PSA

What is PSA?

PSA is the powder member of the UKCP screed additive family. Instead of dosing a liquid, the screeder adds pre-weighed water soluble sachets to the mixer. The sachet film dissolves during mixing and releases the admixture into the screed.

That makes PSA a practical choice for contractors who mix on site and want consistent dosing without measuring jugs, pumps or dispensers.

Where is PSA used?

PSA is designed for applications where the screed is bonded to the substrate, unbonded or floating. The standard screed mix of cement and sand in a ratio of 1:3 to 1:5 is used to create a level layer that receives the final floor finish, such as tiles, wood, linoleum or vinyl.

Traditional screeds of this kind are generally suitable for use in:

• Hospitals
• Schools
• Retail units
• Homes

PSA is also ideal for screeds covering underfloor heating systems.

How to use PSA

Ask our technical support team how many sachets to use for your batch size, then add them whole to the mixer. Mix until the sachets have fully dissolved and the admixture is evenly distributed, then place, compact and finish the screed in the normal way. Our step by step guide to using PSA water soluble sachets walks through the process.

How long does a PSA screed take to dry?

Typically, floor coverings can be installed between 1 and 3 weeks after casting, depending on the screed thickness and drying conditions. As a guide:

• For a 50 to 75mm cementitious screed, allow an average drying time of seven days per 25mm before laying the floor covering.
• For depths below 50mm, the average drying time may be reduced to 3 days, subject to the substrate being free from moisture.

Low temperatures or excessive moisture in the underlying concrete will delay the drying of the screed. Protect the sand and cement screed from premature drying due to wind, strong sun and forced drying conditions.

Check moisture before laying floor coverings

Before laying any floor covering, check the moisture of the screed to ensure compliance with the recommendations of BS 8203. Our article on screed drying times explains what affects drying and how moisture is checked.

Packaging, storage and shelf life

PSA is supplied in 200g water soluble sachets, packed in boxes of 80 sachets. It has a minimum shelf life of 24 months when stored at normal temperature in dry conditions. Keep sachets in their box, away from moisture and wet hands, until they are added to the mixer.

PSA or a liquid screed admixture?

Choose PSA for traditional sand and cement screeds mixed on site, where simple sachet dosing is the priority. For screeds that need a Cat A, C40, F7 classification and up to 60 N/mm², look at the liquid admixture LSA Max. Our guide to choosing the right screed admixture compares them in more detail.

Need help with batch sizes, mix design or drying times for PSA? Talk to our technical support team, or request a sample to try it on your next floor.