Tar Paper Under Tile: A Practical Guide for Floor Installations

Tar paper, also known as asphalt-saturated roofing felt, has long served as a moisture barrier in various construction applications. When it appears beneath tiles in flooring or other substrates, it prompts questions about compatibility, durability, and long-term performance. This article explains what tar paper is, its suitability under tile flooring, potential risks, better alternatives, and practical steps to inspect or upgrade an existing installation in American homes.

What Is Tar Paper And Its Role In Construction

Tar paper is a flexible, paper-like material saturated with asphalt. In roofing, it acts as a secondary moisture barrier beneath shingles. In some older or retrofitted buildings, tar paper found its way into floor assemblies as a lightweight underlayment or vapor barrier, especially when traditional materials were scarce or expensive. Although durable against some moisture exposure, tar paper lacks the robust compression strength, mold resistance, and compatibility with modern tile setting systems that contemporary underlayments provide.

Tar Paper Under Tile Flooring: Compatibility And Risks

Installing tile over tar paper is not universally recommended. In most modern tile installations, the standard underlayment options prioritize stability, moisture control, and proper substrate preparation. Some key considerations include:

• Moisture management: Tar paper can trap moisture if the substrate is not fully dry, increasing the risk of tile debonding or mold growth in damp environments.
• Movement and flatness: Tiles require a stable, flat, and well-adhered base. Tar paper offers little resistance to substrate movement, which can lead to cracked tiles or grout failures.
• Adhesion with modern mortars: Many modern thin-set mortars are formulated for cement backer boards or uncoupling membranes; they may not bond optimally to tar paper alone.
• Dust, debris, and durability: Tar paper can shed fibers or deteriorate over time, compromising tile adhesion and cleanliness of the setting bed.
• Aging and safety concerns: Older tar paper could contain asbestos fibers in some building materials manufactured before the 1980s. If suspect, professional testing and abatement are essential.

In summary, tar paper under tile flooring is typically not the best choice for new installations. It may have historical value in certain retrofit scenarios, but modern underlayment products provide superior performance and reliability for tile floors.

Safer Alternatives To Tar Paper For Tile Installations

Several modern underlayment options are widely recommended for tile floors, depending on the substrate and room conditions. Each option has distinct advantages:

• Cement Backer Board: A rigid substrate that provides a stable, moisture-resistant base for porcelain and ceramic tiles. It resists indentation and offers excellent bonding for thin-set mortars.
• Uncoupling Membranes: Flexible, engineering-driven membranes (such as 1/8-inch uncoupling mats) that absorb substrate movement, reducing the risk of cracks in tiled surfaces.
• Plywood Or Oriented Strand Board (OSB) Underlayment: For wood subfloors, a high-quality underlayment panel, properly installed with a suitable moisture barrier, supports tile stability.
• Foam Underlayments: Lightweight, iso-layer products that can provide sound control and adjust for minor substrate irregularities, when paired with the correct thin-set.
• Moisture Barriers: In areas with high humidity or moisture risk, use a dedicated liquid-applied or sheet moisture barrier over concrete slabs prior to backer board or uncoupling membranes.

When choosing an underlayment, consider the substrate (concrete, wood, existing tile), room conditions (bathroom, kitchen, basement), and expected wear. For most new installations, a cement backer board or an uncoupling membrane offers robust performance and easier long-term maintenance.

Steps For Inspecting And Updating An Existing Tar Paper Underlayment

If a home already has tar paper beneath tile, a cautious assessment and upgrade path is advisable. Here are practical steps:

• Assess condition: Inspect accessible areas for moisture staining, delamination, or soft spots in the floor. Tap test areas to detect hollow sounds which may indicate voids behind the tar paper.
• Test for asbestos: If the home was built before the 1980s, treat any suspected tar paper as potentially asbestos-containing material. Hire a licensed asbestos professional to sample and, if necessary, remove or encapsulate safely.
• Plan removal or overlay: Depending on the substrate condition, decide whether to remove the tar paper and install a modern underlayment or overlay with an appropriate system on top of the existing layer.
• Prepare the substrate: Ensure the subfloor is clean, dry, and structurally sound. Repair any cracks or movement with suitable patch materials before installing a new underlayment.
• Install proper underlayment: Choose cement backer boards or uncoupling membranes per manufacturer guidelines, ensuring full coverage and proper fastener spacing.
• Follow tile installation best practices: Use the recommended thin-set mortar, allow proper cure time, and maintain temperature and humidity levels during installation and curing.

Professional guidance is recommended when dealing with older constructions or potential asbestos. A qualified flooring contractor can provide an assessment, removal, and installation plan tailored to the home’s structure.

Maintenance And When To Call A Pro

Tile floors installed over tar paper, or any older underlayment, require periodic checks for moisture, movement, and tile integrity. Signs to monitor include:

• Cracked or loose tiles or grout: Indicates movement or inadequate bonding.
• Dampness or musty odors: Suggests moisture penetration or subfloor degradation.
• Soft spots beneath the floor: May reveal substrate damage or failed underlayment.
• Could indicate water intrusion or mold growth.

If any of these issues arise, consult a licensed flooring professional promptly. Addressing moisture and substrate integrity early helps prevent costly repairs and ensures a durable tile installation.

Key Considerations For Homeowners

• Tar paper is generally not recommended as a primary underlayment for modern tile floors due to moisture, movement, and adhesion concerns.
• Older properties may require asbestos testing before disturbing any tar paper or similar materials.
• Adopting modern underlayment systems improves tile longevity, load performance, and ease of maintenance.
• Professional evaluation can determine whether removal or overlay is the best approach for an existing installation.