DamSeal - Bituminous Dam Sealing Systems

Site preparation -Shape and compact the dam floor and embankments to a smooth finish, taking out any stones or sharp objects that could rupture the lining under water pressure. Where the surface is coarse, blind it with a sand cushion layer. Remove all reeds, grass and organic material, which would otherwise decompose and form gas bubbles beneath the membrane, then spread a slow-release granular herbicide over the entire surface. The dam floor should sit above the surrounding water table; where it does not, install a subsurface drainage network falling to the lowest point before lining begins.

Anchor trench and fabric placement - Excavate a 300 × 300 mm anchor trench around the full perimeter. Start with the end of a roll in the trench at the midpoint of the embankment, unroll down the slope, across the floor and up the opposite side, cutting off in the opposite trench. Lay the fabric furry side down and allow it to drape loosely rather than pulling it tight. Overlap each successive width by 200 mm, working out creases as you go. Irregular shapes are accommodated by cutting sections to suit and jointing them the same way.

Jointing - Turn back the upper overlap and weight it with bricks or stones. Apply a heavy undiluted coat of sealing compound to the lower overlap, immediately fold the upper overlap back down and press firmly, then broom a diluted coat over the whole joint. Allow joints to set for approximately four hours before coating the main surface. Secure all free edges overnight - wind damage to an uncoated lining is the most common avoidable loss on site.

Coating - First coat: sealing compound diluted 50/50 with water at 1.6 ℓ/m², applied by dipping soft brooms and spreading. Do not pour the diluted product onto the fabric, as it runs straight through. Allow three to four hours to dry. Second coat: undiluted at 1 ℓ/m², which may be poured ahead of the broom and spread. Allow approximately four hours. Third and final coat: undiluted at 1 ℓ/m². Total consumption is approximately 3.6 ℓ/m² excluding joint sealing.

Curing and conditions - Allow 72 hours cure before filling with water. Lay a 250 micron polyethylene underlay over any damp or wet areas beforehand, since free moisture prevents the emulsion from breaking properly. In hot conditions work early morning or late afternoon, particularly for the final coat, when the second coat may be too tacky to walk on during the middle of the day. Keep dust and dirt off the lining, and rinse brooms regularly, storing them in water during any break in work.