HOW TO MIX CONCRETE
I’ve tried all sorts of internet searches to find the answer to this question! I’ve used terms such as “HOW TO MAKE CONCRETE GARDEN ORNAMENTS”, “HOW TO MAKE CEMENT GARDEN ORNAMENTS”, “WHAT IS THE BEST MIX FOR CONCRETE”, “MIXING CONCRETE”, “CONCRETE MOULDS” but I keep getting pages for the actual finished concrete products!
I’ve also asked my customers and some of them have given me their advice, so I’ll try to put everything together on this page for you.
WHAT IS CONCRETE?
There seems to be a basic misconception of what concrete is. What I mean by this is that people often use the words “concrete” and “cement” but what they really mean is concrete!
Basically, cement is the stuff that sets when mixed with water. You mix cement, (which looks like powder), with other things to make either mortar or concrete. If you mix cement powder, gravel (also known as “aggregate”), and sand (aka “sharp sand”) with water, then you’ll make concrete. If you don’t add gravel to your mix you’ll end up with mortar, which isn’t as strong as concrete.
So there you have it: The basic ingredients for concrete are cement, gravel, sand and water. The only question now is how much of each should you use for making garden ornaments.
WHAT IS THE BEST CONCRETE MIX FOR MAKING GARDEN ORNAMENTS?
Well – there’s no fixed answer as far as I can tell. I’ve had differing advice from different people, which is why I’m trying to explain the procedure for making concrete before I actually give any ratios for your mix.
For example, you need the gravel in the mix because this helps the finished cast set really hard. But gravel is obviously chunkier than dust or sand, so you need to be careful not to put too much in because the chunky stone shapes won’t fit into the surface detail of your concrete moulds. The sand and cement will though – it’s just a case of making sure that you don’t use too much gravel because this might stop the other parts of the mix from reaching the surface area detail of a mould.
This is where the importance of the mix comes in. You need your mix to be runny enough to pour into your mould and to let the non-gravel bit of the mix reach the bits of the moulds that will eventually be the outside surface area. However, if your mix is too runny, then your concrete will take too long to set and it won’t be very strong. If it’s too thick, then you’ll get loads of air bubbles on the surface area because the mixture isn’t able to reach into all the crevices.
One rule of thumb that I’ve learned is to do this: Once you’ve made up your concrete mix, use your trowel to poke a line into it. If the line disappears straight away then your mix has too much water. The line should start to disappear a bit, but the ridges that your trowel makes should stay there. Basically, your mix should be pourable but still creamy.
RATIOS FOR CONCRETE
OK – here are some ratios that I’ve been told about:
4 parts sharp sand to 1 part cement.
2 parts sharp sand to 1 part cement.
3 parts mixed gravel and sand to 1 part cement.
As you can see from the above ratios, the top two don’t have gravel included. As far as I can tell this is because if you’re making fairly small garden ornaments then just sharp sand and cement will do. If you’ll be making larger concrete casts like birdbaths etc then the gravel will help to strengthen the finished cast.
OTHER MIXES FOR MAKING CONCRETE GARDEN ORNAMENTS
There are other types of cements and sands that you could consider. If you use “Ivory Cement” and “White Sand” then your finished casts turn out a paler, whiter colour.
PROCEDURE FOR MIXING CONCRETE
Once you’ve decided on the ratios you want to use you need to make sure that you thoroughly mix all the dry ingredients before adding any water. After you’ve done this you can add the water a bit at a time until you get the required consistency – (remember the line test as described above).
You need to mix everything thoroughly, but don’t be too rough whilst you’re mixing because this can create air bubbles, which you don’t want because they’ll end up spoiling your casts. When you’re ready, pour the mixture into the mould and wait for it to set. If you notice any bubbles in your mix then it will help if you tap the mould with the concrete mix in it because this will help the mixture to sink into the surface detail and it will also cause any bubbles to rise to the top of your mould, which will eventually be the bottom, (or back), of the finished cast once you take the cast out of the mould.
OK – that’s about it for the time being. I hope that I’ve at least steered you along the right path towards making your own concrete garden ornaments. My main area of interest is in plaster casting, but seeing as though some of the moulds I sell are also suitable for concrete I thought it’d be a good idea to pass on the info that I’ve gleaned from friends and customers to you.
PLEASE feel free to contact me if you think I’ve made any mistakes with my above explanations. (Like I said – I don’t really work with concrete – just plaster – so I don’t claim to be an expert!!). Also – if you’ve got any more advice that you’d like to share with everyone then get in touch and I’ll add your info to my help pages.
Thanks in advance – and.....
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