Self-Leveling Underlayments: Additives That Matter

How to use this guide

This is a practical decision aid for B2B teams. Use it to align procurement, R&D, and operations on which additive levers matter, what to verify on COA, and what signals to monitor. If you share your target flow/pot life/strength and raw materials, we can propose supply-ready additive options.

Where it fits

• Product goal: define the KPI you are optimizing (flow/spread, pot life, early strength, surface quality, crack resistance, cost).
• Application window: ambient temperature, substrate moisture/porosity, layer thickness, and finishing method.
• Binder system: cement type and blend (Portland/CSA/gypsum-based), fillers, and whether polymer modification is required.
• Constraints: VOC/odor limits, low-dust handling, bag/BigBag packaging, and storage humidity control.

Key decision factors

• Substrate moisture & temperature: shifts water demand and set behavior; impacts edge curl and cracking risk.
• Workability window & set time: mix → pour → finish → walk-on timing must be repeatable.
• Compatibility: cement chemistry, filler grading, polymer package, and interactions (especially dispersant + retarder).

The additive “jobs” that make or break SLU

A self-leveling underlayment succeeds when it flows without segregating, releases trapped air, sets on schedule, bonds reliably, and minimizes shrinkage cracking. These are the core building blocks:

1) Dispersant / superplasticizer (flow with less water)

• Controls: spread/flow at fixed water ratio, strength potential (lower W/B), pumpability.
• Watch-outs: overdose can cause bleeding/segregation; cement/fines sensitivity is common.
• Procurement hint: request active content/solids and a dosage range by binder type.

2) Viscosity & water retention (stability on the floor)

• Controls: anti-bleed, segregation resistance, water retention on porous substrates, edge stability.
• Common tools: cellulose ethers (water retention) + VMAs (stability/rheology).
• Watch-outs: too much viscosity reduces leveling and can trap air (pinholes).

3) Defoamer / air release (surface quality)

• Controls: pinholes, craters, foam during mixing/pumping, surface “tightness.”
• Watch-outs: overly aggressive defoaming can reduce workability or affect adhesion in polymer-rich systems.
• Practical tip: evaluate at realistic mixer speed + water temperature; air issues are process-sensitive.

4) Set control (pot life + walk-on time)

• Controls: open time, set time, early strength curve, schedule reliability.
• Watch-outs: interactions with dispersants are common; temperature swings can invert behavior (too fast/too slow).

5) Polymer modification (bonding + toughness)

• Controls: adhesion to substrate/primers, flexural strength, abrasion resistance, crack tolerance.
• Watch-outs: polymer can increase air entrainment and influence set; tune defoamer and rheology together.

6) Shrinkage & crack risk (dimensional stability)

• Controls: drying shrinkage, edge curl, microcracking under fast drying conditions.
• Common tools: shrinkage reducers and/or fibers depending on strategy.
• Watch-outs: validate across thickness range and curing conditions (drafts/low RH accelerate cracking).

Additive cheat sheet (what to adjust first)

Specification & acceptance checks

When comparing additives and blends, ask for data you can verify on receipt:

• Identity: product name/grade, manufacturer, and batch/lot traceability.
• COA (typical): solids/active content, pH (liquids), viscosity (if relevant), density, and appearance.
• Powder controls: moisture, bulk density, and (if relevant) particle size or sieve residue.
• Compatibility notes: cement/binder compatibility and known interactions (e.g., retarder + dispersant).
• Packaging: bag/BigBag/drum/IBC, liner type, moisture barrier, closures, labeling.
• Safety: up-to-date SDS, dust handling notes, PPE, storage/temperature limits.
• Logistics: lead time, Incoterms, shelf life, storage humidity requirements, pallet configuration.

Handling & storage

• Moisture control: many SLU additives (especially powders) are humidity sensitive—store sealed and off the floor.
• FIFO discipline: label partial bags; reseal opened packaging promptly to prevent caking and dosage drift.
• Mixing discipline: keep water dosing and mix time consistent—SLU performance is highly process-sensitive.

Troubleshooting signals

If performance drops, these are common early indicators and what to check first:

• Slow set / weak early strength: temperature, retarder carryover, excess water, cement variability, or dispersant incompatibility.
• Segregation / bleeding: dispersant overdose, insufficient stability package, or filler grading/fines shift.
• Pinholes / craters: air release mismatch, high shear mixing, dirty substrate/primer incompatibility, or viscosity trapping air.
• Cracking / shrinkage: high water ratio, rapid drying (drafts/low RH), thick sections, or missing shrinkage mitigation.

If you share your binder/filler blend, target spread/pot life, and jobsite conditions, we can usually narrow down the root cause quickly.

RFQ notes (what to include)

• Target spread/flow (test method used) and desired pot life / set window (mix-to-pour, walk-on time).
• Binder system (cement type/blend), filler type and grading, and whether polymer modification is required.
• Application thickness range and substrate type (porosity/moisture), plus primer system if used.
• Temperature and humidity window; curing expectations (draft control, early traffic).
• Primary failure risk to avoid (pinholes, segregation, slow set, cracking) and acceptance criteria.
• Estimated monthly volume, packaging preference (bags/BigBags/drums/IBCs), delivery country, documentation needs (COA/SDS).

Educational content only. Always follow site EHS rules and the supplier SDS for safe use.