Hydrophobic coating on acrylic sheets?

[adam smiz]

Hey guys,

Does anyone have any experience using a hydrophobic coating on acrylic? I am trying to prevent the absorption of moisture in my pieces to hopefully stop warping from occurring. After talking with Plaskolite they thought of this being a possibility. So right now im looking at hydrophobic coating, standard krylon acrylic sealer, or even like an acrylic sealer for paintings? The catch is it need to dry clear as these are on clear pieces. Any experience would be greatly appreciated!!!

[Clark Pace]

Hey guys,

Does anyone have any experience using a hydrophobic coating on acrylic? I am trying to prevent the absorption of moisture in my pieces to hopefully stop warping from occurring. After talking with Plaskolite they thought of this being a possibility. So right now im looking at hydrophobic coating, standard krylon acrylic sealer, or even like an acrylic sealer for paintings? The catch is it need to dry clear as these are on clear pieces. Any experience would be greatly appreciated!!!

?? What is warping? The acrylic? What, and when is it warping? Do you have pics?

[Dan Hintz]

Hey guys,

Does anyone have any experience using a hydrophobic coating on acrylic? I am trying to prevent the absorption of moisture in my pieces to hopefully stop warping from occurring. After talking with Plaskolite they thought of this being a possibility. So right now im looking at hydrophobic coating, standard krylon acrylic sealer, or even like an acrylic sealer for paintings? The catch is it need to dry clear as these are on clear pieces. Any experience would be greatly appreciated!!!

If your pieces are warping, it means you have different temps or humidity levels on either side. If you store your panels upright with a small separation between them for air circulation, warping shouldn't be an issue. Trying to prevent it with a rattle can is a recipe for long-term disaster.

[Clark Pace]

If your pieces are warping, it means you have different temps or humidity levels on either side. If you store your panels upright with a small separation between them for air circulation, warping shouldn't be an issue. Trying to prevent it with a rattle can is a recipe for long-term disaster.

I thought you meant while bending or engraving it was warping.

I've always been told to lay your acrylic on a flat surface. That is generally how the plastic companies store their acrylic. Also when I worked at a cabinet ship, we stored out wood horizontally also.

Any material we stored up right tended to warp more.

Now having spacer might help. I've never tried it.

[Mike Null]

I can't recall ever having a warping issue with acrylic. I usually store mine flat in stacks but some is standing. I haven't seen a difference.

[Doug Griffith]

It could be that the OP is referring to finished parts being hygroscopic in which case a different material such as polystyrene might be a better fit. Lazering won't play well here though.

[adam smiz]

Sorry for the delay! These are finished parts that go over aquariums, so I have heat on one side and humidity on the other side. With 1/4" I was getting about a 1/16 upward warp. I've bumped up to 3/8 as recommended by the engineer I spoke with and he said this would help. I am just wondering if there is a more permanent solution to this issue.

[Dan Hintz]

These are finished parts that go over aquariums, so I have heat on one side and humidity on the other side.

Well, there ya go! You have the worst-case scenario right there.

[adam smiz]

I sure do, the chemist called it the perfect storm!

[Kev Williams]

These types of plastic will eventually bend towards gravity wherever possible, and the warmer it is, the faster it will happen.

This is a 3' x 4' x 1/4" thick piece of ABS, it used to be flat, until I leaned it over a stair railing in the back yard (to steer laser smoke)... This is what it looks like after a year, between gravity and the heat of the morning sun...



Of course, ABS is less rigid than cast acrylic, but given enough time, cast will do the same thing...

[Dan Hintz]

These types of plastic will eventually bend towards gravity wherever possible, and the warmer it is, the faster it will happen.

This is a 3' x 4' x 1/4" thick piece of ABS, it used to be flat, until I leaned it over a stair railing in the back yard (to steer laser smoke)... This is what it looks like after a year, between gravity and the heat of the morning sun...



Of course, ABS is less rigid than cast acrylic, but given enough time, cast will do the same thing...

Just to be clear, that's a heat/melt issue, not humidity... and I doubt the OP is working with so much heat on his fish tank lamps to cause that kind of warpage (else the fish would be dead in short order). The warpage he's experiencing is likely temporary... if he removed the sheeting form the poor conditions, it would right itself. The problem he's facing is the conditions are essentially permanent.

[Rich Harman]

... so I have heat on one side and humidity on the other side. With 1/4" I was getting about a 1/16 upward warp...

Sounds like it is heat (temperature difference) that is causing the warping, not the humidity.

[Ross Moshinsky]

Well there are three ways you could handle this situation.

1. Treat the symptom. I doubt a coating will do it, but I don't know that industry. My guess is there is a way to either lower the temperature or lower the humidity but without seeing what we're talking about, we really can't get specific with suggestions. Introducing a fan seems like the most obvious solution but I have no idea if that would work in your application.

2. Increase the thickness of the acrylic. As you've already mentioned, this will likely fix your problem.

3. Change materials. There are a lot of different acrylics out there. Swapping to a different type of acrylic may just take care of your problem.

If I were you, I'd just go thicker and adjust my pricing/design.

[Doug Griffith]

Well there are three ways you could handle this situation.

1. Treat the symptom. I doubt a coating will do it, but I don't know that industry. My guess is there is a way to either lower the temperature or lower the humidity but without seeing what we're talking about, we really can't get specific with suggestions. Introducing a fan seems like the most obvious solution but I have no idea if that would work in your application.

2. Increase the thickness of the acrylic. As you've already mentioned, this will likely fix your problem.

3. Change materials. There are a lot of different acrylics out there. Swapping to a different type of acrylic may just take care of your problem.

If I were you, I'd just go thicker and adjust my pricing/design.

There could be a fourth.

I might also consider going with 2 layers of material stacked on top of each other without bonding. Each would have it's own thermal expansion rate. A non hygroscopic material such as styrene could be used on the water side.

It's all just guessing without knowing the application.

[Norman Roberts]

I have been in the business of building acrylic aquariums for 35+ years. Acrylic used to cover an aquarium will always warp, extruded will be worse that cast. We use polycarb to cover openings and it works well, not good for laser applications.

If you post photo of what your are trying to accomplish, someone may have an idea.

You may want to try an acrylic with a scratch resistant coating, this may work, but may be too pricy.

The 3/8 acrylic will eventually warp, will just take longer