it could work but youd need a silicon mold release spray and time you buy spray foam paint and everything its cheaper to buy decs...

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Even with a boatload of mold release, you likely would not get your foam bird out.

Check-out Smooth-On, Inc. Search for Rebound 25 and watch the mold making videos...

Now:
Why not just coat the decoy you intend to make copies of with a sealer(several coats of urethane) and then Rebound 25 (3-6 coats); the initial coat should be very thin, building the mold's thickness up with subsequent coats. Next, cover with a polystyrene resin and fiberglass coating;mark the longitudinal midline of the decoy and form a vertical fin-like ridge out of non-sulfur containing clay down the midline of the bird; now, cover the vertical face of this fin with foil. When complete, add another two fiberglass polystyrene resin layers over the non-fin side. When this is dry, remove the clay, but leave the thin layer of foil in place to enable you to seperate the two sides of the containment shell. Lay another 2 layers of figerglass on the other mold half to form a second fin over the remaining half of the shell. You now have a Rebound/decoy complex to foam and a hard containement shell over the silicone mold. Now, split the fiberglass shell vertically into its two halfves. Do no cut into the silicone mold. Clamp the shell back together and drill several (4-5) holes through the vertical fin, after removing the clay layer and foil. Now, all you have to do is bolt the fiberglass shell pieces together around the mold after removing the decoy body master. Bolt the 3" fiberglass and silicone lip around the mold body to a 1/4" thick plexiglass sheet by drilling a series of holes for even bolt spacing and placement. Now you have a rigid container surrounding your silicone mastermold. All you need do now is fill the void where the decoy was with water, pour it off into a measuring cup to determine the mold's volume and let the mold dry.

With the mold volume now known, you can mix two part foam (8lb)and pour it through several 3/4" pour holes in the plexiglass in an exact quantity to minimize waste via overexpansion. Some guys clamp the mold and plexiglass unit to a piece of shelving to force the foam to expand fully within the mold to get a slightly denser decoy.

I prefer to add a styrene plastic(Smooth Cast 300) layer after I spray the mold with release agent to get a hard shell that will surround the foam decoy body.

You can knock out about forty decoys before the Rebound master mold begins to deteriorate(it will start to turn white in the sections that are starting to stress from the heat generated from the expanding foam reaction). Fifty-seven is my maximum per mold...

 

Check out workingdecoys.net

Lots of info on how to make molds . And most people on there believe if you just copy say a ghg deke then your pretty much stealing. Up to you

I think though saying your upside down if you make your own dekes is BS because the foamers especially if your making divers will out last any manufactured ones no matter how you care for them. Plus you can paint them and shape them how you like.

We hunt over 7 lines of 2part birds and they stay on the boat from say mid October until ice out when we take the boat off the lift. And they look great still, except for some heads that were made with lower foam. I wouldn't use anything less than 16lb

Tony




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Well said.and they are very cost effective when you have a decoy hunter in the rig. The minimum I run is 8 lb on body's.

 

Sounds like it won't work then... I was just lookin at ways to build my spread. In shop I have been making a bunch out of expandable beads and gorilla glueing weighted keels on. Those work really good. So I was looking for a way to make some at home... What if you coated the outside of the wood mold with Vaseline? I had to do that when I was making jig molds to get it to release from the plaster of Paris

 

My neighbor frank is trying to sell his molds on Craigslist he has 8 or 9 different species.
They would work a lot better

 

WorkingDecoys.net. TONS of info. I'm working on my 3rd fiberglass mold. I use 2# foam for mine. Works great but 4# is better.

 

I know this is an old thread, but I found it very informative. I am new to decoy making, but was hoping to make a few specialty duck species decoys for myself that aren't commercially available using 2 part expanding foam. I can see if you want to try and get feather detail how a silicone+fiberglass mold would be useful. If you're just going for basic blocks is there any reason you can't just use mortar for a mold with mold release? Would it be enough to take the pressure/heat?