Plasticizer Mortar Mixture: How Much Plasticizer Is Enough?

When building with mortar, it is important to use a plasticiser as it helps the render adhere to the wall. The amount of plasticiser to be used depends on the amount of cement and the type of sand used. For example, for every 25kg of cement, the recommended amount of plasticiser is 70-140ml. The type of sand also matters as building sand will turn out smoother than sharper sand, no matter the amount of plasticiser used. It is also important to note that the longer the mixing time, the more workable the sand becomes.

How much plasticizer for mortar?

The amount of plasticizer depends on the cement quantity

The amount of plasticizer to use when mixing mortar depends on the quantity of cement used. Typically, the instructions on the plasticizer bottle will specify how much is required relative to the amount of cement. For example, a plasticizer might instruct you to use 70-140ml of the product for every 25kg of cement. This means that if you are using 1.8kg of cement, you should mix in around 8ml of plasticizer.

It's important to follow the manufacturer's guidelines for exact measurements. However, it's worth noting that the type of sand you use can also impact the workability of your mortar. Building sand, for instance, will result in a smoother mix than sharper sand, regardless of the amount of plasticizer used.

If you are hand-mixing your mortar, keep in mind that it will be harder to achieve a smooth consistency. The longer you mix, the more workable the sand will become. You can also adjust the amount of plasticizer to suit the sand you are using. For a 'belle' mixer, you might use about half a teacup of plasticizer per load, whereas for a barrow, you would use around a quarter of a teacup.

Additionally, if you are only preparing a small amount of mortar, you can add a teaspoon of washing-up liquid to your mix. However, it is always best to use a proper plasticizer that is specifically chemically engineered for mortar applications.

Mix mortar hard to get the benefit of plasticizer

When mixing mortar by hand, it can be challenging to achieve a smooth and buttery consistency, even with the use of a plasticiser. To overcome this, it is essential to put in the effort and mix the mortar vigorously. This means continuously turning it over, beating it, and chopping at it with a shovel or any other suitable mixing tool. The intense mixing action, along with the addition of plasticiser in the water, introduces millions of microscopic air bubbles into the mix, giving it that desirable buttery texture.

While it may be tempting to add more water to achieve a smoother consistency, this is not the solution. The key to success lies in the elbow grease you put into mixing. If you have access to a cement mixer, creating a well-mixed batch of mortar becomes much easier. The drum of the mixer tosses the mortar around repeatedly, ensuring a thorough mix. However, if you're mixing by hand, be prepared to put in some extra effort.

The type of sand you use also plays a role in the final consistency of your mortar. Building sand tends to produce a smoother finish, whereas sharper sand may not yield the same level of smoothness, regardless of the amount of plasticiser used. Adjustments may be necessary depending on the sand you're working with. If you're stuck with poor-quality sand, consider substituting lime for plasticiser, as this can yield better results.

As for the amount of plasticiser to use, it's important not to go overboard. The recommended amount is typically around 70-140ml per 25kg of cement. For a "belle" mixer, aim for about half a teacup of plasticiser per load, and for a barrow, a quarter of a teacup should suffice. However, these amounts may need adjustment depending on the specific sand you're using. Remember, the key to achieving the desired consistency lies not only in the plasticiser but also in the mixing process itself, so don't shy away from putting in some good old-fashioned muscle power!

Adjust the amount of plasticizer according to the sand

When adjusting the amount of plasticizer in mortar, it's important to consider the type and quality of sand being used. The ratio of sand to cement and the mixing process can impact the final consistency of the mortar.

For a standard mortar mix, a common ratio is 4 parts sand to 1 part cement. However, the type of sand used can vary, and this will affect the workability of the mortar. Building sand, for example, tends to result in a smoother mix, while sharper sand may require more effort to achieve a consistent texture.

The quality of the sand also plays a role. If you're working with poor-quality sand, consider using lime instead of a plasticizer to improve the mortar's workability. In some cases, a small amount of dish soap, such as a teaspoon of Fairy Liquid, can be added to the mix to enhance its plasticity.

To adjust the amount of plasticizer based on the sand, it's recommended to start with a small amount and gradually increase it until the desired consistency is achieved. For example, if using Febplus or a similar product, the amount of plasticizer added should be directly related to the amount of cement in the mix, typically ranging from 70-140ml per 25kg of cement. However, it's important not to exceed the recommended dosage to avoid potential negative effects on the mortar's strength and durability.

Additionally, the mixing process is crucial when working with plasticizers. The mortar should be mixed thoroughly and vigorously, with constant turning, beating, and chopping to incorporate air bubbles and achieve the desired "buttery" consistency. A cement mixer can be advantageous for this process, but it is still possible to achieve satisfactory results with a hand mix, although it may require more effort and time.

Follow manufacturer guidelines for exact measurements

When mixing mortar, it's important to follow manufacturer guidelines for exact measurements of plasticiser to ensure the best results and avoid any negative consequences. Each brand of plasticiser will have its own specific instructions, and adhering to these instructions is crucial for achieving the desired outcome.

The amount of plasticiser required can vary depending on several factors, including the type of mortar, the specific plasticiser product, and the intended application. By following the manufacturer's guidelines, you can determine the optimal amount of plasticiser needed for your specific project. These guidelines take into account the unique properties of their product and provide recommendations based on extensive testing and research.

For example, a popular plasticiser product, Febplus, provides detailed instructions on the packaging. According to the manufacturer, the amount of Febplus required is directly related to the amount of cement used. The recommended dosage is 70-140ml of Febplus per 25kg of cement. By following these guidelines, users can ensure they are using the correct amount of plasticiser for their specific mortar mix.

In addition to following manufacturer guidelines, it's important to consider the quality of the sand used in the mortar mix. The type of sand can impact the workability of the mortar, and different sands may require adjustments in the amount of plasticiser used. For instance, building sand is more likely to result in a smooth mix, while sharper sand may require additional plasticiser to achieve the desired consistency.

By following the manufacturer's guidelines for exact measurements and taking into account the specific materials and conditions of your project, you can ensure that your mortar mix contains the appropriate amount of plasticiser. This will help you achieve the desired results and avoid any potential issues that may arise from using too much or too little plasticiser. Remember to read the instructions carefully and make adjustments as needed based on the specific requirements of your project.

Use plasticizer only in the scratch coat when plastering

When plastering, it is recommended to use plasticizer only in the scratch coat. The scratch coat is the first base coat that is applied to wood or metal lath. The surface of this coat is then scratched to provide a rough surface for the next layer of the base coat to adhere to.

Plasticizers are used to improve the workability of the mortar and to help it adhere to the wall. They are especially useful when working with a poor quality sand that is difficult to mix smoothly by hand. However, it is important to note that plasticizer will not make a sharp sand smooth, no matter how much is used.

The amount of plasticizer to be used depends on the amount of cement in the mix. Typically, the recommended amount is 70-140ml per 25kg of cement. For a "belle" mixer, this would be about 1/2 a teacup of plasticizer per load, and for a barrow, it would be about 1/4 of a teacup. However, these amounts may need to be adjusted depending on the quality of the sand being used.

It is also worth noting that while not necessary, adding lime to the mix can be beneficial. Lime makes the mix more pliable, helps to stop cracking, and creates a nice finish. Hydrated lime should be used with cement and can be sourced from building suppliers.

Frequently asked questions