An architectural play-model: Part 1

 

David Neat, architectural model, 2018

I was asked to make a model of gallery rooms newly added to a private house in Hampshire, and have been working on this part-time for the last few months. The focus was on the interiors, since the idea was that the owners could use the model to explore different arrangements of the contents, but it was agreed that the model could also have an aesthetic presence of its own .. as a sculptural object in itself .. so I took the freedom to stylize aspects of the exterior and to avoid fussy detail. After initial talks with the friends who’d commissioned it the model developed its ‘plaything’ nature .. somewhere between dollshouse and construction kit .. as it progressed. From the beginning the plan was that there would be detachable sections, making it possible to peer into parts of rooms, but that these ‘building blocks’ could be quickly and cleanly reassembled again. This suggested a baseboard with cavities into which room sections could be slotted into place .. further adding the qualities of ‘jigsaw’ and ‘puzzle’ to the aspect of play.

We wanted the roof structures to be represented, mainly to illustrate how the interiors are crowned by these light-receiving cones. But I only wanted to ‘outline’ them as it were, and they needed to be detachable. Giving them any suggestion of their external nature would have made them too heavy-looking, so I took advantage of their separateness to make them  ’emblems’ in yellow Palight.

David Neat, architectural model, 2018

David Neat, architectural model, 2018

David Neat, architectural model, 2018

 

Working with Palight and Palfoam

Once again I wanted to use my favourite foamed PVC for most of the build, because it is one of the most manageable and versatile materials I know! Using this would also mean that the individual ‘room blocks’ would not become too heavy while still being structurally very solid. At the chosen scale of 1:25 the main walls came to roughly 15mm thick in the model, while the interior walls could be represented with 5mm. I had quite a large stock of 5mm, but I chose to build each section of thick wall as a ‘sandwich’ i.e. solid 5mm PVC both sides, with a 5mm thick framework in between. This was partly to reduce the weight ( and therefore the stress on the boxes ) a little more, but also because I wanted to build in a continuous groove along the tops of the walls to slot the ceilings into. In retrospect I wouldn’t do it this way again if I could help it .. it was an awful amount of cutting, sanding, aligning and gluing!

David Neat, architectural model 2018, detail of foamed PVC walls

Here in the UK Palram’s ‘Palight’ brand foamed PVC is available in white or a small selection of colours, and comes in a few different thicknesses. But of the white only the 1mm thickness is actually Palight. In the thicknesses from 2mm to 10mm ( there used to be thicker, but no longer it seems) the material is Palfoam. This is important to know, and to check when ordering, because Palfoam is softer. This makes it even easier to cut ( with a scalpel for example, as I do, and especially if one cuts along the extrusion grain i.e. along the less bendy direction ) and it glues together even stronger because the cut edges are more porous. But the surface of Palfoam is much more susceptible to scratching, so something needs to be done about it if it’s being used for a model that’s going to be handled.

David Neat, architectural model 2018, white wall texture samples

I knew that I was going to clad the outsides anyway with whatever I came up with for the brickwork effect, so my first task was to find a covering which would be suitable for the interior walls, which in reality were just white-painted plasterboard. Apart from the practical durability aspect I wasn’t happy with the idea of just white PVC walls anyway .. it’s the most uninteresting, lifeless form of white! One possibility was cladding the interior with Daler Rowney ‘Georgian’ oil painting paper ( on the left above ) which is quite a tough 250gsm, primer-coated and ‘linen’ textured paper. This is available as pads or sheets. The other idea was evenly stippling Polycell’s Fine Surface Polyfilla directly onto the PVC ( shown on the right ). I’ve textured PVC this way before  so I know that it stays put and resists scratching better than the plastic alone. It’s tricky at times to maintain an even quality of stipple, and the oil painting paper was the easier and quicker of the two to do, but I was worried that the paper could scuffing at the edges after repeated handling. Fine Surface Polyfilla is also a more sympathetic, slightly warmer white, so I chose this for the wall treatment.

David Neat, architectural model 2018, detail of stippled texture on walls

 

Simulating polished concrete

The most important aspect of the interior, the part which needed to look ‘convincing’ above all else, was the polished concrete floor. Especially so, since floors assume greater significance in models than in real life, because we’re mostly looking straight down on them. That usually can’t be helped, but it’s one of the reasons why we chose to make the model in removable parts, making it possible to get more of the ground level perspective.

David Neat model-maker, architectural model 2018, polished concrete floor

David Neat model-maker, architectural model 2018, polished concrete floor

I was originally going  to go with a method I’d tried before, using matt photo prints of actual concrete and achieving the polished look by spraymounting clear acetate on top. I’ve used this technique for very convincing marble or polished wood, easy to play around with because the parts can be ‘tweaked’ separately instead of having to achieve it all-at-once, and satisfying to look at because the surface effects ‘come from within’ rather than lying opaquely on top. Incidentally, it’s interesting to observe from the last three photos how .. even in simulations! .. the particular warm greenish-grey of concrete can alter quite a bit dependent on the light. I’ve noticed many times in real life how much concrete can change its mood under different lighting.

David Neat model-maker, recycled paper

As I was saying, I’d planned to create the concrete with photos but by chance I happened to have a cheap, recycled paper that worked even better as a basis. These (above) were file dividers found in a £shop which I’d kept because their back surface was interesting. The grey ones were a good basis in terms of colour and mottling, a suitable warm greenish-grey, though a little too dark and too even. But I found that if I use a sanding sponge on the paper  I could make it lighter, while giving it a bit of animation.

David neat model-maker, simulating cocrete with recycled paper

David Neat model-maker, concrete effect samples

Embossing the back first with a serrated modelling tool created other distinctive patterns in the paper when sanded. I didn’t want this kind of patterning in this case, but it’s an interesting effect.

David Neat model-maker, polished concrete simulation using recycled paper and acetate

I had to cut the floor pieces out of 2mm Palfoam first, clad these in the paper ( spraymounting down using 3M’s Craft Mount, the strongest ), modify the paper surface by sanding, vacuum the surface to remove any dust .. then I could apply the acetate. This is straightforward ‘transparency film’ designed for printing on, sometimes also called ‘OHP film’ ( for overhead projection ). Hence it’s surface feels slightly rough on one side, because there are micro-deposits of clear priming material to help the ink to fix. It is this side of the acetate that needs to be spraymounted, then laid and firmly rubbed down over the paper. Now the glossy side of the acetate is on top. This is usually too glossy for a polished concrete surface ( though it depends what look you’re going for) so I take some of the gloss away by rubbing either with a kitchen scourer or very fine sanding sponge ( the kind painter/decorators use for matting paintwork ). This will deepen but also slightly lighten the effect.

David Neat model-maker, samples for a polished concrete floor

I felt in the end that my polished concrete was still a little too dark and not ‘beige’ enough, so I gave all the pieces a light and mottled dusting with Belton Molotow ‘Stone grey light’ spray paint. Above .. to the left is an example of the photoprint method (which in this case was far too busy and specific); in the middle is the recycled paper/acetate version; and on the right the final adjustment adding a dusting of spraypaint.

In the next part I will be talking about the baseboard, describing my methods for staining woodwork, and a ‘generic’ or stylized treatment for the brickwork.

 

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More on gluing, surfacing and repairing styrofoam

I’ve been slowly adding to my page on Shaping styrofoam in the Materials section, partly because I saw that it was one of the most visited pages. I wanted to consolidate the scraps of knowledge I’ve gained over the years on gluing styrofoam and the range of options for finishing or reinforcing the surface. I also wanted to look into a more satisfactory method of making repairs which I found, as you’ll see from the photos  .. well, very satisfying!

More on gluing styrofoam

I’ve bonded pieces of styrofoam together with a strong, double-sided carpet tape for years and they’re actually much more permanent than I’d first imagined. I have composite forms made many years ago which have been well-used as teaching examples and show no signs of coming apart! A few observations are necessary though! .. the two surfaces have to be smooth and flat against each other; if these surfaces have been sanded to make them fit, all dust should be removed, ideally vacuumed using a brush attachment. For the same reason the best bond occurs between the slightly ‘skinned’ surfaces of the sheet as it comes. When using the tape it’s particularly important to avoid placing it too near to where the styrofoam will be carved or sanded if one wants a seamless join .. but this applies almost equally when using most glues. But if it’s impossible to predict, or avoid, gluing in an area which will later be carved through or sanded, I’ve found some of the following options most suitable because they offer the least resistance.

For example what works surprisingly well as a bond between flat styrofoam sheets is spraymount, by which I mean the permanent spray-glue types from 3M. 3M’s ‘Craft Mount’, which is the strongest of their range, is particularly suited because it has a little more body. It should be sprayed on both sides to be joined (different to how it’s normally used), and it’s best to wait a little i.e. half a minute, before the two pieces are firmly pressed together. As with all contact glues, even the ‘instant’ ones, the bond will hold straight away but needs a day or two to get stronger. But the same applies with this as with double-sided tape .. the surfaces must be completely flat against each other and dust-free to bond strongly enough! Spraymount never sets completely hard, even though it’s grip is strong. When cutting through a glued edge the glue may catch the blade a bit but one can get used to this. It will sand reasonably well, especially if the tackiness gets mixed with styrofoam dust. For the same reason, I’ve found that it can help to dust the piece with talc while sanding.

If you want to glue pieces of styrofoam together which do not lie completely flat against each other .. you will need something ‘gap-filling’. There’s hardly anything more gap-filling and instant that hot-melt glue! Contrary to what you might have read elsewhere, hot-melt glue will work reasonably well with styrofoam .. as long as it’s not too hot! One just has to know how to manipulate it. Polystyrene foam is much more heat-sensitive than polyurethane foam .. it softens already at 90°C (193°F), while the temperature of hot-melt glue is around 180°C or more. So there is bound to be some melting of the styrofoam surface, but if you experiment and are careful you can find just the right number of seconds to wait before pressing the surfaces together, cooling the glue down a little but not so much that it fails to stick. Obviously it’s not possible to cover a whole surface, even a small one, with hot glue before most of it hardens. Think of this more like ‘riveting’ .. applying very quick spots of hot glue which will secure the pieces at those points once the glue has cooled. This method is definitely not for carving into or sanding though.

Another option is provided by the ever multi-tasking polyurethane! It’s common practice in scenic work and prop-building to use a rigid-setting, 2-part polyurethane foam to bond other foams such as styrofoam together. A small amount of the two parts must be mixed together in the directed ratio and then brushed quickly onto the joint before the foam pieces are pressed together. The resulting foam will expand to fill any gaps in the joint but the pieces must be held firmly in position while this is happening, otherwise they’ll be forced apart. Often this is easier said than done because the expanding foam exerts quite a force, but generally with these polyurethane foams and glues the less gap there is the stronger the joint will be. Prop-makers and sculptors are more likely to use the foams which are supplied in two separate parts and which need to be manually mixed .. a good source is a sculptor’s supplier such as Tiranti .. but the ‘instant foam’ tube cartridges sold for wall repairs or insulation are similar.

Gorilla glue is yet another option .. a polyurethane glue that comes as one part, so no mixing is necessary, and which foams while curing on contact with moisture. What this means is that both surfaces to be glued need a light misting first .. best with a small pump spray. The glue needs to be applied thinly to just one of the surfaces before the two pieces are pressed together. Below are two blocks of styrofoam already sprayed .. just enough to dampen the surface, certainly not dripping wet!

Gorilla Glue test, styrofoam moistened

Gorilla Glue can be deposited in spots if preferred, and these will spread once the pieces are squeezed together. It is not necessary to spread the glue beforehand over the whole surface but here I used a coffee stirrer just to distribute it better. What is very important to note (and not included in the manufacturer’s directions!) is that the glue should be dropped from the nozzle without letting it touch the wet surface! If it does moisture will contaminate the bottle and some of the glue will set inside .. as I found out when I tested it for the first time!

Gorilla Glue test, applying the glue

Below, I have weighted down the two pieces with a solid metal block. This was sufficient, although where possible it is always better to clamp the pieces together (sandwiched between flat pieces of wood to protect the styrofoam). The expansion occurs after a minute or so, 3-4 times in volume according to the manufacturer, and if the pieces are properly clamped the excess is forced outwards rather than upwards. If, because of the shape of the pieces, it is difficult to clamp without damaging the surface, masking tape or cling-film could be used to bind them together but these could give way a little and there may well some shifting as the foam expands. I had to correct the alignment of these blocks a few times before the foam stopped moving them.

Gorilla Glue test, weighting down

A couple of hours are needed for the glue to cure. Here below is a section through the seam line, cut with a knife then sanded. If it is properly cured the glue sands through well …. although it is different to the styrofoam it is much more alike than other glues. Also the bond is as strong as they say it is! I think polyurethane grabs on the styrofoam particularly well .. at least, I couldn’t pull the blocks apart.

Gorilla Glue test, section through the seam

More on surface treatments

If the surface is going to be reasonably protected .. I mean, if it’s not going to be handled and if it’s shielded from knocks etc. .. a good coat of acrylic paint may suffice. Acrylic paint will toughen the surface slightly, but by no means protect it from any handling, even if careful. Coating first with non-waterproof Pva glue and then painting will do a little more, and the same applies if coated with Pva or a water-based varnish afterwards. But the surface will still be very susceptible to scratches or dents.

If Paverpol is added to the paint mix .. more than half by volume .. greater surface strength can be achieved. Paverpol is a Pva-type medium manufactured in the US mainly for the hobby market and is intended for painting on fabrics or foams to give them a much tougher surface. For example fabric will become rigid and almost ‘resin-hard’ if soaked with it and the manufacturer recommends it for outdoor sculpture. It will not impart the same degree of toughness when painted on styrofoam because it doesn’t infiltrate far into the surface, but a couple of coats using Paverpol will be stronger than either regular Pva or acrylic alone. On its own Paverpol is quite viscous (a little more so than straight Pva glue usually is) but with careful brushing can be worked into a detailed surface without clogging it noticeably. In fact, whether applied straight or mixed with either powder pigment or acrylic paint for an opaque colour, the first coat will emphasise much of the porous foam surface and appear matt with an even roughness. If this is allowed to dry completely (needing a good few hours or preferably a whole day) and then painted again, the pores will start to be filled. Especially if combined with careful sanding between each coat using a medium grit sandpaper (for example 120-200 grit) a fairly smooth finish can be achieved. This must be applied as evenly as possible because raised streaks in the Paverpol will be tough to sand down!

Paverpol fabric strengthening medium

The next option is either painting or coating with a ‘polyfilla’. I make this distinction between ‘painting or coating’ because certain polyfillas can be thinned with water to a gesso-like consistency without losing too much of their strength and can be smoothly painted on. Polycell Fine Surface Polyfilla is in my experience the best of these. It is bought ready-made in tubs; it’s particularly smooth; thins evenly with water; sticks very well to sanded styrofoam and is far less subject to shrinking and cracking than other types. It also retains a little flexibility when dry. To get an even, lump-free cream with water it’s best to ‘condition’ some of it first either in a bowl with a spoon or on a clean glass plate with a spatula or palette knife. As you work it around it will become more liquid and if this is continued while adding water a few drops at a time you will gradually get something like the consistency of gesso, without any lumps.

The forms below were carved/sanded in styrofoam; the sanding stage finished with a flexible foam-backed sanding pad (see below) to achieve the smoothest surface. They were then painted with a thin coat of Polycell’s Fine Surface and left to dry for a day. After this a second coat was applied and then a third, which was left as before. The final treatment before painting was a careful sanding with a very coarse (60 grit) sandpaper which imparted a visible grain, softened with an overall rub using finer (240-300 grit) sanding cloth. The surface achieved with this polyfilla is not any tougher than the Paverpol, but it is much easier to sand, making it more ideal if the aim is an even, glass-smooth one. I painted these with Humbrol matt enamel, which is thin enough not to clog surface detail or add any additional texture but opaque enough for a rich and streak-free coverage.

Finished forms in styrofoam, coated in polyfilla, re-sanded and painted

I waited a few days for the paint to reach maximum hardness (although thin, the enamel dries very hard and durable) then rubbed carefully with a fine sanding sponge (these look similar to kitchen washing pads) to bring out some of the grain.

But an equally smooth and even harder surface can be achieved using a more specialized material. Casting resin is not usually considered as a medium for thin coating, mainly because it’s thought that it will fail to cure properly under a certain thickness. This may be true of some, but I’ve used both general-purpose (GP) polyester resin and special types of polyurethane resin many times for this, mixing in very small amounts and applied like a varnish .. with consistently good results! Polyester resin cannot be used to coat styrofoam because the styrene part of it will eat into the surface. However, polyester resin will work perfectly on polyurethane foam and, with predictable logic, polyurethane resin works perfectly on polystyrene foams such as styrofoam!

Uncoated and coated styrofoam 'heads'

The ‘head’ on the right above was painted with a small amount of Tomps Fast Cast polyurethane resin, first mixed together quickly and then worked with a soft brush into the styrofoam surface. I chose this brand because of its low viscosity, designed to cure even in very thin sections. After about an hour this cured enough to be sanded, just to even out the surface a little, before being coated again. More careful sanding followed, and finally one more coat. The overall coating is now akin to eggshell in thickness and hardness .. but in important respects stronger because it is supported uniformly by the rigid foam underneath. An ‘industrial’ ceramic-look smoothness can be achieved using a mixture of careful rubbing with special sanding ‘cloth’ (blue/green below) or thin layers cut from the surface of a nail parlour sanding block. These will flex with the shape, unlike sandpaper. Polyurethane resin sands surprisingly well for something so hard .. even easier to sand than some fillers!

Foam-backed and cloth-backed sanding materials

Below I’ve included the stages in the shaping of these ‘heads’ .. starting with a block shaped on a template, then sanding away from a centre line.

Stages in styrofoam shaping

The concaves for the eyes were started with a curved sanding tool, similar to the one used on the form at the beginning of Shaping styrofoam. These are easy to make, involving only a thin strip of sandpaper glued to a former.

Custom sanding tools for making concave shapes in foam

Major repairs or alterations to styrofoam forms

It is a long-established practice amongst carpenters and, in more recent times, restorers to neatly excise a damaged area .. i.e. to cut it neatly out .., glue a new block of the same material in its place, and then reshape this rather than ‘bodging’ with something else like a filler. Most fillers tend to shrink, to varying extent .. inevitable if they rely for hardening on the evaporation of a solvent. They usually can’t be laid on too thickly otherwise they can take an age to harden, and it may take a few goes to fill a deep repair properly. The other disadvantage of using fillers, especially to repair or alter styrofoam is that when set the filler material reacts very differently to sanding than the surrounding foam. It is usually much harder and inflexible, making a seamless transition difficult. The much better way to do it .. patching in with the same material .. is illustrated below.

This test form was made in the same way as one of the components described above .. first rough sanded and then finished with a 120 grit sanding block.

styrofoam repair demo test form

Below is some stylised ‘damage’ ..

styrofoam repair demo 'damaged' form

I sanded away a broad channel, making sure that the bottom of it was flat and smooth. The side edges are not parallel but a little tapered, so that a wedge-shaped block can be slid into position. This means that the block doesn’t need to be perfectly accurate in width.

styrofoam repair demo, damage cut out

In this case I secured the block with double-sided carpet tape. I’ve found Ultratape ‘Rhino’ very reliable so far. The block needs to be slid into position, as I’ve said, but not pressed down until it’s tight against the channel edges. I also slanted the edges of the block a little i.e. making the top surface a little bigger than the bottom, so that when pressed down it squeezes even more tightly into place. Styrofoam will compress a little to make this possible.

styrofoam repair demo 'patch' inserted

Then it was just a matter of re-attaching the semi-circular templates either end of the form (see earlier) to protect the undamaged surface and sanding the block down to the same point.

styrofoam repair demo 'sanded flush'

Just out of interest I tried similar repairs using Gorilla Glue as a filler ..thinking that, since the glue takes so well to the styrofoam and cures with a similar composition it might be an ideal solution. Unfortunately not!

Gorilla glue as filler, test piece

I made some notches with the scalpel, spray-moistened the styrofoam surface, then laid the glue into them making sure to spread it completely over the edges of the cuts. I also spray-moistened the topside of the glue after this was done.

Gorilla Glue as filler, cured foam

I waited a little more than two hours, during which the glue had expanded .. as the manufacturer says .. 3-4 times in volume. The first few millimetres of the cured foam was fine-pored and sandable, ideal in fact, but deeper down the bubbles were much bigger and the consistency soft and fibrous. It was like trying to sand bread! The foam had become weaker and more irregular because it was allowed to expand too much and I’m guessing that it would work better as a sandable filler if it were more confined i.e. by wrapping a non-stick covering over the form before the expansion starts.

Gorilla Glue as filler, sanded down