Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam?

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shareahack

Active Member
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Hi all, I'm thinking about sculpting a full-size t-rex skull out of pink rigid insulating foam (mainly because I was able to acquire a a big pile of old used foam!).

I'll be doing it in manageable sections and then merging everything together at the end.

I have some ideas about covering/finishing the foam but am wondering if any seasoned sculptors out there had any good tips. The goal is to cover/paint/seal the foam to the point where it looks and feels like a museum resin fossil casting.

I really like the darker, more matte weathered look (see attachment):

trex-dinosaur-skull-fossil-museum.jpg


Ideally the final sculpture will be sturdy enough to stand on and could sit outside and withstand the weather and not easily chip paint (a nice garden centerpiece? :)).

My first instinct was to coat the foam with PVA or something to protect it from any solvent use. Then I would cover the entire thing with fiberglass/resin, maybe do some finishing work with Bondo etc and then paint, weather, and seal it.

I'm thinking if I use fiberglass it'll introduce a lot of finishing work because of the grid-like fiber texture so I'm wondering if there's a better alternative - maybe something like Line-X (never used it before)?

Would your local hardware store automotive Bondo resin be good enough or do you think there's a better alternative? (I'll probably need a lot of this stuff)

Luckily there's a lot of margin for error on the texturing because of the bumpy/broken surfaces of natural fossils.

If anyone has any better ideas or time-saving tips I would be eternally grateful. Will be posting progress along the way!

Cheers
 
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CT1138

Sr Member
Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

That's a cast of "Stan" the T. rex, and one of the best preserved skulls to make reference from. I know a lot of museums use painted foam for their replicas, for example, this Sue head that the Field Museum put out for visitors, which they allowed to be touched. Unfortunately, I'm not sure what kind of foam or paint they used, all I know was that it was extremely sturdy.
 

shareahack

Active Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

That's a cast of "Stan" the T. rex, and one of the best preserved skulls to make reference from. I know a lot of museums use painted foam for their replicas, for example, this Sue head that the Field Museum put out for visitors, which they allowed to be touched. Unfortunately, I'm not sure what kind of foam or paint they used, all I know was that it was extremely sturdy.
http://i.imgur.com/7FB4WGO.jpg
Awesome example of what I'd like to have as a finished product. Great-low-profile mounts they're using in that one. Might just stop by the museum this week and see if someone can give me some tips or get some ideas :)
 

shareahack

Active Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

With winter coming up fast I decided to go full steam on the T-rex skull project since most of the work has to be done outside. Here's a quick update on the progress of the skull :)

Here is the scanned 3D model I'm using of what I believe to be the T-rex "Stan" fossil discovered in Buffalo, South Dakota by Stan Sacrison:



According to the Black Hills Institute, the real-life skull has the dimensions of 58" L x 33" W x 68 1/2" H. (approx. 4.8 feet wide) and I really wanted to make mine match the full scale of the original. Because of this I had to chop the skull model into 8 sections so I could work manageable sections on the CNC router (the router can only work with objects inside of a 2' x 4' work area with a depth of approx 4"):



To make these 3D files workable on the CNC machine, I "sliced" them up into layers to match the depth of the pieces of foam I had (3" inch rigid pink insulation foam).

For just the TOP LEFT half of the skull, it took about 5 pieces of foam and a ended up creating a jigsaw puzzle of 25 pieces:



Need to run right now but more updates tomorrow :)
 

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shareahack

Active Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Thanks clonesix looks like exactly what I need. I've already got a bunch of this stuff that I'm going to give a try and see how it holds up with fiberglass:

FXpoxy-Epoxy Resin 2 Gallon Ultra Clear UV resistant (50-60 sq ft) Countertops, Table Tops, Bartops[/h]
61KrucyYo%2BL._SL1000_.jpg


Seems like pretty standard epoxy and just going to mix and smear it on the foam with fiberglass. Was even thinking of using old pink 'hair' fiberglass insulation with the epoxy as the 'skin'. Thinking it might be dangerous to inhale if sanded but might be a cool experiment.
 

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cavx

Master Member
Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

I am using a very similar product now. If the parts are greater than 5mm thick, this stuff seems to set up nice and the parts can be quite strong, but if they are thin, they may/will remain flexible for some time.

The stuff I am using has a potlife of almost an hour, demold time after 24 hours and post cure time of 7+ days if not baked. Bake at 70 degrees C for 3 hours to make it hard.

Yes you can use this with fibreglass matting (woven or chopped) and it will saturate and set like a rock.
 

shareahack

Active Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Yes you can use this with fibreglass matting (woven or chopped) and it will saturate and set like a rock.
For sure I've got both of the woven/chopped Bondo stuff meant for auto body work. I feel like if I plaster it on the foam it's going to leave behind a grid-like texture that i'll have to spend more time finishing (with either more resin on top or sanding it down etc).

What do you think about using that pink cotton-candy type fiberglass insulation?

section-link-insulation-8fd3321e24469b09232b0d46000732e4330ddb48f68e131716cb8054344feac2.jpg

I mean it's fiberglass...the strands are nice and small, you can use as little or as much as you want, and you can bend/form the strands to the foam surfaces easier.

I'm wondering if I combine this stuff with resin it would achieve a nice strong shell over the foam that might be easier to control with less artifacts when cured?
 

cavx

Master Member
Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

What do you think about using that pink cotton-candy type fiberglass insulation?

View attachment 761627

I mean it's fiberglass...the strands are nice and small, you can use as little or as much as you want, and you can bend/form the strands to the foam surfaces easier.

I'm wondering if I combine this stuff with resin it would achieve a nice strong shell over the foam that might be easier to control with less artifacts when cured?
I have only ever used this stuff in wall/roof cavities. I see no issue with it as long as you get full saturation of the epoxy.

Just bought 7.5KG of fast(er) set epoxy so hopefully mix, degas, pour and demold all in a day. Last time I used this stuff, parts were still soft for about 24 hours, but then set rock hard. We are also expecting the temp to reach 37 degrees C today, so really happy that will ensure my parts kick properly.
 

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shareahack

Active Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Pink foam would be a nightmare to work with. Go to Home Depot and 'borrow' a hand full, then try to get it to lay down smooth with resin.
I managed to do some cuts already with the old pieces of foam I picked up...it actually wasn't too bad! MESSY, but workable. Will post some pics later tonight.

I think that because the foam was aged that it was more brittle/flaky and easier to cut.

This is the old dirty pile foam I grabbed off a guy from Kijiji:

 

13doctorwho

Sr Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

There's a reason fiber glass mat and fiberglass cloth are thin. It would take a lot of resin to soak that pink insulation. I don't think it's as flexible as you think. Generally people do the bulk layers of fiberglass with the cloth (it's thicker and has random threads). Once the desired thickness is reached you put a couple layers of the mat, that's the tightly woven glass. If you want it really smooth when glass layers are cured go over the whole thing with a layer of just resin. With the fibers cured the last layer won't soak into the fibers so it's like painting on a finish coat.
Just be careful and wear a mask... fiber glass and resin is nasty stuff.
 

shareahack

Active Member
RPF PREMIUM MEMBER
Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Pink foam would be a nightmare to work with. Go to Home Depot and 'borrow' a hand full, then try to get it to lay down smooth with resin.
LOL I just realized you meant the cotton candy stuff. Luckily we're in the middle of roofing renos and I've got an abundance of used insulation that's mostly being thrown away because it's all moldy. :thumbsup

- - - Updated - - -

There's a reason fiber glass mat and fiberglass cloth are thin. It would take a lot of resin to soak that pink insulation. I don't think it's as flexible as you think. Generally people do the bulk layers of fiberglass with the cloth (it's thicker and has random threads). Once the desired thickness is reached you put a couple layers of the mat, that's the tightly woven glass. If you want it really smooth when glass layers are cured go over the whole thing with a layer of just resin. With the fibers cured the last layer won't soak into the fibers so it's like painting on a finish coat.
Just be careful and wear a mask... fiber glass and resin is nasty stuff.
Thanks 13doctorwho, good advice. I'll do some tests of all techniques mentioned above. Luckily the texture of the skull is going to be lumpy and imperfect so there's lots of room for error.
 
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Lear60man

Master Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Haha. Yea I was talking about the cotton candy stuff. The stuff in post #11 is perfect for sculpting....mold and all!

Nice kitty BTW.
 

shareahack

Active Member
RPF PREMIUM MEMBER
Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Here's a photo of the CNC being used to cut out the foam T-rex pieces. Pink snow everywhere!



Each piece of foam is 2' feet x 4' feet. In 3 days of cutting and 5.5 pieces of foam later, I managed to cut out enough pieces to build up just 1/4 of the skull (the top left half):



Lots of fun punching out the pieces from the foam like a giant hobby model kit:



And finally we have something that's starting to look like a T-rex! Still lots of gluing, shaping, and excavating the overhangs to do. I'd say I'm about 20% done:

 

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kwalsh0000

Sr Member
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Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Love the concept man esp the last pic and how it goes together. Great way to merge techniques. Cant wait to see progress.
 

shareahack

Active Member
RPF PREMIUM MEMBER
Re: Full Sized T-Rex Dinosaur Skull - advice on coating/finishing/painting rigid foam

Made a bit more progress on skull. Good news, all the cutting is finished! Just need to manually carve out the overhangs and finishing touching up/sanding (the fun part).

I used PL construction adhesive to glue the pieces together and then bamboo BBQ skewers to temporarily hold them in place:









Started roughing out the top internal geometry of the skull by hand:



A couple bonuses I've learned:

The teeth overhangs that (stretch across the whole model) are actually useful in protecting the teeth while I work on other parts of the skull. Since they're so skinny they'd be super delicate if they weren't being reinforced by the overhangs. I'll be cutting out the teeth as the last step before fiberglassing.

The PL construction "300 foam board" glue is actually NOT ideal for foam-on-foam gluing. It doesn't fully cure and leaves the pieces somewhat repositionable...but it does grab well and adequately holds the sculpture in tact...it has the texture/consistency of peanut butter.

I used the standard PL 3X on the more structural parts of the model and it works great, cures very hard and grabs the foam well.

The bonus of using the weaker PL 300 for this particular project is it made carving out the internal skull structures way easier when cutting by hand. The PL 3X is very hard to cut through with a knife/saw.

Happy [Canadian] Thanksgiving!
 

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