The reservoir roof was allowing water ingress into the water storage area below, presenting a contamination risk. Upon exposure of the roof it was found that a previously installed Methyl Methacrylate (MMA) waterproofing membrane had been poorly applied by another contractor.
We suspected that the MMA had been either improperly mixed, over applied or exposed to moisture prematurely. This resulted in the membrane not forming correctly, creating a sticky ‘chewing gum’ like substance.
We proposed the application of a WRAS approved polyurea waterproofing membrane from SPI Performance Coatings.
Following the removal of failed waterproofing membrane by others a weatherproof enclosure was erected to enable heating and dehumidification to be established to ensure strict adherence to the Instructions for Use (IFU).
During the removal of the failed waterproofing membrane a poorly filled drainage channel and corroded expansion joint was exposed that would require further detailing.
Initially all surfaces to be coated were prepared by method of vacuum controlled diamond grinding to ensure a suitable surface for the new polyurea waterproofing membrane to adhere to. Our clients process is that concrete reservoirs must pass a flood test prior to the application of the waterproofing membrane and that the first layer must be Regulation 31 approved.
To achieve this the concrete was treated using Markham Global Aquron 2000. This material works by penetrating up to 200mm into the concrete and forms a hydrogel, that fills the porosity of the concrete.
A regulation 31 approved fairing coat was applied to the concrete upstands to make these good. The exposed steel expansion joint was prepared to SA2.5 as per ISO 8501-1 in line with the manufacturers instruction for use. The blast profile was checked and recorded using a surface profile needle gauge to ensure optimum adhesion to the steel.
This expansion joint, cracks and other details were then sealed using Materbuilders Masterseal 930/933 waterproofing bandage system.
Following a successful flood test anchor rebates were cut to terminate the new polyurea waterproofing membrane into. All concrete surfaces were primed using SPI EP200 applied in two coats as per the manufacturers IFU. The second coat was blinded with quartz aggregate to provide an excellent mechanical anchor for the subsequent polyurea membrane.
Double priming is essential when coating concrete surfaces with polyurea to properly seal the concrete in order to minimise pin holing in the polyurea waterproofing membrane. Because polyurea membranes are applied at approximately 80 degrees centigrade and polyurea exotherms upwards of 100 degrees centigrade once mixed in the spray gun. This heating effect on the substrate will heat any entrapped air in the porous, which if not properly sealed by double priming will heat and expand causing pin holing.
Excess quartz was removed using soft brooms and vacuums prior to the application of SPI Polydeck WRAS pure polyurea. This was spray applied to a nominal thickness of 2mm, with intricate areas first being ‘cut in’ prior to the application of the entire membrane.
All of our applicators are trained by the Polyurea Development Association to ensure that the have the necessary knowledge to apply this highly technical material correctly.
Because polyurea waterproofing membranes are spray applied they seamlessly waterproof structures such as the reservoir roof, without welds or seams like roll applied membranes, which are always a weakness. SPI Polydeck WRAS can elongate nearly 400%, meaning that any movement or cracking in the structure should be accommodated without allowing water ingress into the reservoir below.
As part of our standard quality assurance the polyurea membrane was checked for porosity using a DC holiday spark tester and any pin holes marked prior to touching in using the same material.
Finally all termination points were sealed using a Regulation 31 approved sealant as per best practice when applying polyurea coatings.
To ensure compliance with all of the various manufacturers technical data sheets and instructions for use heating and dehumidification was employed throughout the works. This was test during application using Defelsko Positector 6000s and during cure using temperature logging equipment.
