The Accidental Smallholder Forum
Community => Coffee Lounge => Topic started by: escapedtothecountry on May 18, 2013, 03:17:53 pm
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I bought a fibre glass mould so at I could knock up some concrete flower pots. I've put the concrete in.... Now what are the odds that I can get the pot out tomorrow.... Or will I be stuck with an expensive paperweight?
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I've heard farmers saying when they make concrete bases for barn support pillars they use fairy liquid in the ply mould to allow the concrete to free. Maybe fibreglass doesn't need it tho as it has a bit of flex?? #fingerscrossed
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You need to grease the mold with shuttering oil first before pouring concrete or it will never release from the mold. most builders merchants stock it. :fc:
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Was advised to spray with mr sheen or an oil diesel mix.... Lets see...... Tomorrow
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:fc: :innocent:
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Yes my thoughts exactly :fc: :fc:
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Release the mould tomorrow. But dot not move the pot for a week to give the concrete time to gain strength. Did you vibrate it well....or poke well with a stick ?
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Stick poking method. Yes was guided to release the pot tomorrow. Thanks re not using for a while. Will leave it to strengthen somewhere.... That's if it does come out!
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how did it go?
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Pot didn't stick so got that right.... Concrete mix was too dry so crumbled..... So will make second attempt.
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What was your mix, I would suggest something like 3 gravel 2 sand 1 cement. Put a squirt of fairy liquid in the mix it will help with workability to compact it into the mould. Do lots of poking with your stick, in layers as you fill the mould.
Good luck !
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Was advised by maker of the mould to use 4 sand to one cement. Will play around with ratios to get it just right before I buy some white cement so future pots come out colour of sand used. Luckily have lots of sand and cement from rebuilding one of my out buildings.
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I've seen Unibond used as a plastisiser for cement ,makes for better molecular bonding. but don't forget to oil the mold first , :fc:
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I am really interested in this - sick and tired of spending a fortune on terracotta for it all to crack. Where did you get your mould from?
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We are going round in circles here so … time for a basic lesson in concrete to help you achieve your goal.
Cement- the grey powder in bags which is the magic ingredient you add to aggregate (along with water) to make concrete.
Aggregates—Are the sand and gravel you use.
Gravel—Stone added to the mix can be round, or angular and available in different sizes eg 6mm 10mm or 20mm.
Sand- Also added to the mix—IMPORTANT there are essentially 2 types of sand:
1. Soft sand, also known as yellow sand or building sand…..This is the stuff you use to make mortar for laying bricks—usually a ratio of about 5:1 Sand :cement- it is essentially a gap filler with little or no structural strength. If you have ever knocked down a brick wall you may have noticed you can pick up the bits of mortar from between the bricks and snap them with your hands.
2. Sharp or coarse sand--- The sand you use for making concrete—as its name suggests it has larger grains and hence is moving towards having some structural strength.
When you mix concrete the idea is that the sand fills the gaps between the gravel to make a solid mass.
(Reading between the lines from your last post, you have used your left over soft sand ? You really need sharp sand )
Water- Concrete does not dry, it cures…it is a chemical reaction. The cement you add to the mix reacts with the water. You should really add exactly the amount of water to react with the amount of cement you have added to get maximum strength… Otherwise the excess water which is left over will create voids in the concrete reducing its strength. (the excess water will sit in the mix until it dries. leaving a void) Usually if you only added this much water you would end up with a mix that is far too dry to work with…ie to tamp, or compact into complicated moulds. Hence practically we add enough water such that the mix is of the consistency or ‘workability’ that we want this will be too much water. (ok we have lost a bit of strength… but we are building flower pots not the Humber bridge !)
Plasticisers-- So this is where plasticisers fit in… They are an additive which you can put in your mix to improve workability—By adding some plasticiser workability is improved hence you don’t need to add as much water so strength is maintained. As tizala rightly points out you can go to the builders merchants and buy some plasticiser , usually in 5 litre containers—if your going to make a lot do this, otherwise fairy liquid will do. Add about twice what you would put in a washing up bowl to a bucket of water, stir the water and use this to make your concrete.
The ratio of aggregate to cement will determine strength--- If you work on 5 aggregate to 1 cement you will be about right. (your supplier told you 4:1 so not that different)
Now as a twist- render which you might face a wall with is made with say 4 sharp sand: 1 soft sand:1 cement…..The sharp sand provides strength whilst the soft sand gives a nice smooth finish.
So what mix do you need for your plant pots ? Well you need strength, so mortar is no good. You need to work it into a small mould---20mm aggregate probably wont fit (what is the wall thickness of your pot ?) I think you can buy 6mm chippings in bags from builders merchants. So how about 2.5 chippings:1.5 sharp sand:1 soft sand:1cement , ….this keeps your 5:1 aggregate:cement ratio, soft sand will help give a nice finish,chippings and sharp sand will give strength.
Add your water and plasticiser or fairy liquid as little as gives a nice workable mix to get into your mould.
You can buy concrete dies to effect colour as well as using different coloured sands.
Don’t forget to poke your concrete lots as you fill the mould, this compacts it and gets the air out---It is an essential part of the process.
Ive never actually made pots and havent seen what size the mould is you have, but i think this should be somewhere close. Hope the info helps.
Stu
Give a man a fish he eats for a day.
Teach a man to fish he eats for a life time.
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I made some concrete slabs many years ago using moulds... i used a 3 sand 2, gravel (4mm) 1 cement...oil the mould 1st
the secret to the perfect slab was the vibrating table.... same as the poking stick ..but the table worked perfect..i made it using a 2nd hand washing machine motor attached to a large sheet of ply.. the motor was fitted loose yet secure, this cased the vibration
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I took the grinding wheels off my grinder and fixed a sleeve on one end of the shaft with a big pinch bolt then screwed it to the frame of the table which held my moulds . The spped of RPM and the slight unballance of the pinch bolt made a fantastic vibrator table .
If you want to make a big rustic trough planter for herbs make the outer skin using 3/4 ( 19 mm construction ply of similar use screws and battons on the outer faces of the box frame ( no top & no bottom paint it with veg cooking oil a couple of times on th internal faces and then put a big block of polyestyrene expanded foan in the middle evenly spaced so the gap inbetween will form the walls about 3 inches thick ( 75 mm ) . Set this on a sleet of builders plastic and make you concrete usinfg a 6 mm ( 1/4 pea grit or gravel mix a bucket of dry peat into the mix work it in well and pour it into the mould when done after making it ever so slightly sloppy , push several pointed round greased sticks down into the polystyrene block so you get drainage holes and leave to cure for 14 days .then unscrew the mould sides and gently turn the trough on its back or onto some battons .
If you want some sort of personalization of it all add a wired on object to the outer walls is plastic letters or a motiff in relief so long as it does not reduce the wall thickness too much or router a design into the wall before assembly .. Remember that numbers need to be a certain way round for them to be the right way round on the finished item .( been there done it and failed ::) )
Best thickness for the base is about the same as the walls or very slightly thicker You can add a water proofer to the mix if you don't want the pots to hold water in the walls during winter and end up with the frost cracking them .If you do this forget about using wash liquid or a plasterciser like FEBMIX as they counteract each other .
Pour some petrol on the polystyrene to dissolve it and leave for another 14 days for the concrete to get a reasonable strength . the end product should be failry pourous and have slight colour and a decent rustic weathered texture
One big long coffin sized trough I made had a hollow wooden boxform in the centre covered in 2 inch thick expanded polystyerene sheeting which had rounded corners for greater strength of the finished item .
I was able to unscrew this inner box and used a spade to ease the polystyrene foam off the concrete . after 28 days of curing .
Ii gently hose pipe washed the remainder of the marks off after scraping of the worst of the remains .
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I suppose that motor is now fixed to your bed..! :innocent: