Microcement Over Plywood & Subfloors | Installer How-To — Microcement USA

If you install microcement, sooner or later a client's going to point at a plywood floor and ask if you can finish it. The answer is yes, you can. But plywood is the substrate that punishes shortcuts. Get the prep wrong and you'll be back fixing cracks.

Here's how to do it right. This one's for the trades.

Why Plywood Needs Extra Respect

Concrete is stable. Plywood moves. It flexes underfoot, it expands and contracts with humidity, and panels can shift at the seams. Microcement is a thin, rigid coating at 2 to 3mm. If the floor under it moves and you haven't controlled for that movement, the finish telegraphs it. That's where cracks come from.

So the whole game over plywood is the same thing said three ways: stiffen it, decouple it, and reinforce it. Nail the prep and the finish coats are the easy part.

Step 1: Check the Subfloor Is Stiff Enough

Before anything goes down, the floor has to be solid. Walk it. Feel for deflection and bounce. A floor that flexes when you step on it isn't ready.

Make sure the plywood is thick enough and properly fastened to the joists, with no loose or squeaky panels. Screw down anything that moves. If the structure is too bouncy, that gets addressed first, sometimes by adding a layer of ply or sistering joists. You can't finish your way out of a soft floor.

Step 2: Clean, Sand, and Prime

Once it's stiff and tight, prep the surface.

Clean off dust, grease, and anything that'll fight adhesion. Lightly sand the plywood to give the primer something to grab. Vacuum again.

Then prime. The Forcrete primer is there to bond the system to the substrate, and on a porous, moving surface like wood it matters even more than on concrete. Don't rush it and give it the dry time it needs.

Step 3: Reinforce With Mesh

This is the step people skip and regret. Over plywood you embed a reinforcing mesh, usually fiberglass, into your base coat. The mesh bridges the panel seams and spreads any small movement across the surface instead of letting it concentrate into a crack right over a joint.

Lay your base, set the mesh into it while it's wet, and lap the edges so there are no gaps. Pay special attention over every plywood seam. Those joints are the weak points, so cover them.

Some installers add a decoupling membrane between the ply and the system for floors with more movement. On a questionable subfloor, that extra layer buys you insurance.

Step 4: Build Your Base Coats

With mesh embedded, build up your base coats per the system. Let each coat dry fully before the next. Dry time between coats is not optional and it's not labor time you can quote away, so plan the schedule around it.

Knock down any high spots between coats so you've got a flat, sound base before the finish goes on.

Step 5: Finish Coats and Seal

Now it's familiar territory. Apply your finish coats with your trowel technique, working the color and texture the client signed off on. Thin, even passes.

Once cured, seal it with the Forcrete sealer. The full system is what makes it waterproof and durable, so don't leave the sealer off or shortcut it. Sealer protects the floor and locks in the finish.

Common Mistakes to Avoid

• Skipping the mesh. The number one cause of cracks over wood.
• Finishing over a bouncy floor. Fix the structure first, every time.
• Rushing dry times. Coats need to cure. Trapped moisture causes failures.
• Thin primer coverage. Wood is porous. Prime it properly.
• Ignoring seams. Treat every panel joint as a crack risk and reinforce it.

Want to Learn the Full System Hands-On?

Reading the steps is one thing. Feeling the trowel and seeing the mesh set into a base coat is another. Our two-day, hands-on training in Logan, Utah walks you through prep, mesh, base, finish, and sealing on real substrates, including the tricky ones like plywood.

And your tuition comes back as product credit, so you walk out ready to take your first job with material on hand.

For more application know-how, see our guides on microcement floors and microcement bathrooms.

Get certified with us. Learn the system from people who install it for a living.

Check training dates →