Hard Coats, what's the best?

[Specter]

I have been scrounging for many, many months for the best ways to hard coat foam. I create a lot of 2D and 3D foam props for outdoor use. I've studied a lot of different methods, but haven't quite found the best one to use yet. I know there's A LOT of very knowledgeable members on this site who have many years of experience behind them. I'd love to pick your brains a little on various methods.

Quick background- many of our props are moved throughout the year. They get dinged, dropped, smashed, etc. They also sit outdoors all year long. I make the props out of various materials, depending on the application (wood frame, metal/emt tube, pink or blue foam board, beaded foam, great stuff, polyurethane foam, paper mache, joint compound, plaster, fiberglass, etc). I really would like to find the best way to hard coat these 'sculptures'. The general public usually are not close enough to contact the props, however, at times they might be.

I live in AZ- the summer temps and heat are extreme, but is also exposed to freezing/cold and wet weather throughout the year. Most props that sit outdoors year round end up weathered and destroyed within 1-2 years. The only way around it I've found is Fiberglass- which, is too expensive and time/energy intensive to do.

Here's some of the methods I've found, and some info on them as to why they may or may not work. Please feel free to correct me if I am misguided on some of these things.

Fiberglass
Pros: very hard and good enough for structural use and contact w/ public. Not affected by weather.
Cons: Expensive, very labor intensive when you consider multiple layers, sanding/prepping for paint, etc. May have to prime/coat before if the medium under it will be eaten by the resin.

StyroSpray 1000
Pros: Cheap in comparison. Easy to apply with brush, roller, or spray w/ hopper gun.
Cons: Only works in humid environments- too dry here in AZ to achieve the results they claim- even creating a humid environment doesn't work. Sags on verticals. Peels/warps according to others.

Polyurea/Bed Liner
Pros: Very hard, tough shell. Dries within seconds, completely water tight.
Cons: Expensive equipment (can have outside pros spray it cheaper), must have good experience/training applying it to be done correctly, surface is bumpy due to very fast drying times, must be sanded before it will accept paint. Will have to prime/sand before paint to achieve smooth surface.

Polyurethane Spray Shell/Polyurea/Hybrid
Pros: Fast dry time, hard shell, can be sanded/painted.
Cons: Expensive equipment, must be primed quickly in order to paint afterwords, can get drips/bumps- not always completely smooth.

Plural Component Cartridge Systems (Polyurethane/Polyurea/Hybrid)
Pros: Fairly cheap to get started compared to other systems ($1k for gun, case of material, air masks/suits, mixing nozzles, etc, then another $1500 for air compressor)
Cons: Need much more material than you expect, driving costs up, have to switch out mixing nozzle once you take finger off trigger ($3-5ea), VOCs, etc.

Epoxy
Pros: appears to be industry standard, easily available, fast drying times, hard shell, can be tinted/mixed with fillers, etc. Self-leveling.
Cons: ???

Gel Coat
Pros: ???
Cons: ???

Misc Foam Coats
Pros: Easy to apply (brush/roll, not sure if spray), cheap
Cons: may not hold up to extreme weather, possibly same cons as StyroSpray 1000? Not sure how hard the shell is.

Bondo, Plasters, Joint Compounds, etc
Pros: Easily available, easy to apply via trowel, etc. Can be sanded/painted.
Cons: Cracks (especially when prop is moved, or has a little give as when used over EPS, etc), does not hold up to weather, HEAVY.

Cement/Portland/Dryvit, etc
Pros: cheap, troweled on, dries very hard, holds up to weather, great for permanent installations.
Cons: heavy, cannot be sanded/shaped too easily, will break/crack over EPS and some dings, etc. Not meant to be moved around much.


Again, I'd love to get some insights as to what works, what doesn't, what's the best overall solution. I've yet to try Epoxy- and it seems that many of you use that for the hard shell. How well does it handle weather? Just how hard is that shell? Will it crack if the prop is dropped or tipped over/banged around a little? Do you need fiberglass cloth, or is it just as hard with the Epoxy alone?

I look forward to hearing your input!

[tuck]

Jim,

You didn't say exactly what kind of "foam" you are using to make your props. Enlighten us, please.

[Specter]

Thanks for the reply! I use a wide variety of materials but for foam specifically I'll use beaded styrofoam, blue or pink board (owens or Dow), sometimes polyurethane and/or great stuff where applicable.

Any thoughts?

[tuck]

Thanks for the reply! I use a wide variety of materials but for foam specifically I'll use beaded styrofoam, blue or pink board (owens or Dow), sometimes polyurethane and/or great stuff where applicable.

Any thoughts?

You could use HDU (High Density Urethane) foam to make your props with, but it's expensive. It's much denser and harder than styrofoam but not impervious to breakage, scrapes and dings.

One thing you might try to repair your dinged up props with is interior/exterior grade spackling by DAP, available in quart size tubs at your local home store. It trowels on like butter, is pink when applied and turns white when dry. It dries quickly, sands easily, and takes paint well enough for quick repairs.

Bottom line in my opinion: You're using super cheap materials to make your props with and looking at expensive hard coats that can be difficult and costly to apply. Forget the hard coats and carry on. When one of your props gets damaged beyond repair, chunk it and make another.

[Specter]

wow- thanks for the reply! Yes, I agree. Using cheap base materials is a real problem. I'm going to look into HDU next time a project comes up. Great tip in the DAP, I'll give that a shot as well.
Anyone else?

Thanks!

[tuck]

Jim - a picture is worth a thousand words. If you can upload and post some photos of your typical props and talk about sizes, thicknesses and such, more folks would chime in, I'm sure.

[joe]

Jim,

You've done an excellent job with all the descriptions. They are exactly what I would have found.

The Gel Coat is very attractive for those using bead board or eps foam. It's much like automotive paint except it doesn't attach the foam. Also it sets up fast and hard as a brick.

There is a new texture coat offered by Sherwin Williams. As usual it's a hopper gun or roller material. I believe it's called out at texture crete and feels like it has sand in it. Comes in three textures but I've only seen the light sand variety. We'll be using some next week. I've been invited to post more about it on the "Sign Routing Forum". It's hard to keep up with all the new products but a hardcoat for foam has been the most illusive.

Our biggest failure has been with Styrospray. I lost a good $1000. on a church sign using their product. I'd advise everyone to stay away from that stuff.

Joe Crumley
www.normansignco.com

[Gary Campbell]

Joe...
You may want to do a test with the Gel Coat. It is a tinted Polyester resin, same as Fiberglass resin with a pigment added. My guess is that the styrene in the Gel Coat will eat both beadboard and EPS foams. Very few sealers will stop styrene. Works great on marine HDU foams.

[bleeth]

Correct regarding Gel coat. It will melt styrofoam and many of the expanded foams. Epoxy based coatings will not. I was hoping by now Bill P would chime in. He did a bunch of exterior carvings and used an easy to apply hard coat but I can't remember the name of it for the life of me.
There are also "dryvit" type products that are used by a lot of the architectural foam people. I believe the up front spray equipment is a bit pricey but if one does a bunch of it that gets spread out pretty quick.

[joe]

Boys,

I'm ready to throw in the towell but our next door neighbor has, what I told was Gel Coat, that the apply to experimental spy playnes which are hot wired out of bead board.. They tint it with a small tube of color and shoot it on. It's amazingly hard when dry. I'll wonder over on Tuesday an take a photo or two and get more info.

It stands to reason if it's quick drying, there must be some kind of accilerator which means it will attach foam. Thanks for posting. I'm very careful about posting information which isn't correct.

Bill P. is sold on Apoxy. All the epoxies I'm familiar with are thick enough they need to be brushed on. Haven't heard of a good solution for using epoxy on vertical surfaces.

Joe Crumley
www.normansignco.com