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Old 06-11-2018, 10:56 AM
Moulder Moulder is offline
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Default Questions on building a styrofoam buck.

I'm slowly in the process of building a styrofoam buck of a grill shell to make flexible shape patterns from. I plan on using MDF as the wooden base to attach the foam to. Blue Dow insulation foam from lowes, and drywall mud instead of bondo for the final shape. What is the best kind of adhesive/glue to use to attach the foam to the MDF and to itself? I have some 3m super 77 spray adhesive. Would that be a satisfactory choice? Didn't Kerry use liquid nails? My main concerns are a good bond, won't eat the foam, and is sandable.
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Old 06-11-2018, 09:56 PM
BTromblay BTromblay is offline
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Hi,

I had heard that Great Stuff spray foam works good for gluing foam together. I have not tried it for my self, so please try it first.

B
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Old 06-12-2018, 04:30 AM
route56wingnut route56wingnut is offline
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Cass showed me the best I have seen and that is to mix Bondo very light and it won't melt the Styrofoam and will allow for sanding as well
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Old 06-12-2018, 06:43 AM
mark g mark g is offline
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I've used gorilla glue which is expanding polyurethane. I cut grooves in the foam for the glue to flow through as it expands. Adding some moisture to the joint helps encourage the expansion and shortens the cure time. But this is an informative video with a surprising conclusion (Glidden Gripper)
https://www.youtube.com/watch?featur...&v=rnOegaOKu38
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Old 06-12-2018, 08:18 AM
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Kerry Pinkerton Kerry Pinkerton is offline
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James, I didn't recall but found it in the art deco thread. http://allmetalshaping.com/showthrea...highlight=Deco It'd down toward the bottom of the page. Some good description of the process. I topcoated with bondo.



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Old 06-12-2018, 08:52 AM
kcoffield kcoffield is offline
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Default Bonding Polystyrene

I've worked with expanded and extruded polystyrene extensively in lost foam patterns for metal casting and resin/cloth lay ups. I'm sort of surprised to see the 3M 45 and Bondo mentioned because I've found they both attack polystyrene. When you see "extremely flammable" on the spray can it usually means toluene which aggressively attacks PS. The carrier in polyester (Bondo) also attacks PS. That said, if you mist the 3M 45 on, there just isn't much solvent to attack the PS. If you mix the bondo hot so it kicks quickly you can get away with it too. If you apply polyester resin directly to PS in an attempt to lay glass cloth on it, it will rapidly reduce the PS to a gooey mess.

Most spray contact adhesives designed for PS foam are latex based (3M 77 I believe). The carrier doesn't attack PS but it dries slower. I hate using contact cements of any kind to bond PS because when you try to sand or work the seem it balls up, loads up your tools and abrasives, and also doesn't sand evenly at the joint, especially a glancing/feathering joint.

Most Epoxies (try a sample first) don't attack PS so they work well for glue. If you coat the PS surface with epoxy laminating resin or epoxy paint first it seals the PS and you can usually apply just about anything on top of it.

For laminating PS sheet, I've found shellac works well. The solvent for shellac is alcohol which does not attack PS and still dries relatively fast. If you paint a layer of shellac on the foam, let it dry, and then paint on a second layer, it reactivates the first coat. When it gets tacky, it will stick sheets together like contact cement and if you time it well, still allows a little re-positioning before it sets. It machines/works better at the joint than the contact cements because it hardens but it still will cause an imperfection when shaping the foam across the joint because of the difference in hardness. Clamping the sheets in a press helps this by keeping the joint thin.

Plaster adheres fairly well to PS and though heavy, is an easy to work top coat. Do yourself a favor and build a hot wire to rough things out....keeps the dust and mess down.

Best,
Kelly
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Last edited by kcoffield; 06-12-2018 at 08:55 AM.
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Old 06-12-2018, 10:10 AM
mastuart mastuart is offline
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Dan What do you mean by Mix the bondo light?
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Old 06-12-2018, 10:27 AM
billfunk29 billfunk29 is offline
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Default Hot wire

Ditto on the hot wire for roughing. Be sure to have ventilation though.
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Old 06-12-2018, 12:00 PM
cliffrod cliffrod is offline
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Quote:
Originally Posted by kcoffield View Post
I've worked with expanded and extruded polystyrene extensively in lost foam patterns for metal casting and resin/cloth lay ups. I'm sort of surprised to see the 3M 45 and Bondo mentioned because I've found they both attack polystyrene. When you see "extremely flammable" on the spray can it usually means toluene which aggressively attacks PS. The carrier in polyester (Bondo) also attacks PS. That said, if you mist the 3M 45 on, there just isn't much solvent to attack the PS. If you mix the bondo hot so it kicks quickly you can get away with it too. If you apply polyester resin directly to PS in an attempt to lay glass cloth on it, it will rapidly reduce the PS to a gooey mess.

Most spray contact adhesives designed for PS foam are latex based (3M 77 I believe). The carrier doesn't attack PS but it dries slower. I hate using contact cements of any kind to bond PS because when you try to sand or work the seem it balls up, loads up your tools and abrasives, and also doesn't sand evenly at the joint, especially a glancing/feathering joint.

Most Epoxies (try a sample first) don't attack PS so they work well for glue. If you coat the PS surface with epoxy laminating resin or epoxy paint first it seals the PS and you can usually apply just about anything on top of it.

For laminating PS sheet, I've found shellac works well. The solvent for shellac is alcohol which does not attack PS and still dries relatively fast. If you paint a layer of shellac on the foam, let it dry, and then paint on a second layer, it reactivates the first coat. When it gets tacky, it will stick sheets together like contact cement and if you time it well, still allows a little re-positioning before it sets. It machines/works better at the joint than the contact cements because it hardens but it still will cause an imperfection when shaping the foam across the joint because of the difference in hardness. Clamping the sheets in a press helps this by keeping the joint thin.

Plaster adheres fairly well to PS and though heavy, is an easy to work top coat. Do yourself a favor and build a hot wire to rough things out....keeps the dust and mess down.

Best,
Kelly
Great info, Kelly. Thanks for sharing.
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  #10  
Old 06-13-2018, 12:16 AM
Moulder Moulder is offline
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Just an fyi on cutting the foam. Bosch makes jigsaw blades that are amazing for this. They have both long and short blade lengths. If I can remember I will find them and post the part numbers. They make no dust or mess.
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