A mortar screed is a cement-based or polymer-modified layer of mortar applied over a structural concrete slab to:
- Provide a level and smooth surface.
- Achieve accurate floor levels and falls.
- Improve floor strength and durability.
- Act as a substrate for the final floor finish (epoxy, tile, vinyl, etc.)
1. Leveling and Surface Correction
- Concrete slabs are often rough and uneven.
- Mortar screed ensures a flat, level surface suitable for high-performance coatings or finishes.
- Prevents waviness, undulations, and pooling in final floor systems.
- Acts as a thickness build-up layer where epoxy or SL systems cannot economically correct unevenness (e.g., >5mm).
- Helps correct falls/slopes in wet rooms, car parks, etc.
- Increases load-bearing capacity and shock resistance.
- Especially important under heavy-duty epoxy systems, forklifts, or machines.
- Provides a clean, dry, and textured surface suitable for primers.
- Reduces the risk of delamination or blistering in floor finishes.
- Easier to repair or patch than full concrete.
- Acts as a sacrificial layer that protects structural slab integrity.
| Type | Description |
| Cement-Sand Screed | Standard 1:3 to 1:4.5 mix used for general leveling |
| Polymer-Modified Screed | Improves bond, flexibility, reduces shrinkage |
| Epoxy Mortar Screed | High-strength screed for industrial and heavy-load areas |
| Self-Leveling Screed | Pourable compound for thin leveling layers (3–10mm) |
Step 1: Surface Preparation
- Clean concrete slab thoroughly: remove oil, laitance, dust.
- Mechanically grind or scarify if necessary.
- Dampen surface (saturated surface dry – SSD) before screeding.
- Brush on a bonding slurry (cement + SBR latex + water or epoxy primer slurry).
- Apply screed wet-on-wet while the bonding agent is still tacky.
- Mix cement:sand ratio (1:3 to 1:4.5) by weight or volume.
- Add water slowly for workable, non-slump consistency.
- For polymer screeds, add admixture as per supplier instructions.
- Place mortar onto the floor area and spread evenly.
- Use screed battens or screed rails for leveling reference.
- Compact with trowel or wooden float to ensure no voids.
- Use aluminum straight edge or darby to level.
- Trowel smooth or leave textured depending on final finish.
- Keep covered with wet hessian or curing compound for at least 5–7 days.
- Avoid traffic until full cure is achieved (usually 7–14 days depending on thickness).
| Application | Screed Thickness |
| Standard cement-sand | 25–50 mm |
| Bonded screed | Minimum 15–25 mm |
| Unbonded (on plastic sheet) | ≥50 mm |
| Floating (on insulation) | ≥65 mm (domestic), ≥75 mm (industrial) |
| Epoxy mortar screed | 5–15 mm typical |
| Issue | Cause | Prevention |
| Cracking | Shrinkage, poor curing | Use proper water/cement ratio, cure well |
| Debonding | Poor substrate prep | Always clean, roughen, and use bonding slurry |
| Hollow sound | Inadequate compaction | Press and compact well during placement |
| Surface dusting | Weak mix, overwatering | Use proper mix and good curing |
| Uneven finish | Poor levelling tools or method | Use screed rails and straight edges |
- Always follow manufacturer recommendations for polymer or epoxy-modified screeds.
- Apply in manageable sections to avoid cold joints.
- Where epoxy or self-leveling will be applied later, leave surface slightly textured (not polished).
- Always protect screed surface from early drying, water exposure, or foot traffic during cure.
Screeding is highly recommended when:
- The slab has undulations >3 mm over 2m.
- A slope or gradient is required (e.g., for water drainage).
- The surface is too rough or porous for direct epoxy.
- You want to raise the floor level economically before final coating.
US 11120 
GB 8294 
AU 7463 
CA 7382 
IE 4198 
NZ 3967 
BR 1302 
CN 976 
