Planning a custom ballast box

[Musdalen]

I have been wondering about the pressure issue. Concrete is dense stuff, but it doesn't flow really well. I'm more worried about it flowing out of a gap in my box where it goes around the outside of the hitch. I should probably jam something in there, but will it matter much if pressure is that great? THere will be 21" of head on that concrete.

I'm also wondering about how much bracing is needed outside the box to keep it from bulging too badly. I'll work on that tonight and then coat the inside of the box with some marine spar varnish to keep the cement from sticking too badly (I hope).

 

[olPete]

I have been wondering about the pressure issue. Concrete is dense stuff, but it doesn't flow really well. I'm more worried about it flowing out of a gap in my box where it goes around the outside of the hitch. I should probably jam something in there, but will it matter much if pressure is that great? THere will be 21" of head on that concrete.

I'm also wondering about how much bracing is needed outside the box to keep it from bulging too badly. I'll work on that tonight and then coat the inside of the box with some marine spar varnish to keep the cement from sticking too badly (I hope).

I had pretty bad bulging issues, but my mould was something flimsy cut in half.. perhaps, you could tie the two sides together with 3 or 4 wires and then clip them off/grind them level once the concrete has cured?
I had some leakage from where I put my pool-noodles in the end of my weights, (that was purely so I could put a bale spike in there to lift them onto the implement), but it really didn't make any difference in the end as I just rubbed it away a few hours after pouring. It was quite a loose fit in the hole, at a guess 1/8" gaps in places. The liquid came out at the start of the pour but quickly staunched itself. Maybe lost a quarter cup each time.
Pete

 

[Musdalen]

I LIKE that wire crosstie idea. Might do it.

But here is what I have now. I've patched the gaps around the hitch with spackle - not very strong but the cracks are very small. I would imagine that the aggregate will help prevent flow through those cracks should they break. Now to just add some finish to the wood to keep cement from seeping into it and bonding.

View attachment 500459

 

[olPete]

that looks great, I don't imagine you'll have very many issues at all. Is your ply smooth side in? You may be able to simply wet it with a cloth before you pour, if has the smooth side. Probably better ways to do it, I just wet and then wipe with a kitchen detergent, actually putting a coat of something on will be beneficial.
I usually put some detergent in the concrete too, but I don't think it's necessary, I just do it out of habit.