HDPE tank

[_erik_]

Hey everyone!

I have gotten som sheets of HDPE (for free!) and is thinking about building a tank out of them. The sheets are 20mm (aprox. 4/5") thick and measure 100x50cm (40x20").
So for simplicity I'm going for a 100x50x50xm (40x20x20") tank. Front will be a HDPE sheet with a hole cut in it for glas (similar to how its done in plywood-tanks). Bracings in the top middle and along the sides. How would you guys build the tank? Just screws and a sealant? Reinforced angle irons (angle brackets) on the corners? Something else?

I'm grateful for any suggestions or experiences anyone here might have!

/Erik

 

[jjohnwm]

F fishdance
wednesday13

 

[HeaDnShoulderS]

I wouldn't build one with hdpe. When you start using thicker hdpe, it doesn't like to flex and will break. Plus, the only way you'll get it to be water tight and solid, is to weld it. There's not much out there when it comes to any kind of glue or solvent welding product with hdpe.

 

[wednesday13]

Hey everyone!

I have gotten som sheets of HDPE (for free!) and is thinking about building a tank out of them. The sheets are 20mm (aprox. 4/5") thick and measure 100x50cm (40x20").
So for simplicity I'm going for a 100x50x50xm (40x20x20") tank. Front will be a HDPE sheet with a hole cut in it for glas (similar to how its done in plywood-tanks). Bracings in the top middle and along the sides. How would you guys build the tank? Just screws and a sealant? Reinforced angle irons (angle brackets) on the corners? Something else?

I'm grateful for any suggestions or experiences anyone here might have!

/Erik

Some where on here J johnptc built a tank with HDPE… had the pics on my computer back in 08’ lol… can’t find them to save my life. His tank was roughly 8’x4’x4’, built with 1/2” material and used a 2” acrylic window bolted in and sealed with DOW brand corning silicone as a gasket. It had a 2-4” tubular steel cage around the mid portion of it to prevent bowing.

I myself built a 650gal HDPP tank with a full 2” angle iron frame and 1/2” steel square stock as supports every 8” in 09’. I did not trust the quality of my plastic welder that was still a $350-400 unit so i used an additional 45mil EPDM liner inside the HDPP and went with a 3/4” acrylic window un bolted. The silicone i used was “Hutton Products Gold Label Aquarium and Pond Sealer”. The tank is still running today …

Now back to HDPE…
The main problem with this material and HDPP is they are petroleum based. Therefore, no silicone, epoxy or sealant of any kind will EVER stick to it. Its just not possible with oil inside the product. The proper way to “seal” this type of material is with a plastic/heat welder and rods of the same material. A “real” one lol… “entry level” plastic welders run $800-1500 for a good unit. Alot of the affordable and reliable ones are $1500+… This method is very valid for tank construction. They make sumps for tanks this way as well as large tanks for an array of applications. These type of tanks most definitely need to be supported with a steel or wooden cage if using 1/2” material on a large scale…They make them “factory built” with strips of material perpendicular to the sides also for support on larger tanks but this would be pretty unsightly for a fish tank and take up more space. The “free standing” tanks in this material are heat welded inside and out for strength also.

HDPP and HDPE are much softer than acrylic and bow alot more before breaking. It is not a brittle material IMO… Cuts very easy on a table saw or skill saw. Much easier than acrylic. It will take being drilled and bolted but it will also heat up and swell. I do not recommend trying to screw it like plywood tank construction through the thickness. You’ll end up with a wavy mess of sheets and most likely puncture through somewhere u dont want too. Again its very soft.

Ur proposed tank dimensions and material thickness are 100% plausible. In my opinion you do not even need a steel or wooden cage. Normal tank construction with some euro bracing up top will hold it just fine. I had a HDPE sump bigger than that in 1/2” with no bracing but it did have baffles. Heat weld all ur seams inside and out.

I do not recommend glass… any flexing in the HDPE will crack the glass…Acrylic is a must here IMO and it really should be bolted in with a silicone or rubber gasket. I dont think the tank is large enough to make enough water pressure to hold it in without bolts…

Final answer after my rant of info lol… its not worth it for a 70g tank. The price of a good plastic welder will be more than a new or used 70 gal tank. The acrylic for the window will probably be the cost of a used 70g tank also lol… Threw me off for a bit seeing 100x50x50 i think right away in my mind that scale in inches even tho u clearly wrote cm. Just habit…

 

[_erik_]

Some where on here J johnptc built a tank with HDPE… had the pics on my computer back in 08’ lol… can’t find them to save my life. His tank was roughly 8’x4’x4’, built with 1/2” material and used a 2” acrylic window bolted in and sealed with DOW brand corning silicone as a gasket. It had a 2-4” tubular steel cage around the mid portion of it to prevent bowing.

I myself built a 650gal HDPP tank with a full 2” angle iron frame and 1/2” steel square stock as supports every 8” in 09’. I did not trust the quality of my plastic welder that was still a $350-400 unit so i used an additional 45mil EPDM liner inside the HDPP and went with a 3/4” acrylic window un bolted. The silicone i used was “Hutton Products Gold Label Aquarium and Pond Sealer”. The tank is still running today …

Now back to HDPE…
The main problem with this material and HDPP is they are petroleum based. Therefore, no silicone, epoxy or sealant of any kind will EVER stick to it. Its just not possible with oil inside the product. The proper way to “seal” this type of material is with a plastic/heat welder and rods of the same material. A “real” one lol… “entry level” plastic welders run $800-1500 for a good unit. Alot of the affordable and reliable ones are $1500+… This method is very valid for tank construction. They make sumps for tanks this way as well as large tanks for an array of applications. These type of tanks most definitely need to be supported with a steel or wooden cage if using 1/2” material on a large scale…They make them “factory built” with strips of material perpendicular to the sides also for support on larger tanks but this would be pretty unsightly for a fish tank and take up more space. The “free standing” tanks in this material are heat welded inside and out for strength also.

HDPP and HDPE are much softer than acrylic and bow alot more before breaking. It is not a brittle material IMO… Cuts very easy on a table saw or skill saw. Much easier than acrylic. It will take being drilled and bolted but it will also heat up and swell. I do not recommend trying to screw it like plywood tank construction through the thickness. You’ll end up with a wavy mess of sheets and most likely puncture through somewhere u dont want too. Again its very soft.

Ur proposed tank dimensions and material thickness are 100% plausible. In my opinion you do not even need a steel or wooden cage. Normal tank construction with some euro bracing up top will hold it just fine. I had a HDPE sump bigger than that in 1/2” with no bracing but it did have baffles. Heat weld all ur seams inside and out.

I do not recommend glass… any flexing in the HDPE will crack the glass…Acrylic is a must here IMO and it really should be bolted in with a silicone or rubber gasket. I dont think the tank is large enough to make enough water pressure to hold it in without bolts…

Final answer after my rant of info lol… its not worth it for a 70g tank. The price of a good plastic welder will be more than a new or used 70 gal tank. The acrylic for the window will probably be the cost of a used 70g tank also lol… Threw me off for a bit seeing 100x50x50 i think right away in my mind that scale in inches even tho u clearly wrote cm. Just habit…

Thank you for a great, very informative answer!

Buying a decent plastic welder is certainly out of the question due to the cost. You are right about acrylic being expensive aswell. Maybe I will make a sump/emergency (windowless) tank out of the HDPE instead.

Are you sure screwing the tank together (with holes pre-drilled and silicone as a gasket) wont work? What if I reduce the height somewhat, would that make it possible?

 

[fishdance]

You can use cheap plastic welders but the expensive welders are more forgiving (much easier to use). Scraping out a deep V along both sides of all seams to provide more adhesion area (and a gully to fill) is recommended. You can also play with a soldier iron (normally used for electronic wire connections).

You can screw HDPE sheets with a thin strip of EPDM rubber between to create a watertight gasket seal on a shallow tank like yours. The thicker the HDPE sheet, the stiffer so the greater the spacing between screws can be.

 

[_erik_]

You can use cheap plastic welders but the expensive welders are more forgiving (much easier to use). Scraping out a deep V along both sides of all seams to provide more adhesion area (and a gully to fill) is recommended. You can also play with a soldier iron (normally used for electronic wire connections).

You can screw HDPE sheets with a thin strip of EPDM rubber between to create a watertight gasket seal on a shallow tank like yours. The thicker the HDPE sheet, the stiffer so the greater the spacing between screws can be.

I have done (or maybe more like tried to do) some simple HDPE welding in the past, some modding for my fishing kayak. A little with a soldering iron, but mostly with a heat gun. Results weren't great. Maybe because I'm just terrible at it, I'm not sure.. But either way I do not feel comfortable trying to weld a fish tank together, the risk of me messing it up are far too great.

Please if you could clarify, do you say that it is possible to use only screws and EPDM rubber to build the tank (without any welding)?

EDIT: Thank you for taking the time to help me out!

 

[wednesday13]

Thank you for a great, very informative answer!

Buying a decent plastic welder is certainly out of the question due to the cost. You are right about acrylic being expensive aswell. Maybe I will make a sump/emergency (windowless) tank out of the HDPE instead.

Are you sure screwing the tank together (with holes pre-drilled and silicone as a gasket) wont work? What if I reduce the height somewhat, would that make it possible?

Honestly, with ur material being free… and after F fishdance comment of using epdm liner inside the screwed joints i would try it lol…should b able to buy rubber gasket material also pretty cheap… ur proposed dimensions would work fine for u material thickness. Its a tired and true concept for tank window seals… should work the same way for a seam/joint. Most def. Use a drill press and or a jig to get ur drilled holes straight and it should work well. If it does id then cut a hole out for a window … scrap polycarbonate can be found as cheap as $1 a lb. in my area. U might be able to find a piece local. You only need 1/4” poly carb. It drills and bolts well for even large window applications on poly type tanks.

 

[fishdance]

You need reasonably high temperatures so a typical heat gun wouldn't work well. Localising the heat so only the area you want becomes translucent (bonding by melting).

Have you considered using a gas flame torch? Put in some holding screws to keep the tank shape in place and melt the outside seams just enough to waterproof. I would not bother trying to weld the inside seams if your inexperienced with improper tools.

 

[Disturbed.)]

I've been down this road. I have a 48X18x12 LDPE tank. Free materials and fancy ideas end up getting pretty expensive lol. But I'm an experienced metal fabricator that wanted to learn plastics.
I wouldn't mess with building a tank out of it unless you are only doing it to learn how to weld plastics. If that's your plan, you can get a cheap handheld welder and either melt your own rods from milk jugs or buy some and practice away.
Buy a good quality respirator, you don't want want to be breathing the offgas. The trick is getting the temp just right and having plenty of patience to wait on your puddle. Just don't get your hopes up for an outstanding or even water tight tank for quite some time. And flex is ridiculous with this stuff. My material was way thinner so I fabbed a steel cage and stand from the start and it still flexed. I started wrapping it in plywood and that's where the project died.
Chemical weld products exist for LDPE and HDPE here in the US, I'm guessing you are in the UK, but they are just as bonkers expensive as buying an entry level chinese made plastics welder here. Good luck