Grout is one of those things that people usually don’t think about until they suddenly have to. Maybe you’ve spotted dark spots creeping between your bathroom tiles, or perhaps your kitchen backsplash isn’t looking as crisp as it used to. The question that often follows is simple but important: is grout waterproof?
The short answer is no, grout is not naturally waterproof. But don’t worry—I’m not just going to leave you with that. In this guide, I’ll walk you through what grout really is, how it behaves when it comes to water, what you can do to protect it, and the sneaky ways moisture tries to slip into places it doesn’t belong.
1. What Exactly Is Grout?
Grout is basically the filler between your tiles—a mixture of cement, sand, and water (sometimes with added polymers for strength and flexibility). Its main jobs are:
- Holding tiles in place so they don’t wiggle or shift.
- Filling gaps to create a smooth, finished surface.
- Blocking dirt and debris from collecting in the spaces between tiles.
But here’s the catch: grout, especially cement-based grout, is porous. Imagine it like a sponge or that old hoodie you can’t wear in the rain—it absorbs liquid easily. That means if water sits on it, some of it will seep in.
I learned this the hard way when I tiled my first bathroom floor. I assumed grout was some kind of magic waterproof glue. Fast forward six months, and I noticed discoloration between tiles near the shower. That was the moment I discovered grout’s dirty little secret—it’s water-resistant at best, not waterproof.
2. Why Grout Is Not Waterproof
The main reason grout isn’t waterproof lies in its porous structure. Even if grout feels solid and rock-hard to the touch, on a microscopic level it has tiny holes and pathways.
When water comes into contact with grout:
- It soaks in rather than bouncing off.
- Over time, stains and mildew can appear.
- In wet areas like showers, constant exposure to water speeds up deterioration.
Think of grout like a coffee filter. No matter how strong or thick it looks, water will always find a way through if it’s not sealed.
And here’s something most people don’t realize: even epoxy grout, which is marketed as highly water-resistant, isn’t 100% waterproof. It’s much better than cement grout, but it can still let moisture sneak around edges or behind tiles if your installation isn’t perfect.
3. The Difference Between Waterproof and Water-Resistant
A lot of the confusion around grout comes from mixing up “waterproof” and “water-resistant.”
- Waterproof means no water can penetrate—ever. Think of a rubber raincoat.
- Water-resistant means it holds up against some water, but not indefinitely. Think of a wool sweater—great for a drizzle, terrible for a storm.
Most grout falls firmly into the “water-resistant” camp. It can handle small splashes here and there, but prolonged exposure will eventually let water pass through.
That’s why in showers, bathrooms, and kitchens, grout needs backup—sealants and proper waterproofing membranes beneath tiles.
4. What Happens If Grout Gets Wet?
Here’s where things get serious. If grout is left unsealed or poorly maintained, water will:
- Seep into grout lines.
Over time, this darkens the grout and causes discoloration. - Reach the subfloor or wall behind tiles.
This can weaken tile adhesive and cause tiles to loosen. - Create the perfect home for mold and mildew.
Moisture + warmth + darkness = mold’s dream vacation spot. - Damage structures beneath.
Wood floors, drywall, and even concrete can eventually suffer from water damage.
I once visited a friend’s house where their shower grout had gone unsealed for years. At first, it was just a few stains. But one day, a tile literally popped off the wall, revealing black mold underneath. The repair ended up costing way more than just sealing the grout from the start.
5. Types of Grout and How They Handle Water
Not all grout is created equal. Let’s break down the main types and their relationship with water:
Cement-Based Grout
- The most common type.
- Affordable but very porous.
- Absolutely needs sealing in wet areas.
Epoxy Grout
- Made with epoxy resins instead of cement.
- Far more water-resistant than cement-based grout.
- Resistant to stains and mold.
- More expensive and trickier to apply.
Urethane Grout
- Pre-mixed and flexible.
- Fairly resistant to water and stains.
- Easier to maintain than cement grout, but also pricier.
If your bathroom or kitchen is a high-moisture zone, epoxy grout is usually worth the investment. But even then, sealing can add an extra layer of protection.
6. How to Waterproof Grout with Sealer
Here’s the good news: while grout isn’t naturally waterproof, you can make it water-resistant by applying a grout sealer.
Here’s how to do it:
- Clean the grout thoroughly.
Remove dirt, soap scum, and any mildew. If you don’t, you’ll be sealing the dirt in. - Choose the right sealer.
- Penetrating sealers soak into grout and protect it from within.
- Membrane-forming sealers create a layer on top but can wear down faster.
- Apply with a small brush or applicator.
Work carefully along grout lines. - Wipe off excess.
Don’t let sealer sit on the tiles—it’ll leave a haze. - Reapply every 1–2 years.
Sealing isn’t forever. It’s like sunscreen—you need to reapply.
I like to think of grout sealing as giving your grout a raincoat. Without it, your grout is standing in the storm wearing nothing but a cotton t-shirt.
7. How Long Does Grout Last Without Sealing?
In dry areas, like a tiled fireplace or an accent wall, unsealed grout can last a long time without major issues. But in wet areas, like bathrooms or kitchens:
- Unsealed grout can start showing problems in as little as 6 months.
- Mold and mildew may appear within a year.
- Structural damage behind tiles can happen after 2–3 years of constant water exposure.
That’s why sealing isn’t just a “nice-to-do”—it’s a must-do if you want your tile work to last.
8. The Cost of Ignoring Waterproofing
Here’s a stat that might surprise you: according to HomeAdvisor, the average cost to repair water damage in a bathroom is $2,500 to $7,500. Compare that to a $20 bottle of grout sealer and a Saturday afternoon of work.
Ignoring grout maintenance can lead to:
- Replacing entire sections of tile.
- Removing moldy drywall.
- Paying for professional mold remediation.
I had a relative who thought sealing grout was overkill. After five years, their shower tiles started falling off, and the wall behind was black with mold. The repair? Over $10,000. A little prevention could have saved them a vacation’s worth of money.
9. Tips for Keeping Grout Dry and Healthy
Here are a few habits that will extend your grout’s life:
- Wipe down tiles after showers. A quick swipe with a squeegee removes lingering water.
- Ventilate bathrooms well. Use fans or open windows to reduce moisture.
- Clean grout regularly. Use mild cleaners and avoid harsh bleach that weakens grout.
- Inspect grout yearly. Look for cracks, gaps, or discoloration that signal water damage.
Think of grout like your teeth—you can’t just brush once and expect them to last. Consistent care makes all the difference.
10. When to Call a Professional
Sometimes, grout problems go beyond DIY fixes. Call a professional if:
- You see tiles coming loose.
- There’s mold growing beneath or behind tiles.
- Water damage has spread to subfloors or drywall.
- You’re dealing with large-scale regrouting or resealing projects.
Professionals can also apply advanced sealers that last longer than store-bought versions, and they’ll spot hidden problems before they become disasters.
Conclusion
So, is grout waterproof? No—it’s not. Grout is naturally porous and will absorb water over time. But with the right care, sealing, and maintenance, you can make grout highly water-resistant and protect your home from expensive water damage.
Here’s the bottom line: grout is like a hardworking but vulnerable teammate. It does its job of keeping tiles in place, but it needs backup—sealants, membranes, and regular care—to stand up against the relentless power of water. Take care of it, and it’ll keep your kitchen, bathroom, or tiled floors looking beautiful for decades.
FAQs
1. Is grout waterproof?
No, grout is not naturally waterproof. It is porous and will absorb water unless it’s sealed.
2. How often should I seal grout?
Most experts recommend sealing grout every 1–2 years, depending on how much water exposure it gets.
3. Can I shower without sealing grout?
You can, but it’s risky. Unsealed grout in a shower will absorb water, leading to mold and damage over time.
4. What’s the best sealer for grout?
Penetrating sealers are usually best because they soak into the grout and provide long-lasting protection without leaving a surface film.
5. Does epoxy grout need sealing?
Epoxy grout is highly water-resistant and usually doesn’t need sealing, but sealing can provide an extra layer of protection in very wet areas.