I need the waterproofing done as soon as possible after concrete pouring.
How can I reduce the time delay for concrete curing?
It is normal practice for concrete to cure for 28 days ( less in summer) before applying a membrane. This is to ensure that there is little or no free moisture in the concrete that may cause blistering and / or loss of adhesion.
Naturally builders want to reduce this delay and frequently query this restriction. Whether the curing time can be shortened depends on the membrane to be used and the application as well as the ambient temperature.
Solvent based urethanes are more sensitive to concrete that is not fully cured and normally require the full curing time. This can however be reduced if the substrate is primed with a water based epoxy (WBE), especially those brands that will still work on a damp surface. The concrete should certainly "feel" fairly dry and pass a rubber mat test as repairs to blisters are a difficulty and often result in delamination if not done properly and look unsightly.
Much depends on the application. Obviously membrane roofs are more critical than areas that are subsequently covered or back filled, while sheet membranes are much safer than liquid applied. Torch on SBS is most tolerant of inadequately cured concrete because of its superior adhesion, easy of repair and being strongly reinforced, the odd blister has no effect on the water tightness of the system. When only a few days curing is permissable, vent sheets and vents should be used and all upturns mechanically fixed.
The primer normally used for SBS is solvent based which requires a dry and fully cured substrate ("oil and water do not mix") but WBEs may be used if the concrete is damp. Since primers for SBS are not normally applied to plywood,
surface ground concrete or blockwork, any surface moisture will be flashed off by the hot propane gas flame moments before the molten surface of the roll adheres to the substrate.
Reinforced concrete walls are more of a problem than concrete because the block is so porous and absorbs water like a sponge. Protective measures include
cementing the shrinkage of the core, so there is no mini dam at the top
micky pinning the SBS at the overlaps if drop height exceeds 1.8m,
fixing mechanically where the membrane is terminated with a Z section pressure seal,
back filling as each
stage is membraned and protected with protection board