Joining PVC panels - hot gas welding AND solvent? - Sump construction.

[FishTruck]

I was able to make a water tight box using solvent and cheap PVC board from home depot - working my way up to making a big sump. An 8 x 4 sheet is about 60 dollars. 1/2 inch thick. Very cheap compared to acrylic, very easy to join with solvent, lighter, and easier to acquire. It's also flexible (not good) and I am not sure how strong the solvent joined joints are compared to acrylic. I think I can overcome the flexibility with lots of joints and a euro-brace type of top.

Ultimately, I am looking to build something about 6 feet long, 18 inches high, and 24 inches wide. There will be baffles and other supports about every 18 inches as well as bracing top and bottom. Making a mid sized prototype this weekend.

Question: What would happen if I made a sump using solvent, and then re-enforced the critical joints using hot gas welding? Would the remnants of the solvent bond somehow interfere with the hot gas welded joint? I can get a hot gas welder and PVC sticks for about 160 dollars from Amazon. It also might be easier to just chamfer the edges and JUST weld it. Most of the opinions I have found suggested doing something more than just solvent joining the edges. I could also cut DADOs - but the precision needed to get it right would lead to swearing and wastage of material - in my hands.

The schematic shows the white 1/2 inch PVC, red and orange are baffles and vertical shelf supports, and the blue triangles would be room for hot weld beads. I could weld the vertical joints in the same way - just not shown here.

Any other tips for joining PVC panels are also welcome?

 

[crusso1993]

@Elder1945 is probably one of the best resources here for input. Hopefully he's not too busy and will chime in.

 

[User1]

I always thought that you treat the pvc sheet similar to a sprinkler pipe. Just sand, primer, and glue. It seems I over simplified it and that isn't the case.

I'm interested though because I've entertained using the same sheet of pvc to also make one. Sheets are super affordable and can be managed via wood tools. So easy to route out a groove on the bottom and sides and even add a 2" euro brace.

 

[lapin]

I have never test PVC sheet joint strength. With that out of the way.......
With PVC, general industry rule of thumb that you can expect 60% - 80% of the bulk material strength from the weld if done properly.
I would not think that a "1 time heated rod weld" would distort the material enough to cause a problem with a solvent weld since you are adding material. However people have been known to heat PVC pipe welds to separate the pipes. So I could have this wrong.

 

[FishTruck]

So far, the solvent joined edges seem to be very strong. I think I am going to get a plastic welder and try it out.

 

[FishTruck]

Well... a 12 x 12 x 12 inch box works great.

My 24 x 24 x 24 inch box seems really FLIMSY - and at larger sizes, the expanded PVC is less easy to work with. The bracing necessary is getting complex. Solid PVC 3/8 inch thick would be a better material - but that is hard to get and fairly expensive.

A six foot sump? Each 72 x 24 inch panel would be holding back about 600 lbs. of force. I am going to say that home depot expanded PVC 1/2 inch thick just isn't strong enough.

Moving on to plywood. My new plan is to build a series of small boxes / sort of a modular sump. I need something that will be easy to move into the new house.

 

[biecacka]

Could you insert more baffles and use them as cross support?

Corey

 

[FishTruck]

Perhaps. I read one account of a guy who build a 6 x 2 x 2 grow out tank with this stuff, and his main problem was the baffles failing (solvent did not hold). He ultimately solved the situation (I think) by using wood screws. So maybe with 3/4 inch thick baffles and screws it could be done with 1/2 inch extruded PVC.

My main issue was making a sump that would be light enough to move easily to my new house. I think I am going to make three small sumps with Plywood / epoxy.

 

[User1]

Thanks for the information in the thread. I've been considering the use of PVC sheets but didn't move on it because I wasn't sure how to actually glue them together. At first I was thinking you treat it just like PVC plumbing. Sand, rough, apply primer, glue, and set. Nope.

On the three small sump part. I am also looking into something similar but not to make out of plywood. I've been looking at rubbermaid or similar food grade 20 or so gallon storage bins. Plan is to add bulkheads for them to overflow into one another and use Unions for quick disconnect. Then I could do something like drain box, refugium or center holding area, and the last one holding return pumps.

I've found some nice containers but some of the prices after shipping has not been that great so far haven't found anything that I think would work at a good price point.

 

[crusso1993]

@Laith - just had a large sump built out of PVC panel. I believe the thickness was almost .75" and the builder screwed them together. Maybe @Laith can offer more insight.

 

[User1]

@Laith - just had a large sump built out of PVC panel. I believe the thickness was almost .75" and the builder screwed them together. Maybe @Laith can offer more insight.

That is interesting. I've heard that the PVC sheets can more or less be treated like plywood or other hardwood sheets. The wood tools would work. That was one reason why I was interested.

 

[Laith]

@Laith - just had a large sump built out of PVC panel. I believe the thickness was almost .75" and the builder screwed them together. Maybe @Laith can offer more insight.

Yes, 19mm (3/4”) PVC panels were used. They were glued together and screwed as well...

 

[FishTruck]

Thanks for the information in the thread. I've been considering the use of PVC sheets but didn't move on it because I wasn't sure how to actually glue them together. At first I was thinking you treat it just like PVC plumbing. Sand, rough, apply primer, glue, and set. Nope.

On the three small sump part. I am also looking into something similar but not to make out of plywood. I've been looking at rubbermaid or similar food grade 20 or so gallon storage bins. Plan is to add bulkheads for them to overflow into one another and use Unions for quick disconnect. Then I could do something like drain box, refugium or center holding area, and the last one holding return pumps.

I've found some nice containers but some of the prices after shipping has not been that great so far haven't found anything that I think would work at a good price point.

@Laith - just had a large sump built out of PVC panel. I believe the thickness was almost .75" and the builder screwed them together. Maybe @Laith can offer more insight.

0.75 inch solid PVC would be great - no doubt.

Keep in mind... I was playing around with the cheap EXTRUDED PVC - 1/2 inch thick from Home Depot. This is less dense and less sturdy than solid PVC. Also, I was just using plain Oatey PVC cement. I never got to the point of actual welding, trying a better solvent, or re-enforcing the solvent bonds with screws. The Q and A on the material says that it is not even strong enough to build shelves - due to flexibility issues.

I have also looked at alternative containers (stock tanks etc...), but having a truly square profile simplifies the control of water flow, placement of filters and baffles, and minimizes the overall space taken up by the sump.

 

[Laith]

I'm using 19mm PVC for my 2m sump (78"), my 150 liter top up container and my 270 liter fresh saltwater container for AWC. The two containers have transparent panels in the front so I can see in them.

I would think anything thinner and/or less dense would cause issues for this use. But the 19mm solid PVC is perfect (so far at least!).

The great thing about using PVC is it is so easy to work with in terms of making holes for cables/tubes or gluing things to such as float switch brackets/probe holders etc. ;Happy. And for the sump, if I want to raise a baffle (or add one) you can just glue an extra piece of PVC. If you want to remove a partition/baffle you just cut it out...

My build thread shows the containers being made and how I added float sensors and an emergency backup float switch to the topup water container. Also has pictures of the finished sump in place.