The key to keycoat in your concrete

What is keycoat and how and when do you use it in concrete?

We’ve mentioned keycoat in some of our other blogs, and you may also have heard a builder using the term. So what exactly is it, and why would you add it to cement or concrete?

Keycoat is a general term not a product name and it is manufactured by different companies. It has a few slightly different names, but the words ‘key’ and ‘coat’ will be in the name somewhere.

It is a water-based acrylic latex, liquid cement additive designed to increase water resistance as well as flexural and adhesion strengths of cement-based powders, such as adhesives, screeds and cement-based plasters. What does this mean? It helps these powders stick and gives them some flexibility in movement. It provides a strong adhesive bond to smooth surfaces such as masonry, block and pre-painted walls.

Where to use it? If you have a wall that is suffering from damp, the plaster will become powdery and the paint will flake off. The plaster itself will also come off the wall. To fix this problem, chip the wall clean and then paint it with keycoat. Use a block brush to apply the keycoat and make sure you work it into every crack and corner. Allow the keycoat to dry and then replaster. As it is water-based, keycoat is easy to clean up after application. Brushes can be cleaned with water.

In this case, keycoat should also be added when mixing the plaster. Around two litres should be added to 5 kg of plaster mix. Check the label for mixing ratios.

Keycoat is often used as a sort of primer before plastering tiling a wall, especially when there are potential damp issues. It is not, however, a failsafe method of repairing damp on its own. You will need to fix the underlying problem causing the damp before painting on the keycoat.

Keycoat is also a useful additive when mixing concrete that will be used around water, such as the bee bath that we made in another blog, or bird baths, concrete countertops, ponds or drainage gullies. In these cases, we don’t want the water to seep into the concrete. It can also be used as a seal, painted onto cured concrete.

Keycoat is an important additive to use in cement work, so the next time you’re buying your concrete supplies, add a bottle of keycoat to your trolley – there’s nothing better than being prepared.

Everything you need for your next concrete project is available from Builders, whether instore or online at builders.co.za.