I'm going to be making some large square planters out of concrete. Basically
3x3x3, with sides about 3" thick. I'd like the finish to be as smooth as possible.What kind of concrete/cement should I use? Can I just run to the Lowes/Menards/Depot and pick up some quickcrete?
Sorry for the cross post. I wasn't sure where this subject belongs...
Thanks in advance :)
Tim
If you want smooth, don't use concrete. the pebbles in the aggregate will show on the surface of the mold. Only on surfaces you can float will it appear smooth.
I suggest you either use ordinary Masons Mortar or Sand Mix. Both of these have no pebbles and will harden just like concrete but with a more uniform appearance. Both are similar, I think the grade of sand inside makes the primary difference (possibly the ratio od portland to sand as well) the quickcrete website has some info.
For a planter, often people will mix polystyrene (little balls inside a bean bag chair) AKA Styrofoam is as an aggrigate to make it much lighter. The foam takes the place of the pebbles. You may have to experiment with mixtures of polystyrene, portland cement and sand to get a look you like.
I have also seen people sponge on a slurry of almost pure portland cement onto the surface to fill in any pits and smooth the appearance after removing from the mold.
Finally make sure the mold is smooth and coated with some kind of mold release so that it in and of itself does not mess up the appearance.
He could always just cast the planters, and then polish them.
Reminds me of helping my grandfather (late '50's) build a "grease trap". It was about that size and heavy. He built it right next to the hole in the ground it had to go into. He made the outside box, and then the inside box and poured the piece as a solid piece.
I agree with a light weight approach for this type of container.
INGREDIENTS NEEDED:
Horticultural perlite Peat moss Portland cement Plastic tub (for mixing ingredients) Dust Mask or Surgical mask Gloves Water Drop cloth
2 cardboard boxes (one slightly smaller than the other) Wooden dowels Chicken wire or Fibermesh Mason?s trowel
Oren
"My doctor says I have a malformed public-duty gland and a natural deficiency in moral fiber, and that I am therefore excused from saving Universes."
Not if you build a mold. I've built dozens of pads up to 3' high for air conditioning condensers using 5/8" plywood and the sides come out almost perfectly smooth.
yup , build the outside wall of mold with sanded ply , shellac to waterproof and smooth , used motor oil as a release agent and normal quick crete to pour, use a slightly wet mix .
Be aware that concrete weighs in at close to 100 lbs per cubic foot so you will need to reinforce your molds.
Pound the mold while filling to help remove air bubbles.
Wire mesh in the mold will help keep the sides from cracking.
Good luck with it.
Well, it depends on why you want big-ass concrete planters. If you're trying to stop drunk drivers hurtling off the corner before they plow into your livingroom, skip the pearlite.
(or car bombers, or whatever. note that a 3' high planter isn't big enough to stop a tank.... :-) )
I was thinking I'd build the mold with 3/4" ply, then line the inside with Masonite so it's mucho smooth. waddya think?
Any other "cleaner" release agents I could use? ;)
Hmm, perlite.. crushed or expanded? (based on what I've read on the web )
where do you find the stuff?
Peat moss. Seriously? ;)
Bags of it are in a garden center, same stuff used in plants to help aerate the soil
First link is step by step...nice pictures.
Oren "My doctor says I have a malformed public-duty gland and a natural deficiency in moral fiber, and that I am therefore excused from saving Universes."
I don't use a release agent and have never had a problem. Plain old sheathing plywood is plenty smooth enough, especially if you are going to paint the planter. Just use a wet mix and after pouring tamp it down to eliminate any bubbles as marks recommended. Pound a bit on the side of the mold, too.
Possibly that white "tile board" Masonite stuff would leave a good finish. Also consider rigid foam board insulation and the possibility of routing decorative features in the foam to cast them into the planter.
Pete C.
For some reason many, many years ago diesel fuel was painted on plywood with a brush. Supposedly to prevent any sticking of the wood to the cement. My guess this was the petroleum. What little I form myself, I whack it with a hammer here and there to settle things also.
Oren "My doctor says I have a malformed public-duty gland and a natural deficiency in moral fiber, and that I am therefore excused from saving Universes."
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