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Hi all,
I'm looking for some advice as to whether I need to add some stiffening frame-work to some fake car panels.
I have the job of creating some car panels that will just fit right on top of an actual car for a theatre show. They need to be light and easily removed and then replaced later. My thoughts are to create individual PM "shells" for each quarter panel, door, bonnet etc - maybe with some sticky velcro dots underneath to hold them in place.
Ideally I think I would like to avoid using something like chicken wire due to having to protect the car with more layers etc.
If I use woodworking PVA (yellow PVA) in high concentration - only using enough water to help with spreading it - will a PM shell have enough intrinsic strength to be handled the way I'm describing? How many layers do you think I will need to do?
If not, are there any other thoughts as to how to stiffen the panels easily and without too much weight? A resin coating? Balsa wood strips? Bamboo stakes on the edges? Or do I need some kind of lattice framework? Or just lots of PM layers?
Many thanks for your help!
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Wrap the wing with aluminium foil, taking it round all edges or taping it where it won't fold around an edge. Use brown packaging paper, which is flexible but strong, also taking it around the edges. Paste with a mixture of PVA and CMC or wallpaper paste (or in this case since it is not likely to be long lived, boiled flour paste . . did I really say that????)
Apply about six layers and allow to dry thoroughly. Paint to the car colour.
Separate carefully from the car, cutting along the edges to release. You may find that the shaping allows it to hold on to the real wing sufficient for your needs but otherwise you will have to work out a method for the particular situation.
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Thanks dopapier - so, just to confirm - you are saying that six layers of brown packing paper pasted together should be enough to hold it's shape?
Should I glue the first layer to the aluminium foil? Or is that just to protect the car?
Can I do the six layers in one hit, or do I need to let each layer dry before commencing the next?
Thanks so much for your help!
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What's the stiffening for? Are they being handled by actors taking them on and off the car during scenes? Or are they being handled by techies? In my experience actors are rougher on props and sets than technical folk. (I've been both.) Also, how are you storing them ... are they propped up on a wall so need to hold their shape with the weight of the others resting on them? If so, you'll want to reinforce the places where they'll be handled the most and where they'll sit when stored.
I'd try it David's way first. 6 layers. I do multiple layers at a time and let them all dry together (of course I've never done anything as big as a car!) ... Keep in mind that since the inside of the paper mache is against the tin foil and car the outside will be dry when you take it off, but the inside will need additional drying time.
Another option would be to create them out of chipboard or cardboard, with a paste made from glue and plaster. There's a video on the Science Channel website discussing this technique for making dress forms.
Here's the link:
http://science.discovery.com/videos/how … -form.html
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Yeah it's being handled by actors - and yes you are correct! Actors will definitely be rougher on them.
They will probably live on the car when stored and they only come off for one scene. They will only have to last one week at the most, and they will be painted to make the car look like it's old and battered, so I'm not too worried about dings and scratches - just that they will hold their shape to easily put back on.
Sounds like 6 layers of brown paper is the go. I'll do a test run and see how it goes.
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I've had a couple of notifications of new replies on this topic, but when I come here, there's nothing new...strange.
Well, I did a test piece and it's worked brilliantly! Thanks for the help guys.
I used decent PVA watered down about 6 parts PVA to 1 part water.
However, I'd like to know what people use on the top layer to smooth out the overlap lines? I used butcher's paper (thick white/cream paper) and tore the edges - not cut.
I even sanded before painting, and the lines still show up under the paint.
Do people use some kind of plaster jointing putty, or "builder's bog" as a top coat and just smear it over the top, effectively smoothing the joins?
Cheers!
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I use a homemade gesso made of whiting (ground chalk also known as calcium carbonate) Just put the chalk into a container and add enough water to cover. Let it sit to settle. Once the chalk has settled thoroughly and the water is clear, carefully pour the water off of the top. I usually let it settle several times, pouring each time until I can remove as much water as possible. Then add glue to reach the consistency desired for painting. I also add a little linseed oil (boiled is fine) at the rate of about a teaspoon per cup, this makes the gesso flow a little better. It's not necessary, but it does help. Then just paint on a layer or 2 on depending on the depth of your lines, letting it dry between layers and sand. It dries quickly, sands easily and allows a very smooth finish.
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Awesome - thanks for the detailed explanation.
What is the benefit of this recipe over say - what builders use to patch plasterboard walls?
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This recipe flows and does not go on in a thickk layer and is therefore not as likely to crack. It is self leveling and doesn't require nearly as much sanding. It's like painting on the drywall mud as opposed to frosting with it. Much easier to control in my opinion.
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Sweet, that sounds perfect then. The only probs with self levelling is I'm making these panels on the car itself (so vertical for the most part). Although I guess I could just do that after its all dried and lie the panels flat.
Thanks very much.
Now I just have to find calcium carbonate.... Artist supply shops?
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You can find it at Sherwin Williams paint stores in 1 lb tubs, or pottery supply or ceramic stores in larger quantities. They call it whiting. I also THINK you can find it aquarium supply stores and health food stores, but not too sure about those.
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Oh to apply it on a vertical surface, just mix it to a consistency of a good paint. It will hang on just fine. Just apply thinner layers. I paint it on odd shaped pieces often.
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gwpac said "I've had a couple of notifications of new replies on this topic, but when I come here, there's nothing new...strange."
Ocassionally spammers place advertising material in the Forum. Whatever the nature of the message, you would get an immediate notification but my guess is that a Moderator has seen it first and deleted it. So don't worry, you didn't miss anything of value.
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When you're asking around to find a source, be sure to give them all its common names: whiting, calcium carbonate, chalk. Some people know it by one name and not the others. You can ask for whiting and they immediately say they don't carry it, with their hand on a 50# bag labeled 'calcium carbonate'. It's used with swimming pools, as an additive for art paints, stained glass artistry,
If you have a potters supply nearby, start there first.
Whatever your source, make sure it doesn't have any additives.
Sue
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Thanks for the reassurance regarding the notifications.
Thanks also for the further info on how to ask for 'chalk'!
Anyone here from Australia - any tips on what local shops might hold it? I'm sure I can track it down from the above descriptions, but it would obviously be quicker if I could go directly to a known supplier.
Cheers
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Try Northcote Pottery Supplies -- website: http://www.northcotepottery.com.au/home
142 - 144 Weston Street, Brunswick East 3057, Victoria Australia
Tel 03 9387 3911
[see Prices, appears to be called whiting]
Clayworks -- website: http://www.clayworksaustralia.com/
6 Johnston Crt, Dandenong 3175, Victoria, Australia
Ph +61 3 97916749
[see Prices, "Raw Materials", listed as calcium carbonate]
Walker Ceramics -- website: http://www.walkerceramics.com.au
Phone 03 87616322 Email sales@walkerceramics.
[see Raw Materials, called Calcite (OMYA 10) "A purer form of whiting"
Some may be distributors, just ask who would sell to you nearest your location.
Sue
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Wow! Thanks for that! 
I will chase those down.
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Yep pottery suppliers are your best bet, and the quality is usually good too. I'm fortunate to have one across town, which is a long way in Houston, but I buy in 50lb batches so I only have to make the trip once a year (maybe 2 since my projects keep getting bigger and bigger). Mail order is good, but the shipping gets prohibitive. Some of your better specialty paint stores (house type paint) do carry it, they call it whiting or sash putty, so if you have one in the neighborhood, you might want to give them a try before going out of your way.
Last edited by paper soup (2012-03-21 19:41:33)
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Hi all, and especially paper soup!
An update, as I said, my prototype was brilliant - very rigid and strong, looked great with metallic spray paint on it.
Now I'm trying with the real thing. Firstly I'm using brown wrapping paper (on a big roll like you would find at a post office etc) instead of a slightly fluffier white wrapping paper (almost like blotting paper). It seems to be not quite as rigid as the prototype - although it may not be fully cured yet.
Secondly, and most importantly - I want to check the gesso recipe with you as it just seems to crack and flake off very easily - it has no flexibility at all. When you handle the panel it naturally flexes a little, and consequently the gesso cracks all the time.
As you suggested I made a thick slurry of calcite and water, added PVA, a dash or two of linseed oil.
What do you think is going wrong?
Or is this formula just not really suitable for something that is going to flex?
Many thanks for your help.
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Acrylic-based gesso may be better for this particular use, as it seems to have a bit of flex to it. Paper Soup's recipe looks good for things that don't flex at all.
Sue
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Is that something you buy pre-mixed or is there a recipe I can source?
Where would you buy something like that?
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I would think that you could find it at most fine-art supply places, those that sell paints for artists (oils, watercolors, acrylics, etc). The most common use is probably sizing framed painters' canvases. It runs about $7 USD for 250 ml of an economy brand, but comes in all sizes.
'Acrylic gesso' should be the standard name.
Here's an American link and description: http://www.dickblick.com/products/blick … ite-gesso/
Sue
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OK that's great. Thanks for the link, I know what Im looking for now.
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I've added a bit of plaster to my glue when I want more rigidity with fewer layers. (And by a 'bit' I mean 1tb per ~10oz of paste.) ...
As for covering up paper lines and still maintaining flexibility ... I'd suggest trying a thin version of monster mud, ie, add a little bit of drywall compound to latex paint to thicken it ... the latex should retain it's flexibility enough to not flake or crack. (You could try just adding calcium carbonate to latex paint as well and see ...) ...
-- b
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