The Skim Coating Conundrum: Mastering The Art Of Thin-Set Mortar Application

Thinset mortar is used to level out uneven floors and walls before tiling. The thickness of the skim coat depends on the surface being levelled and the material being used. For example, a simple concrete and water mixture can be used to level out an existing concrete floor, while a mixture with added lime can be used to skim coat walls. In general, a skim coat of thinset mortar should not exceed a thickness of 1/2 inch, as it may become unstable and shrink.

Thinset is not the best option for levelling floors

The primary concern with using thinset for levelling is shrinkage. Thinset can develop micro-cracks and weaken the mortar, causing it to pull away from the substrate. This can result in a weakened bond between the tile and the floor. Thinset is designed to function within a specific thickness range, typically between 3/32 and 1/4 inches. Using it for levelling can result in a reduced thickness for the tile installation, impacting the overall strength and durability of the flooring.

Additionally, using thinset outside of its intended range can void the manufacturer's warranty. There are specific levelling mortars and self-levelling compounds designed for this purpose, which provide a more suitable solution for levelling floors. These products are formulated to reduce shrinkage and ensure a strong bond.

Another drawback of using thinset for levelling is the difficulty in achieving a smooth finish. Thinset is sticky and challenging to smooth out with a trowel. It requires additional steps, such as using a 'rub-stone' to grind the thinset smooth and vacuuming the dust before proceeding with tiling.

Furthermore, thinset may not be suitable for all types of flooring. For example, vinyl tile is too flexible and can be susceptible to showing unevenness when installed over thinset. In contrast, self-levelling cement provides a smoother and flatter surface, making it a better option for vinyl, laminate, and wood flooring.

While thinset can be used for minor adjustments in floor levelling, it is not the ideal choice for significant levelling work. Using products specifically designed for levelling floors will result in a more professional and long-lasting outcome.

A skim coat of thinset can be used to repair old concrete or finish wall and floor surfaces

To use a skim coat of thinset to repair old concrete, start by preparing the surface. Remove any chipping or peeling paint, dirt, or debris. Fix any drainage problems and repair cracks in the concrete. Once the surface is clean and level, mix the thinset with water according to the manufacturer's instructions. Apply the thinset to the surface using a trowel or a long-handled squeegee. For vertical surfaces, use a concrete mix specially designed for this purpose, which typically contains additives that aid the bonding process. For horizontal surfaces, you can apply the topcoat using a trowel or a long-handled squeegee and press down to force it into any remaining imperfections.

When using a skim coat of thinset to finish wall surfaces, it is often referred to as skim coating or mudding. This process can be used to repair damaged walls, smooth down intentionally applied wall texture, or cover a popcorn ceiling. Start by preparing the wall by covering areas that will not be skim-coated and removing faceplates from outlets and light switches. Then, mix the drywall compound according to the product instructions. Use a light-body drywall compound, as it is easier to sand smooth. Roll out the compound onto the wall using a paint roller, working in small sections to avoid drying. Use a drywall knife to skim out the compound, applying more pressure to one side to ease out imperfections and leave a low ridge on the other. Let the skim coat dry, then finish with light sanding.

Skim coats of thinset can be an effective way to repair and renew concrete surfaces or finish wall surfaces. By following the proper preparation and application techniques, you can achieve a smooth, durable, and wear-resistant surface.

A skim coat of thinset can be applied to a concrete block to create a smooth finish

To skim coat a concrete block, you will first need to determine the area that requires skim coating. If you are skim coating a concrete floor, you can use a simple mixture of concrete and water to fill in any cracks or level out the surface. If you are skim coating a concrete block wall, you can add a little lime to the mixture to create a stickier compound that adheres more easily to the vertical surface.

When mixing your skim coat, use a low-speed drill to avoid whipping air bubbles into the mixture. Add water in small amounts until you achieve a spreadable consistency that is thicker than peanut butter but not soupy or runny. Allow the mixture to set for several minutes after the initial mix so that the water can fully soak into the concrete, then mix it again before applying.

Before applying the skim coat, prepare the concrete block surface by lightly scraping away any loose cement or other substances. Cover the floor and any remaining furniture with plastic drop cloths to protect them from the skim coating process.

Start applying the skim coat at the top of the concrete block wall, working your way down and across the surface. Use a cement trowel to spread the mixture onto the wall, using the flat side of the trowel to smooth it out. Remove any excess cement with the edge of the trowel in a scraping motion, aiming for an even coat. Allow the skim coat to dry for at least 24 hours before painting or further finishing.

By following these steps, you can apply a skim coat of thinset to a concrete block to create a smooth and refreshed surface.

A skim coat of thinset can be applied to a wall before tiling

When preparing a wall for tiling, the goal is to create a flat, dry, solid, and structurally sound surface that is firmly attached to the wall studs. The wall should have no flexibility or movement that could damage the installed tile and grout. In wet areas, such as shower walls, additional precautions are necessary.

If you are tiling over existing tile, it is essential to ensure that all of the tiles are intact and secure. If there are any loose or cracked tiles, they must be repaired or replaced. If the existing tile is beyond repair, it is recommended to remove the tile and install a piece of wallboard in its place. The wall should then be cleaned with TSP (trisodium phosphate) or an ammonia-based cleaner to remove any grease or oil, ensuring that the tile adhesive will properly secure to the surface.

Before applying a skim coat of thinset, it is crucial to remove any loose paint, wallpaper, or old tile from the wall. Once the wall is clear, check for any defects, such as holes or gouges, and fill them with drywall spackle or joint compound. Sand the wall with medium-grit sandpaper to create a smooth and uniform surface. It is important to note that thinset cannot be sanded, so the finish will depend on how well it is applied with a knife.

When using thinset as a skim coat, it is essential to mix it with water to achieve the proper consistency. The mixture should be spreadable but not soupy or runny. Let the mixture set for several minutes after mixing, and then mix it again before applying it to the wall. If you are skim coating walls, you can add a small amount of lime to the mixture to create a stickier compound that adheres better to the surface.

While thinset can be used as a skim coat in some cases, it is important to consider the limitations and potential issues. Thinset is not designed to be used for significant build-up, and it may shrink or crack if applied too thickly. Additionally, it is crucial to follow the manufacturer's instructions and recommendations for the specific thinset product you are using.

Thinset is grittier and sandier than other floor levelers

Thinset is a type of mortar used for tiling. It is not designed for levelling, but it can be used for minor levelling corrections. The maximum recommended thickness for thinset is around 3/8 inches to 1/2 inches. If you need to level a floor, it is recommended to use a self-levelling compound instead of thinset.

Thinset is grittier and sandier than other floor levellers because of its composition. Thinset is made up of Portland cement, sand, and water. The sand in thinset is what gives it its gritty and sandy texture. Other floor levellers, such as self-levelling compounds, may have a finer texture or use different materials, resulting in a smoother finish.

The grittiness and sandiness of thinset can make it more challenging to work with. It requires proper mixing and can be time-consuming to sand and level. If not mixed correctly, it could crumble. Additionally, the thickness of the thinset layer can affect its stability, and it may need to be compressed with tile on top to prevent air bubbles from forming.

To achieve a smooth and level floor, it is generally recommended to use a self-levelling compound or a different type of levelling product specifically designed for that purpose. These products are designed to self-level and create a smooth, flat surface without the need for additional sanding or grinding. However, thinset can be used for minor levelling corrections if necessary, as long as the thickness does not exceed the recommended limit.

Frequently asked questions