LSA Max

What is LSA Max?

LSA Max is a liquid admixture for semi-dry screeds. It has been specifically developed to provide rapid drying times together with high early and ultimate compressive and flexural strengths in bonded, unbonded and floating screeds.

The admixture also contains a superplasticiser, which improves the finishing characteristics of the screed. That helps screeders achieve a dense, closed surface ready to receive the final floor covering.

What does Cat A, C40, F7 mean?

Screed performance is commonly described with strength classes. C40 denotes a compressive strength class of 40 N/mm² and F7 denotes a flexural strength class of 7 N/mm². Category A is one of the in situ crushing resistance (ISCR) categories in BS 8204-1 and allows a smaller indentation than Categories B and C when the laid screed is tested. Together, they describe a strong and robust floor.

Where is LSA Max used?

LSA Max is suitable for semi-dry screeds in a wide range of situations:

• Bonded screeds from 20mm thick, laid directly onto a prepared concrete base
• Unbonded screeds from 35mm thick, laid over a separating layer
• Floating screeds laid over insulation
• Underfloor heating, where the screed encases or covers heating pipes
• Internal and external floors

Because it delivers high strength, LSA Max allows thinner screeds to be laid without compromising strength. That is particularly useful in refurbishment work and in any build up where floor height is limited.

How to use LSA Max

Getting the water content right is the most important part of a good semi-dry screed. Care should be taken not to over water the mix. Bear in mind that sand can be supplied with a high water content, so allow for the moisture already in the sand before adding any more.

The correct consistency is semi-dry. You should be able to squeeze a handful of the mix into a ball that is firm, but no water can be squeezed from it.

Good practice on site:

1. Check the sand on delivery and adjust the added water to suit its moisture content.
2. Add LSA Max at the dosage advised by our technical support team. Never estimate the dose.
3. Mix thoroughly so the admixture is evenly distributed through the batch.
4. Carry out the ball test on each batch before it is placed.
5. Compact the screed fully and finish it while it is workable.
6. Protect the fresh screed from draughts, strong sun and frost while it cures.

For dosage, mix design or advice on a specific build up, contact our technical support team. You can also read our guides to screed drying times and laying semi-dry screed over underfloor heating.

Packaging, storage and shelf life

LSA Max is supplied in 20 litre and 200 litre drums and 1000 litre IBCs, so smaller contractors and high volume users can both buy in a size that suits them. It has a minimum shelf life of 12 months when stored at normal temperature in dry conditions. Keep containers closed when not in use.

LSA Max or PSA?

Choose LSA Max for semi-dry screeds where very rapid drying and a Cat A, C40, F7 screed with up to 60 N/mm² achievable are the priority. For traditional sand and cement screeds dosed on site from water soluble sachets, look at PSA.

Our article on choosing the right screed admixture compares the options in more detail, and the LSA Max product news explains how it helps programmes.

Need advice on dosage, mix design or a thin bonded screed? Talk to our technical support team, or request a sample to try LSA Max on your next job.