Why does acrylic warp near saltwater?

[stevenp]

I've always wondered this. Does anyone know why?

 

[maurod]

Define Warp....

 

[JohnK]

If it's a tank cover, the heat will do it. Otherwise?

 

[Pat H.]

Actually I've read that acrylic can/does absorb some water. If this is true the side facing the water would expand and the side away would not causing it to warp. That's my hypothesis anyway

 

[Tstone]

Has to be heat that is causing this or it could be the acrylic is not thick enough for the pressure of the water pushing on it.

I don't think it will absorb water.

 

[Pat H.]

Has to be heat that is causing this or it could be the acrylic is not thick enough for the pressure of the water pushing on it.

I don't think it will absorb water.

I've had it happen to 1/4" acrylic covers on an unlit sump.

 

[Tstone]

hat

I've had it happen to 1/4" acrylic covers on an unlit sump.

How much span was there for the 1/4 inch to cover? The weight of the acrylic will over time warp itself, near water or not, if the span is wide enough.

My 3/4 inch covers were/are just as flat as they were 4 years ago.

 

[Pat H.]

hat

How much span was there for the 1/4 inch to cover? The weight of the acrylic will over time warp itself, near water or not, if the span is wide enough.

My 3/4 inch covers were/are just as flat as they were 4 years ago.

About 10 x 16, warped in both directions (length and width).

I did find this to back up my absorbtion theory though.

http://www.3d-cam.com/materials/acrylic.asp

"Water Absorption .3-2 % "

 

[Tstone]

So .3-2% ain't much but it would add weight to the cover there by warping it. So that proves my weight theory.

Damn We are too smart.

 

[Pat H.]

So .3-2% ain't much but it would add weight to the cover there by warping it. So that proves my weight theory.

Damn We are too smart.

Hehe...got me

 

[JohnK]

I can't elaborate on specifics, but from what I've read acrylic does abosrb water, and extruded absorbes far more than cell cast. Do you know which kind of acrylic we're talking about?

I bet Gustavo could fill in the blanks here.

 

[stevenp]

I've read about it absorbing water as well, but I also wondered if the salt has anything to do with it. Maybe it warps just as bad near freshwater?

IME experience it doesn't matter how thick the acrylic is, and it has nothing to do with heat. Unless it has reinforcements such as ribs, it will warp when placed near saltwater.

 

[Rick M]

Gravity

One word, gravity. Acrylic is not as rigid as glass. Even if these covers were over fresh water, no water, heat, no heat, they word warp as noted. I used to fabricate many things, (non aquiaium oriented products), and this was an issue. We had to go to thicker sheets to account for warping.

Rick

 

[stevenp]

Rick, in my cases it's had nothing to do with gravity. The acrylic was laying flat on top of egg crate (nowhere near a heat source either) and it warped badly.

 

[Tstone]

Rick, in my cases it's had nothing to do with gravity. The acrylic was laying flat on top of egg crate (nowhere near a heat source either) and it warped badly.

This is something IME have never heard of or seen. Strange. Is your house possessed?

 

[stevenp]

This is something IME have never heard of or seen. Strange. Is your house possessed?

Well, I did find a chicken foot tied to a string in one of the closets when we moved in

I've talked to other members outside the forums who've had problems with acrylic warping. We always talk about posting something on forum about it but never do.

 

[Pat H.]

I think a better description of this is curling not warping. IME the acrylic has not only warped but curled up away from the surface it's resting on. Gravity??

 

[stevenp]

Pat, exactly, it's curling up towards the ends.

 

[Pat H.]

I have made several covers out of 1/4" polycarbonate (Lexan) that stay perfectly flat, not even a hint of curling with a small light fixture on top.

 

[Clam Man]

I think its called memory its in the process when they make it ok question answered next one please .steve stop down to plastic's unlimited they can tell you more bring the piece with you.