cause poor adhesion and make the Kerdi membrane ineffective.
Should You Paint Drywall Before Installing Kerdi Membrane?
No. Kerdi membrane should be applied on plain drywall. You don’t have to paint it, prime it or do anything to the drywall.
Painting drywall before installing the Kerdi membrane is a waste of time and resources. You will also be lowering the adhesive strength of the thinset that is used to bond the Kerdi membrane to the drywall.