Frame Welding

[Kenn]

After three days and nights of looking on the net and talking to many people, I have decided to give up the idea of using aluminum. I now plan to build a tank out of plywood with several coats of epoxie. In my search I found ready-made tanks that were close in size but either would not hold as much or were to big to fit my space. I have built many things using wood and epoxie so I know what is ahead of me. I once built gas tanks for a flat bottom boat back it the day. Anyway I did learn that if you need a custom size you need to build it. I always though the big builders used plastic to save money and did not want to spend the time and money to build one out of amuminum.

[Dragonslayer140]

Kenn, what about building the tank out of aluminum and then coating the interior with some type of protective coating, This is pretty much what they do with aluminum drink cans. Would think that an epoxy or perhaps a corrosion coating such as NO-OX-ID (NO-OX-ID rust preventatives & conversion coating prevent corrosion) could be applied to the interior thru a removable hatch in the top or poured in and then roll the tank around to coat it and drain out the excess. not sure how that would compare cost wise or durability in the elements compared to a plywood tank. I would be afraid of moisture working its way into the plywood from inside or outside and causing delamination or rot. Then again I am way to type A and tend to over think everything lol.

[Kenn]

Dave great minds do think alike LOL. I spent many hours trying to find a product to paint the inside of the aluminum tank. Some concerns I had were not just the tank walls but the aluminum adapter I made. If I coated the adapter with epoxy, it would add enough thickness that the rubber seal would not fit as it should. If I machined the adapter to make room for the epoxy, it would make for a very thin (read weak) part. I checked into pour-in type products and found most are for steel and very little information on aluminum. I am not to worried about water getting to the wood. I will be able to get to all side and the bottom of the tank after the coach is done. If an aluminum tank developed a leak it would have to be removed to make a repair but the wooden tank could at least be glassed over on the outside to get me home. I have used epoxy with good results on many project including boats (gas tanks & and many other areas), race cars body, wings and lots of parts. Yesterday I cut all of the plywood and today I will start on the epoxy. I plan to lay all of the sheets flat and roll and brush the epoxy on before I glue it all together. When the tank is glued together I will do the outside. I really wanted to make it out of aluminum. At some point I need to move on and being the only decision maker I thought the wood/epoxy made the most sence. I will post pictures as the tank develops. Thanks for your thoughts, I do appreciate them. Kenn

[#90-GTSC]

What kind of plywood? Marine grade?

[andyg]

I have heard of folks building plywood tanks and lining them with fiberglass and it worked OK. Be sure to make the box strong because water is heavy. Containing that water takes a bit of strength when it starts to slosh around.
P.S. I'm not convinced that there would be a problem with aluminum.

[Kenn]

I am using 15/32" exterior grade from Lowes. I am using three layers of 9 once cloth on the inside and two layers on the outside. The inside joints will have an adhesive fillet shaped with a spoon and covered with more cloth. The outside joints will have several layers of cloth. I am installing a tank monitor system made by Tech-Edge Manufacturing in Sweethome Oregon (541) 610-3116. This is a system that mounts foil tape on the outside of the tank and reads through the tank wall. I will be putting the tape on the inside of the tank and running the wires to the outside. The foil tape will be glassed over on the inside.

[Ran D. St. Clair]

Sounds like a good plan. I have done lots of similar work with West Systems epoxy and glass. You are going to need to do something to rough up the surface at the corner jounts since you will have already glassed the inside of the individual plywood sheets. Peel ply is supposed to be an easier way to go but I always just go at it with an auto body disk sander to knock off the shine. The corners need to be extra strong. All that weight will try to bulge out the sides and convert any cube to a sphere.

[Kenn]

Today I epoxied the aluminum strips and copper pads to the inside of the end panel. I drilled a hole and then made small cuts with a hand saw to pass the copper pads through without cutting any wires. I stuck the sensor module to the outside. I used 3" cloth tape and then 4" cloth tape followed with a full layer of cloth. No if I ever needed to change out the sensor it would be possible without going inside the tank. Next up is all of the inlets 1 1 1/2" vent, 2 1 1/2" drains and a 3" toilet going in with a 3" dump valve going out.

[Kenn]

I have been working on the inlets and the outlet for the holding tank. I used stainless thread anchors on the floor of the tank to recieve the 1/4 20 bolts that hold the dump valve to the underside. I used epoxy (thickend) and several layers of cloth on the inside. I will use a good marine sealant on the outside. I made fiberglass flanges to mount the rubber grommets that will hold the abs drains. Today I epoxied the baffel in the center. I will use cloth on the glue joints and then be set to glue the top and bottom on. This has been a big time eating part to build. On the good side it will hold 80 gal.

[Kenn]

More pictures.