Don’t Skip the Underlayment: The Foundation of a Great Laminate Floor
So, you’re putting in new laminate floors? Getting the underlayment right is extremely important. I think many people overlook this step. This layer is what makes your floor feel solid under your feet. It also blocks moisture and quiets down any squeaks. It might look simple, like you just roll out a pad. But I recommend you take your time, as your whole project depends on these first steps. I want to help you avoid some simple mistakes that can mess up your new floor.
Step 1: Prepare and Inspect the Subfloor
A good subfloor preparation is the most important step. I start by removing all the old flooring, like carpet, tile, vinyl, and any old glue, nails, or staples. You need to expose the bare subfloor to create a solid base.
Give the subfloor a good cleaning:
– I always sweep, vacuum, and mop the entire area.
– Get rid of all debris and dust. Leftover grime can cause issues with your underlayment and result in an uneven floor.
Key Inspection Points
I always inspect the subfloor for these things:
Water Damage: Check for stains, mold, mildew, or any soft spots. If you have a concrete subfloor, I recommend making sure the moisture content is below 12%. This helps prevent future warping.
Structural Problems: Look for loose boards. Walk on them to check for squeaking, which indicates movement. Sagging areas can also make the new floor unstable.
Uneven Surfaces: Sand down high spots and use a patching compound to fill in low spots. The subfloor levelness should not change by more than 1/8 inch over a 6-foot area.
Pest or Insect Damage: Be on the lookout for signs of termites or rodents. These pests can weaken the subfloor’s structure.
Other Flaws: I also check for gaps, buckling, deep scratches, or any other odd surfaces. I think it’s best to repair these before you start the installation.
If a moisture test shows the levels are too high, I suggest you install a dedicated moisture barrier. This will prevent damage down the road.
Step 2: Level and Repair Your Subfloor (Checking Flatness, Patching, Sanding, and Fixing)
Before you roll out the underlayment, I find it’s critical to get the subfloor flat and smooth. This one step is the secret to a quiet laminate floor that will last for years.
Check Subfloor Flatness
I recommend using a 6- to 10-foot straightedge or long spirit level. Place it in multiple directions across your subfloor to check for inconsistencies.
Mark any dips, humps, or sloped areas you find. Most laminate manufacturers and industry standards require your subfloor to be level within 3/16 inch (4.7 mm) over a 10-foot span.
Failing to meet this measurement can cause defects in your new floor and may void your warranty.
Fill Low Spots and Dips
For minor dips (less than 1/4 inch deep), I suggest you use a self-leveling compound.
For moderate dips, a patching or floor-leveler compound gives the best results.
Mix and pour the compound. It will spread on its own and fill in the low spots.
Pay attention to drying times. It takes about 1–4 hours for the initial set. A full cure can take up to 24 hours. I always recommend following the product’s specific instructions.
My practical tip: If you spot a dip that’s 1/4 inch deep over a 2-foot section, just fill that area with a self-leveler for the best performance.
Sand Down High Spots
You can tackle raised areas with a belt sander, floor grinder, or hand planer.
Sand until the subfloor is even with the rest of the floor. Your straightedge should lie flat over the spot.
You must clean up all the dust with a vacuum. I know from experience that any residue can interfere with underlayment adhesion and create noise later.
For high plywood seams, sand them down until they are even with the panels next to them.
Secure and Repair Panels
I suggest walking around the room to listen for squeaks or give.
Secure any loose boards with wood screws or ring-shank nails. I find it works best to place fasteners every 6–8 inches on panel edges. Place them every 12 inches in the middle of the panel.
For extra squeaky areas, you may need to add more fasteners. You can also inject adhesive under the subfloor if needed.
Special Repairs for Plywood Subfloors
Fill cracks or holes with wood filler or a patching compound. Let it dry completely, then sand it smooth.
If the plywood has significant damage or won’t get flat, I recommend you install a new 1/4-inch plywood underlayment right over the old subfloor.
Step 3: Choose the Right Underlayment for Laminate Flooring
choosing the right underlayment is a big deal. It affects your floor’s lifespan and comfort. I suggest you consider four things: your subfloor type, moisture risk, how much soundproofing you need, and your budget.
How to Match Underlayment to Your Subfloor
For Wood or Plywood Subfloors:
I recommend foam underlayment for basic cushion and sound-dampening. This is the most budget-friendly type, at $0.22–$0.75 per sq. ft.. I like the 3mm foam for more comfort and quieter steps. You should check that it won’t make the floor too high for your doors or stairs.
For Concrete or Moisture-Prone Areas (Basements, Kitchens):
I suggest a vapor barrier underlayment (2-in-1 or 3-in-1). These cost about $0.30–$0.85 per sq. ft.. They handle both moisture and sound in one layer. A 3-in-1 silent vapor barrier, often 2–3mm thick, is a great choice. This product will stop dampness from damaging the laminate. It keeps the planks from swelling or warping.
For Great Sound and Heat Insulation:
If you want the best insulation, I recommend cork or rubber. They are excellent at blocking noise and keeping your feet warm. They also fight mold and stand up to heavy pressure. These materials cost more, about $0.65–$1.25 per sq. ft. I believe they are a great investment for apartments or upper floors. They are perfect if you need to control both moisture and sound. Cork is also eco-friendly and is a fantastic choice for concrete subfloors.
What About Built-In Underlayment?
Some laminate planks have underlay already attached. If you have these, you just need a plastic sheet vapor barrier over the concrete. I suggest you don’t add extra foam padding. Too much padding can mess with the locking system. It might also void your warranty.
Step 4: How I Acclimate Materials for a Laminate Floor Install
Before I start installing underlayment or laminate, I make sure to let all the materials acclimate. This means letting them get used to the room where they will be installed. In my experience, this one step prevents future headaches. It helps you avoid expansion, shrinkage, cupping, or gapping, which are common reasons that floors fail.
How Long to Acclimate and at What Conditions
Minimum time I suggest: 24–48 hours
My preferred time: 48–72 hours. I might even wait up to 96 hours if the room is humid or the climate is very different from where the flooring was stored.
Room conditions I maintain during this period:
Temperature: 64–90°F (18–32°C)
Relative humidity: 25–65% (I make sure it never goes over 75%)
Step 5: Install a Moisture Barrier for Laminate Flooring (If Needed)
if you’re Installing Laminate Flooring over concrete or below-grade subfloors, a moisture barrier is a must. If you skip it, water vapor can come up from the subfloor and ruin your new flooring. This can cause warping, swelling, and it might even cancel your warranty.
Why You Need a Moisture Barrier
You have to use a moisture barrier for all concrete subfloors and any installations in a basement.
I find this step is critical in high-moisture environments, such as basements, bathrooms, and kitchens.
I suggest you always check the flooring maker’s guide. If you don’t use the recommended barrier, you could lose your warranty.
Choosing the Right Moisture Barrier
I recommend a 6-mil (0.15 mm) polyethylene vapor barrier. This is the product I use most often for this job.
Your options include:
Plastic sheeting made for flooring
Vapor barrier rolls
Underlayments with a built-in vapor barrier (I’d check your underlayment type first. Some already have this feature, so you may not need an extra layer.)
How I Install a Moisture Barrier for Laminate Flooring
I roll out the plastic sheeting (for example, 6-mil polyethylene) along the longest wall.
Then I extend the sheet 2–4 inches up each wall. This extra material protects the joint where the floor and wall meet. You can trim it after the floor is installed.
As you add new sheets, overlap each seam by at least 6–8 inches. I think 8 inches gives you extra security.
Tape all the seams with waterproof or vapor barrier tape. This is a critical step to create one solid, sealed layer.
Press the corners down firm and make sure there are no wrinkles or air bubbles.
I inspect the entire surface for tears, holes, or gaps. If I find any, I patch them with vapor barrier tape before I lay down the underlayment and laminate.
For big installations, I suggest you double-check for full coverage. You want no gaps where vapor could get through.
Step 6: Roll Out and Place the Underlayment for Laminate Flooring
To get a smooth and durable laminate floor, you must roll out the underlayment the right way. Here’s my method to ensure every roll is laid perfectly.
Start From the Longest Wall
Begin by unrolling the underlayment along the longest wall in the room. You must follow the manufacturer’s directions. Placing the foam or moisture barrier side correctly is vital. If you put it down wrong, you will lose both moisture resistance and cushioning.
Standard roll size: Underlayment rolls come in widths of 3 to 4 feet and lengths of 25 to 100 feet.
For a 10-by-12 ft room (120 sq ft), my experience shows that one to two standard rolls will cover the space, depending on the brand and how much you overlap.
Getting a Perfect Fit—Edge to Edge
Place the first roll’s edge right against the wall. I make sure to avoid gaps. Open spaces can cause future problems with moisture or sound.
If your underlayment has an attached adhesive strip, I recommend laying it so the strip faces the open part of the room. This makes it simple to join the next roll and helps keep your vapor barrier sealed.
Trim any extra underlayment at the end of each row with a utility knife or shears. A rule I always follow: Do not let the underlayment run up the wall. It needs to stay flat on the floor so it won’t cause issues with baseboards or molding.
Step 7: Secure Seams and Remove Excess Underlayment
After you lay out the underlayment, you need to secure the seams. Getting this right is very important. A good seam seal stops moisture and keeps the underlayment from moving. It also helps your laminate floor stay quiet and even for years.
How to Join and Tape Underlayment Seams
Push all underlayment edges together without any overlap. The only time you should overlap them is if the manufacturer’s directions tell you to. doubling up seams creates high spots under the laminate planks, which leads to an uneven floor.
I suggest you make sure every seam is gap-free. Press the joints together so you can’t see any space between the underlayment sheets.
Taping Seams for Moisture Protection and Stability
Seal all seams with the tape your underlayment’s manufacturer recommends. Your choices include:
Duct tape
Specialized seam tape
Pre-attached adhesive strips (I see these often on modern flooring underlayments)
For most jobs, I recommend you use tape that is at least 2 inches wide. Place it over each seam and press down hard. This creates a strong moisture barrier and keeps the underlayment from shifting.
If your underlayment has tape already attached, just peel the backing off and press it down to seal. I’ve found this makes the installation up to 30% faster than taping by hand.
If you have a foam or cork underlayment with no adhesive, I think duct tape is a great choice. It secures the seams well and improves moisture resistance.
Cutting Away Excess Underlayment
Once you secure all the seams, you need to trim away any extra underlayment. Cut any material that goes up the walls or sits in doorways.
I recommend using a sharp utility knife and a straight edge. This will give you a clean, straight cut.
You must leave a 1/4 inch gap around the room’s edges and any fixed objects. This little space gives the floor room to expand and contract with changes in temperature or humidity. This is key to preventing the floor from buckling.
Step 8: My Final Check on the Underlayment
Before you lay any laminate planks, I suggest doing one last check of the underlayment. this one step saves you from future problems and expensive repairs. It helps create a floor that lasts a long time.
Look Over the Underlayment Surface
I recommend using both daylight and a work light to examine the entire underlayment surface.
Look for raised seams, trapped debris, bubbles, or any wrinkles. These things can create bumps in your final floor.
Run your hand along the seams and panels. You want to feel for smooth, level transitions and make sure the underlayment is secure. There should be no movement or shifting.
Check for a Flat and Level Surface
I use a long straightedge or a 6-foot level to check the floor’s flatness.
Make sure the underlayment is not off by more than 1/8 inch (3.18 mm) over a 6-foot area.
For rooms over 10 feet long, the subfloor and underlayment should be within 3/16 inch (4.7 mm) across the entire length. Anything more can lead to gaps or buckling in your laminate.
If you find high spots, sand them down. For low spots, I use a suitable leveling compound. Let it dry before you check the spot again.
Check the Seams, Joints, and Edges
Confirm that all seams fit together with no gaps or are taped correctly, based on the maker’s instructions.
I use special seam tape if required. This creates a solid vapor barrier and stops any movement.
Pay attention to edges along walls, in doorways, and at transitions. You want complete coverage with no exposed subfloor.
Clean the Whole Area
Remove all your installation tools, empty packages, and any leftover materials from the room.
Sweep or vacuum the underlayment until the surface is clean and has no dust. I believe this is key to helping your laminate planks connect well and lay flat.