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Old 10/13/2018, 11:11 PM   #1
diastech
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HDPE for baffles?

I have a question. I am building a new DIY sump and I am looking to save a few bucks as well. I bought a 75 gallon glass tank from Petco on sale to use for the sump. I have made baffles on my current sump with lexan & acrylic, but I found HDPE sheets much cheaper than the acrylic. I used aquarium safe silicone on my current sump to bond the baffles to the glass and its held up pretty good for 2 years now. Will the silicon work just as well on the HDPE?



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Old 10/14/2018, 05:08 PM   #2
Gorgok
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As i understand, it will stick worse if not equal to HDPE as to acrylic. But as with acrylic you can sort of cheat by sandwitching the baffle with silicone fillets on both sides and it will probably be fine for a long time.

I can't imagine HDPE sheeting being cheaper than glass though... glass is cheap.


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Old 10/15/2018, 12:39 AM   #3
sfsuphysics
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You won't be able to bond silicone to hdpe, you might be able to create a silicone gasket that sticks to the glass, but it won't stick to the HDPE.


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Old 10/15/2018, 06:32 AM   #4
diastech
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I see, the silicone seems to hold the lexan / acrylic I used on my first sump build. Trying to do the same thing with HDPE may not hold as strong as it does with the acrylic?

I was going to use black HDPE for some of the baffles because it is for the refuge section and I didn't want the fuge light to bleed over. Into the skimmer chamber.

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Old 10/15/2018, 09:04 AM   #5
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Quote:
Originally Posted by diastech View Post
I see, the silicone seems to hold the lexan / acrylic I used on my first sump build. Trying to do the same thing with HDPE may not hold as strong as it does with the acrylic?
Correct..
There is better potential for sufficient adhesion with lexan/acrylic vs with HDPE..
In general silicone + acrylic does not work well at all.. But you can get lucky sometimes..
There is one silicone that HD sells near the acrylic sheet that "bites" into the acrylic and you MUST ensure its properly cured before putting it in water as its toxic until cured for marine life..

You can easily get colored cast acrylic from here..
estreetplastics.com
Pricing is great there..

You can also spray paint the clear. Note: you may have some problems with chipping paint over time and must ensure its fully cured/dried before exposing it to water..


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Old 10/15/2018, 11:35 AM   #6
der_wille_zur_macht
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HDPE floats. It's very buoyant. Using it as baffles means it'll constantly be fighting to break loose and float. Combine that with poor adhesion to silicone and you'll probably wake up one morning to find your baffles aren't baffling any more.

As mentioned, acrylic doesn't stick well to silicone either but at least it's not fighting the bond.


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Old 10/17/2018, 02:10 AM   #7
sfsuphysics
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Quote:
Originally Posted by diastech View Post
I see, the silicone seems to hold the lexan / acrylic I used on my first sump build. Trying to do the same thing with HDPE may not hold as strong as it does with the acrylic?
In a nutshell HDPE has a relatively low surface energy not as low as say teflon but fairly low, which means things don't stick to it because of surface tension in the surface... or at least that's what little chemistry I tried to find out while looking for something to bond two surfaces together chemically.


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Old 10/17/2018, 02:25 PM   #8
mkj
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i like to use tiles for baffles. Silicone sticks to tile better than glass. I like to use white ones for refugiums plus they are very cheap, easy to cut at home with $2 tile cutter and easy to replace.


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Old 10/17/2018, 04:08 PM   #9
diastech
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Thanks all for the replies. I ended up ordering from estreetplastics. Thier prices are real good. I got the acrylic I needed for the same price as the HDPE I was looking at. But the shipping is pricey.

I didn't know HDPE wants to float, that there is enough for me to not consider it further. Thanks again for the great info on HDPE.

The tile idea is different, that is perfect for a refugium because its opaque, but I do end up cutting the acrylic in certain areas to make a subtle flow through it so it might not best suit my needs. But it's a great idea!

I am located in new England, can you suggest any other online acrylic dealer closer to me? Something with great prices as estreetplastics but hopefully cheaper shipping costs because closer?

I tried shopping around locally to find a plastics dealer and there isn't anything close by.

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Old 10/18/2018, 12:57 PM   #10
sfsuphysics
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Take a peek at ABS sheets as well. Not sure how high you need your baffles to be but...
https://www.amazon.com/ABS-Sheet-Thi...s%2Bsheet&th=1

12" x 24" at roughly 1/4" thick, for $12.12 + 5.40 shipping for 1, shipping per unit changes depending upon how many you need. You can also get 24" x 24" if you really need the added height, but if you only need a little more than 12" you'll have lots of waste. Although I'll admit, I'm not quite sure how stiff the stuff will be for baffles, it might be that it bends too much and pulls away from the glass/silicone.


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