Covering Concrete with Plastic: Good or Bad?

Covering Concrete with Plastic: The Right and Wrong Way

Covering concrete with plastic is excellent for curing—it retains moisture and prevents rapid drying. But doing it wrong leaves permanent discoloration patterns. This guide covers exactly how to cover concrete correctly to get the benefits without the problems.

Why Covering is Good: Moisture Retention

Covering concrete with plastic provides essential moisture retention for proper curing.

How It Helps

• Prevents rapid drying: Slows water evaporation from the surface
• Maintains moisture: Keeps concrete moist for proper hydration
• Prevents cracking: Slow, even drying prevents shrinkage cracks
• Improves strength: Proper hydration creates stronger concrete

The Science

Concrete needs water to cure properly. The chemical reaction (hydration) between cement and water requires moisture. If water evaporates too quickly, hydration stops, and the concrete never reaches full strength. Covering slows evaporation, allowing proper hydration.

How to Cover Correctly

Proper covering technique prevents problems while providing benefits.

Step 1: Use Smooth Plastic

• Type: Clear or white plastic sheeting (4-6 mil thickness)
• Condition: Smooth, not wrinkled
• Size: Large enough to cover entire surface with overlap

Step 2: Place Smoothly

1. Lay plastic flat: Don't allow wrinkles
2. Start from one edge: Unroll smoothly across surface
3. Smooth as you go: Work out any wrinkles immediately
4. Overlap edges: Extend 6-12 inches beyond concrete edges

Step 3: Secure Edges

• Weight down: Use sandbags, bricks, or stakes
• Secure all edges: Prevent wind from lifting plastic
• Check regularly: Ensure plastic stays in place

The Wrinkle Problem: Permanent Discoloration

Wrinkled plastic creates permanent discoloration patterns that can't be removed.

Why Wrinkles Cause Problems

When plastic wrinkles:

• Creates contact points: Wrinkled areas touch concrete directly
• Blocks moisture evenly: Uneven contact creates uneven moisture distribution
• Causes discoloration: Areas under wrinkles cure differently than smooth areas

What Discoloration Looks Like

• Pattern matches wrinkles: Discoloration follows wrinkle lines exactly
• Lighter or darker areas: Different shades where wrinkles were
• Permanent: Can't be removed or fixed

Why It's Permanent

The discoloration is caused by different curing rates. Areas under wrinkles hydrated differently than smooth areas. Once cured, this difference is permanent. No amount of cleaning, sealing, or treatment can fix it.

How to Avoid Wrinkles

Prevention is the only solution.

Technique 1: Smooth Application

1. Unroll carefully: Don't rush—take time to lay it flat
2. Have help: Two people can lay plastic smoother than one
3. Work from center: Start in middle, smooth outward
4. Fix wrinkles immediately: If you see one, fix it before it sets

Technique 2: Use Large Pieces

• Fewer seams: Large pieces mean fewer joints
• Less wrinkling: Fewer pieces mean fewer opportunities for wrinkles
• Easier to manage: One large piece is easier than many small ones

Technique 3: Alternative: Wet Burlap

If you're concerned about wrinkles, consider wet burlap instead:

• No wrinkles: Burlap conforms to surface without creating patterns
• Retains moisture: Stays wet, keeps concrete moist
• Requires rewetting: Need to keep burlap wet

When to Cover

Cover concrete after finishing is complete but before it starts to dry.

Timing

• After finishing: Once final troweling or texturing is done
• Before surface dries: While surface is still dark/wet-looking
• Typically: 1-2 hours after placement (depending on conditions)

How Long to Keep Covered

• Minimum: 3-7 days
• Longer is better: Up to 14 days for best results
• Keep moist: Check that plastic retains moisture underneath

Checking Under Plastic

Periodically check that curing is proceeding correctly.

What to Look For

• Moisture on plastic: Condensation indicates concrete is staying moist
• No drying: Surface should still look dark/moist
• Proper temperature: Should feel warm from hydration heat

If Surface Dries

• Lift plastic carefully: Don't wrinkle when checking
• Mist with water: If surface is dry, lightly mist with water
• Replace plastic smoothly: Put back without wrinkles

Alternatives to Plastic

If you're concerned about wrinkles, consider alternatives:

Wet Burlap

• No wrinkle issues
• Requires keeping wet
• Good for smaller areas

Curing Compounds

• Spray-on membrane
• No covering needed
• Prevents moisture loss

Insulated Curing Blankets

• For cold weather
• Provides insulation and moisture retention
• More expensive but very effective

The Bottom Line

Covering concrete with plastic is excellent for curing—it retains moisture and prevents rapid drying. But wrinkled plastic creates permanent discoloration patterns that can't be fixed. Lay plastic smoothly without wrinkles, secure edges, and keep covered 3-7 days minimum. If you're concerned about wrinkles, use wet burlap or curing compounds instead. The benefits of covering are significant, but only if done correctly.

Take time to lay plastic smoothly—the few extra minutes prevents permanent discoloration that can't be fixed.

Need help with concrete curing? Contact Local Concrete Contractor. We ensure proper curing methods that protect your concrete investment.