Parging a block wall is a simple process that can dramatically improve the aesthetic appeal and durability of an exterior concrete block foundation. Parging refers to applying a cement-based stucco or plaster onto a wall surface. The purpose of parging a block wall is to hide and even out the uneven textures and mortar joints of the concrete blocks below. It creates a smooth, uniform appearance while also protecting and sealing the blocks from moisture damage.
Materials And Tools Required
A proper amount of material proportionally mixed together with the right type of tools can help in a smooth process.
- Parging Mix: Pre-blended mixes work best for beginners, but you can also mix your own using masonry cement, sand, and water.
- Trowel: Use a 12-16 inch margin trowel to apply the parging mix.
- Margin Guide: A 2×4 or straightedge helps create straight corners and edges.
- Scrub Brush: Used to prep the block surface prior to application.
- Bucket And Hose: For mixing and keeping tools moist while working.
- Brush (Optional): Use a soft bristle brush for knocking down peaks.
- Joint Tool (Optional): Used for shaping and smoothing the parging over mortar joints.
Surface Preparation
Thorough surface preparation of the block wall is crucial before applying any parging material. It all begins with scrubbing the entire surface area clean using a stiff brush to remove any dirt, grease, algae, mildew, or other debris that may be present. Particular attention should be paid to all mortar joints, ensuring any loose or crumbling mortar is scraped away.
Once scrubbed, rinse the entire surface with water to remove cleaning residue and allow it to fully dry. Only a clean, dry surface will provide adequate bonding for the parging to adhere properly. Proper preparation at this stage will save time and frustration later during application and lead to a long-lasting, professional-looking result.
Mixing The Parging Mix
For a pre-blended mix, simply add clean water a little at a time into a bucket and mix with a trowel or paddle until fully dissolved and reaches a thick, peanut butter-like consistency. Consistency is important – too thin and it will run, too thick, and it’s hard to apply. For a scratch coat, mix slightly thicker than a finished coat.
Applying The First Coat
To apply the first coat, also known as the scratch coat, fill the margin trowel with a small scoop of parging mix from the mixing bucket. With the trowel held nearly flat against the wall, apply the mix using broad, horizontal strokes to create a relatively smooth and even layer about 1/4 to 3/8 inches thick across the entire surface.
It’s important not to overwork the coat and leave any unsmoothed sections, as subsequent coats will fix these. For best results, work from the bottom up using the margin guide alongside to ensure straight lines and an even application. Once complete, inspect for any thin spots and add a bit more material as needed before the coat dries.
Applying The Second Coat
The second or finish coat should be applied only after the first coat is completely dry, which typically takes 24 hours. This final layer helps smooth out any imperfections left from the initial application. Scoop another small amount of parging mix onto the trowel and apply with thinner, overlapping strokes across the entire surface to completely cover the scratch coat.
While the second coat is still wet, use a brush or the back of the trowel to skim it, knocking down any bumps or textures to create a perfectly smooth plane. Pay close attention to smoothing around any moldings, corners, or protrusions. Once flat and even, allow the second coat to fully cure before proceeding with any protective sealers or paint if desired.
Curing The Parging
Curing the parging properly is a critical step to allow it to reach full strength and durability. For at least seven days after the final coat is applied, keep the surface continuously moist by misting it with a water bottle several times a day. This promotes a full chemical reaction and prevents premature drying and cracking.
Also, protect the area from direct sun, wind, rain, or frost, which can cause cracking or damage during the curing phase. Covering with plastic sheeting secured with tape can help maintain moisture. Correct curing allows the parging to fully harden so it can withstand weathering and withstand cracking or peeling in the future. Neglecting this stage can compromise the longevity of the finished surface.
Painting The Parged Wall (Optional)
For a seamless, finished appearance, consider painting the parging once fully cured.100% acrylic-based, water-based masonry paint designed for concrete/stucco is best. Apply two thin coats with a wide brush using long, even strokes. Paint helps protect the surface while blending in the parged area.
Troubleshooting Common Issues
- Cracks: These occur when the parging dries out too quickly due to improper curing. It prevents the concrete from fully curing and strengthening.
- Peeling: Caused by insufficient bonding to the substrate, usually due to inadequate surface preparation like a dirty or loose surface.
- Dusting: A powdery, chalky finish indicates the mix was too dry during application. More water is needed for proper hydration.
- Blisters: Small bubbles under the surface usually mean moisture was trapped between coats. Vent circulation holes to allow drying or slash and smooth out bubbles.
- Uneven Texture: Applying subsequent coats before the prior is cured leads to an inconsistent, bumpy surface. Allow full drying between each coat.
- Thin Spots: Areas that appear slightly recessed likely weren’t coated thickly enough initially. Fill low spots by hand with additional material.
- Crumbling: Exposing new parging to moisture, frost, or weather too soon results in damage before it can cure fully. Protect during curing.
Conclusion
By taking the time to carefully prepare, apply, and cure the parging in the correct manner, block walls can be beautifully transformed. Parging provides a cost-effective, long-lasting solution compared to other wall surfacing options. It improves the curb appeal of a home’s foundation and can increase its resale value by providing a finished look without the higher cost of removing and replacing blocks. Homeowners will enjoy the improved look and protection of this timeless masonry treatment for their home’s foundation.
