In this issue, we explain why Stopgap 1100 Gypsum smoothing underlayment works and what makes it different to our other underlayments.
Where it’s needed
Stopgap 1100 Gypsum was designed specifically for use over calcium sulphate based screeds, such as anhydrite or alpha-hemihydrate. A traditional cement-based smoothing underlayment applied over these screeds can cause the compound to fail – but why? How does Stopgap 1100 Gypsum resolve this problem?
Why it is needed
Prior to the application of a cement-based smoothing underlayment over a calcium sulphate screed, priming is essential. This is because the water added to form the smoothing underlayment mixture causes the production of a mineral, ettringite, between the calcium sulphate screed and the underlayment. Ettringite is formed when traditional cement-based smoothing underlayments are mixed with water, and helps to chemically bind water into the compound. This results in a weak layer between the calcium sulphate screed and the underlayment which can be detrimental to an installation.
A match made in heaven
For this reason, a compound that is chemically similar – a calcium sulphate based underlayment – is a much more reliable option when working with calcium sulphate screeds. Priming is still essential when using Stopgap 1100 Gypsum over a calcium sulphate screed in order to reduce the absorbency of the substrate, which gives the product a better working time, and to promote adhesion. However, by using a similar product incompatibility issues are avoided and, even if there is any moisture on the screed, no ettringite will be formed between the screed and the underlayment, as calcium sulphate compounds do not react in the same way as other cement-based products.
The importance of drying time
It is, however, still very important to allow the underlayment sufficient time to dry before applying adhesives and installing floorcoverings. When water is added to the Stopgap 1100 Gypsum powder, some is locked into the compound and any excess water is evaporated, leaving behind gypsum crystals.
If the water is not given enough time to evaporate, and excess water remains in the product, it will be trapped in the product as soon as floorcoverings are installed. This excess water prevents the underlayment from being able to set completely, and compromises the strength and function of the product.
For this reason, F. Ball recommends that you wait 24 hours after applying Stopgap 1100 Gypsum before installing carpets, and a further 24 hours before installing vinyl floorcoverings. This is because carpets are breathable, and excess moisture can dissipate through the carpet in the days following the installation, whereas vinyl floorcoverings are impervious to water and any excess moisture will have nowhere to go, thus leaving the moisture trapped in the substrate.
Find out more
To find out more about Stopgap 1100 Gypsum and the rest of our range of underlayments, click here. You can also see Stopgap 1100 Gypsum in action in our video.
If there’s a product in the F. Ball range that you’d like to find out ‘why it works’, please let us know by using the contact link in the menu at the top of the page.