Concrete Posts.

[Egon]

Are you going to add any colour to concrete when you cast your posts Lloyd?:thumbsup:

 

[forgeblast]

I was thinking, as i was driving to work, about a sculpture class i took.
You could buy one wooden post with the cut outs, and then use a mold material,
like smooth on 40, or some other casting material to make a flexable mold. This mold would pick up the grain of the wood and if you added the right color it would be stained during casting, making it look like a wooden post.

 

[EddieWalker]

I don't think I would put anything in the post for holes. It's makes it too hard to get the post at the right height. It's real easy to drill holes in concrete with an SDS Rotary Hammer or a SDS Max. I have both, and for smaller holes under an inch, they either will do. You can even get cordless SDS Rotary Hammers that will do the job easily.

Set your posts and then drill where you need the holes.

Depending on how good you are at measuring depth of holes to set your posts, I might also make them about six inches longer then you need them, and cut them off after they are set. Just make sure not to put the rebar all the way to the top so you don't have to cut through it. A diamond masonary blade will go through it easily. It's loud and dusty, but real easy to cut. Then you can polish off the ends to look real nice with a grinding masonary grinding wheel on a 4 or 4 1/2 inch grinder. Might even bevel the edges for a real custom look.

Eddie

 

[Lloyd_E]

Thanks all...

I will do a drawing and get back to you. Eddie sounds like too much work !

Later...

 

[forgeblast]

Just wondering would you cast them with rebar sticking out and then throw cement in the hole, or cast it as one unit and then just dirt back fill.
Also how would you support the rebar so that it doesnt sink through?

 

[Lloyd_E]

Forgeblast,

I just plan to back fill. I will probably need to put wire in concrete so I can haul them out. I am looking at release agents also. I assume the rebar will not sink due to the stiffness of the mix.

Mold Release Agents, Mold Release Agent Innovators, Releasing Agents, Compounds, Huron Technologies, Detroit, MI, Michigan

The attached pdf shows the followingage1 rough layout of 2x6 on 4"x8" plywood; Page2 showing portion in ground - large gray block - plus fence rails; Page3 fence rails only.

Dan, how big of a slot? My thoughts are if I am going to make a mould for smaller slots shouldn't I just enlarge them for the rails to go through? I assume on the back side of the slots would be a large backing plate or washer...

Not sure if I should add colour of not...

Do you think a heavy coat of rubber cement or contact cement would act as a release agent?
Or several coasts of varnish and maybe spray with oil...

The four circles represent 4 1/2" pvc pipe ganged together. This will give me a 2" vertical adjustment.

I am going to walk property and count posts but I think initially I will need around 180.
If I could cast 12 every 2 days it will take me 30 days to do the job.

 

[tcartwri]

Precast is the way to go. It is surprisingly cheap, and you could probably get the local home depot, or home hardware to bring them in to save on shipping.

Like these.

Woodcrete Rail - Artisan Precast

 

[Egon]

2 mil plastic would make for a pretty good release agent.:thumbsup:

Note: Commercial made posts would probably be made with no slump concrete and pressed into the mold under high pressure. Then cured in a temperature moisture controlled environment.

 

[forgeblast]

Concrete | Eliminating Surface Voids in Concrete | Smooth-On - Mold Making and Casting Materials | Silicone Rubber, Urethane Rubber, Liquid Plastic, Casting Resin, Lifecasting, Epoxy Resin, Rigid and Flexible Foam

I have used this product before, so i can say it does work.
I have also cast about 60 lawn edgers, to cast them i used spray on veg oil. We also used on more porus things 3 coats of murphys oil soap.

that precast webpage has some products really like their rail fence.

 

[ultrarunner]

Precast is the way to go. It is surprisingly cheap, and you could probably get the local home depot, or home hardware to bring them in to save on shipping.

Like these.

Woodcrete Rail - Artisan Precast

I've seen this product in the City of Livermore CA... they use it to separate the bike paths from traffic lanes along the landscaped median.

 

[tcartwri]

I'm not sure what would happen if a horse tried to run through a concrete post though. We had a mare than snapped an 8in cedar post off at the ground when she got spooked. Pretty sure the concrete would not give at all.

The posts I linked to, are pretty high end, but I think you could find generic posts for 10 to 12 $ a piece.

 

[RobertBrown]

Forgeblast,
The attached pdf shows the followingage1 rough layout of 2x6 on 4"x8" plywood; Page2 showing portion in ground - large gray block - plus fence rails; Page3 fence rails only.

Consider making the molds so that the sides lock together using the top and bottom portions. What I am getting at is, the posts are less likely to want to come out of a form with 3 sides regardless of the release agent. If you could dissassemble the form by knocking off the top and the bottom (short sides), then remove the outer posts, knock off the innner sparations (long sides) and so on. I think you will have better luck re-using them.
As Egon mentions, a thin plastic wrap that runs horizontly across the mold or from long side to long side, dipping down into the mold may work very well. I'm thinking even thinner than 2 mil something like what you would use for food preparation. The problem with using a plastic wrap is when it folds and bunches up on corners with more than 2 sides. If your only using it in one direction a careful installation should eliminate this issue, Then use whatever release agent on the top and the bottom(short sides).

 

[ultrarunner]

I'm not sure what would happen if a horse tried to run through a concrete post though. We had a mare than snapped an 8in cedar post off at the ground when she got spooked. Pretty sure the concrete would not give at all.

The posts I linked to, are pretty high end, but I think you could find generic posts for 10 to 12 $ a piece.

I think the concrete rails would give way... I saw a bunch of teenagers sitting on a rail one day... the next time I dove by the rail was damaged... it looked like the concrete separated from the re-bar.

 

[magicheater]

There are many concrete fence posts in South America as well. They make power poles of concrete too. Seems a more permanent solution. If we had the mind of the American Indian philosophy of planning 7 generations beyond we might all have concrete fence posts!

 

[bearhawk]

If you could find a place that has real form plywood like Plywood Concrete Forms I would make your form out of it. I Like RobertBrowns idea of being able to disassemble the form to remove the post. I think one of the pdf's above had the plan designed like that.

 

[texasjohn]

Been there, doing that...I have a source of free concrete culverts...defects in manufacturing...

Pick one of these suckers up, go to where you want a corner, plunk it down and there it sits. No drilling holes, no bracing posts. It doesn't rot. It doesn't pull out of the ground.

Wrap your wire around it, pull tight with ratchet strainers, all done.

I use T posts as line posts. Yes, they will rust away... in over 100 years.

 

[heehaw]

i tried buying precast post an rails several years ago: don't remember the price now, but i do remember thinking it was outrageous: at the time a yard of concrete, 4000psi was less than $100, an the labor couldn't be very much...but i never got around to making them myself..still think its a great idea..good luck.
heehaw

 

[dmccarty]

If I was going to cast my own concrete posts I think I would have the form set up to imprint height indicators....

Would be handy setting the post and might be useful depending on the fence material.

Later,
Dan

 

[Lloyd_E]

Thanks all.

A lot of great ideas especially the height imprint - every foot should work.
I also like the idea of dismantling the form; top and bottom could be hinged while the
2x6 form walls could be pegged into position and held in place with weight during the cure time. I am thinking of using epoxy or 4-6 coats of gloss varnish on everything and spraying with release agents...

keep them coming...

 

[dmccarty]

Buying concrete from a plant is going to e MUCH cheaper than using bagged concrete. I figured a 8'x6"x6" post would take about 2 CF which would take 4 80 pound bags of concrete at almost $4 a bag which is $15-16 a post. OUCH.

If I got a truck load of concrete at $85 a yard it works out to a bit over $6 a post. But one would have to have a bunch of forms ready to handle a cement truck load.....

Coloring the concrete would be a big plus. I noticed that the bagged concrete company sells color for concrete. Our house has colored concreted floors. I had to go to a mason supply store to get the tint and drop it off at the plant. I forgot the exact ratio but it was 2-3 bags of coloring per 7 yards of concrete. Or there abouts.

Course 7 yards of of concrete would make about 94 posts.

Later,
Dan