Article with recommendations for proper mixing of adhesive mixtures for tile and grout installation. One of the essential things for a successful and professional tile installation is the proper preparation of the adhesive mixture. Knowing how to mix the adhesive correctly is important to achieve the strongest possible bond and therefore the long-term strength of the tiles on the substrate. Improperly mixed adhesive can cause problems during installation or even lead to loose tiles. In our article, we will explain a few key steps for preparing the right adhesive mixture and also the reasons for them, regardless of the brand or type of adhesive used.
Before you start…
The key to preparing an adhesive is to know its type and properties, which you will find written on its packaging. You should definitely know at least the basics, such as the mixing ratio of glue and water, the workability time (the longest time between mixing and the mixture being usable) and the curing time. If you know this information, it is an essential step for proper adhesive preparation.
For a better understanding of how cementitious adhesives work and what happens during their preparation, let’s explain a few basic facts from a chemical and microscopic point of view. Adhesives commonly consist of a few basic ingredients: sand, Portland cement, lime, and (usually) various chemically manufactured additives that help the adhesive mixture hold water for longer periods of time. These additives can also give the final product various properties such as flexibility, strength, faster setting time, etc. Most modern adhesives have at least one type of additive.
Understanding how cement works in a mix and why mixing principles need to be followed at different stages is key to ensuring a successful outcome. Cement is activated by a process called hydration (quenching). Dry cement molecules are inert – they do nothing at all until they are mixed with water. As soon as water is added to the cement, the molecules use this water to form small crystals. The more water a molecule has available, the longer and thicker the crystals will form.
These cement molecules not only form growing crystals next to each other, but they also form on top of each other and can also block each other. This is how cement gains its strength and the longer it is exposed to water, the stronger it becomes. In the case of adhesive, the crystals will not only grow around the other crystals, but will also grow into the pores of the tile and the substrate. This is how a strong bond is achieved.
When a modifier (e.g. polymers) is added to the mix, a stronger bond with the tiles can be achieved. The more modifiers the adhesive mixture contains, the stronger the bond will be, as polymers allow water to be retained longer in the prepared mixture. When the polymers are exposed to water and are evenly dispersed in the mix, they surround the cement molecules and allow them to access the water for longer (the water does not evaporate through the polymers). This process produces a longer, thicker cement crystal than a glue without a modifier.
Technical equipment
Equally important is the selection of the right mixing tools – stirrer, mixing whisk and container. Always use a low-speed mixer. Most adhesive manufacturers recommend mixing on low speed to allow a minimum amount of air into the adhesive and achieve a more even mixture. You should also use spiral mixing whisks rather than so-called “beaters” to better prevent excess air from entering the mixture. The right container is also important, allowing you to mix the whole mixture perfectly without creating lumps and dry spots. Combine the right mixer and whisk with a Rubi rubber bucket and you have all the equipment you need to properly prepare your adhesive mixture.
1. Initial preparation of the adhesive mixture
First, start by pouring water into the bucket. This will reduce the amount of dry glue particles in the air. If you put the dry glue in the bucket first and then add water, some of the dry glue will float to the surface. It will then be harder to stir all the dry glue, which will also stick to the sides of the bucket. Add the glue to the water and stir, adding more glue or water as needed to achieve a thick consistency – about the creaminess of thick peanut butter. It is necessary that any standing swirls formed in the top of the glue do not subsequently spill back into the lower layers.
Most manufacturers recommend five to ten minutes to mix the adhesive, which may seem like too long. But we recommend that you follow this time, as it will help you achieve the desired mixing and saturation of the individual cement molecules as well as the additives in your mix. Sometimes it happens that even professionals mix the mixture only until they get a consistent mixture of powder and water. Ideally, you should stick to the recommended time, but realistically, you probably won’t. That’s why you’ll always do better if you stir a little longer than you think is sufficient for the necessary mixing of the mixture.
You can add more glue or water at the initial mixing stage to achieve the desired density. In the later stages of mixing, this is no longer advisable because if you add more water or glue after the quenching stage, the glue will weaken considerably. The glue should be thick enough to roll over the trowel when scooped. If it runs off, it is too thin and you need to add more powder to the mix.
2. Extinguishing
The extinguishing phase is very important! In this phase you can influence the correct mixing of the adhesive mixture the most. Extinguishing means leaving the mixed glue untouched for about ten minutes. It is essential to leave the adhesive at rest for the chemical composition to work properly. Failure to do this and use it immediately after the initial mixing of the mixture will lead (quite quickly) to the adhesive hardening and becoming non-functional. Then the tile adhesive will not stick or cure properly. Properly done quenching will also give you maximum working time after the adhesive is fully mixed.
Most modern modified adhesives have powder additives (usually some polymer) added to the dry mix. Simply put, these additives, such as cement, are activated by hydration, but they work a little differently. When water is added to the cement, crystals begin to grow in the mixture and this is how the adhesive gains its strength. The longer the cement is exposed to water, the longer the crystals grow. The longer the crystals grow, the stronger the cured product will be.
As soon as you add water to the additives, the molecules in the additives absorb the water. Think of an additive molecule as a cotton swab. The outer layer of the additive will be hydrated, but the inside will still be dry. Quenching gives the additive enough time to fully saturate.
If you don’t leave the adhesive in the quench phase long enough, the mixture will have dry polymers. The dry polymers will consume water from the cement and cause it to set quickly. If the cement does not have enough water to continue to form crystals, the growth and hardening process will essentially stop. Therefore, do not allow the adhesive mixture to quench for too short a time, as this will weaken the adhesive and create potential bonding problems. Lack of crystal formation in the cement leads to poor bonding with the tiles and substrate. Allow the additives (modifiers) to dissolve completely so that they are properly represented in the adhesive mixture.
3. Final mixing of the mixture
Once the adhesive has been allowed to sit for a period of time, it is necessary to continue mixing until the mixture is final for even distribution of the ingredients throughout the adhesive mixture. This process helps spread the polymers and water throughout the mixture to achieve a consistent and properly mixed adhesive during setting and after curing.
Do not add more water or dry glue to the mix at this stage! Excess water would break down the mixture. There is already water between the glue molecules, separating them from each other. The further apart the molecules are as the cement crystals grow, the harder it is to get them to bond together, which is where the bonding strength of the adhesive comes from. If the crystals cannot fully bond with each other, the final product will be weaker. Incidentally, this is also why it is undesirable to allow an excessive amount of air in the glue mixture.
If the adhesive is properly mixed, it should have standing grooves when spread with a trowel without slumping (picture).
So how to mix the glue correctly? Let’s summarize the basic rules:
- Do not add too much water – this will weaken the mixture.
- Stir slowly so that a minimum amount of air is trapped in the adhesive mixture.
- The glue should be fairly thick, about the thickness of thick peanut butter.
- The thickness and consistency of the premixed mixture should be the same as that of the final mix.
- Firefighting is essential!
- Do not add more water or glue after extinguishing.
- Know the processing time of your adhesive, pay attention to when it starts to set.
A properly mixed adhesive mixture is very important for a successful and long-lasting tile installation.
As you’ve had a chance to read, getting the mixing right isn’t exactly easy, but if you get it right, not only will you appreciate it during the actual bonding, but your customer will too. In our shop we offer a wide range of tools and accessories for the professional preparation of adhesive mixtures.
This article was written in cooperation with profiobkladac.sk