Screed and mortar are two materials commonly used in construction and flooring applications, but there are some key differences between them. Getting familiar with when to use screed vs when mortar is the better choice for your project is an important part of planning.
Overview of Screed and Mortar
Screed refers to a smooth layer of concrete or cementitious material that is laid over a rough surface or subfloor to provide a flat, level base. It acts as the foundation for installing tile, stone, or other flooring materials. Screed is often fortified with reinforcement fibers and typically contains a coarse aggregate for strength and durability.
Mortar is a workable paste made of cement, lime, sand, and water that hardens to bind building blocks and bricks together structurally. It creates strong adhesion between masonry units like brick, stone, tile and acts as a load bearing component in these types of building projects. Compared to screed, mortar has higher amounts of cement and sand.
Key Differences Between Screed and Mortar
While both screed and mortar involve cement-based materials, there are some notable ways they differ:
- Purpose – mortar binds surfaces together structurally whereas screed creates a smooth subfloor surface for applying other floor finishes
- Location – mortar is primarily used on vertical surfaces and exteriors while screed is mainly used for horizontal interior surfaces
- Strength – mortar typically has very high compressive strength to bear heavy loads in masonry structures while screed is less about load-bearing strength and more about providing a durable, level base
- Thickness – a mortar joint is usually under 1 inch thick, and screed is typically 1-4 inches thick depending on the application
- Finishing – mortar joints are finished and tooled to create weather tight seals between masonry units, screed is later finished with additional flooring treatments
The ingredients also differ in exact proportions, mortar often has higher cement ratios for greater structural strength while screed may have more aggregate fillers and reinforcement additives for surface leveling performance.
Uses for Screed vs Mortar
Understanding whether to use screed or mortar depends greatly on the specifics of your construction or flooring project.
Applications for Screed
Some typical uses where screed is the appropriate material choice:
- Under-tile floor leveling for tile installations
- Creating smooth subfloors prior to adding finished flooring
- Ramps, sidewalks, and garage floors
- Leveling sunken concrete slabs
- Patios, pool decks, and terraces prior to finishes
Screed is ideal for situations calling for a very flat, durable surface ready for additional treatments especially horizontal surfaces.
Applications for Mortar
In contrast, mortar has some unique applications where it’s preferred over screed:
- Structural bonding of masonry elements like brick, concrete masonry units (CMUs), stone, ceramic tile
- Mortar joints between pavers
- Stucco basement walls
- Stone veneers
- Chimneys
- Retaining walls
Essentially most vertical structural building elements that require heavy load bearing strength and weather tight seals.
Screed vs Mortar: Composition and Performance Factors
Now that we’ve covered the core differences in purpose and applications between screed and mortar, let’s look at how their ingredients and material properties differ.
Screed Composition
Typical screed contains:
- Cement – usually Portland cement, provides binder for strength/adhesion
- Sand or fine aggregate – fills voids evenly for good workability
- Coarse aggregate – enhances strength and stability
- Water – activates cement to allow screeding and leveling
- Reinforcement – polymers, fibers increase durability and resistance to cracks
Desirable properties in quality screed:
- Strong adhesion to substrates
- Effective self-leveling and flow before setting
- High resistance to impact/abrasion
- Minimal shrinkage as it cures to avoid cracks
- Withstands foot traffic, loads without damage
These factors allow screed to serve reliably as an underlying base for finished flooring.
Mortar Composition
Mortar usually consists of:
- Cement – hydraulic cements like Portland provide bonding strength
- Lime – enhances workability and flexibility
- Sand – fills spaces between masonry units
- Water – activates cement ingredients for application
- Admixtures – air entertainers, retarders, and plasticizers
Advantages that quality mortar offers:
- High compressive strength and bond strength
- Effective workability and consistency
- Good abrasion/weathering resistance
- Controlled flexibility to withstand movement
- Consistent setting times for easier application
Mortar is able to bear heavy structural loads thanks to these robust properties.
Current Building Codes for Screed and Mortar
If you are working on a construction or masonry project with screed or mortar, it’s wise to be familiar with the relevant building codes for your region.
The standards regulate criteria like:
- Concrete performance specifications
- Cement types allowed
- Aggregate gradations
- Mix proportions and water content
- Cold/hot weather procedures
Referencing your local building codes ensures your screed/mortar meets minimum quality, safety, and durability criteria. Failure to follow the codes could result in cracks, leaks, or even collapse over the lifetime of the building.
Some of the main model codes to check based on your area:
Knowing the required standards will inform your choice of ingredients, mixing methods, site preparations, and placements procedures when working with either screed or mortar.
Tips for Working With Screed vs Mortar
If you’ll be the one actually placing and finishing screed or mortar on a project, here are some best practices to do quality work:
For Screeding:
- Clean surfaces thoroughly before pouring new screed
- Ensure proper expansion joints and isolations
- Use screed rails, boards, and guides to level perfectly
- Avoid overworking the screed mixture
- Control environmental humidity and temperature
- Cure under plastic sheeting post-placement
For Mortaring:
- Clean and dampen masonry surfaces first
- Batch consistent volumes for color uniformity
- Use fulll bedding mortar coverage, avoid voids
- Tool joints for optimal consistency and fill
- Remove excess mortar promptly before hardening
- Allow proper curing time before adding loads
These tips will lead to successful screed/mortar installation free of flaws or cracks over the long term life of the project. Consult experienced construction pros if you need guidance.
FAQs
Can screed also be load-bearing like mortar?
While screed provides a very durable, hardened base for flooring finishes, it is not formulated to have the same structural load-bearing strength that mortar offers in stacked masonry structures. Additional rebar or post tension cables may be required if screed will have heavy permanent loads.
Is mortar waterproof?
On its own, standard mortar allows some moisture transmission and absorption, meaning it is considered “water resistant” but not fully waterproof. Special water-repellent admixtures or coatings must be added to achieve true waterproofing.
What texture should screed have before adding flooring?
Properly placed screed should have a smooth, consistent, and clean texture ready for thinset, tile, or other floor finishes once hardened. Any irregularities or gaps can telegraph through the final floor.
Can colored pigments be added to mortar?
Yes, introducing inorganic mineral oxides to the mortar mix allows changing its color. Common choices are red, brown, black, and gray to achieve desired aesthetic effects in brick/stone structures.
What thickness is typical for an under-tile screed layer?
Screed depths under tile can range from 1-1.5 inches for floor applications. Some self-leveling compounds can be feathered down to 1/4 inch. Never tile directly over screed less than 1 inch thick.
Conclusion
Knowing when it’s best to use screed vs mortar comes down to understanding their differences in composition, strengths, and applications. Mortar has high structural bonding strength for masonry projects with heavy loads. Screed offers a cement foundation to achieve very flat, smooth, durable surfaces ready for additional finishes and treatments in horizontal flooring zones.
Following proper codes and installation methods for each respective material is also key for satisfactory long term performance. With the right screed calculations and product choice for your specific building needs, both screed and mortar can provide reliable solutions.