Waterproofing Roofs, Basements, Below Ground Structures, Bridges and Other Structures

Polyurethane (PU) waterproofing

Holderchem PU waterproofing of flat roof products, whether used during the construction of a building or thereafter, show full water tightness characteristics, special resistance to weathering, UV resistance, reliability and durability, elasticity, and good adhesion to concrete, cement, mortar, terrazzo, and other substrates.

The Holderchem PU system is a highly flexible solution that easily resolves issues arising from the sealing of difficult points such as corners, edges, jointing of flat roof outlets particularly if not with good slopes. A good application of the product creates a continuous, elastic membrane with excellent mechanical strength, without joints or seams, and is used for both total sealings of flat roof surfaces and for local waterproofing of cracks.

It is important to ensure that prior to application, the substrate is dry, with a moisture content of less than 4%, and free from loose particles, dust, grease, etc. To dehumidify, blow cold air at high speed, or warm air, across the floor, which will increase water evaporation into the dehumidifier. The time it takes to dry will depend upon how damp the concrete is. Moisture readings should be taken to ascertain when it is dry.

Local repairs of roof concrete or cement elements can be carried out using the polymer-modified repair products Batimix Mortar 603 or the polymer fiber reinforced polymer product Batimix Mortar 620. Cracks wider than 1 mm on the substrate have to be initially primed locally and sealed with the Holderchem polyurethane which can be supplied in two colors, white and gray, as Batimix PU 350. In the case of cracks < 1 mm, no sealing is required. In the event consulting engineers and contractors feel the need to create an inclination layer, it can be done using the ready-to-use, cementitious floor screed Batimix Mortar 741.

Promptly upon the material used for smoothing the substrate drying, apply as a primer, the one-component polyurethane product, Batimix PU Roof Coating 451 after stirring it, albeit only slightly to avoid air entrapment, until it becomes homogeneous. It is important it is applied in an even manner across the clean and dry concrete surface, with a brush, roller, or spraying device.

Apply over the edges, pipe joints, metal and ventilation elements joints, and at the intersection of horizontal and vertical surfaces a coat embedding polyester fleece. Apply another layer of the same PU product by brush or roller while the surface is still tacky within the time frame specified in the product application guideline. Apply a second coat crosswise and a third coat where reinforcements have been used, again within the timeframe between one layer and next specified on the technical datasheet.

Alternatively, apply a second coat and also crosswise of Batimix PU Coating 460 G2C for a top coat to achieve a flooring with sturdier characteristics.

Holderchem PU coatings may be applied when the temperature of the substrate is not lower than 5°C and not higher than 35ºC. It should be noted that low temperatures retard curing while high temperatures accelerate curing. High values of humidity may affect the final finish of the membrane.

As a very rough estimate, the total consumption of polyurethane, waterproofing liquid membrane for a primer, and two top coatings of the single component product hovers around 2.0-2.5 kg/m², depending on the substrate.

Bituminous waterproofing membranes

Bituminous waterproofing membranes form a thin layer, generally 2 to 4 mm thick of watertight material over a surface. They are laid above the structural slab and below the finish tiles. They are designed to be strong, flexible, tear-resistant, and elastic so they can stretch to cover cracks and also move with the building. They are laid in a way that prevents at all cost puddles of water from forming, to avoid water seeping in the structural slab. Membranes exposed to the sun should be UV resistant.

Bituminous membranes are often selected for waterproofing roofs, basements, below ground structures, bridges, and other structures. BATIMIX bituminous sheet membrane waterproofing products include both APP and SBS torch applied products. Details for each product are contained in the individual Product Data Sheet.  APP - Atactic Polypropylene, which is used to improve the properties of the distilled bitumen basis, provides heat and UV resistance that may be required in certain climates. SBS - Styrene Butadiene Styrene, which is also used to improve bitumen, is more appropriate in cold temperatures but not recommended for applications where UV exposure is anticipated. Membranes are glued to substrates with a hot tar-based adhesive using blowtorches.  Sheets overlap about 10 cm and may also be joined by melting them. Polyester backed fiberglass-reinforced modified bituminous membranes are normally installed as a base layer in multilayer systems. They are suited for application on heat-sensitive substrates, such as timber and heat insulation materials. They can be applied as a base layer on rough and uneven surfaces or over sound rubber, PVC, bitumen acrylic, or polyurethane membranes. Bituminous membranes can last longer than the often manufacturer stated 10 year’s lifetime.

Liquid applied membranes, which are delivered to customers in liquid form, are either sprayed or brush-applied on the surface. The liquid cures in the air to form a seamless, joint-free membrane. Although preferred because of the joint free characteristic that may be more readily achieved than with sheet-based membranes, control of the thickness is harder. Thickness is determined by the amount of bituminous liquid used per unit area. To avoid cold joints, contractors will attempt to apply the product as quickly as possible to finish up the area on the same day. Cold joints can be done by overlapping a new membrane over an old one. If a concrete screed is to be applied over a waterproofing membrane, the membrane is made rough by throwing a thin layer of sand by hand over the wet membrane; the sand sticks to the membrane providing a rough surface the concrete can adhere to. Liquid membranes are definitely preferred when dealing with complex shapes or for waterproofing the junction of a column and beam.

Membranes must be UV resistant if exposed to sunlight to avoid degradation. They must have a high elongation factor to stretch over cracks. They must not tear even if a reasonable force is exerted. They must withstand wear and tear.  They must be chemically stable and must in the case of structures that will come into contact with food be food-safe.