Epoxy Coating

[LawnJockey]

I am buying a place that has a failing septic tank lid.  The tank itself has been inspected and is fine.  It is at a hard to get at location so casting a lid and hauling it in would be a problem.  I am thinking about fabricating a steel form that would be epoxy primed and then left in place once the concrete is poured.  In the past I have used Zspar 646 epoxy primer for jobs where tough protection is required but I am wondering if there isn't a cheaper equal product out there that doesn't have the "marine" price premium.  Any suggestions?

 

Thanks

[fergy]

Could you not just use form ply and then just let it rott ?

Our septic tanks here are only 5' round yours may be different 

[ianinsa]

We commonly use precast fence planks/ concrete lintels as permanent shutters. 

[LawnJockey]

Well that is an option but it is a pretty large tank and I do not think plywood alone would support the weight of the pour thus there would have to be a framework below.  The idea of a steel form which could be reinforced from above by just tacking some angle on top of it and pouring over the whole thing eliminates that problem. I certainly don't want to climb in it to remove forms.  That would be like the end of the movie The Magic Christian.

I have never seen precast fence planks here.  These days you have to worry so much about liability I would be nervous about using something that wasn't designed for a load carrying application.  I feel pretty comfortable with poured concrete with lots of rebar in it.

[ianinsa]

LJ, bear in mind that the "shutter" needs to hold the weight of the wet concrete and once that has cured its redundant, however if you leave boards, shutterply etc. To rot Murphy will ensure that they block the outlet  . You could even use plastic(ridged)fiberglass sheeting etc. By wiring it upward! Ie. Stack bricks either side and span a pole across then tie the sheets with long(12") wire to support them. When the concrete has cured snip the wire off and take away the poles and brick stacks. 

[DSW]

Stupid disappearing posts again

[Charlotte]

Reply could be more creative if you would provide dimensions. Epoxy paints are all close to the same price.  Try looking at local paint company sites.   

[DSW]

Lets try again.

Knowing more details about your situation like size and access conditions would help. We often get large septic tanks with two and three piece lids. That's done to keep the weight under that the crane on the truck can handle.

Working inside a tank is very doable. 1st thing is you have the tank pumped all the way down. You should anyways on a regular basis. Since the lid is off, now is the best time to do so. If it hasn't been pumped regularly, the sludge may have become like rock at the bottom and reduced your tank capacity.  Often they'll pump the tank, then come back with a load of clean water and flush it several times to free up what's in the bottom. At the same time take the chance to spray down the tank with disinfectant and pressure wash the walls.

A tyvek suit, rubber boots and gloves take care of the rest. I've lost count of the number of tanks I've had to work in and around doing excavation and working for the septic guy I plow for in the winter. It's not a pretty job, but someone has to do it. That includes changing out pumps inside the tanks in sand mounds and transfer tanks.

You are going to want at least 4" to 6" of crete minimum on top of the tank, more if you want it to take serious weight like a vehicle on it's own.  Amount will be based on tank size. Concrete weighs 150 lbs to the cubic foot dry. Wet you are probably looking at 200-225 lbs. That's a lot of weight to support overhead. You will need a lot of shoring to support this. Things go bad fast when floor forms fail.

 

Steel in concrete is badly misunderstood. Concrete is good in compression, but bad in tension. Steel helps transfer tensile loads to compression loads by making the concrete compress in the tensile areas. two problems with this. #1 concrete is porous, and steel will rust if too close to the surface, so minimum is usually 1 1/2" to 4" of concrete coverage to prevent rusting. #2 is that steel only works if it's as far from the neutral axis of the slab as possible. Steel in the middle of the slab is neither in compression or tension, and adds zero to the strength. To add the most strength, the steel would need to be just below the surface of the concrete, but have enough coverage to transfer the load. That's not possible in a 4" slab. It's not even terribly practical in a 6" slab. Even in 6" of crete, you only have 3" from neutral axis to edge, and the last 1 1/2" can't be used due to coverage and corrosion issues. That's not much added strength at all. Heavy duty commercial lids have cast in place beams incorporated in the lids to add strength.

[LawnJockey]

Sorry for the slow reply I have not had computer access the past few days.  So far the best price I have been able to find for high build epoxy is from Jamestown Distributors.  That said, Smith and Company makes a penetrating epoxy that is specifically for treating crumbling concrete.