What to Put Under Laminate Flooring on Concrete: A Designer's Guide to Perfect Underlayment for Concrete Slab Floors

When you're installing laminate flooring over concrete, one of the biggest decisions is what to put underneath it. As someone who's tackled everything from basement remodels to high-rise apartments, I've seen firsthand how the right underlayment transforms not just the look but the feel and longevity of a space. If you’re staring at that gray concrete and asking yourself what goes between it and your beautiful new floors, you’re not alone—this is one of the most common questions my clients ask.

Here’s the short answer: you absolutely need an underlayment for laminate over concrete. But picking the right one—moisture barrier, foam, cork, or even combination options—depends on your home, your goals, and your DIY comfort level. Let's unpack your options.

Level of Detail & Time: Why Concrete Needs Special Prep

Before choosing an underlayment, start with the basics: ensure your concrete is clean, dry, and level. Even slight moisture or bumps can cause headaches down the road. In older homes, I’ve used a simple moisture test—taping plastic sheets to the slab and checking for condensation after 24 hours—to decide if extra moisture protection is needed. This small step prevented major issues in a Seattle basement project last year, where untreated concrete would've wrecked a gorgeous oak-look laminate.

For a fast overview, here’s the breakdown:

ConditionUnderlayment NeededNotes Dry, Level ConcreteStandard foam (w/ vapor barrier)Most common choice Potential Moisture6-mil poly vapor barrier + foamPrevents damage Soundproofing DesiredCork or specialty foamAlso adds comfort Radiant HeatingThermal-rated foam/corkCheck system compatibilityIf you’re considering installing a room planner to visualize your basement transformation, try mapping different underlayment options to see how thickness or material might affect door swing or transitions.

Choose the Right Tools and Underlayment Types

There’s a dizzying selection, but in most American homes with concrete subfloors, your shortlist should include:

1. Foam Underlayment: The classic option. Most brands offer versions with an attached vapor barrier, which is essential on concrete. Good for most rooms except those with high moisture risk.
2. Moisture Blocker (6-mil Poly): If you’re laying laminate in a basement or slab with any past leaks, lay this sheet first. Tape seams tightly.
3. Cork Underlayment: Excellent for sound dampening and thermal insulation. Thicker than foam; just make sure your laminate’s manufacturer allows it.
4. Combination Underlayment: Some modern laminates come with an underlayment attached—double-check specs; otherwise, adding another layer can void warranties.

In my experience, using a 2-in-1 foam/vapor barrier is a DIY-friendly route, as long as you seal all seams. For unique layouts, digital tools like a 2D floor planner speed up calculations on material you’ll need (especially for oddly-shaped rooms or tight closets).

Common Mistakes & Fixes: Stories from Real Projects

Let’s talk about what not to do! One of my clients, Mark, skipped the moisture barrier because his slab "seemed dry." Within a year, the edges of his laminate started to cup and the boards buckled—a costly redo. Lesson learned: concrete can release moisture for years after pouring.

Other common pitfalls include:

1. Not taping vapor barrier seams or leaving gaps—think of it like a raincoat with holes.
2. Overlapping underlayment too much—creates unevenness underfoot.
3. Forgetting to undercut door frames to allow the flooring and underlayment to slide underneath. Small details, big impact.

If you want a surefire plan before moving heavy furniture back, consider using a home design software to double-check every detail virtually.

AI-Assisted Modeling: Smarter Planning for DIYers

Even as a pro, I turn to digital modeling when planning large installs. AI tools can simulate how sound or heat travels through various underlayment combos—especially useful for open-plan living spaces. For first-timers, uploading your floor plan to an AI floor planner can help visualize thickness and door clearances (which is way easier than fixing a sticky door later!).

Case Study: Modern Family Basement in Ohio

In a recent Ohio remodel, we wanted sound dampening for the kids' playroom atop an old concrete slab. The solution was a combination of 6-mil vapor barrier, topped with cork underlayment under the laminate. Not only is the floor comfortable and warm, but it’s also quiet—no more echoing footsteps. According to Houzz Design Insights 2025, nearly 60% of US remodels in 2024 added soundproofing for family spaces—proof this detail really matters.

FAQ

1. What's the best underlayment for laminate over concrete in a basement? A combination of a 6-mil vapor barrier and foam/cork underlayment is typically best. Always check for lingering moisture before installation.
2. Can I skip the moisture barrier if my slab is dry? Experts and manufacturers recommend always including a moisture barrier—even if your concrete feels dry.
3. How thick should underlayment be under laminate on concrete? Most foam underlayments are 2mm–3mm. Cork runs thicker. Always follow your laminate manufacturer's specs to avoid warranty issues.
4. Is cork underlayment better than foam? For sound dampening and warmth, cork is excellent, though pricier than basic foam. It's also eco-friendly.
5. Can I use two layers of underlayment? No. Double layers can cause instability. Stick to a single recommended layer—add vapor barrier underneath if needed.
6. How do I test for moisture in concrete before installing laminate? Tape a clear plastic sheet to the slab for 24–48 hours. If condensation appears, address moisture before proceeding.
7. Are there underlayments that improve room acoustics? Yes, specialized acoustic foams and cork underlayments reduce echo and sound transfer.
8. Will underlayment help keep floors warmer? Slightly. Cork and foam both provide minor thermal insulation but won’t fully counter a cold slab without radiant heating.
9. What’s the safest option for bathrooms or laundry rooms? Laminate generally isn’t recommended in wet rooms—if used, a full-coverage vapor barrier is a must.
10. Can AI design tools help plan underlayment projects? Absolutely. Digital room planners can visualize underlayment thickness and help estimate materials.
11. How do I handle transitions between different floor heights? Use transition strips. Many design softwares help you preview elevation changes before installation.
12. Do I need to remove old adhesive before underlayment? Yes. Leftover glue can cause unevenness. Scrape and clean concrete thoroughly before proceeding.