Styrofoam Under the Tank

[WarrenG]

Dots wrote: "Styrofoam is mostly air, at the weights we are speaking of, it would be compressed to the point of being worthless. Its best application is as an insulator."

For a tank 24" deep there is about 1 pound of pressure on each square inch of the foam. The foam will not compress like you say from one pound of weight. And if the air was compressed to the point of being worthless there would be virtually no insulating value since it is trapped air that is the insulator. The material other than the air actually conducts thermal energy.

Styrofoam does not catch moisture very well, especially from a tank, at least not on the two I've had it under for around 15 years. No mold at all, even though it gets splashed occasionally.Foam rubber that can offset the imperfection of a nail/screw head or ridge in the wood is too flexible and doesn't provide a stable platform unless the stand constrained the perimeter of the tank. Many of the foam rubbers and neoprenes will absorb far more water than styrofoam.

If water gets under the tank I'd much rather have a sheet of styrofoam there to block/contain it's movement instead of wood that will absorb the water. And since there will not be even a 1/128" gap between the bottom of the tank and the foam the water won't move anywhere-it won't even get there to begin with.

 

[dots]

I was thinking about this a lot last night and this morning, the picture above got me thinking more. There is little information available to be readily found because foam is not used primarily to transfer loading evenly, which is the main purpose of this application, to correct the voids in the surface that could cause stress concentrations and failure.

Some considerations:
Glass tanks need even distribution on the edges primarily
Acrylic needs it all across

Foam is historically used in impact force force instances, once compressed it is in a plastic state (won't spring back to it original shape)

Polymers such as this come in two flavors:
open cell and closed cell, both have different mechanical properties.

When one says "styrofoam" I think of blown polystyrene which is a closed cell type, (which is mostly air, as can be shown when a styrofoam cup was placed on an ROV on a dive). However, what the ability to transfer loads and characteristics when compressed is what I am looking for.

Open extruded polystyrene as seen in the picture above is used in building applications.

Historically, polystyrenes are used in thremal applications and sandwiched between stronger materials.....like steel doors, I am unsure if it trasfers the loads through these void areas or low spots and solves the problem or just covers it up.

And if under compression, it does fill the void and tranfers the load, what about the places that were fine before?

In the case of a foam gasket under a home window, the foam is mearly a means to stop air flow.

After thinking more, I am unsure about if it does any good at all to redistribute stress concentrations, and may even create some, which may be the wrong application for the material.

Regardless, my main point was not to use this as a replacement for construction quality and will have to do some more research on foams and the mechanical properties while in compression.

Reminds me of the old cartoon gag when the guy takes off his jacket for the lady and they walk arcoss, but when the villan steps onto it, falls in.

 

[WarrenG]

dots,

The purpose of the foam IS NOT to transfer the load evenly, it is to spread the load evenly. It is to overcome any irregularities/projections in the surface of the stand under the tank, to dampen noise and vibration, and to insulate.

Get a piece of wood that has 8 square inches. Put a nail through it that protrudes 1/4" inch. Now put a gallon of liquid (8 pounds) on top of the board and hold you hand flat under the board. The nail punctures your skin because the entire 8 pounds is applied to the nail and into your hand. Take the nail out and it doesn't hurt to support that load because it is distributed evenly across the board.

Put a nail into a piece of plywood but let the head of the nail protrude 1/16" or so. Take a piece of styrofoam 3/8" or thicker and apply one pound of force per square inch across the entire surface (you can use a gallon of liquid on top of 8 square inches of wood). This is the same amount of pressure a 24" deep tank will apply. The top surface of the foam will be perfectly flat and the underside will have the indentation of the nail head. A softer foam could do the same, but when you try that you'll see that the board on top of the softer material can move laterally.

The reason there is a localized indentation is because the pressure is greater at that location (the entire 8 pounds is applied only to the nail head) until the foam compresses enough in that local area to redistribute the eight pounds to the entire area under the weight.

The same will apply to a glass tank. The area on the underside of the frame will carry the entire load of the tank, and this is probably enough pressure to crush the foam in that local area. But once the foam crushes the thickness of the frame's protrusion, the entire load of the tank will be carried equally by the frame and the bottom of the tank (glass). When this happens there will be about one pound of pressure on EACH square inch of foam under the 24" tall tank.

Your styrofoam cup underwater analogy is greatly flawed. The aquarium applies ONE psi to styrofoam that is 3/8"+ thick. The underwater ROV at a depth of 240 feet applies ONE HUNDRED psi to a cup (foam) that is 1/8" thick. 1psi is not enough to push all the air out of styrofoam so its original characteristics will remain.

Get your own piece of foam, measure its thickness very carefully, apply ONE pound of weight evenly to each square inch of surface area and measure the foams' thickness again.

 

[kevin95695]

Words, words, words.

After about 6 lines of text the avg RC surfer loses their

Huh? What were they saying?

So what did you science guys decide after the arguing?

 

[WarrenG]

<a href=showthread.php?s=&postid=11441949#post11441949 target=_blank>Originally posted</a> by kevin95695
Words, words, words.

After about 6 lines of text the avg RC surfer loses their

Huh? What were they saying?

So what did you science guys decide after the arguing?

Are you saying we should just let incorrect information sit out there, or do you think people who do care about the topic will appreciate accuracy? Do you think illustrative examples are worth including in a post?

 

[BodiBuilt]

Yea...what Kevin said!

I say "it's better to have used foam and not needed it,than to blow your new tank onto your wife's carpet..." (lol)

 

[ThunderDog]

I agree with Warren but that doesn't help the discussion much. I have not used Styrofoam in the past but plan to in the future since most of the large tank build threads I've read on RC show it being used and if there were issues with mold or other downsides to using Styrofoam under tanks I think it would have been identified and discussed in those instances when the owners have done multiple tanks in the past.

 

[dots]

The industry is split on the topic.

All-Glass says placing foam under the tank will void your warranty as the engineers believe that it will cause uneven settling and cause stress point.

Glass cages says it doesn't matter and it can be used.

Most agree Acrylic tanks should be supported throughout and this is a good means to do so.

I could not find a single other constant compressive load bearing application for polysytrene extruded rigid insulation. This application goes against the design and primary application by compromising the R-value if compressed as all the weight is transfered through the material to the supporting structure.

The behavior of polymers, especially in applications in which they are not designed for, may have unpredictable results particularly as the volume and weights increase with tank size.

I spent a considerable amount of time trying to find the behavior of this material under compression and applications simmilar in which we are attempting to use the material for. The lack of either fails to prove or disprove the application at this time.

This lack of experimental behavioral data of the material under constant compressive loads over time explains the wide range of opinions on the topic.

 

[kevin95695]

WarrenG: Info is good. But Occam's Razor RULES!

All'y'all: If the average third grader won't read it... The average American won't. If you want your posts to be: Read, understood, and internalized -- Keep them concise. Look the term up.

Easy definition of "concise" = click here.

 

[dots]

The problem is, there is no manual for this hobby. Often, things like this need to be hashed out and every angle looked at. When its all been said and done a million times with predictible results, you answers will be short and sweet.

 

[WarrenG]

24" of water = 1 psi = no crush.


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