Creating surfaces with Kapa-line foamboard

There are various different types of ‘Kapa’ brand foamboard. Most of them differ from regular foamboard in that the paper covering can be carefully peeled off to use the soft foam layer beneath. This foam layer can be easily inscribed, carved, sanded, embossed or generally ‘broken down’. The product named ‘Kapa-line’ (with an ivory/beige foam inside) is the best to use for this purpose, available either 3, 5 or 10mm thick. Below, the paper layer needs to be carefully peeled off in strips to avoid damaging the foam surface too much. The foam is polyurethane (different from the polystyrene in standard foamboard) and is stronger, much denser though still soft. It can also be glued well with solvent glues, including superglue, without dissolving. It accepts all paints very well, even thin watercolour, and I’ve used either DecoArt or Rosco acrylic for these examples.

Once the paper has been stripped (on one side or both as one prefers) it is usually not robust enough on its own for larger constructions such as walls. It should be glued to a stronger (card or plastic) backing form. This should be cut out first, including any door and window openings . For a simple rectangular wall the foam can be stripped on one side and glued to the backing form paper side down. Its easier to cut the piece a little bigger and trim it once on the backing. Either permanent spraymount, UHU (applied on both sides as a ‘contact’ adhesive) or a good double-sided tape can be used. If the template backing form is complicated (with doorways and windows) I recommend removing all paper from the foam sheet, gluing as above, trimming close but not quite on the outline and sanding down-‘squaring off’ the edges using a right-angled sanding block as shown below. In fact this particular example was clad piecing together separate strips of foam to achieve square edges around the window and doorway without having to sand afterwards. All that then needed sanding were the outside edges.

Different kinds of brickwork are simple to achieve in the foam. The main tool needed is just a ‘push lead’ pencil (0.5mm best for 1:25 scale work). Brick divisions or ‘mortar lines’ can be inscribed in the foam (horizontal lines first) guided by a ruler and not pushing too firmly with the pencil. It’s best to start with a gentle stroke but this can be followed by a deeper incision if a more pronounced effect is wanted or if one purposely wants to fracture the line a little. I recommend taking the trouble to draw up a small sample of scale brickwork which can then be used to mark spacings. The brickwork template shown represents the ‘Flemish bond’ arrangement of bricks common for most structural walls especially in older buildings. Make sure if you can that the brick arrangement fits in ‘comfortably’ around openings. Vertical spaces between bricks are easiest achieved by pushing with a small screwdriver or a piece of wood you’ve shaved down to a similar shape.

Here I’ve started to make the brickwork look more ruined by ‘scratching’ away with the point of a scalpel. Alternatively a small piece of wood can be used to push single bricks or whole sections in. Once pushed they will stay and will not expand back even with painting. I have crumbled the surface even more by beating it with a small wire brush.

I always paint a thorough basecoat on surfaces first, often a ‘mid’ or average colour, and then achieve most of the final affect through dry brushing on top.

As well as using pencil or wire brush to create effects, I often impress the ends of metal tubes, in this case creating the effect of street cobbles.

A fairly recent discovery of mine was that, if a small wire brush (available from £shops usually in packs of 3) is dragged strongly a few times over the foam surface it gives a texture not unlike heavy, weathered wood. These samples have been basecoated, awaiting their final colours.

Kapa-line foam is not only very impressionable, it will hold that impression. Anything that’s strong enough to press in will create an effect. Here for example I’ve used decorative jewellery ‘findings’ and dental modelling tools to create different patterns.

The thick (10mm) version of Kapa-line foam can also be ideal for building up whole structures, especially if all paper is removed. For the concrete structures in progress below I made the thicker bits by gluing 2 layers together and then breaking down with wire brush and scalpel. All joins were glued using superglue, though this may need a couple of tries because thin superglue will soak into the surface too quickly. If Paverpol (mixed with acrylic or dry pigment to achieve the right colour) is used as a basecoat the surface becomes a lot tougher. These have been given an additional dry brushing in a lighter green/grey but still need the stains and ‘blooms’ of old concrete added.

When layering colours it’s important to keep a record of which, including the order, so that one can repeat the effect if successful. There may be as many as 7 different colours needed to simulate brickwork convincingly.

Where to get it in the UK and abroad

It is unfortunate that Kapa-line foamboard is a relatively rare find in the regular art/craft shops in the UK .. but it is at least available from the leading model-making specialist 4D modelshop  and a number of other suppliers online. For a list of sources in the UK and a comparison of current prices see my page Updated sources/prices of specific materials which you will find in the Suppliers section.

Kapa-line is one of a number of lightweight foamboards (all prefixed by the word ‘Kapa’) characterized by a polyurethane foam core, manufactured by the German firm 3A Composites. After a lengthy search I have to confirm that it is not available in the US, in fact hardly anywhere outside Europe with the exception of Singapore, and one supplier in Australia.

The only solution if you live in the US is to use another product with similar properties .. but so far I haven’t heard of any possible candidates. The most likely would be another foamboard with a polyurethane core as opposed to polystyrene. The polystyrene layer in regular white foamboard is too insubstantial .. just not enough to hold impressions well, too weak to carve or sand and incompatible with any solvent glue. I’m assuming that regular, cheaper foamboard in the US is similar. I’ve had some success with certain types of black foamboard here because the dyed foam has a slightly better, denser consistency and the paper detaches more easily, but it is still no match for Kapa-line.

Finding out whether a brand of foamboard has a polyurethane core as opposed to polystyrene may not be so easy .. the shop assistants are unlikely to know. Instead you have to go by whatever product information is on the website, or you have to phone the manufacturer. If a foamboard is advertised as having superior strength, resistance to warping or heat, compatibility with solvent glues and sprays, or that the foam is denser and cuts more cleanly .. it’s very likely to be polyurethane-core.

‘Balsa Foam’ was suggested as a possible alternative, but having looked at the information I could find, I very much doubt it. In the first place it is obscenely expensive for the simple material it is and it only comes in block form. It looks harder, probably more brittle, which may make it more suitable for sharp carving but unsuitable for the purposes shown here.

If anything styrofoam (by which I mean the proper, blue ‘Styrofoam’ trademarked by Dow Chemicals) would be a better and hopefully cheaper option. It offers much more than foamboard polystyrene. See the end of my article Shaping styrofoam under ‘shaping’ in the Materials section for further information on obtaining styrofoam.

Alternatives to Kapa-line foamboard in the UK

I only discovered recently that there is another manufacturer of polyurethane-core foamboard which could have similar properties, but neither this type is widespread unfortunately. It is quite a bit cheaper though .. at least for the 3-5mm. London Graphic Centre produce their own brand called Premier Polyboard available from their London shop and online. Just like Kapa-line it comes in 3.5mm, 5mm and 10mm thicknesses but unlike Kapa-line the sheet size is the more standard A1 and there are also options down to A3 (except for the 10mm). The cost of an A1 sheet (November 2014) is £6.50 for 5mm thickness and £4.99 for 3.5mm thickness, inclusive of VAT.

The 10mm thickness is not available in A1 for some reason but instead in Imperial, 20 x 30 inches upwards (really odd for a shop that strives to be up-to-date!). A sheet of 20” x 30” (500x760mm) is £10.00 and for 30” x 40” (760x1000mm) £16.00. So unfortunately this thickness costs quite a bit more than the Kapa-line generally does, unless you buy in bulk.

I did some tests on small pieces of the 5mm. In short, I was very impressed with how the foam surface compared with Kapa-line. It is different though .. in some ways not as good but in other ways better! The paper covering is tougher (on one side also a little thicker than the other) and it’s a little harder to pull off the foam .. but it does separate cleanly. The foam itself is pure white rather than cream and is denser/tougher than Kapa-line and also more flexible, ‘springy’. I tried a sample of brickwork using my usual method, as above, and there was really no adverse difference except that the Polyboard needed a little more force to inscribe it or texture it with the wire brush. The main difference discovered when I sanded was that it has a little more resistance .. it doesn’t crumble so readily, it shreds more. So sanding is not quite as effortless, but on the other hand it was possible to get an even smoother finish when fine-sanding. When testing the way it took impressions the difference became even more marked .. it’s more like pressing into marshmallow! Kapa-line fractures if pressed to deeply, but this didn’t. There was a little ‘spring-back’ but actually not enough to matter. I haven’t tested painting with acrylics yet .. but I know that all rigid foams, whether polyurethane or polystyrene, will take acrylic well. I can’t speak yet for working with the other thicknesses .. it happens sometimes that the composition of rigid foams varies according to the thickness.



28 thoughts on “Creating surfaces with Kapa-line foamboard

  1. Just found this Blog and Im Very happy. It’s a goldmine for DIY terrain makers like myself.
    In regards to hardening I use a mix of superfine grain filler, glue (white – for adding “fluff” like foliage to model railway terrain), paint and water when I base paint.
    Slight risk of filling in details unless you get the mixture right.

    • Good to hear! .. and thanks for the info! Do you use a ready-mixed filler in that recipe or a powder one? I always find it’s difficult to mix those ingredients together (as you imply) because either the pva glue or the binder in the paint reacts with the filler, suddenly making it far too ‘stodgy’ and one needs to keep adding little amounts of water while working to keep it reasonably fluid? There’s something else you could try, if you can get hold of it .. Rosco Foamcoat .. very quick drying, no shrink, remains smooth and brushable. Usually it’s only available in large quantities but 4D London sell small pots. Still rather expensive though at c.£12 for 500ml.

      • I’ve been using a few different brands of both glue and fillers and have experienced what you mention with it getting too thick and “cludgy” (I’m Swedish so my use of words might be a bit odd).
        I almost always use ready-made mixtures when it comes to fillers though. Unless I get the opportunity to use free stuff (looting the my dad’s garage for old unused stuff for example). When it gets too thick, as you say, just add more water/paint to the mix.
        When the mixture gets too wierd I make a new batch for the precision/detail work and save the thicker mix to use with base constrution or mix it up with “cleansed (+120degree for >20 minutes)” coffe grounds to make naturalistic terrain (base for woods etc). I work mostly in 1:56 to 1:100 scale.

        Current ingredients in my mix is Bostik Quick Filler, Noch Grass Glue and some Flügger Wall paint.
        I’m always on a budget for my projects so I cannot afford to use specialist ingredients.
        The bonus effect of the mix is that it creates a surface similar to concrete in texture that is really easy to paint.
        The liquid resin you mention is probably better for stiffening the foam, but I imagine there a higher pricetag that comes along with it too.🙂

  2. very interesting techniques and thanks for a fascinating blog. Is there any way the finished textures can be hardened so they can form a tough moulded surface? I’m thinking of possibilities in picture framing but obviously the end result needs to be quite robust when attached to a frame.

    • The hardness coating that can be achieved, without enlarging the surface or losing detail, would be using polyester resin. This goes on well and doesn’t affect the foam. But it’s still fragile to hard knocks. See my article ‘Shaping styrofoam’ in ‘Materials’ / Shaping

  3. Thanks for sharing your insights and “trade secrets” with us, top-notch!!!
    One question I would like to ask: Do you have a special technique for creating the impression of roughcast or plaster on a styrofoam surface?

    • Not particularly Auld Nick, but I would certainly recommend Polycell’s ‘Fine Surface’ polyfilla for anything like this because it is sticky, strong .. and one of the most versatile!

      • Thanks for the hint! Now that you mention it, that should indeed do the trick.
        I am wondering though whether I possess adeqaute fine motor skills to do it since the filler should be spread thinly on the surface.
        Well, there’s only one way to find out… Thanks again for your reply!

  4. Thanks for sharing this. Could you please tell me what kind of plastic is used to go on the inside part of the wall? When you are referring to ‘card’, are you referring to card stock or cardboard? Where can I get this plastic or card that you are referring to, and what names do they go by? Thanks.
    ” It should be glued to a stronger (card or plastic) backing form.”

    • In this case the inside part of the wall is plastic .. ‘Palight’ foamed Pvc .. which I find even easier to cut than cardboard, and much more versatile. Have a look at the article in the ‘Materials’ section under ‘constructing’. I’ve also put guidelines on finding it in other countries.

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    • Thanks Thomas!

      Yes, from sources I’ve looked at briefly i.e. Blick etc. it looks like ‘Balsa Foam’ is similar to Kapa-line foam in that’s it’s polyurethane, light and relatively soft. So a number of the same things can be done with it .. but I doubt that it lends itself so well for making impressions. It looks like it’s harder, less flexible .. in other words more in the ‘Oasis’ direction? It’s also a shame that it’s so ludicrously priced!

      • There are also polyurethane sheets in the U.S. used for CNC prototyping. Called “Prototyping Foam Boards,” they are available in a wide range of sizes, densities, etc. And if you think the price of Balsa-Foam is ludicrous, wait ’til you see the price of these prototyping boards! My experience, by the way, with Balsa-Foam is that it holds a fairly good impression.

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  7. Would you, by chance, know what the USA equivalent would be for this product? It is hard to figure out from this side of the ocean. Thanks! Thelma S. in Tucson

    • No, I’m afraid I don’t yet. When this question has come up before from the US I’ve asked to be kept informed .. but nothing yet! It might help to search in terms of ‘polyurethane foam’ rather than styrene foam though, since this is partly what makes it different in this context.

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  9. This is awesome and I am wanting to make a old western town (small version) for a Christmas version village) I think would work just fine~ thanks again for the info.

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    • Thanks Jason! I’m assuming ‘elmer’s board’ is a US product, because I’ve heard of the ‘Elmer’s glue’ you have there. I’d also assume that, if it is a fairly standard foamboard the core is probably polystyrene foam rather than the polyurethane foam in ‘Kapa’ products. Here in the UK most of the cheaper foamboard brands have polystyrene inside and, with a few exceptions, the paper covering is stuck fast and can only be removed with detailed perseverance, damaging the foam surface in the process. The exception, I’ve found, is black foamboard. Though not as easy as Kapa to ‘defrock’, the foam itself must be different due to the black pigment colouring it and it is also a bit denser than the white version. I’m interested to know though .. is Kapa-line foamboard commonly available where you are?

      • I haven’t seen it here. Can you tell me the address of where you get yours along with some prices on the thicker ones?

      • Have now put ‘quick view info sheets’ in the Materials section showing current prices and suggesting possible sources (Kapa-line will be in both ‘Constructing’ and ‘Surfacing’ sections).

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