Why Priming Your Subfloor Before Latex Screed Is Absolutely Essential
When it comes to creating a perfect, level surface for your new flooring, applying a latex screed (or self-levelling compound) is a tried-and-tested method. But there’s one crucial step that far too many people skip — priming the subfloor.
Whether your base is plywood, OSB, or concrete, applying the right primer or sealer before the screed goes down isn’t just good practice — it’s essential to the longevity and performance of the entire floor.
See the images of Hasan here dutifully applying his primer!
Let’s break down why.
🧱 1. Primer Creates a Strong Bond
Both concrete and timber-based boards are porous. Without primer, they’ll absorb moisture from the latex screed too quickly.
This rapid drying prevents proper chemical bonding, which can lead to:
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Poor adhesion
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Cracking
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Sections of screed lifting or debonding
A primer acts as a barrier and bonding agent, helping the screed grip tightly to the subfloor so it becomes one solid, stable layer.
💧 2. It Controls Moisture and Suction
Different substrates absorb moisture differently:
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Concrete can draw water out unevenly.
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Plywood or OSB can swell or delaminate if exposed to excess moisture.
Priming seals the surface and ensures even curing of the latex compound.
Without it, you could end up with patchy drying, pinholes, and surface dusting — all signs of a failed screed.
⚡ 3. It Prevents Air Bubbles and Pinholes
As the latex screed is poured, air trapped in the substrate will try to escape upwards.
If the surface isn’t sealed, that air escapes through the wet screed, forming tiny pinholes or craters.
Primers close off the pores, preventing air from rising and giving you a smooth, flawless finish ready for any floor covering.
🪵 4. On Timber Subfloors, It Adds Stability
Plyboard and OSB naturally move slightly with changes in temperature and humidity.
Primers — especially those designed for timber — improve flexibility and adhesion, allowing the latex to expand and contract with the subfloor without cracking or lifting.
⚠️ 5. What Happens If You Skip It
Here’s what can go wrong if you skip the primer step:
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Latex screed lifts, curls, or debonds within weeks.
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Cracks appear across high-traffic areas.
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Pinholes and dusty patches ruin the finish.
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On timber, moisture causes warping or swelling.
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Your new flooring (especially LVT, vinyl, or carpet tiles) starts bubbling or loosening shortly after installation.
In short: skipping primer can turn a professional job into a costly redo.
✅ The Bottom Line
Priming before latex screed isn’t an optional extra — it’s part of the system.
It ensures:
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Strong adhesion
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Consistent curing
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Moisture control
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A smooth, durable finish
Whether you’re working over concrete, plywood, or OSB — always use a primer recommended by the screed manufacturer. It’s a small step that guarantees big results.
Watch Hughie apply his floor primer and show you how to do it! How to apply floor primer video.
