Waterproof coating & membrane

What is waterproof coating & membrane

To prevent the entry of water through seepage or moisture damp inside an RCC structure waterproofing is used. Generally, after completion of construction work of a structure waterproofing work is carried out. The process of waterproofing can be carried out in many ways. However, it can be broadly classified as: 

• Coating – By the use of Polyurea coating as a waterproofing membrane.
•  Membrane - By using the waterproofing membrane.

Waterproofing coat (PU):

• Surface Preparation – The surface is inspected for any structural defects such as cracks, undulations, and honeycombs if found it shall be rectified before coating. Right angle junctions between slab & perpendicular wall/column shall be treated by coving the junction (75mm x 75mm generally) & filling it with a polymer-modified mortar. The surface shall be free from dust, loose materials, cracks & in saturated surface dry (SSD) condition before the application of a waterproofing chemical.

Crack repairs: Grooves filled with PMM

•  Priming - The surface in SSD condition shall be primed, in cases where there are deep undulation & can affect the waterproofing coating shall be repaired by mixing silica floors with primer to give the primer a body by which it can be filled. Not all waterproofing coating requires primer applications.
• Waterproof coating – The chemical is generally in liquid form & has to be sprayed mechanically or brushed manually depending upon the chemical & area of application. Polyurea coating has to be done by spraying by special machines that mix the hardener & coating just before spraying as it sets within minutes. Usually, 2 coats of these chemicals are provided & in a perpendicular direction for better tensile effect.

PolyUrea waterproofing coat

• Protective Layer – To protect the coating from wear & tear as the coating thickness usually varies between 1.5 – 2 mm, screed concrete is done. A minimum of 15 mm thickness around the drainage point shall be kept for better protection. Integral waterproofing compounds shall be used in the screed to give a better watertight effect.

 Waterproofing Membrane:

• Surface Preparation – The surface is inspected for any structural defects such as cracks, undulations, and honeycombs if found it shall be rectified before coating. Right angle junctions between slab & perpendicular wall/column shall be treated by coving the junction (75mm x 75mm generally) & filling it with a polymer-modified mortar. The surface shall be free from dust, loose materials, cracks & in saturated surface dry (SSD) condition before application of waterproofing chemicals.
• Priming - The surface in SSD condition shall be primed, in this case, the primer has to be applied for better bonding between the waterproofing membrane & concrete surface.
• Waterproof membrane – Typically the membrane comes in 250 mm x 25 m x 3 mm (the thickness depends generally on the area of application along with its purpose). The membrane is to be laid on the concrete surface with an overlap of the membrane not less than 100 mm. The overlapped portion is heated using blow torch for better sealing. The end of the membrane is filled with PU sealant or bituminous sealant.

Waterproofing membrane

• Protective Layer – To protect the coating from wear & tear the membranes are coated with a bituminous coating to extend its life as these membranes are generally followed by screed concrete as in case of waterproofing coatings.