How to Lay Fresh Concrete Over Old Tar and Flagstones

Renovating your patio can be an exciting project, but it can also present challenges, especially when dealing with a layer of old tar and flagstones. This guide will walk you through the steps to properly prepare the surface and lay fresh concrete, ensuring a durable and long-lasting result.

Issues with Laying Concrete on Tar

Laying fresh concrete directly on a layer of old tar is not ideal due to several potential issues:

Bonding Problems

Tar creates a non-porous surface that can interfere with the proper bonding of the new concrete. Cracks and peeling may occur as the concrete cures and ages, leading to uneven and unstable surfaces.

Moisture Issues

Tar can trap moisture beneath the concrete, increasing the risk of damage from freeze-thaw cycles or mold growth. This can lead to structural issues and unsightly damage to your patio.

Surface Preparation

Contaminants and residue from the old tar can interfere with the setting and curing of the new concrete, resulting in poor quality and durability.

Recommended Steps

To ensure a successful renovation, follow these steps for proper surface preparation and concrete installation:

Remove the Tar

The best approach is to remove as much of the tar residue as possible. You can use:

A heat gun to soften the tar for easier scraping. Chemical solvents designed to dissolve tar. Ensure you follow safety guidelines and manufacturer instructions.

Clean the Surface

After removing the tar, ensure the surface is clean and free from any remaining residue. A pressure washer can be very effective for this task, but be cautious not to damage the underlying concrete.

Repair the Base

Check the base for any damage or unevenness. Fill in low spots or cracks with a suitable repair compound to ensure a level and stable foundation.

Use a Bonding Agent

If you cannot remove all the tar, consider using a concrete bonding agent designed to improve adhesion to challenging surfaces. This will help ensure a strong bond between the old and new concrete layers.

Pour the Concrete

Once the surface is adequately prepared, you can proceed to lay the new layer of concrete. Follow the recommended thickness guidelines to ensure proper strength and durability. Proper curing and maintenance are essential for a long-lasting result.

Alternative: Concrete Resurfacing or Overlaying

Another option is to put a new layer of concrete over existing concrete, a process known as concrete resurfacing or overlaying. This involves:

Proper Preparation

Clean the existing concrete surface thoroughly to remove dirt, debris, and loose material. Repair any cracks or uneven areas.

Apply a Bonding Agent

Using a concrete bonding agent or primer can help create a strong bond between the existing and new concrete layers.

Apply the New Layer

Prepare the concrete mix or overlay material according to the manufacturer's instructions. Spread the mixture evenly over the existing surface using appropriate tools. Follow recommended thickness guidelines for optimal strength and durability.

Cure and Maintain

Proper curing and maintenance, including water curing or the use of curing compounds, can prevent premature drying and cracking. Following these steps ensures a successful outcome.

I hope this information helps! If you have any further questions, feel free to ask. Consulting with a professional can provide additional guidance and ensure the best possible results.