This is a version of the basic info sheet I provide for teaching sessions focusing on ‘shaping’ materials for model-making and small-scale making. It represents a small selection chosen for their availability, versatility and ease of use.
Prices shown are from May 2017 and adjusted to include VAT. Full addresses of suppliers can be found in the ‘Suppliers’ section.
Soft polyurethane foam (Kapa-line foamboard)
This special type of foamboard is available in 3, 5 and 10mm thicknesses. The paper layer can easily be stripped off to use the rigid foam core for building shapes or creating surfaces. Easy, smooth carving and sanding. Use any glue (PU foam is not damaged by solvents) or double-sided tape for assembling. Most foamboards from Kapa (e.g. Kapa-graph, etc.) can be used in this way, but standard polystyrene-filled foamboard cannot. Obtainable 4D modelshop, greatart.co.uk, London Graphic Centre Price Kapa-line 70x100cm – 3mm £9.10, 5mm £10.30, 10mm £12.70 (4D)
Only for Kapa-line (polyurethane foam), and ensure fully ventilated workplace, use good respirator masks or work outside. GP (general purpose) polyester resin from Tiranti £9.78 per 1kg, catalyst £2.42 per 50g. Mix in very small (10g) amounts and catalyse at 2% (i.e. 4-5 drops per 10g of resin). Coat using soft brush, watch out for hair loss .. the brush, that is! Working time is c. 14mins in warm room, to 18mins in cooler room. Average setting time 20mins, ready for light sanding after a few hours. Forms are better left outside to set if conditions are relatively dry.
The resin toughens the surface of the otherwise fragile polyurethane foam considerably! It’s also without any loss of detail because the resin infiltrates a little into the surface of the foam, combining with this to form a shell. The resin can also be mixed with a little pigment. A thin polyurethane resin, such as Fast Cast from Tomps, can also be used and is safer to use indoors, but has much less working time and is not as strong.
Paverpol is a tough Pva-like formulation from the US which is designed to be painted onto fabrics, giving them a hard and rigid surface. It works very well on the surface of foam, with a similar effect. Best to apply a diluted coat first if the foam surface will absorb, then 1-2 straight coats. There are no health issues, but it doesn’t give as strong a surface as resin. There are unfilled and pigment-filled versions available. Obtainable www.paverpol-uk.co.uk Price c. £15.95 per kg (500g also available). Delivery used to be £5.95 flat rate.
Finer version of common ‘polystyrene’, usually light blue in colour. Made for roof and wall insulation. Can be easily carved and finely sanded. Caution: superglue, UHU or most spray paints will dissolve surface. ‘UHU Por’ or polyurethane ‘Gorilla Glue’ can be used to bond, or carefully placed strips of double-sided tape. Most commonly available in sheets of 25mm or 50mm thickness. Obtainable 4D modelshop (different types and thicknesses), some builders suppliers, panelsystems.co.uk, hindleys.com Price e.g. sheet 25x600x1250mm £13.50 (4D). Price has remained the same for a number of years!
Depron foam sheet
Also a thin polystyrene foam sheet but more rigid and available thinner (2,3,6 and 9mm in white and grey). Without paper covering, most popular with aero-modellers. Must be glued with ‘foam friendly’ adhesive as above. Obtainable depronfoam.com Price Used to be very cheap and for single sheets, but as from 2017 only in bulk £40-£120 per box.
A flexible foam, mainly in sheet form, available in a wide variety of colours, densities and thicknesses. Can be firmly bonded together with EvoStik Impact adhesive, Dunlop Thixofix or (in some cases) superglue. Can be bent more with heat. Easy to cut with a sharp knife, cannot normally be sanded though. Obtainable Pentonville Rubber Co, 4D, some hobby or craft shops. Price varies
Supplied in granules which can be easily softened/fused in hot water (62 degrees C) or with a heat-gun (even with a hair dryer) to form a malleable mass which then hardens as tough as nylon (according to suppliers) when cool. Can be repeatedly re-heated and re-used. Shaping achieved more by moulding than modelling as this is difficult, whereas it presses very well into forms. Obtainable Maplin, mindsetsonline, 4D Price £17.94 per kg (mindsets); £28.50 per kg (4D); £22.99 per 500g Maplin
Fragile as constructional material, better suited in combination (i.e. as cladding over a more solid core) or as easy means of making wood shapes which are not structural. Rough sanding will create fibrous surface, wire brushing will increase this effect. Quite difficult to sand down ‘against’ the grain, much easier along it. Obtainable 4D, most art or hobby shops Price varies, but usually cheap e.g. 4D £4.20 for a 9.5x100x915mm sheet