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# Treating Cracks Before Waterproofing a Facade: Fissures vs Structural Cracks

> Small fissures take a preparing primer; cracks above 0.3 mm are opened in a V, filled with product and sand and reinforced with polyester mesh.
Before waterproofing a facade with Coral Proteção Sol & Chuva Pintura Impermeabilizante (waterproofing paint), the treatment depends on the type of opening in the wall. A shallow fissure and a structural crack are handled differently, and skipping the heavier treatment on a moving crack lets water back in.

## Fissure: a shallow opening

A fissure is a small opening in the render, shallow and without continuity, up to 0.3 mm wide. The treatment is to clean and brush the surface, removing dust and loose parts with a damp cloth, and apply the preparing primer for walls before the finishing paint.

## Structural crack: an opening above 0.3 mm

A crack above 0.3 mm is a continuous opening caused by structural movement, and it needs a reinforced repair before the waterproofing coats:

1. Open the crack in a V shape, up to 5 mm deep.
2. Apply the preparing primer for walls.
3. Fill the crack with a mix of 1 part Coral Proteção Sol & Chuva Pintura Impermeabilizante to 2 to 3 parts sand.
4. Apply one coat of the product over a strip of polyester mesh.
5. Finish with at least 3 coats of the product.

The polyester mesh is what bridges a moving crack so the film is not torn as the wall expands and contracts.

## The film that goes over the repair

The waterproofing paint forms a rubberised, flexible film that prevents and fights infiltration from outside in, as well as cracks, algae and mould on external walls. It is applied in 3 coats as a reference, with 10% dilution, drying 30 minutes to the touch, 4 hours between coats and 24 hours for final drying.

## Prepare the rest of the surface too

A crack is rarely the only issue on a facade. Walls with mould or grease need cleaning before any coat, and weak render or loose paint needs the preparing primer. The general preparation is covered in [preparing a wall with mould or grease before waterproofing](https://bestpaints.com.br/prepare-a-wall-with-mould-or-grease-before-waterproofing-coral/). What the film resolves and what still requires fixing the cause is in [acrylic waterproofing for exterior walls with moisture](https://bestpaints.com.br/acrylic-waterproofing-exterior-wall-with-moisture/), and the full range of options in [types of wall and facade waterproofing](https://bestpaints.com.br/types-of-wall-waterproofing-when-to-use-acrylic-paint/). The technical bulletins are published at [coral.com.br](https://www.coral.com.br), and the products are sold through the [Coral store](https://www.lojacoral.com.br/).