FLoor leveling and other advice for 2500g tank build

[Kentrob11]

Hey everyone...I've been a lurker here for a while but haven't posted much but am now nearing the point where I can start on my large tank build so I figured I would start drawing on the experience of some of you to get things started. I am planning a 12 x 7 x 6 tank constructed on stacked, glued and screwed 2x8's and a single 54" x 118" viewing window made of 1 1/2" or 2" thick acrylic(not sure which yet). The current plan is to line the inside of the tank with 3/4" plywood and then a layer of 3/8" thick black HDPE plastic sheet welded at the seams. This will be a saltwater reef tank...

This is going into my basement...I built the house about a year and a half ago and had a 12" thick footing poured under the basement floor where the tank was to go so I'm covered there. As with most basements, the basement floor grades slightly downward from the wall towards the center so I need to frame off the proposed tank perimeter and put some sort of self leveling compound down to build the tank on. I would imagine it would only be about 1-2" thick at the point furthest from the wall but I was hoping to get some insight as to what material would be best for this since it will have so much weight on top of it.

The second question I had was concerning the use of screws or nails for building the 2x8 structure itself. I am well versed in the ability of nails to back out over time but if the 2x8's are sandwiched together and glued, I would imagine that wouldn't be an issue for those 2x8's that had another 2x8 on top of them, no? I would think that only the very top layer would need to be screwed down....Obviously time saved would be the main reason for this question. I have a framing nailer and could make much quicker work of the tank build if I could do it that way....Thoughts?

Kent

 

[Tyler2012]

Use screws throughout the whole tank.


Sent from my iPod touch using MonsterAquariaNetwork app

 

[jsodwi]

If the floor is out that bad, I would frame out the area where tank is going to sit and pour a 4" concrete pad and make sure it is dead on level.

 

[Kentrob11]

I don't think it's that bad really...I'll have to get down there with a level and see for sure. I wouldn't want leveling issues to cause problems down the road. Does anyone else have any input on acrylic thickness for a 54" tall viewing pane? I think I'm going to have to go 2" but was hoping maybe someone had experience doing 1.5" in a similar sized build...

 

[CJH]

I am planning a 12 x 7 x 6 tank constructed on stacked, glued and screwed 2x8's. The current plan is to line the inside of the tank with 3/4" plywood and then a layer of 3/8" thick black HDPE plastic sheet welded at the seams.

The basement floor grades slightly downward from the wall towards the center so I need to frame off the proposed tank perimeter and put some sort of self leveling compound down to build the tank on. I would imagine it would only be about 1-2" thick at the point furthest from the wall but I was hoping to get some insight as to what material would be best for this since it will have so much weight on top of it.

The second question I had was concerning the use of screws or nails for building the 2x8 structure itself.

I like the idea of a 3/8" layer of protection but do have some concerns with that in general and with HDPE specifically. 3/8" HDPE is most commonly available in 4x8 sheets so at the dimensions you're considering there is going to be a lot of waste. But that's a fairly minor concern.

A concern of more significance is the strength of a structural thermal weld in HDPE - it's not all that great. When you heat weld HDPE the molecular arrangement changes and the joint itself becomes more brittle than the surrounding material. This is not a huge deal but it does mean you want the back of the HDPE perfectly supported by the plywood. Let's say in a lower corner there is a 1/8" gap between where the three HDPE panels meet with the three plywood panels. I would not trust that joint to hold up to 7' of water pressure unless the plywood met the HDPE perfectly.

With the design you're considering it will be difficult to build a perfect plum, level and square box (because dimsional lumber is not perfect flat or straight on one edge) so you'll have to take extra care to make sure the HDPE seam you're welding at a given time is perfectly flush with the plywood behind it. This is not something that can't be overcome but it won't exactly be easy either.

My biggest concern is how you'll attach the acrylic window since I don't know of a caulk type material that is flexible enough for installing an acrylic window in water that deep AND that will stick to HDPE. Materials that bond to HDPE and other low surface energy plastics are being developed frequently nowadays but last time I checked none were flexible enough for window installation.

You could possible bolt the window in place with some sort of gasket material but again you'll have to take care that the area where the window will overlap the HDPE is close to perfectly flat.

I think combining the stacked lumber approach along with a thermally welded plastic liner is creating some unique difficulties. None are impossible to deal with but I wanted to point then out.

Have you considered a plastic with greater surface energy like PVC? This would allow you to bond sheets to plywood and would allow you to solvent weld thicker or additional matieral over and along all the interior seams? You could also get away with thinner material since you wouldn't need the thermal mass to absorb the heat of the weld.

Some food for thought.

I would not pour a thin, self-leveling layer to hold up to well over 30,000 pounds in such a small area. I would instead scribe your bottom layer of lumber to the floor and build off of that platform.

As far as screws vs. nails, I say use screws where ever water pressure will be acting to pull a screw out of it's hole. You can get away with framing nails where ever you just need the sheer strength.

 

[wcgunns]

I plan on using the HDPE sheets as well on my 20'x5'x3' 2250g build. Not sure why more DIY tanks have not been built this way.


Sent from my iPhone using MonsterAquariaNetwork app

 

[sashimimaster]

use a self leveling mortar like they use for tile work. But if it's more than 1/2" valley you will need more bags. Each bag was $50 the last time I remember. I used high strength concrete with little bits of fiberglass in it for mine. But mine was so off I needed 4 bags and had to build up 2" on one end.

 

[Kentrob11]

CJH- Thanks for your input! This is exactly the kind of help I was looking for...I originally planned on using PVC sheeting but after some research it appeared that for heat welded seams, HDPE seemed better due to availability of larger plastic welding services around here . After reading your suggestions I may return to black PVC sheet...As far as the ability to built the support structure square and plumb, I knew it would be a challenge to get it perfect but I figured through careful selection of lumber and the use of level set floor to ceiling form jigs to keep things as square as possible, I could get pretty close.

So as far as lining the tank with PVC is concerned...When we say thinner material are we thinking maybe 1/4"? I would think that would be strong yet flexible enough to mitigate and slight irregularities in the inner tank perimeter. Then maybe use 1" wide triangular filet rods glued into the corners? I had even thought of a 1/2" or so thick layer of Dow 795 over every seam for extra protection...

Acrylic viewing pane...I have a friend that lives in Wisconsin that has a 20,000 gallon in his home. I have spent a decent amount of time with him on this build but his is concrete so there are some differences. His method for attaching the front pane is consistent with those used but well built public aquariums...Instead of the glass smashed up against a beat of silicone on the front of the tank, it's actually pressed up against foam pads in a frame with a 1" gap between the perimeter of the glass and the inside edge of the frame it sits in. That gap is then completely filled with Dow 795 for a roughly 1x2" Dow seal. You can look at his build by going to reeffrontiers dot com and going to the aquarium engineering sponsor forum. It's an incredibly impressive build...Anyway, I had planned on doing this viewing pane the same way. I would have to incorporate that frame for the window when building the 2x8 support structure.

As far as the leveling issue is concerned, How exactly would you scribe the lumber? I had the same concerns about the ability of some floor leveling compound to hold that much weight...Thanks a ton for your help!!

Kent

 

[Kentrob11]

sashimimaster- I am a little concerned about the ability of a leveling compound to withstand that much continuous weight...I really need to see exactly how level it really is. I'll check that out tonight...

 

[CJH]

As far as the ability to built the support structure square and plumb, I knew it would be a challenge to get it perfect but I figured through careful selection of lumber and the use of level set floor to ceiling form jigs to keep things as square as possible, I could get pretty close.

So as far as lining the tank with PVC is concerned...When we say thinner material are we thinking maybe 1/4"? I would think that would be strong yet flexible enough to mitigate and slight irregularities in the inner tank perimeter. Then maybe use 1" wide triangular filet rods glued into the corners? I had even thought of a 1/2" or so thick layer of Dow 795 over every seam for extra protection...

Acrylic viewing pane...I have a friend that lives in Wisconsin that has a 20,000 gallon in his home.

As far as the leveling issue is concerned, How exactly would you scribe the lumber? I had the same concerns about the ability of some floor leveling compound to hold that much weight...Thanks a ton for your help!!

Kent

A stacked lumber design is going to be the most difficult way to build a tank and keep it level, plum, square, etc. It's also very expensive and I think once you want that level of overkill you should be considering other designs as well. But if that's what you want to do then I'd consider drying your lumber out down to furniture grade wood and finding a shop that can joint one edge and face and then run the opposing face through a planer. But jointing 12' long lumber is not exactly the easiest thing to do. You might need to find a shop with one a large molder than can handle 2x8 stock that long.

As far as your friend and the window design, I like that you're wanting to do something other than the traditional approach but I think you still need to have some sort of bond to the HDPE and I'm not sure I'd truse 795. Of course if you switch to PVC then that should work fine.

As far as PVC vs. HDPE, there is a custom plywood tank company in Europe who only builds tanks with PVC sheets laminated onto plywood. I assume they use a vacuum bag to bond the sheets to the plywood. I believe they use 1/8" thick PVC which is 125 mils thick. Compare that how thick epoxy layers on wooden kayaks or other boats are and that's still a lot of protection. I would solvent weld some sort of PVC angle or strip over ever seam. I'd have to look at available extrustions to see what's available.

I would just make sure that you use solid PVC and not the foamed PVC sheets that are used on the sign industry.

As far as scribing, I guess it really depends on how you build your bottom. But if you use 2x8s on edge for the bottom platform then just start at the low area and shim a 2x8 in place so it's level. Then scribe along the contour of the floor to transfer the shape of the floor to the 2x8. Then saw the material out and you'll have a 2x8 that fits the floor. Then move onto the next one. Now you have to take care to make sure the next piece is scribed so it's level and the top matches up with the previous scribed piece. This will be time consuming.

I would get a helper and a string and pull it tight at various places across the floor to see how bad it is.

If you want to start with a bottom layer laying flat on the floor then I think you'll need to lag the bottom plate to the floor so it's tight and flush. Then you'll need to make up for level with the subsequent layers. Again, using a stacked lumber design will make this more difficult. If you space our your framing you can cut blocking between the first and second layer that level things out as you go.

I simply would not trust a self leveling compound to hold up. If you're that concerned then I'd drill into the current floor and add rebar and reinforcement and pour a fairly thick floor over the current one. Since you'll have a cold joint you really need this secondary, leveled floor to have the compression strength to hold up to the weight.