Anhydrite and cement screeds are two popular types of floor screeds used in construction projects. Screeds provide a smooth, level surface for floor finishes and play a critical role in creating durable and functional floors. As we advance into 2024, the debate continues over which screed offers the better performance and value. This article examines the pros and cons of each to help you decide whether anhydrite or cement is better for your next project.
Anhydrite Screed Overview
Anhydrite screeds are made from anhydrite, which is a type of gypsum or calcium sulfate. Anhydrite screeds have been growing in popularity in recent years as an alternative to traditional cement and sand screeds. Here are some key things to know about anhydrite screeds:
Fast Drying & Installation
One of the main advantages of anhydrite screeds is they dry very quickly, often in as little as 24-48 hours for a 30-40mm thick screed. This allows floor finishes to be installed faster. It also enables faster overall project completion timelines.
Excellent Thermal Conductivity
Anhydrite conducts heat extremely well. Anhydrite screeds have high thermal conductivity, meaning they efficiently spread warmth through the floor. This helps regulate indoor temperatures.
Hardness & Durability
Once fully cured and dry, anhydrite develops incredible hardness and strength over time. Top quality anhydrite screeds have compressive strengths exceeding C35 grade after 90 days. This makes them very durable for high traffic areas.
Lighter Weight
Anhydrite is lighter than cement screeds, weighing about 50 Kilograms per square meter once dried, compared to 75 Kilograms for cement. This reduced weight puts less strain on building structures.
Cement Screed Overview
Cement screeds remain the most common type of floor screed used. Cement screeds consist of a mixture of ordinary Portland cement combined with sharp sand and aggregate in certain ratios. Here are some of the notable attributes of cement screeds:
Proven & Familiar Technology
Having been used for over 100 years, contractors know cement screeds well. The installation process and drying times are familiar and predictable. Many workers are highly experienced at working with cement screeds.
Excellent Compressive Strength
The 28 day compressive strength of C25 grade cement screeds often exceeds 30 N/mm2. Higher grade C35 cement screeds can reach 45 N/mm2. The high compressive strength makes cement screeds highly resilient.
Compatible With Any Finish
Cement screeds work well with virtually any floor covering or finish, including tiles, natural stone, vinyl, and epoxy coatings. There are no special considerations as the alkaline chemistry of concrete is compatible with all finishes.
Lower Cost
In most areas, cement screeds cost less per square meter to install compared to proprietary anhydrite screed products, which must be purchased from specific manufacturers. This makes cement screeds the more affordable option.
Screed Drying Times Compared
One of the biggest differences between these two popular screed options is the drying times:
- Anhydrite screeds can be walkable in as little as 24 hours. Floor finishes can follow within 48 hours if conditions are adequate.
- Cement screeds take much longer to dry. These screeds may need 7-14 days before they are ready for foot traffic, and 21-90 days to fully cure to lay finishes.
The faster dry times of anhydrite screeds allow faster completion of projects from start to finish. Contractors should account for slower cement curing times in their project scheduling.
Screed Thickness Differences
There are also some notable differences in screed thickness between the two types:
- Anhydrite screeds are typically between 30-40 mm thick. Thinner sections down to 20mm are possible in some cases.
- Cement sand screeds need to be a minimum of 40mm thick on ground floors, and 50mm on upper floors. Thicknesses of 65mm+ are often used.
Thinner anhydrite screeds mean less concrete and finishing materials required. This can help reduce costs compared to thicker cement screeds.
Screeds and Underfloor Heating
Underfloor heating compatibility is an important factor to consider when selecting screeds. Here is how anhydrite and cement screeds compare:
- Anhydrite has excellent thermal conductivity. Anhydrite offers the highest output and efficiency from underfloor heating systems thanks to its superior ability to transmit heat.
- Cement screeds work well with underfloor heating too. Though not quite as efficient at conducting heat as anhydrite, concrete still performs admirably to spread warmth through floors.
Either type of screed can be effectively combined with underfloor heating. Just note that anhydrite’s faster dry time is particularly helpful to allow quicker installation of heating pipes and wires.
Floor Load Weights
The final dried weight of screeds per square meter is another difference. Here is how anhydrite and cement screeds compare:
- Fully dried anhydrite screeds weigh approximately 50 Kilograms per square meter.
- Comparable thicknesses of cement screeds weigh roughly 75 Kilograms once cured and dried.
The lower density of anhydrite results in an over 30% lighter floor construction. This causes less loading on building structures. It is particularly beneficial where weight allowances are limited.
Screed Costs In 2024
Let’s look at typical screed material plus installation costs per m2 in 2024:
- Anhydrite screed costs range from £50-70+ per m2 supplied and professionally installed.
- Cement sand screeds usually cost between £30-50 per m2 for materials and professional installation.
Cement screeds are often the less expensive option, though anhydrite prices can overlap with lower grade or thin cement screeds. Improved productivity from faster anhydrite drying times also helps offset some cost differences.
Screed Sustainability
Eco conscious construction is increasingly important in 2024. Regarding sustainability:
- Anhydrite screeds have an excellent environmental profile. Gypsum is abundant, and production has relatively low CO2 emissions.
- Cement screeds have a larger carbon footprint. Cement production is emissions intensive, contributing about 8% of global CO2 output.
Anhydrite screeds offer environmental advantages over standard cement. Specify “green” cement blends help improve concrete screeds’ eco-friendliness.
Screed Performance Over Time
Over years or decades, here is how these two screed types typically perform:
- Anhydrite screeds maintain their hardness, strength and integrity for the long term. They are not vulnerable to erosion or cracking.
- Cement screeds hold up well also, but may develop minor cracks as buildings shift or settle. Cracks can allow moisture ingress if not repaired.
Both offer high durability and performance. But anhydrite screeds maintain smoother, defect free surfaces over decades of use.
Screed Repairability
No floor lasts forever, so repairability is useful. Here is how screeds compare if repairs are ever needed:
- Anhydrite screeds can be difficult to patch or replace sections of. Proprietary anhydrite products must be precisely colour matched and bonded to old areas.
- Cement screeds are comparatively easy to repair. New cement can readily be bonded to old screed. Colour match is simpler. Damaged sections are quicker to cut out and patch.
Cement screeds have simpler repair procedures. But with proper care and maintenance, quality anhydrite or cement screeds should rarely if ever need repairs.
Noise Insulation Properties
Excess noise transmission through floors is a common problem in multi level structures. Here is how these screeds compare for sound insulation:
- Anhydrite on its own offers minimal noise insulation capability, as it is fully non porous once cured. Dense aggregates can be added to improve sound dampening.
- Floating cement screeds over acoustic mats or membranes provide excellent impact and airborne noise insulation between floors. The resiliency of cement screeds greatly cuts noise transfer.
While cement screeds have better inherent noise blocking qualities, anhydrite screeds can also be adapted to achieve necessary noise reduction ratings.
Screed Flexural Strength
Flexural or tensile strength indicates a screed’s ability to bridge gaps and resist cracking under tension:
- Fully cured anhydrite screeds achieve good tensile strengths of 5-7 N/mm2. This allows reliable spanning of structural movement joints without compromising integrity.
- Cement screeds develop higher
- flexural strength in the range of 6-9 N/mm2 depending on exact mix designs. This allows solid spanning of structural bays without requiring intermediate joints.
- While cement screeds have the edge for flexural toughness, anhydrite still rates highly enough for reliable structural and seismic joint bridging.
Screed Chemical Resistance
Resistance to liquids, chemicals, oils or other contaminants is necessary in many commercial and industrial flooring applications. Here are the key differences:
Anhydrite screeds have moderate chemical resistance, but are damaged by acidic materials over time. An epoxy coating improves acid and chemical protection.
Cement screeds stand up well to dilute acids, oils and many chemicals due to the alkaline properties of concrete. Higher grade concretes offer even better protection.
For the highest chemical resistance demands like food plants or pharmaceuticals, specify specially treated cement screeds. But anhydrite works for typical commercial use.
Installation Considerations
Installing screeds requires careful planning and execution to ensure proper curing and performance. Here are key installation factors:
Anhydrite screeds have strict supplier guidelines for storage, mixing, pumping, joints and curing. Precise water ratios and drying conditions must be maintained.
Cement screeds are more forgiving and better known to contractors. But care is still needed for base prep, reinforcement, bay sizes and curing to prevent shrinkage cracks.
Anhydrite screeds demand tight control and standards compliance to achieve advertised strengths and drying times. Cement gives crews more leeway.
Conclusion
We’ve covered numerous performance factors, costs, strengths and weaknesses of both cement and anhydrite screeds as popular types of floor screeds. Anhydrite offers faster drying and construction times, high thermal conductivity, lighter weight and excellent hardening over time. But cement screeds provide better affordability, flexibility, repairability and noise insulation. As we advance deeper into 2024, both screed options will continue seeing high demand from contractors and building owners. Consider the criteria in this article carefully, and choose the best match for your specific floors and facilities.
Frequently Asked Questions
How thick should my screed be?
Anhydrite screeds are typically 30-40mm thick. Cement screeds usually range from 40mm to 65mm+ thick depending on floor loading.
Can underfloor heating be used with either screed?
Yes, both screed types offer excellent compatibility with underfloor heating systems. Just note that anhydrite transfers warmth more efficiently.
Which screed costs more per square meter?
Cement screeds generally have lower material and installation costs per m2 compared to proprietary anhydrite products. But anhydrite’s rapid construction time can help offset the difference.
Which screed needs the least repairs long-term?
Quality anhydrite and cement screeds both offer exceptional durability. But minor shrinkage cracks are more common long-term with cement. Anhydrite maintains smoother surfaces.
Which screed has better noise insulation?
Floating cement screeds over acoustic underlays provide superior airborne and impact sound insulation between floors.