i was thinking of using great stuff

[philb]

I am building a 12' fishing boat and a using expoy i was think that great stuff foam would be easy to use for the hull.

i know it is a closed-cell foam and it can be sanded and shaped, but not sure if you can resin over it.

any info. will help

thanks

[lewisboats]

I don't thing it would have any strength in shear or compression...it is afterall only designed to fill gaps and eliminate air leaks around doors and such. It would be OK for filling areas for flotation if it was used to fill plastic bags.

Steve

[rwatson]

Are we talking hardware style foam that says "not suitable for boatbuilding" or the expanding foam (high or low density) you get from boat suppliers ?
If it is the latter, yes, of course you can, using fibre glass cloth of course, like your fishing boat does.
There is at least one builder who has done it slightly differently
check out www.bourneboats.com.au for example.

[PAR]

Great Stuff is a closed cell polyurethane (I'm pretty sure), but it's not very economical to use in the aerosol cans. They have three kinds, small, medium and large expansion rates. The large gap filling stuff would be the most economical, but frankly it'll take a hell of a lot of cans to fill just a small area.

It's also pretty low density stuff, though does have some good stick-em qualities. It degrades very quickly from UV.

You're much better off buying the two part polyurethane foams and pouring it into spaces you need it. You can also accurately predict how much you need for a specific cavity you're attempting to fill, which is not possible with the aerosol cans.

What isn't shown in the Bourne Boats site, are is the hundreds of hours spent laying 'glass and goo, plus the huge effort fairing it smooth. I think using foam sheets would be a better way to get a fair hull and you wouldn't have to worry about the steel mesh rusting in time.

[kach22i]

I looked up information on their website, they do "claim" that it's closed cell. However based on my experience, once you cut away the protective outer shell it very much acts (and looks) as an open cell and absorbs water.

I have lots of Great Stuff inside of my hovercraft (repairs), it absorbs moisture and adds weight.

[ted655]

Here is the final point on foams. Why use them at all? If " to keep my boat from sinking" is your answer, then consider this 1 simple fact. Only polystyrene (styrofoam) is impervious to water, Spray in, pour in place, all 2 part "container" foams absorb water. That makes them ALL, sponges. Once they absorb water, they hold it, adding weight to the boat. poured into boat spaces, this stuff is there forever. It is very tenacious, sticks good & is hard to remove.
Ya'll do what you will, but no foam other than polystyrene belongs in wet or even damp environments
If you want to foam your boat, then you will have to buy & cut & fit & glue (PL tube adhesive works good), polystyrene.

[marshmat]

"Great Stuff", "Zerodraft", etc..... these things are often abused in ways they were never meant to be.

They are designed to seal and insulate gaps in a wall- around a window frame, in a mouse hole, beside an air conditioner hose pass-through, etc.

There are a number of strikes against this stuff for anything other than those intended uses. It has major compression set problems (push it more than a tiny bit, and it won't spring back). It starts to break down under very little elongation or compression. Without the skin that forms on its surface as it cures, it isn't really air, vapour or water tight for any significant length of time.

I have to agree with Ted- polystyrene is the only foam I trust to be truly and completely waterproof more or less indefinitely. I should note that my own boat does have 2-part polyurethane foam in the bow flotation compartment- in a fully sealed compartment, above the waterline, above the bilge and never subject to anything more than normal atmospheric humidity and the occasional bit of rain on its glass-over-plywood top.

[captainjsw]

Dont risk it use the stuff that designed for boat building - Like Diab - SP Systems etc. Correctly designed your boat will be lighter, stiffer and perform better. Will probably cost less too as not as much money will need to be spent on epoxy and glass etc
John

[PAR]

There are polyurethane closed cell foams and frankly all I use (two part, pour in stuff). It doesn't have to be the "Styrofoam" brand to be effective or closed cell. Polystyrene foam can also be had in a closed cell formulation, though I have little experience with it. I've had the fortune to dig into boats that I've added polyurethane foam to, several years after the fact with no absorbed moisture. If using a foam as a structural element, using the correct density foam requires some research on the builders part, but both will work. I use a 2 pound foam for floatation and an 8 pound foam for structural elements.

[ted655]

Polystyrene is not a user mixed 2 part foam. It is made in large factories, where styrene is infused with carbon dioxide, forming small "beads". Then steam heat & pressure is used to force these hot little beads into sheets, billets or coffee cups, etc.
.
Like I said, some will do as they will, but no matter how it's worded or marketed, polyurethane will eventually absorb water if the 2 meet for an extended time. They have no business in a bilge area OR where water will stand for extended time. It will work as unsinkable ballast.

[PAR]

The two part polyurethanes typically used as floatation in boats, meets or exceeds military Specification P-21929B, further if used to incase or bed fuel tanks (a very common practice) it's compressive and density strength complies with ASTM D-1621 & 1622 (respectively).

In short, typical 2 pound foam will not absorb more then .6 ounces per cubic foot of foam (after 30 days emersion at 20') and withstand 60 PSI within 10% deflection.

The properties of the 2 pound product I use.

Density ASTM D-1622
Molded, overall pcf 3.4
Core, pcf 2.7
Yield cu.ft./gal. 3.0 ±

Compressive Strength, 10% deflection, ASTM D-1621
Parallel, psi 25.3
Perpendicular, psi 30.5

Compressive Strength Change, Mil-P-21929B, % change 2.35

Initial K-Factor, ASTM C-518, BTU in/hr ft<= 0.141

Shear Strength, psi
ASTM C-273 31.0

Tensile Strength, psi
ASTM D-1623 51.9

Water Absorption
ASTM D-2842, lb/ft<= 0.083%

Tumbling Friability,
ASTM C-421, % loss 11.1

Closed Cell Content
ASTM D-2856, % 95

Compression Set, Mil-P-21929B, % loss 0.97

Oil Resistance
ASTM D-471, Mil-P-21929B Pass

Dimensional Stability
ASTM D-2126, % volume change:

@ -20°F 1 day .2, 7 days .1, 14 days .2, 28 days .3
@100°F (100% Humidity) 1 day 1.3, 7 days 2.1, 14 days 2.5, 28 days 3.5
@158°F 1 day .3, 7 days 1.0, 14 days 1.5, 28 days 1.8
@158°F (100% Humidity) 1 day 5.3, 7 days 7.0, 14 days 7.9, 28 days 8.9

It's important to speak what we know folks, not speculate or offer unfounded suggestions. Speculation, beliefs and guess work should come with a warning as such or be confined to the open forum, where clearly anything goes.

[Pericles]

PAR,

Thank you for your observations and those figures. Have you figures for the 8 lb foam and who supplies it please?

It would be interesting to learn from Ted655, which authority he cites to base his conclusions that only Polystyrene is impervious to water. Ike points out that most boat builders use 2 part polyurethane foam for flotation purposes.

http://newboatbuilders.com/pages/flot2.html

He then mentions that Polystyrene dissolves on contact with petroleum products #29 What's wrong with foaming in fuel tanks?

http://boatdesign.net/forums/showthr...ight=fuel+tank

"In my opinion everything. First what are the pros.
Foaming in allows the builder to not have to put in a mounting system for the tank. Ii prevents the tank from moving. It provides some amount of cushioning from shock and vibration.

Now for reality: but first a little history. The Federal Regulations allow you to foam in tanks, but only under the following conditions: the foam must be resistant to gasoline, other petroleum products, bilge cleaners, etc. In other words all the stuff that dissolves polystyrene foams (styrofoam). So you have to use a polyurethane or polyethylene foam. Typically polyurethane foams are used. The same stuff used for flotation.

Second; and by far most important the sheer strength of the bond between the tank and the foam is required to be greater than the sheer strength of the foam itself. This is so the foam will break before the bond does.

Requirement one is easy. There are plenty of foams on the market that are resistant to all kinds of chemicals.

Requirement two is the hard part: in reality it is almost impossible to achieve. In fact when the Coast Guard included this requirement they did it specifically to discourage foaming in tanks. They couldn't outlaw it because it was a common practice at the time (the late 70's) but they wanted to make it difficult to achieve.

In practice what happens is this. The builder puts some foam in, puts the tank in and adds foam to fill the compartment, essentially suspending the tank in the foam. They then put down the deck and no one sees the tank again until it has to be replaced.

What is important is what happens after the tank is in. Aluminum forms a natural oxide on it's surface to prevent it from corroding. If you remove or even scratch this coating and moisture is allowed to get to the actual metal you get corrosion. Normally in the open air the surface repairs itself. The oxide reforms and all is well. However to get a really good bond between the metal and the foam you need to remove the oxide. I have not met anyone yet in 34 years who does that. If you leave the oxide then the bond is not as good as it should be. Plus that, with shock, vibration, slamming and everything else that goes on in a boat the bond begins to deteriorate. As soon as that happens then moisture can get between the foam and the tank.

Additionally, the regualtions require that on gasoline powered boats, that the fittings on the top of the tank be accessible for iinspection. So the tank top is not foamed over. Sometimes the builder just foams the bottom and sides of the tanks, others foam the top but leave spaces for the fittings. This leaves a place for water to collect where it can't run off.

So what happens eventually with foamed in tanks is that the moisture gets between the foam and the tank and corrodes it.

Also, the foams used are two part foams. That is, two chemicals are mixed along with a blowing agent and the resulting compound foams up. This reaction has to take place within a narrow range of temperature and humidty. If it's too cold you get cow pies or bread dough. If it's too hot then the reaction happens too quickly and it breaks the walls of the foam cells resulting in what looks a lot like broken glass. Either way, if you don't get nice closed cell foam, the foam can then absorb water. Now you have a sponge attached to your aluminum tank. Again this results in corrosion. So, I have for years told builders to avoid foaming in tanks. People still do it though.

I have also tried to get ABYC to eliminate the same requirements from their fuel system standard, that it is say no foaming in of tanks. But I haven't been succesfull at that either. I have been involved with several research studies on failures of aluminum tanks and the vast majority of the tanks that failed in short periods of time, say 1 to 5 years, were foamed in. I even saw one that had only been in the boat 6 months and it had holes in the bottom, corroded from th outside in. Foaming is just not a good practice in my humble opinion."

Those are Ike's views and I have no difficulty in accepting all his advice and yours, without equivocation.

Pericles

[ted655]

="It would be interesting to learn from Ted655, which authority he cites to base his conclusions that only Polystyrene is impervious to water. Ike points out that most boat builders use 2 part polyurethane foam for flotation purposes." ===
.
Aw gee guys, I'm not an engineer. It doesn't take long to whip out specs & equations to show my ignorance. I find no shame in that. The above is a proper question for sure.
My authority is research & careful attention to the wording (or lack of wording), that legal consultants require on product descriptions. Add a bit of old age & observation in the school of hard knocks. Not much authority I guess. It's just an honest opinion I offer on a take it or leave it basis I have no dog in the hunt, so there is no agenda.
I love it if i can get someone to question my advice, it means I sparked a doubt, or forced a discussion. I like when a subject is put under more inspection by more people. I'm not a gadfly, my purpose is to not argue on every issue.
Many first timers & newbes come here for help in making decisions which may be the only advice they seek. I want them to see ALL sides of the cube, without being overly contentious or argumentative to the rest.
.
Let me close by saying that the very last thing we want to do is accept as "authority", the fact that "many manufactures" are embracing a particular practice or product.
Too much damn junk out there to ever do that.

[Pericles]

Ted,

We are better served in the UK, I guess.

http://www.spray-insulation.co.uk/buoyancy%20foam.htm

They state that "Handi Foam is a two part polyurethane foam cures chemically and has a closed cell structure making it impervious to moisture. In fact, when sprayed to a depth greater than 3 inches, Handi-Foam has a permeability rating of less than 1!! This is why 2 component foam is ideal for buoyancy and flotation applications."

I'll go with that. Sometimes it's necessary to trust the manufacturer. Using your mindset of questioning received knowledge, I doubt I'd ever complete my boat. After all it's not necessary to know how safety matches are manufactured, it's enough to know how to strike them.

Pericles

[ted655]

===== "After all it's not necessary to know how safety matches are manufactured, it's enough to know how to strike them. " ====
Viva la difference! I use strike "anywhere". More dangerous to carry in your pocket, but when the 1/2 that is embedded in the paper strip on yours gets wet or glazed, mine will strike on my zipper.
.
Urethane foam is like a boat hull its self. Impervious to water until pierced.
Between the governmental safety requirements, rising costs & economy of speed production, the foam manufacturers are under tremendous pressure to come up with "something, anything" that can be on- site poured. Maybe they have. OR maybe the line has been blurred in order to relieve these pressure.
Here is what is MORE likely to happen HERE on this forum, I believe.
We accept that 2 parts are waterproof. Once on that slippery slope we lose track of the ones (and there are a lot) which are poor quality. Next thing we know the collective opinion is that 2 part foam is OK.
There may be a few that can serve the boat flotation issues, but it's a small expensive club. A club I'm NOT willing to let cheap foams like "Great Stuff" join.
Let us be very careful with our advice on 2 parts in the future, this thread will too soon fade away.