# Geofoam casting deck



## JakeHaznedl (Jan 6, 2019)

has anyone done or have any information on securing geofoam for a base on a casting deck? Will be topped with plywood so I can put a seat on the front of my 16’ stumpknocker. First boat always wanted to customize one for myself that maybe my son would want to keep someday. I use geofoam in stadium applications very regularly and would fasten it the same way but just want to be sure there isn’t a more correct way with a marine application.


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## DuckNut (Apr 3, 2009)

That foam, from what I see, is standard white foam. It will have flotation properties but that is about all.


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## JakeHaznedl (Jan 6, 2019)

It’s a 29 density foam and super sturdy was really trying to figure out the best way to adhere it if there was one other than I’ve typically used in other applications


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## yobata (Jul 14, 2015)

JakeHaznedl said:


> It’s a 29 density foam and super sturdy was really trying to figure out the best way to adhere it if there was one other than I’ve typically used in other applications


Epoxy may work, try some on a test piece. Some resins may melt some foams...


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## JakeHaznedl (Jan 6, 2019)

10-4 thanks for the help!


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## DuckNut (Apr 3, 2009)

JakeHaznedl said:


> It’s a 29 density foam and super sturdy was really trying to figure out the best way to adhere it if there was one other than I’ve typically used in other applications


Gel foam 29 is 1.8lb per cuft. Coosa 26 is 26 lbs per cuft
Compression strength 10.9 vs 1,060
Flexural strength 50 vs 4,050
Modulous 1,090 vs 215,100

Not even in the same ballpark.

Now, how can you use this stuff. If you were to use it as a foundation to build your deck and build over it you would have a nice base filled with flotation foam. In that case all you would need would be some hot glue. When you glass over it and attach to hull the foam will not move anyway.

To build the deck itself out of this as in a composite sandwhich, I don't think so.


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## JakeHaznedl (Jan 6, 2019)

This stuff was used to put a loading dock with a 40’ bridge across the 2 stacks, I’m not even close to worried about the strength of it. It’s hard enough to break your hand if you punch it. Geofoam not gel foam, we use the lighter density stuff as a base for concrete in movie theaters primarily. I’ll just attach it how I was planning on. Thanks guys


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## DuckNut (Apr 3, 2009)

JakeHaznedl said:


> This stuff was used to put a loading dock with a 40’ bridge across the 2 stacks, I’m not even close to worried about the strength of it. It’s hard enough to break your hand if you punch it. Geofoam not gel foam, we use the lighter density stuff as a base for concrete in movie theaters primarily. I’ll just attach it how I was planning on. Thanks guys


Sounds like you got a handle on it.

I never heard of it so I looked it up. Here is where I got my specs.
https://www.geofoam.com/?pdf=Foam-Control-Geofoam-TechData.pdf&id=2263


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## Fishtex (May 10, 2014)

Great idea, I mean if you know it all why bother us. I work in aerospace and we never make these kind of assumptions, it’s crazy, no idea of the real strength of the foam, peel strength, tensile, compression, in this application with glass, etc. what resin, polyester, vinyl ester, epoxy? Compatibility? It’s a simple job for what you are describing, so I would suggest at least use the known materials and lay up and do it correctly.....same amount of effort and maybe a bit more cost. Just some friendly advice, no offense.


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## DuckNut (Apr 3, 2009)

Fishtex said:


> Great idea, I mean if you know it all why bother us. I work in aerospace and we never make these kind of assumptions, it’s crazy, no idea of the real strength of the foam, peel strength, tensile, compression, in this application with glass, etc. what resin, polyester, vinyl ester, epoxy? Compatibility? It’s a simple job for what you are describing, so I would suggest at least use the known materials and lay up and do it correctly.....same amount of effort and maybe a bit more cost. Just some friendly advice, no offense.


I understand this, however in this application I think he would be fine. The way he wants to use the foam is not for structural integrity of the hull but simply for support, shaping and framework. 

Most decks have nothing but air under them and when the rebuild is complete there is no flotation in the hull. He will at least be better than a lot of these rebuilds in that respect.

I don't blame him at all for giving it a shot. After all it sounds like he can get it for free and many stringers have been made with items not on the nmma approved list (i.e.: blue foam, downspouts, etc). When he is done the deck will be attached to the hull for lateral support.

One thing he should try before is to make sure epoxy sticks. He could also eliminate the plywood and just use several layers of glass. His boat has a front seat that is 1/8 thick which is hollow, just covering the block with glass would be an improvement. I just don't see the need for the wood in this case because he is not spanning air but is supported with the foam.

Worst case scenarios, he will tear it out and redo it. That would be a cheap lesson for the knowledge gained.


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## Fishtex (May 10, 2014)

DuckNut said:


> I understand this, however in this application I think he would be fine. The way he wants to use the foam is not for structural integrity of the hull but simply for support, shaping and framework.
> 
> Most decks have nothing but air under them and when the rebuild is complete there is no flotation in the hull. He will at least be better than a lot of these rebuilds in that respect.
> 
> ...


Got to agree with you on testing. The delamination could happen with one resin, but not another, and it could be that it happens over time. I’ve seen some real adverse reactions when some kinds of foam encounter certain resins/chemicals, etc.

I guess I get skeptical about substitutions for proven materials/methods after seeing so many boats over the years with really crappy repairs/mods due to the wrong materials and substandard workmanship. I’m used to industry standard materials and methods, we don’t deviate, ever. Some of the advice I hear on forums about how to perform repairs.......it’s unfortunate as I’ve had to pass on a lot of boats that could have been really nice hulls if done correctly, you always worry about what you can’t see


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## DuckNut (Apr 3, 2009)

Fishtex said:


> Got to agree with you on testing. The delamination could happen with one resin, but not another, and it could be that it happens over time. I’ve seen some real adverse reactions when some kinds of foam encounter certain resins/chemicals, etc.
> 
> I guess I get skeptical about substitutions for proven materials/methods after seeing so many boats over the years with really crappy repairs/mods due to the wrong materials and substandard workmanship. I’m used to industry standard materials and methods, we don’t deviate, ever. Some of the advice I hear on forums about how to perform repairs.......it’s unfortunate as I’ve had to pass on a lot of boats that could have been really nice hulls if done correctly, you always worry about what you can’t see


Exactly. And because it is non structural it won't hurt to try.

Think of it this way...he builds a deck out of several layers of glass and attaches it to the hull. Then he slides the foam in underneath. The foam won't do anything that the glass wouldn't already have done except for adding weight and flotation.

If this were structural, no way without a lot of testing, a lot of testing. However, even if it were structural would it matter if it broke apart? Not where I fish because it is shallow and I could walk back to shore


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## JakeHaznedl (Jan 6, 2019)

Thank you! I just have access to the geofoam for free so I’m using that as a base. That other stuff looks incredible though


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