The $5 Shims That Stop Your Laminate from Creaking

Most guys skip the leveling compound. They think the underlayment will hide the dip. It won’t. I spent three days grinding concrete on a job last month just so the floor wouldn’t click like a castanet. That job was in a high-rise where the slab looked like the surface of the moon. If you think a thin sheet of foam is going to bridge a half-inch valley in your subfloor, you are setting yourself up for a symphony of squeaks. I have been on my knees for twenty-five years, and I can tell you that the sound of a floor rubbing against itself is the sound of money leaving your pocket. Laminate is an engineered system, not a rug. It relies on geometry and the laws of physics to remain silent. When that subfloor is uneven, the locking mechanism undergoes a stress cycle every time you take a step. Eventually, those plastic and fiberboard tongues snap. Then you are looking at a full tear-out.

The phantom sounds in your hallway

Laminate floor creaking is caused by vertical movement within the locking joints of the planks. This movement occurs when the subfloor flatness exceeds the manufacturer tolerance of 3/16 inch over a 10-foot radius. Friction between the HDF core and the locking tongue creates the audible clicking or snapping sound. To fix this, the installer must ensure the substrate is perfectly level before the first plank is laid. Most people ignore the basics. They see a small dip and assume the padding will handle it. It is a lie. That dip creates a void. When you step on the plank over that void, the plank bends. That bend is called deflection. Deflection is the enemy. It is what ruins the integrity of your floor.

“A floor is only as good as the subfloor beneath it; deflection is the enemy of every joint.” – Master Flooring Axiom

Why your subfloor is lying to you

Subfloors are rarely as flat as they look. Whether it is a concrete slab or a plywood deck, there are humps and valleys. In the world of hardwood floors and laminate, we talk about the flatness tolerance. If you take a 10-foot straight edge and find a gap larger than the thickness of two nickels, you have a problem. On wood subfloors, we use cedar shims or asphalt shingles to build up the low spots. For concrete, we use self-leveling underlayment. The goal is to create a plane, not just a surface. I have seen guys try to use grout or even cardboard to fill these gaps. That is amateur hour. The material used for shimming must be non-compressible. If it compresses, the floor will eventually move again, and the creak will return. You need a material that can withstand the thousands of pounds of pressure exerted by furniture and foot traffic over the years.

The chemistry of the clicking sound

The core of most laminate is High-Density Fiberboard or HDF. This is essentially wood fibers compressed with resins like urea-formaldehyde. When the floor moves, these fibers rub against each other. At a molecular level, the friction generates heat and static. This is why some cheap floors sound like they are crackling. The wear layer on top is usually a coat of aluminum oxide. It is incredibly hard, which is great for scratches but terrible for sound. It acts like a resonator. If there is a void underneath, that hard surface amplifies the sound of every movement. This is why the $5 investment in shims is the most important money you will spend. By supporting the locking joint from underneath, you eliminate the friction. No friction means no sound. It is simple engineering that most DIY types ignore because they are too focused on the color of the wood.

The 1/8 inch that ruins everything

Expansion gaps are the lungs of your floor. If you do not leave a 1/4 inch to 3/8 inch gap around the perimeter, the floor has nowhere to go when the humidity rises. It will hit the wall and start to peak. Peaking is when the joints lift up, forming a tent. This puts massive pressure on the locking system. I once saw a floor in a humid basement that had lifted three inches off the ground because the installer tight-fitted it against the baseboards. You need to use spacers, or shims, during the install to maintain this gap. Do not trust your eyes. Use the plastic shims. They are cheap, and they ensure that the floor can breathe. If the floor cannot move horizontally, it will move vertically. Vertical movement leads to the very creaking we are trying to avoid. In showers and bathrooms, this is even more dangerous because moisture will get into those stressed joints and cause the core to swell.

Why thick underlayment is a trap

A common mistake is buying the thickest, softest underlayment available. People think it will feel better underfoot. In reality, too much cushion is a death sentence for laminate. The extra padding allows for more deflection. Think of it like walking on a mattress versus walking on a sidewalk. The locking mechanisms are designed to sit on a firm surface. If the underlayment is too soft, the tongue and groove act like a hinge. They are not hinges. They are rigid connectors. When they are forced to act like a hinge, they fail. You want an underlayment with high compression strength. Look for materials like cork or high-density rubber. These provide sound dampening without allowing the floor to bounce. The $5 shim approach works best when the underlayment is thin and firm, providing a stable base for the shims to do their job.

Technical specifications for professional results

When selecting materials, you need to look at the data. Do not just look at the picture on the box. Here is a breakdown of what actually matters for a silent, durable floor.

A checklist for a silent floor

Before you click the first two planks together, you need to go through this list. If you skip a step, do not call me when your floor starts talking back to you.

• Check the subfloor moisture with a pinless meter. Concrete should be under 4 percent.
• Sweep every single grain of sand and dust. A single pebble under the plank will sound like a firecracker.
• Use a 10-foot straight edge to find every dip and hump.
• Shim the low spots with non-compressible materials like asphalt shingles or specialized plastic leveling shims.
• Ensure the expansion gap is consistent around every wall, door frame, and pipe.
• Acclimate the flooring in the room for at least 48 hours. The moisture content of the wood needs to stabilize.

The moisture barrier and the death of laminate

If you are installing over concrete, you need a 6-mil poly film. No exceptions. Concrete is like a sponge. It holds moisture that moves upward through capillary action. This moisture hits the bottom of your laminate and causes the HDF core to expand. When it expands, the joints tighten and start to creak. Eventually, the edges will cup. I have seen beautiful floors ruined in six months because someone forgot a $20 roll of plastic. In regions with high humidity, this is even more vital. The hydrostatic pressure can push moisture through even the tiniest cracks in a slab. Protecting the underside of your floor is just as important as protecting the top. This is especially true if your home has a crawlspace. The damp air from the ground will rot your subfloor and your finish floor from the inside out.

“Subfloor flatness is not a suggestion but a structural requirement for floating floor integrity.” – Flooring Industry Standard

Final thoughts for the job site

Installing a floor is a mechanical process. It requires precision and a respect for the materials. If you treat it like a puzzle, you will fail. You have to treat it like a machine. Every part needs to fit perfectly, and every part needs the right support. Those $5 shims might seem like a small detail, but they are the difference between a floor that lasts thirty years and one that becomes an annoying chore to walk on. Take the time to prep. Sand the high spots. Fill the low spots. Use the right spacers. When you walk across that floor in the middle of the night and it is silent, you will know the work was worth it. Do not be the guy who cuts corners. The floor always tells the truth in the end.