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Discussion Starter #1
Hey Spooky People!

This isn't so much a request for a tutorial as it is a "am I going about this correctly" guide. The entrance to our haunt is a sort of fall-down-the-rabbit-hole type deal. I want to build a rock arch similar to this:



It's not going to be that wide as I only have about 5' between the two walls we're building this, but it will be about 10' tall at its highest point. I need it to be lightweight as we will be creating it off-site and then installing it outdoors.

My current plan is to build the skeleton with PVC or 2x2" lumber, while having pieces branch off like arms to create more of a skeletal support structure. Chicken wire will be attached to this skeleton, followed by screen mesh and then some kind of muslin or fabric coated in monster mud. I will Drylok and/or polyurethane over this fabric once dry to get it really weatherproof, then apply final paint.

Will this work? Should I spray-foam (Great Stuff) inside the chicken wire before applying the screen mesh to provide more support, or is this redundant? Do I even need the screen mesh over the chicken wire?

Here's my conceptual design for this arch entrance:



Thanks for any guidance you folks might have!
 

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Discussion Starter #3
Ideally it would be one piece, but I'm open to doing it in a few pieces. That would very likely make it easier to store later on. I didn't think about the Monster Mud being heavy though. Yikes! Is there a lighter weight coating option? Some kind of Drylock/water mixture maybe?
 

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If it were me I'd do away with the muslin/fabric, and I'd do a light weight frame (as stated above) in three pieces. I'd put chicken wire over the entire frame, and spray foam over the chicken wire. While the foam is wet, I'd sprinkle sand and light gravel for texture, then paint when dry. This might be your lightest option. Keep it hollow on the inside to further lighten the assembly. Make sure you install anchor points before the spray foam.
 

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You may want to use screen if you are going the foam route so the holes will be smaller and the foam have more to grab hold of. With screen I think the foam would expand thru both side better than with chicken wire unless you got very small hole chicken wire. I would order the big 2 part foam it would be cheaper than buying cans of Great Stuff.
 

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Discussion Starter #6
If it were me I'd do away with the muslin/fabric, and I'd do a light weight frame (as stated above) in three pieces. I'd put chicken wire over the entire frame, and spray foam over the chicken wire. While the foam is wet, I'd sprinkle sand and light gravel for texture, then paint when dry. This might be your lightest option. Keep it hollow on the inside to further lighten the assembly. Make sure you install anchor points before the spray foam.
Keeping it hollow inside is definitely my ideal route. What do you mean by 'anchor points'? Like points of contact within the frame to attached the wire to?

You may want to use screen if you are going the foam route so the holes will be smaller and the foam have more to grab hold of. With screen I think the foam would expand thru both side better than with chicken wire unless you gout very small hole chicken wire. I would order the big 2 part foam it would be cheaper than buying cans of Great Stuff.
Yes, I think I would definitely keep the screen. Use the chicken wire to get the rough form and then screen over that so the foam doesn't spray through. I've looked into the 2-part foam spray stuff (like Tiger Foam) and I just can't tell if it's going to be better cost-wise than buying 90 - 100 cans of Great Stuff. The cheapest 2-part stuff goes for about $270 for 200 board ft. I can get 75 cans of Great Stuff from Home Depot for the same price. But what will last longer? I also have 2 huge trees I need to make, so if one product might yield more leftovers after the arch is done, I might just do that.
 

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Discussion Starter #7
So I think I'm going to go this route (skip to step 7): https://www.instructables.com/id/Outdoor-Paper-Mache-Easter-Island-Head/

I will be building my skeletal structure with 2x4, 2x2, and any other wood scraps I can come up with, attaching and shaping chicken wire to create the rock forms, then going over that with screen mesh, and finally the "towel mache" mix in the above link. I have so many projects in this haunt pipeline, mostly stuff I've never attempted before. HOLY CRAP WHAT AM I GETTING MYSELF INTO?!
 

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Discussion Starter #10
Thanks for that! I have indeed looked into that very install. Allen Hopps has some old videos on his YouTube of his own version of it, and the whole project is beyond messy, though it would almost certainly be the fastest. I'd be looking at spending around $300-$600 in TigerFoam (the least expensive of the spray foams that I've looked into) depending on much it covers...it's hard to say how far a 200 board foot kit will go, but I hope it would do at least the entire arch with some left over.
 

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I agree with everyone that said about using expanding filler foam. I have done similar projects. Lay out plastic sheeting, lay down your support "skeleton" and then start building layers of foam until you achieve your desired shape, size, height, etc. Let it dry then simply stand it up and peel or cut away the plastic sheeting.
 

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I agree with everyone that said about using expanding filler foam. I have done similar projects. Lay out plastic sheeting, lay down your support "skeleton" and then start building layers of foam until you achieve your desired shape, size, height, etc. Let it dry then simply stand it up and peel or cut away the plastic sheeting.
Were you using Great Stuff? And wouldn't that leave one whole side of the arch flat since it would be laying down?
 

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[/QUOTE]

Were you using Great Stuff? And wouldn't that leave one whole side of the arch flat since it would be laying down?[/QUOTE]

Correct. One side is flat. I used mine as an entry way to my garage. You could simply repeat the process and glue or caulk the 2 halfs together
 

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I have to agree with everyone who said that using anything but foam for your basic structure will give you a very heavy project. From past experience I wouldn't use PVC for this project. Use wood for the supports. The overall finished weight will hold up much better with solid wood than hollow plastic.

https://www.ehow.com/how_12095679_make-fake-rocks-using-expandable-spray-foam.html is a bare bones guide to using spray foam to make fake stone. You can use the general guidelines to create an entire wall of stone. After it dries you can carve it to give it even more rocky textures. And then comes the command decision on how to coat it.

Paint will protect it just fine because a spray foam cave entrance is pretty much waterproof if you cover up all the wood and wire. But you will be left with a project that can be easily damaged by rowdy crowds. We used Drylok on a couple of our mausoleums and frankly we don't think it protects any better than regular latex paint when it comes to actual impact damage. There's a video on using Flexbond to act as a final coat for foam projects that might be worth a look. It could give you a sturdy, albeit heavy structure if you apply a coat to the entire project. But that might be the trade-off you have to have in order to make a sturdy, impact resistant structure. https://youtu.be/w3r67JXmCY0?list=PLG5Uhh995RKwHX7BG5yKLwIy8A9syX2Zi&t=508 .
 

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Discussion Starter #15
Correct. One side is flat. I used mine as an entry way to my garage. You could simply repeat the process and glue or caulk the 2 halfs together
Ok, thanks for the idea!

I have to agree with everyone who said that using anything but foam for your basic structure will give you a very heavy project. From past experience I wouldn't use PVC for this project. Use wood for the supports. The overall finished weight will hold up much better with solid wood than hollow plastic.

https://www.ehow.com/how_12095679_make-fake-rocks-using-expandable-spray-foam.html is a bare bones guide to using spray foam to make fake stone. You can use the general guidelines to create an entire wall of stone. After it dries you can carve it to give it even more rocky textures. And then comes the command decision on how to coat it.

Paint will protect it just fine because a spray foam cave entrance is pretty much waterproof if you cover up all the wood and wire. But you will be left with a project that can be easily damaged by rowdy crowds. We used Drylok on a couple of our mausoleums and frankly we don't think it protects any better than regular latex paint when it comes to actual impact damage. There's a video on using Flexbond to act as a final coat for foam projects that might be worth a look. It could give you a sturdy, albeit heavy structure if you apply a coat to the entire project. But that might be the trade-off you have to have in order to make a sturdy, impact resistant structure. https://youtu.be/w3r67JXmCY0?list=PLG5Uhh995RKwHX7BG5yKLwIy8A9syXZi&t=508 .
Thanks for the links, Chub! I've seen many of Hollywood Haunter's videos - they're an amazing source of inspiration! I'm definitely leaning towards the Great Stuff route and getting those "foam beaks" that are sold separately to help make each can last a little longer.
 

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I'm not sure if you have seen the foam blocks from Lowes. The ones that come with the trailers that get shipped there but they are nice to work with and they are free. I'm guessing they are 16" x 8"x8". You can glue them together with the spray foam. I have made a 2 piece cave with them and it is light enough to move with one person and probably strong enough to stand on. Mine has lasted 2 years no problem. Finished like Hollywood Haunters did with there pumpkins. Good luck and give us some pictures.
 

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Discussion Starter #17
I'm not sure if you have seen the foam blocks from Lowes. The ones that come with the trailers that get shipped there but they are nice to work with and they are free. I'm guessing they are 16" x 8"x8". You can glue them together with the spray foam. I have made a 2 piece cave with them and it is light enough to move with one person and probably strong enough to stand on. Mine has lasted 2 years no problem. Finished like Hollywood Haunters did with there pumpkins. Good luck and give us some pictures.
I have not seen those. I'm assuming every Lowes gets them with deliveries? Who should I ask about acquiring them - management?
 

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I would assume they do. I have also found them at a farm supply company. Anybody that cells trailers might have them. Usually, after a trailer delivery, they are scattered all around the trailers. I just ask the person at the plant desk if I can have them. If you goto the manager they might get worried about what you are going to do with them and what liability they could have. Good Luck.
 

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Maybe a combination of a PVC framework with chicken wire structure plus underlayment paper?
I did an entire garage cave with underlayment paper like this: https://www.lowes.com/pd/Danco-36-in-x-167-ft-500-sq-ft-Red-Rosin-Paper-Roof-Underlayment/3395978

It would need the chicken wire to provide some structure if you indeed want to move it. I didn't use it because mine was pretty quick and dirty and the underlayment was stiff enough to hold it's shape.

Here's one of my stalagmites:

Cave1.jpg

anyway, the stuff is easy to work with, and easy to paint. AND easy to clean up. Good luck with the build. FUN! Good on you too for the early start.
 

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There have been a number of other posts on weatherization and Monster Mud was not highly thought of and not as weather proof/resistant as one might have hoped. Why not use spray foam to create the effect. With paint, it should be weather proof.
 
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