Tile Underlayment: Yes or No?
Failure to install underlayment before tiling can spell disaster for your tile installation.
Installing tiles without the proper underlayment can lead to cracked grout, loose tiles, leaks — and expensive repairs. Whether you're renovating a bathroom, kitchen, or laundry, understanding when and why to use tile underlayment is essential for a durable and waterproof finish.
In this article, you’ll learn:
What tile underlayment is and why it matters
When you must use underlayment (with real-life examples)
The best underlayment options for different subfloors
What can go wrong if you skip it
So, What is an Underlayment?
Kitchen in Titirangi installed with tile underlay sheets before being waterproofed. Credit: Cozy Tiling
Tile underlayment is a stabilising layer installed between the subfloor and the tile adhesive. It helps create a level, strong base for the tiles and prevents movement that can lead to cracking or water damage.
A typical tile floor has three layers:
Subfloor (e.g. wood or concrete)
Underlayment
Tile adhesive and tiles
Without the underlayment, your tiles rest directly on the subfloor — and that’s where problems begin.
Why Underlayment Matters
Underlayment helps:
Absorb subfloor movement (especially with wood)
Prevent cracking of tiles and grout
Create a level surface for better tiling
Add insulation and waterproofing (depending on the material)
Skipping this step may save money in the short term, but could cost you much more in repairs later.
Warning: Tiling directly on this floor without underlayment can lead to tile failure or costly repairs.
🔹 Real Example: North Shore Project
A returning client in North Shore recently called us, urgently needing waterproofing and tiling. But when our tiler arrived, the wooden floor was not ready — it had no underlayment.
We had to pause the job, explain the issue, and rebuild the floor base correctly. The client hadn’t realised that tiles can’t be installed directly on timber. It was a costly delay — and a great reminder why this layer matters.
🔹 When Do You Need Tile Underlayment?
Here are the two most common situations where underlayment is essential:
✅ 1. Tiling Over Wooden Subfloors
Tiles cannot go directly onto:
Plywood
Particle board
Hardwood
Wood expands and contracts with moisture and temperature changes. This movement causes tiles to pop off or crack. Underlayment absorbs this movement and keeps your tile system stable.
✅ 2. Tiling Over Concrete Slabs
Tiles can be laid on concrete, but:
Concrete absorbs moisture, which can rise into the tile and cause damage
Even old concrete slabs can shift or crack over time
Without a moisture barrier or crack-isolation layer, the movement transfers to your tiles
Solution: use an underlayment with waterproofing or crack protection.
🔹 What Are the Best Tile Underlayment Options?
🧱 1. Cement or Backer Board (Sheet Type)
✅ Most commonly used
✅ Strong, cost-effective
❌ Heavy, not waterproof without extra treatment
Ideal for: Ceramic or porcelain tiles over timber
Recommended product: Tile underlay sheet that can be purchased from Bunning, Mitre 10 or tile shops
🌊 2. Extruded Polystyrene:
✅ Lightweight and 100% waterproof
✅ Easy to cut, provides insulation
❌ More expensive than backer board
Ideal for: Bathrooms and wet areas
Recommended products: Aquamox thermal underlay, Marmox insulation underlay
🔧 3. Flexible Tile Mats
✅ Lightweight, waterproof, easy to install
✅ Some versions include insulation or crack protection
❌ Higher cost but adds great features
Ideal for: Renovations, quick installations, uneven floors
Recommended product: Ardex DS70.
⚠️ What Can Go Wrong Without Underlayment?
Cracked tiles and grout
Water damage under floors
Mould growth
Lifting or hollow-sounding tiles
Failed waterproofing warranty
👷♂️ Need Help Choosing the Right Underlayment?
Not sure what kind of underlayment you need? That’s where we come in.
At Cozy Tiling, we assess your floor type, moisture level, and tile choice — and recommend the most suitable underlayment for a long-lasting result. We serve homeowners and builders across Auckland, providing high-quality tiling and waterproofing services.
📞 Get Expert Advice From Cozy Tiling
Need help with your floor prep or tiling project?
✅ Call us today or
✅ Request a Free Quote
✅ Or simply search “Tiler near me” — we hope you’ll find Cozy Tiling at the top.