Film Faced Plywood Formwork for Coastal Jetty Deck Slab and Sea Wall

A harbour upgrade on an exposed stretch of coast, where a new fishing jetty was built alongside a repaired sea wall. The cast-in-place concrete scope covered the sea wall running behind the quay, the deck slab and edge beams of the jetty, the apron wall at the ramp, and a small pump chamber at the landward end. The wall faces that stayed visible from the water were specified as fair-faced, and the deck pours had to be finished inside the working windows the tide allowed rather than at times the contractor would have chosen.

Three things shaped the formwork choice. The site sat in salt air with humidity that rarely dropped, so panel edges that were not sealed drew moisture, swelled and printed a raised line on the concrete face, while cheaper glue lines failed outright after a few wet and dry cycles. Wind was the second problem: the sea wall panels stood more than three metres high before the pour, on a shoreline with nothing to break the gusts, and stripped sheets stacked between pours had to be ballasted or they lifted. The third was the tide. Deck and apron pours were placed between tides, stripped as soon as the concrete took its set, and the panels cleaned and re-set for the next section inside the same window, which left no time for board repairs or for re-cutting swollen edges. The apron wall also curved on plan, so its panels had to be cut to the drawing rather than assembled from standard units.

The contractor formed the walls, beams and slab soffits with film faced plywood. The panels are built on a combi or eucalyptus core with a water and boil proof phenolic glue line and a film pressed to both faces, supplied at 1220 x 2440 mm in 15 mm and 18 mm thickness and cuttable to the radii on the drawings. The large sheet keeps the number of joint lines down on a sea wall face that was left as struck concrete, and a single sheet weighs between 17 kg and 31 kg depending on core and thickness, so two workers handle it without lifting gear. Every cut edge was painted with waterproof edge sealer in the same shift, which is what stopped the salt air from reaching the core.

The sea wall was backed with steel walers and tied through with tie rods and wing nuts, with inclined braces holding the free-standing panels against the coastal wind before the pour. Deck edge beams used beam clamps, adjusted and closed by one man working from the deck, and the slab soffit and beams were carried on adjustable steel props set out ahead of the pour. On the apron, sheets were cut to the drawing radius and bolted through a drilled line rather than tied, which suited a wall curving on plan. The film releases the concrete without a heavy release agent coat, so the visible faces came away clean and the sheets were washed with water and a soft brush while still wet, then stacked flat on bearers under cover with the faces separated.

Coastal jetty and sea wall formwork configuration:

The panels came through the season with their edges intact. Because the cut ends were sealed as they were made, the swelling that had spoilt earlier board work never appeared, and the sea wall faces were accepted as struck concrete with a single joint line where the sheets met. Stripping inside the tide window worked because the film released cleanly and a sheet only needed a wash and a flat stack before it went back on, not a repair. The better grade sheets held their film through the wet and dry cycling, and the lighter trial boards used on the first section of apron wall were pulled out of the rotation after a few pours.

Wind handling was the point the site team raised most often. Bracing the panels and ballasting the stripped stacks cost time at the start of each section, but it kept the formwork on the deck when the gusts came through, and the supervisor's view was that flat stacked sheets were quicker to sort and re-set than the framed panels used on another section of the quay. The client's engineer noted that the wall faces needed no filling of edge marks, which had been a recurring complaint on the earlier apron work.

Buyers sourcing panels for coastal, port and marine work are welcome to send their sheet sizes, thickness and quantities for a supply review and a project specific quotation, including the anti-slip and marine duty grades from the same panel family.