STEP BY STEP
This is the gap to be spanned, across a ‘dropped’ section of this custom Tim Horn laser-cut plywood baseboard. Initially I’d planned a river but, as I hate creating water features, I’ve opted for an overgrown narrow gauge line, which will suit the industrial surroundings.
Having worked out the preferred height and width of the bridge, parts were cut for each abutment, each consisting of two sides and an outer face. Having marked them out on a sheet of 5mm thick foamboard, they were cut with a sharp scalpel and steel rule.
Additionally, pairs of internal corner brackets were cut from the same foam, using a set square to ensure the mating faces are exactly 90º. When cutting foamboard, always use a sharp blade and cut using several passes, ensuring the knife is held vertically.
Square edges are important for strong, square corner joints. Glue up the abutment structures with a Pva-type adhesive. I used Speed Bond, as it dries more rapidly. Check the angles, add the internal strengthening brackets and add magnetic clamps for extra security.
The abutments were left to cure before the clamps were removed. A roadway base was cut from foamboard to match the width of the abutments, and the exact span discerned. Trim Peco’s plate girder sides to length.
The plate girders were cut down to the required length with a razor saw, removing the two outer panels from each end. I cut just outside the raised upright of the end panel, using a flat file to trim the parts to their final size.
After tidying the edges of the plate girder sides, they were used to measure and cut recesses in the foamboard roadway to form a snug fit. The bridge span and centre line were drawn onto the roadway for easy reference.
The roadway was glued to the abutments, using the span reference lines as a guide. Small weights acted as clamps while the glue dried. With the girders temporarily in place, a set of pilasters were cut and installed.
The foamboard structure was to be clad in Wills coarse stone sheets. These moulded plastic sheets need tidying of excess material along each edge, using a broad, flat file, while checking that all four corners are square.
Having marked out the required dimensions of each overlay, a trimming knife was loaded with a new blade and several cuts were made, working through the plastic. Don’t try cutting in one pass, or the knife will wander off course.
The cut edges of the plastic may need a quick dressing with a flat file to remove any burrs. The recesses for the girders were marked out onto the abutment side wall overlays, then cut carefully with the knife.
Pairs of Wills cornerstones were glued up at right angles before installation. These will act as guides for the wall overlays. The cornerstones need to be staggered when glueing up, and the odd blocks trimmed from each end.
While bonding the stone overlays to the foamboard, the Wills cornerstones are held in place, ensuring a perfect gap at the external corners of the abutments. The wall overlays were bonded with Bostik and clamped.
When the wall overlays had cured, the cornerstone strips were cut to the required length and then fitted permanently, using a liquid poly cement, bonding them to the Wills sheets rather than the foamboard.
Some gaps will invariably appear, which will need to be filled. I used Mr Dissolved Putty (www.scalemodelshop.co.uk), which is perfect for smaller gaps. Apply with a small brush or a cocktail stick/toothpick.
Stone overlays were also cut and fitted onto the pilasters, clamping in place while the glue cured. Again, any gaps can be filled with putty. Styrene strip was added to act as a decorative plinth, and any gaps filled with Mr Dissolved Putty.
When the putty and filler was fully cured, needle files and abrasive pads were employed to tidy up the surfaces, especially the edges of the cornerstones.
Recessed mortar courses can be reinstated with a profile cutting tool, drawn along gently, using the remains of existing courses as a guide. One or two passes should be sufficient. Use a stiff brush to clear away any debris.
A set of large cap stones for the pilasters were cut from rectangles of the 5mm foamboard, carving the upper surface into a chamfered profile with a Stanley knife. The corners were then rounded over slightly. Watch those fingers!
With the cap stones fixed in place with Speed Bond, they were then painted with a coating of the same adhesive. This will seal the exposed foam, preventing future damage, while maintaining a slight surface texture.
After a spray of grey primer, the mortar colour was painted over the whole structure, working into the recessed courses. When dry, the stone colouring was built up with a flat brush, dry-brushing shades over the textured surfaces.
Meanwhile, the Peco girders were held temporarily to a block of wood using double-sided tape, before thin layers of black, grey and red oxide primers were sprayed, aiming for a deliberately patchy appearance.
When the primer was dry, the ‘rust’ began. Deluxe Material’s Scenic Rust kit was used, and work began by brushing the Binder fluid over the girders. I worked on one side of each girder at a time, so they could lay flat while I did so.
After about 30 minutes, the Binder fluid dried to give a very tacky surface, onto which Scenic Rust Powder was brushed, dabbing it into the recesses, ensuring the whole area of each girder panel was covered.
After shaking off any loose Scenic Rust Powder, the Developer fluid was brushed over the surface. Within about six hours, signs of corrosion had started to appear. I then added another coating of Developer fluid.
When I got back to my workshop the next day, the corrosion had developed fully, creating a wonderful array of textures and tones, while the underlying paintwork still showed through in patches.
The process was repeated on the other side of each girder and, when complete, the corrosion effects were sealed with a few light layers of a matt clear coat, sprayed from an aerosol. This also produced a more even, flat sheen.
When the coats were dry, the girders were prepped for peeling paint effects. With a scrap of sponge held with tweezers, masking fluid was dabbed across the surface of the girders, concentrating around the edge of each panel.
The masking fluid was dry within 30 minutes and a generic, dirty grey topcoat was applied by airbrush, using a mix of Tamiya acrylics. Airbrushing is not essential – a topcoat of acrylic or enamel paints could also be applied by brush.
When the paint was dry, the surfaces were scrubbed with a toothbrush, dislodging the masking fluid and causing the finish to peel away. Thus, the rust effects were revealed, showing through below the paintwork.
The effects were pleasingly random and authentic, in terms of colour and texture.
The finished girders were then fixed into the bridge structure using contact adhesive, ensuring that they stood vertically. A few gaps remain to be filled and the paintwork needs touching up in a few areas, but this can wait until the bridge can be installed into the layout.