polycarbonate sheet?

[zeebies]

I want cover the top of a temporary 10 gallon tank with something that won't absorb water and change shape. I don't want to use glass for my application. I have used acrylic before but it ends up being convex.

I can get some polycarbonate sheet. Will this remain flat if it's on top of a running tank? There will also be 25 watts of lighting a couple inches above it.

Other stuff I can use? Thanks for any advice.

[sleepydoc]

No experience, but from what I've read, polycarbonate yellows with exposure to UV, so it may not be the best choice. Why not glass?

[zeebies]

No glass because I need to do some cut-outs for equipment. Also, one piece is easier to deal with. Just trying to keep it simple - no hinges, glued-on plastic end pieces, etc.

[Waddleboy]

acrylic would do it, not sure why yours became convex? Was it too close to a light that you started to melt it? For something like this you can use the extruded and save some money. Cheap stuff at HD or lowes would do

[dwolson2]

Try a thicker acrylic. And polycarbonate is still in the same category as plexiglass(or acrylic as a lot of people call it)

[zeebies]

My understanding of the acrylic problem is that the underside of the sheet (close to the water) absorbed water and expanded ... turned convex on me. Just looking for some sheet goods that will let a little light through but not buckle.

The stuff I used before was 1/4" extruded acrylic and it was under 25 watt lighting.

I'm trying to understand the properties of polycarbonate vs acrylic to see if the poly might hold up better. Or maybe there's something better?

Thanks for the responses so far.

[dwolson2]

Poly will crack or break, where acrilic will gouge. acrylic is a more soft plastic. usually plastics will bow over time. it just depends on gravity or force. most acrylic tanks bow out, because water pushes them out and they warp over time.

[Waddleboy]

why cant you use screen like on windows or doors? Is there a specific purpose you want it to be a harder material?

[zeebies]

My light will be over it and I want to prevent splashing.

[jimmyj7090]

My understanding of the acrylic problem is that the underside of the sheet (close to the water) absorbed water and expanded ... turned convex on me. Just looking for some sheet goods that will let a little light through but not buckle.

The stuff I used before was 1/4" extruded acrylic and it was under 25 watt lighting.

I'm trying to understand the properties of polycarbonate vs acrylic to see if the poly might hold up better. Or maybe there's something better?

Thanks for the responses so far.

Best bet, just use the acrylic and flip it over every week or so. The warping is because of water absorbtion in this type of application, not heat or pressure. Flip it as soon as it starts to warp a bit and it will start warping in the other directon, repeat...

[CandidQuality]

Poly will crack or break, where acrilic will gouge. acrylic is a more soft plastic. usually plastics will bow over time. it just depends on gravity or force. most acrylic tanks bow out, because water pushes them out and they warp over time.

Actually it is the opposite poly will bend, acrylic will break. Neither will hold up to that amount of moisture without bending. Acrylic will be stiffer given the same thickness size.

You could try putting it into a frame, heating it, and introducing a bow, then flipping it over. Look up thermoforming. You can do it in your home oven if necessary(depending on the size of your tank). No vacuum necessary for the shape you would be after. just heat it and it will naturally fall into a smooth dome shape, and still be easy to drill in your holes for tubing, etc.

[zeebies]

Best bet, just use the acrylic and flip it over every week or so. The warping is because of water absorbtion in this type of application, not heat or pressure. Flip it as soon as it starts to warp a bit and it will start warping in the other directon, repeat...

Only problem with this is that flipping won't work because of the cut-outs for equipment. See... it's always something.


Look up thermoforming.

Will do. Still trying to keep it simple though.

[sleepydoc]

I'm not aware of any other viable options. I would either get glass and use a hole saw, or get acrylic and live with the warping. It's not that dramatic and after a certain point it won't warp any more, so you can at least plan for it.

[zeebies]

I'm not aware of any other viable options. I would either get glass and use a hole saw, or get acrylic and live with the warping. It's not that dramatic and after a certain point it won't warp any more, so you can at least plan for it.

I guess that's the verdict. Thanks all.

[thegrun]

You glue on a 1" high stiffener to keep it flat.

[zeebies]

thegrun, could you elaborate please?

[jimmyj7090]

You glue on a 1" high stiffener to keep it flat.

I've tried something along those lines. The sheet still warped, just into a more creative shape.

[thegrun]

If you cut four 1" wide pieces of acrylic or polycarbonate the same length as your cover and glue them to the top of the cover they will act as a stiffener and prevent bowing. I did this to the top cover of my ATO reservoir to prevent it from bowing and three years later it is still flat. In essence you are building a small 1" deep tub.

[incuplayer]

I have had success with siliconing on a smaller strip of plexi to prevent warping and it worked fairly well also.

[zeebies]

grun, just to clarify, do you glue the edge of the 1" strips to the poly or the wider face of the strips? If I visualize a 1" deep tub, as you say, I'm thinking the edges are glued. I want to try your idea... but don't want to mess it up. Thanks.

[sleepydoc]

I dont' know what Grun was thinking, but yes, I would glue the strips on edge. Think of a ruler - it has a lot more stiffness it you stand it on edge vs laying it flat.

[thegrun]

I dont' know what Grun was thinking, but yes, I would glue the strips on edge. Think of a ruler - it has a lot more stiffness it you stand it on edge vs laying it flat.

+1, glue the strips standing up on edge.

[zeebies]

Ok, I'm going to give that a shot. Thanks for clarifying.