The two new soft pits required a waterproofing solution to prevent water ingress into the bridge area beneath. Originally a fibreglass lining was enquired about, however we highlighted potential issues with this such as the negative interaction between polyester resins and the polystyrene fill material. Fibreglass waterproofing systems are also generally rigid, which given the mixed construction might present a risk of cracking and subsequent water egress.
We instead proposed the application of a seamless spray applied polyurea membrane from Sika Masterbuilders. When we attended site to survey however it became apparent that the protruding cable ducts would make the proper application of a sprayed polyurea waterproofing membrane near impossible, given that it would not be possible to have the spray gun positioned anywhere close to perpendicular to the surface as per correct spraying practice.
The consequence of this would be that it would be highly probable that there would be misses and shadowing, resulting in an incomplete polyurea membrane application.
Fortunately within the Sika Masterbuilders product line they offer an unusual hand applied polyurea membrane in the form of MasterSeal M 686 which is specifically designed for intricate detailing applications.
Initially upon arrival on site any protruding polyurethane adhesive was cut flush and concrete sections prepared by method of vacuum controlled diamond grinding. Large defects and areas of damage were made good using a polyurethane jointing compound.
Prior to coating application commencing all surfaces were vacuumed clean to prevent dust and debris disturbing the bond between the polyurethane primer and the substrate.
As part of our standard waterproofing and polyurea application quality assurance the climatic conditions were monitored and recorded at the beginning and during each shift to ensure that the manufacturer’s recommendations were strictly adhered to.
All surfaces were then primed using Sikagard P770 damp tolerant polyurethane primer applied by method of brush and roller.
Any defects in the substrate highlighted by priming were again made good using a polyurethane jointing compound between coats, prior to the application of a second coat of Sikagard P770 as per the manufacturer’s recommendations.
Any loose or unbound quartz was removed using soft brooms and vacuums prior to the application of the hand placed polyurea material.
During application as part of our quality assurance wet film thicknesses were closely monitored – something that is unusual when applying polyurea materials as the conventional spray applied variants react too quickly for this to be possible.
The cured lining was checked for pin holing visually and using a DC Holiday spark tester, with any pin holes identified marked prior to making good using the same hand applied polyurea material.
Finally previously cut termination chases were filled using a polyurethane jointing compound.
