bonding acrylic to hdpe?

Wesdog · Mar 20, 2018

So I'm in the process of deciding how to make a custom tank for a counter top in my house. One issue I have is that there are cabinets about 17 inches above the counter top. So I'm going the custom tank route. I don't have the money to do all acrylic, so I thought I'd use another material for the sides that you can't see. I've found hdpe to be relatively cheap compared to acrylic and custom cut glass. I just can't find a way to find them, if there is. My current idea is to drill pilot holes through the acrylic into the hdpe, screw them together and then waterproof it with silicone. any input would be amazing, thanks!

hijinks7 · Mar 20, 2018

silicone doesn't bond with plastic so it'll never be waterproof. You could get a tap and then plastic screws. Then if you never want to get it off you can seal it with something like weldon 16 like you would with silicone.

hijinks7 · Mar 20, 2018

Also what size are you building? I built a 120g acrylic for like $400ish

Wesdog · Mar 20, 2018

i was planning on building it to be 48"x12"x12", comes to about 40 or 45 gallons, my problem is that to build it out of all acrylic I won't use a whole 4'x8' sheet so it would a waste to buy a 400 dollar sheet of acrylic. You're saying instead of using silicone use weld-on 16, will that bond with hdpe?

cilyjr · Mar 20, 2018

There may be a scigrip ( the makers of weldon) product that will bond hdpe to acrylic but I'm unsure.

I would not use weldon 16 to build a tank. For acrylic to acrylic you would use weld on 3 or 4.

Wesdog · Mar 20, 2018

I've emailed scigrip to see if there's a product that will work to bond acrylic and hdpe, I hope they do because that would make life easy for me.

cilyjr · Mar 20, 2018

Good idea.

Wesdog · Mar 21, 2018

Scigrip just got back to me about bonding acrylic to hdpe, sadly they don't make a product that can do it. The only product I've found that does bond to hdpe isn't food safe, so I'm just assuming it isn't aquarium safe. I'll have to find another way to do this, thanks everyone for the input.

redfishbluefish · Mar 21, 2018

Silicone does stick to plastic if you use the right stuff. Now that said, I've never used this with HDPE. But what I have used on acrylic is this silicone:

I purchase this in HD, but you won't find it in the Paint department with all the other silicones and caulks. You have to go were they sell acrylic sheets (in my store, were they have storm windows) and you'll find it there. About $8 a tube, but it sticks like grim death to acrylic and glass....you won't be able to pull it off.

Wesdog · Mar 21, 2018

redfishbluefish said:
Silicone does stick to plastic if you use the right stuff. Now that said, I've never used this with HDPE. But what I have used on acrylic is this silicone:

I purchase this in HD, but you won't find it in the Paint department with all the other silicones and caulks. You have to go were they sell acrylic sheets (in my store, were they have storm windows) and you'll find it there. About $8 a tube, but it sticks like grim death to acrylic and glass....you won't be able to pull it off.

Good to know, I don't intend to use the silicone to hole the tank together just as a sealant to keep water from escaping out any gaps. Screwing it together will be the main support.

cilyjr · Mar 23, 2018

I'm curious what screws you plan to use and how you plan to screw it in.

I'm seeing it might be very difficult to use self tapping screws into the sides of an acrylic sheet. I'm guessing you would need to drill and tap each individual hole and use a high grade stainless steel machine screw. I don't know that and acrylic screw would stand up to the forces pushing against the sides.

In my mind, I'm not seeing long term success with this project.
That said, it wouldn't be the first time I was wrong about something.

Wesdog · Mar 23, 2018

The plan was to drill and tap each hole, placing them 2 inches apart would distribute the force evenly enough so nothing cracked. I'm turning away from this thought and I'm now looking into just get a custom glass tank made, slightly bigger and have a pro do it.

cilyjr · Mar 24, 2018

I'm not trying to talk you out of this, just pointing out some obstacles I see.

Erica-Renee · Mar 24, 2018

That silicone above will bond to acrylic. I have never tried to use it for hdpe .I suspect it will NOT Hold...
If you are going to mechanically fasten them . I would drill holes from the acrylic into the hdpe , its softer and will hold the screws better. Most abs adhesives will bond the hdpe together.....
IF it were me i would build hdpe parts of the box . Maybe cut a Rabbit for the acrylic to set into.. run a Salt water safe seal around the edge between the acrylic and hdpe.. use a piece of stainless on the outside of the tank to help reinforce the screws.. with the acrylic sitting into the rabbit pushing tight onto the seal. and the stainless band helping you should get a very tight mechanical seal that will last a lifetime........ Having the rabbit will cause you to need thicker hdpe is the biggest down side ...

Good Luck

redfishbluefish · Mar 24, 2018

OK, even though it appears the OP has moved on to other options, this discussion on attaching acrylic to HDPE has sparked my interest. I've used the above referenced "plastic" silicone on acrylic to acrylic, acrylic to glass and polycarbonate to glass, and all worked great....can't peel the silicone off.

One of the tops to one of my Brutes (HDPE) has a hole in it that is no longer being used. I cut a circular disc of acrylic (I think 1/8 inch thick) and sanded both the acrylic and the area around the hole. I also sanded a little part of the center of the lid where I plan to simply put a dollop of silicone (to test pulling it off.)

Disc siliconed to the lid. Now wait for it to cure.

I'll be back in a couple days with results.

Wesdog · Mar 24, 2018

redfishbluefish said:
OK, even though it appears the OP has moved on to other options, this discussion on attaching acrylic to HDPE has sparked my interest. I've used the above referenced "plastic" silicone on acrylic to acrylic, acrylic to glass and polycarbonate to glass, and all worked great....can't peel the silicone off.

One of the tops to one of my Brutes (HDPE) has a hole in it that is no longer being used. I cut a circular disc of acrylic (I think 1/8 inch thick) and sanded both the acrylic and the area around the hole. I also sanded a little part of the center of the lid where I plan to simply put a dollop of silicone (to test pulling it off.)

Disc siliconed to the lid. Now wait for it to cure.

I'll be back in a couple days with results.

im interested to see the results from this, maybe I won't have to abandon thus thought.

paphater · Mar 24, 2018

Look in to weld on 40.

cilyjr · Mar 25, 2018

I am curious how @redfishbluefish experiment works. More interesting would be securing a piece of acrylic to the bottom of a 32g brute after the bottom has been removed, then having it filled with water for a time to see how the pressure effects the seal.

I understand that experiment would cost around $50+ dollars however.

DirtDiggler2823 · Aug 9, 2018

redfishbluefish said:
Silicone does stick to plastic if you use the right stuff. Now that said, I've never used this with HDPE. But what I have used on acrylic is this silicone:

I purchase this in HD, but you won't find it in the Paint department with all the other silicones and caulks. You have to go were they sell acrylic sheets (in my store, were they have storm windows) and you'll find it there. About $8 a tube, but it sticks like grim death to acrylic and glass....you won't be able to pull it off.

I'm doing acrylic baffles in a glass tank for a sump. This stuff will work?

paphater · Aug 9, 2018

DirtDiggler2823 said:
I'm doing acrylic baffles in a glass tank for a sump. This stuff will work?

Since the silicone doesn't really bond that well to acrylic, what you want to do is create a dam around the edge. This will be more than enough for sump baffles.