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Is Thinset Waterproof? (Explained)

Thinset is an essential binding element in the tile installation process. If you do not know a lot about construction, you may have many questions about thinset. What types of thinset to use, or whether it is waterproof or not.

So if you want to clear your understanding on thinset, we suggest you read on. We have discussed several facts and queries related to the element.        

Is thinset waterproof?

Thinset is not waterproof. It is not water-soluble as well. This means the presence of moisture will not affect the thinset by turning it into a liquefied paste. Hence, the tiles or concrete attached to the thinset will not lose their overall structure. However, water does pass through it.

Some major types of thinsets are discussed here. This will help you figure out which one to pick for your installation. 


Unmodified thinset consists of Portland cement, sand, and additives. It does not contain polymers. This thinset is not waterproof and offers shorter drying hours.


Versabond is a brand for modified thinsets. It contains a professional formula that helps provide flexibility and strong bonding. Versabond though not waterproof but moisture cannot degrade its structure.


Schluter is another brand for thinsets and introduces Schluter SET, Schluter ALL SET, and FAST SET. While the first one is unmodified, the latter two are modified thinsets. These thinsets are not waterproof.


Epoxy is a resin-based binder. It is water, chemical, stain, and shockproof.

The non-porous quality makes epoxy an excellent waterproof thinset. However, since it sets pretty fast, it is not recommended to use it in DIY projects.


Polymer is an element found in modified thinsets. It helps in retaining more moisture and allows the growth of crystals.

The setting of the tiles is less porous, making water and salts difficult to penetrate. Again, polymer-based thinset is not waterproof.


Modified thinset consists of polymers that allow better moisture retention capacity and growing of crystals. This offers a sturdy bond and strengthening.

Modified thinsets are not waterproof. They need less water but require enough amount of air to dry. 

How to make thinset waterproof?

There are no direct methods to make a thinset compound waterproof. However, there are several ways to waterproof the whole structure. Some of the most popular ones are introducing Kerdi, Ditra boards or membranes by Schluter, and coating of RedGard.

The first two applications are most suited to Schluter thinsets mortar. In contrast, RedGard is suitable to use with most types of thinsets. For this reason, we will be discussing the process of using RedGard in waterproofing tiles installation. 

About RedGard in short, it is an elastomeric or liquid that allows waterproofing and cracks prevention. The formula is easy to apply and dries pretty fast. 

RedGard can be applied using brushes, rollers, or even a spraying machine. It can easily adhere to concrete, exterior quality plywood, backer board, and decks. 

Preparation of the area:

You have to make sure the wet or the exterior places where the RedGard will be applied has a proper drainage system. The surfaces have to be clean, dry, and structurally sound.

Safety precautions:

Protect yourself by wearing a dust mask, gloves, and safety goggles. 

Applying RedGard:

Either use a ¾ inches rough textured synthetic roller or a V-notch trowel of 3/16 inches by ¼ inches.  

Now, carefully pre-coat all the corners and intersections and spread the solution 6 inches on each side.

Use 6 inches wide fiberglass mesh, if there are changes of plane or gap that is more than 1/8 inches. Put the mesh on the spot and coat it with the RedGard solution.

CUSTOM BLDG PRODUCTS LQWAF1-2 Redgard Waterproofing, 1 gal

Drying of RedGard: 

If you notice the color of RedGard changes from pink to red, the wall is ready for the next step. RedGard usually takes 60 to 90 minutes to dry. 

This depends on the humidity and condition of the site. Apply two coats of RedGard for general waterproofing.  

Applying thinset: 

After the coats of RedGard dry completely, the wall is ready for applying thinset and tile installation. 

SimpleSet Pre-Mixed Thin-Set Mortar 1 QT

Selection of thinset:

RedGard does not bind properly with premixed thinset solutions. So avoid them. Instead, use quality thinset that you get in powdered form. 

Preparation of thinset:

Take 5 pounds of thinset powder in a bucket or a bowl. Now, carefully add cool water until you reach a peanut butter consistency. It is recommended to make thinset solution in small batches.

Final installation:

Apply the appropriate amount of thinset on the RedGard coated wall. Apply on small areas at a time and set your tiles accordingly. 

What is the difference between modified thinset and unmodified thinset?

Modified and unmodified thinsets both have their advantages. Let’s get insights into their major differences.

Presence of polymer:

The most significant difference between modified and unmodified thinset is the presence of polymer. Polymer is only present on modified thinset. It helps to grow crystals and retain more water.

However, the absence of polymer is not a disadvantage for unmodified thinset. In fact, unmodified thinset takes a shorter period to dry.


Both of these thinsets contain elements such as sand, cement, and water retention agent. However, the ratio of these elements differs in amount. 


The application of both types is quite similar. They generally are introduced in powdered form. You can, however, find some premixed modified thinsets as well. When mixing thinsets, try to work with small batches.


Unmodified thinset is an excellent choice for a waterproof underlayment system. On the other hand, for porcelain tiles, a modified thinset is a better choice for it gives incredible flexibility and resistance. 

Can thinset get wet? 

Since the thinset is not waterproof, it can get wet. Again, moisture can pass through it.  

Also, as it is not soluble in water, it will not turn into a messy liquefied paste. This also means the overall structure will be unaffected.  

Thinsets usually get cured 80% within 24 hours. Afterward, moisture cannot affect the thinset bonding. 

The exact amount of water during mixing is crucial. This will keep your installation intact and mold-free for a long time.

What happens if thinset gets wet?

When mixing, if thinsets get wet with too much-added water, it will ruin the whole thinset mixture. Also, you cannot add extra water later to the solution. 

If you are not careful to add the exact amount of water, you will face moisture problems after the tile installation process. Moisture will be trapped into the tiles and may even grow molds. 

Adding the exact amount of water while mixing the thinsets will keep your installation intact for a long time. 

How long can thinset stay wet?

After mixing, thinset should be used within 15 to 20 minutes. So make sure you are preparing thinsets in small batches.

Again, to fully cure, thinsets usually take 24 to 48 hours. It depends on the humidity, temperature, and the overall condition of the place. If you want to be exactly sure, it is advisable to wait 72 hours. 

How to use thinset mortar on RedGard waterproofing?

RedGard waterproofing liquid is applied like paints on the surfaces you want to waterproof. Usually, experts recommend two coats of RedGard. 

You are ready to use the thinset for tiles installation after it completely dries within 60 to 90 minutes.

Before applying the thinset, always remember not to use a pre-mixed thinset. RedGard and pre-mixed thinset do not bind well. Try getting thinsets in powdered form instead.

When mixing, make sure to prepare the mixture into small batches. Also, apply thinset to small areas at a time and place the tiles.

Can I use thinset for shower floor?

Yes, you can use the thinset for the shower floor. It provides strong bindings between tiles and also is resistant to moisture and molds. 

Even though thinset is not waterproof, it is not affected by water. So you do not need to worry about ruining the tiles bonding. 

If you use a modified thinset, your setting will be less porous and sturdy. This means less leaching of water and salt. 

However, in a waterproofing setting, it is better to stick to unmodified thinsets. Modified thinsets take a long time to cure in a waterproof system.

Why can’t you add cement waterproofing to thinset cement?

Waterproofing cement is a Portland cement that has an agent which is water repellent. In contrast, thinset needs to retain moisture.

Also, cement waterproofing can be solid, dense, heavy, and unbending with less flexibility. Therefore, it would not be an easy task to add cement waterproofing to thinset cement. 

Final Thoughts

In general, thinset is not waterproof and is insoluble in water. Thus moisture will not turn thinset into a liquefied mess. Water can still pass through it easily without affecting the structure. To waterproof the overall system you can choose membranes or elastomeric liquid.