EVA plastic can be hard to glue.  Plastics and adhesives often don't work well together because the ingredients conflict over time.  And if they do stick in the beginning, they may not continue to stick. You can use hot glue on EVA (HOT glue from a glue gun, NOT low-melt type), but in time, the glue hardens and tends to release.  For a short-term project, it should be all right, but good long-term results are unlikely. 

The finished helmet has to be larger than your head.  PM shrinks as it dries, and would likely no longer fit, plus, you really should have an airspace between the inside of the helmet and the outside of your head.  So you need to make a form that is at least 1 to 1.5cm (1/2") larger than your head, yet in the shape of your head.

The simplest way would probably be to use a can of that spray foam insulation that expands after it comes out of the can (technically called polyurethane-based insulating foam sealant).  The main brand here across the pond is Great Stuff.  It's used for filling cracks in wall insulation. If you have a choice, get the cheapest one ($4 here in the U.S.)  CAVEAT: I've used this inside molds, but not on the outside, but other people have used it as below, with good results.  Don't have an idiot doing it for you, and keep it under control, off your skin and OUT OF YOUR EYES.  Start around the outside edge of where you want it, then work back toward the back of the head.  If you run out, that's an easier place to patch.  You can't do it yourself, and you can't manipulate the foam when it's wet -- it just collapses.

It's fairly quick and simple, but may take up to an hour to harden enough to take it off safely.  Just put a plastic bag over your head, have a friend fold and tape it to form to your head.  Mark with a felt marker (or tape) where you want your edges.  Don't trim the outer edges, the excess will protect your eyes, skin and clothing.  If this is the first time you or your friend have used this foam, squirt a bit onto some paper and watch what happens, so you can judge how to apply it.  It comes out like a snake of whipping cream, expands, then starts to harden and cure, forming a skin over the top surface in about 15 minutes, and solidifies and can be trimmed/cut in 30-60 minutes.  If the outer surface is too lumpy, wait the 15 minutes or so until you can touch it with your finger w/o it sticking, and press lightly to make the surface smoother.  Your design MUST be able to slip off your head.  If the foam curves around your chin (for instance), you'll have to break it or cut it off, so don't do that.

When the foam has cured (overnight would be good), carefully stuff the inside as firmly as you can with wadded newspaper and glue w/o damaging the foam.  If you intend to make more helmets and want to keep the form, just use another can of the foam and fill up the inside of the form.  REMEMBER THAT IT EXPANDS.  If you do this, insert a sturdy dowel inside, and attach it to a flat platform so will be easy to work on.

If you plan to use Jonnie Good's Paper-Mache Clay recipe from the Ultimate Paper Mache site, YES, the joint compound is necessary.

The actual cardboard helmet:

Find a flat piece of regular, non-coated, corrugated cardboard that is large enough to form your entire helmet.  Soak it in water (with a little detergent), like in a bathtub, preferably overnight.  A slight curve would be okay, but try to avoid forcing creases into it.  The cardboard needs to be wet and pliable.  But this also makes it more delicate and sensitive to ripping, so handle gently.

Once the cardboard is fully saturated, pour the water out of the container and let the excess drain off the cardboard.  You want it in the state of being thoroughly damp and malleable, not sopping wet.  This may take a while, maybe up to a day, but don't let it dry out too much.  Drain with the holes downward.

Carefully center the damp cardboard on your head form so there is extra all around the edges, and hold it in place by pushing a largish nail through the cardboard into the foam form.  Gently start pressing the cardboard to the shape of the form, using a pair of scissors to cut slits from the edge.  Overlap the flap over the cut, then cut out the overlap so the new cut edge meets the first cut edge.  Most of these will be in the shape of a V.  When you have one section finished, push a few straight pins (sewing pins) or very thin nails with heads through the cardboard and into the foam to keep it in place.  Being wet, you can't keep any tape on it until it dries.  Work your way around the head form.  If you accidentally cut too much out and have a gap, don't panic, just pin the short piece in place; using one of your discarded pieces of damp cardboard, cut a piece to fit in the gap, and pin it in place.

Once you're finished, let the cardboard helmet dry on the form.  The edges may need trimming, but don't worry about that until it's dry, and I would take care that it was BONE DRY.

When it's completely dry I would go over all the seams with a bottle of PVA white glue, and let that dry, and then remove the pins.  If the edges need trimming, do it now.  You could reinforce the seams with paper tape (so the shellac below will stick to it). 

Now coat the cardboard with REAL shellac, spray or brush.  It dries quite fast, 30 minutes in a dry place, more if its humid.  Coat it outside and then inside.  Then you can start covering it with papier mache (torn strips* or pulp) or coat it with Jonni Good's recipe (follow her advice).  The shellac will prevent the moisture of the additional layers from seeping through to the cardboard and causing damage and warping.  Be careful -- the helmet is still delicate and can be damaged.

Add as much over the surface of the cardboard as needed (whichever material you choose to use) to make the whole thing firm and rigid.  Flexibility will end up damaging your work. Wrap the edges of the helmet with your covering material(s) for a smooth finish.  And yes, you can use Jonni's recipe over regular papier mache, and you can use pulp papier mache over torn-strip papier mache, and all three if it seems most suitable.

If you have some lumpy spots, wait until the outside is fairly dry (still damp underneath), then press the lumps as smooth as possible with the back of a spoon, pressing down on the surface. 

When completely dry, you may need to sand parts of it (wrap the sandpaper around a small block of wood).  Every effort that you make to keep the surface smooth as you progress will result in less work at the next step.

When your paint and decoration is complete, let dry thoroughly and then coat with several layers of the shellac, or just use shellac on the inside (it's non-toxic when the alcohol in it evaporates) and use varnish on the outside, if you prefer.  If applying either one with a brush, use light, thin coats, not heavy, sloppy coats.

* Torn strips lay flatter and smoother than cut strips.

When you finish your helmet please post in our gallery and we can see how it turned out!

Sue

Shellac:  the Zinsser brand should be available in the UK.  I think the PM sticks better to shellac than to varnish, but that's just my opinion.

Varnish would probably be okay, but I'm not fond of it right next to the skin.  If the pattern for your helmet is large enough to have an airspace all around your head, I would glue some smallish cubes of foam or cardboard inside (spaced apart) so it isn't resting right on your head/skin, if possible.  But you have to use what you can find and afford.

Form... what I mean is the foam form, that you would be shaping your cardboard around, not a mannequin head.  That foam is okay for what it is, but it can't take a lot of pressure w/o breaking, so I was suggesting that you fill the inside with something that can help support it.  Wadded newspaper, if you don't apply too much pressure, should work.  If you have a can of that foam I mentioned, you could line the inside of your cardboard pattern with thin plastic/cling film (after being put together and taped, or whatever way your instructions say), and the cardboard could be filled with the expanding foam to support it as you work.  When your original helmet is finished, you could save the foam shape and use it to make other helmets or headpieces.

It would be easier with photos!

Sue

I hope you've had fun with this.  I live in UK and have bought shellac, though some years ago.
One method I have found very helpful is to make the pulp as smooth as possible, using calcium carbonate as the filler.  I then place a quantity between two plastic sheets and roll it thin (3mm is easily possible), then lifting it off with a spatula and laying it on the form.  It is easy to model and smooth.  Before totally dry it can be burnished with the back of a spoon.  It is best to do as much smoothing as possible at this stage because, once dry, it becomes extremely hard.

I would stick to pasted strips if I were you Danny. It will be difficult to get an even finish with pulp.

I also worry on your behalf about the strips sticking to the foam? Some of these type of materials resist glues. If you have any difficulty, you could wrap masking tape around it to give the Papier mache something to get its teeth into.

As for an undercoat for black.....any darkish emulsion paint (latex) would do well. Use up some leftover decorators paint, or one of those little tester pots. Black usually covers very well, but you may need a couple of coats.

I wouldn't use masking tape.  It may seem to stick initially but eventually can pull away.  A first dilute application of PVA should bond with the surface foam.  Use neat PVA for the first layer of paper (in piece sizes that patch smoothly onto the surface, not folding or wrinkling) then paper with normal paste.  Dry well between each layer and smooth where necessary.

Thanks for the advice so far, this project is slowly working out for the best!

I have found one problem: I've used foam as the first layer of helmet to keep the shape and have used papier-mache as a means of a surface for my paint to sit on, however because the papier-mache has clung to the foam so well, the groves of the joins beneath come through so the helmet doesn't look smooth making it look as if it's made in sections (because it is!).

I have a few ideas for a solution but wondered what people think on this forum:

- I wondered could I lightly sand away the worst of the bulges and do one more complete layer of papier-mache to complete it.

OR

- Mix up some papier-mache clay and try to get an even surface.

Personally I'm leaning more towards the sanding and reapplying  a layer due to not having the ingredients for clay such as boding agents and Linseed oil, however I'm open to everyone's opinion as this will help me and open to other ideas.

Thanks,

Danny

Last edited by dannycronin (2015-01-23 01:58:47)

Thanks for this, I thought I could however doing an Internet search last night it didn't come up with a definite answer, which I thought was strange.

Thanks again and I'll make sure to put some pictures up when it's done

Danny