So what is this white or grey slurry called CONCRETE that we use to make these wonderful decorative garden planters or beautiful garden art statues and plaques?
CONCRETE is made by mixing:
Coarse and Fine Aggregates
Cement powder, when mixed with water, forms a paste. The most common type is portland cement (type I or GP) which is all you need for any small to medium statue or planter. The other types are more expensive and can dry quicker or harder with less heat or no shrinkage. Premixed or Ready mix concrete is more expensive. Simply keep it cheap. Freshness of cement is key though as the minute you open the sealed bag it begins to absorb moisture from the air which will make the lumpy and useless when mixed and poured. Before buying check the bag and make sure it is soft and pliable with no damage to the bag. When not using the cement keep in a dry, well aired place.
Water is mixed with the cement powder to form a paste which holds the aggregates together like glue. Water should be cool, clean, and free from any dirt, unwanted chemicals or rubbish that may affect concrete. Too much or too little water with not allow the concrete to set properly so add slowly to get the mixture to get like a thick stew but soft and creamy.
Aggregates are of two basic types:
COARSE: crushed rock, gravel or screenings.
FINE: fine and coarse sands and crusher fines.Sand should be concreting sand and not brickies sand or plasterers sand.
Aggregates should be:
STRONG and HARD A stronger, harder aggregate will give a stronger final
concrete. Never use a crumble or flakey rock like sandstone.
DURABLE to stand up to wear and tear and weathering.
CHEMICALLY INACTIVE so the aggregates don’t react with the cement.
CLEAN Dirt or clay sticking to the aggregates will weaken the bond between paste and aggregates.
GRADED Aggregates should range in size so that they fit together well. Rounded aggregates give a more workable mix. Angular aggregates make concrete harder to place, work and compact, but can make concrete stronger.
Look for the next post on Admixtures and what they do……
Well it has been a few months and time for a new article on my blog about using concrete molds to make decorative garden features with cement. In today’s article I thought I would review the different types of molds available today in the marketplace.
- Steel or aluminum
These molds date back 60+ years and would be the original method for backing all those wonderful birdbaths we may still see today. The advantage to these molds as they may still be in existence today, so durability. The disadvantages are the high cost for the molds, the pure weight of just the mold itself, and the inability to get the finer detail you can get with rubber. If you are lucky enough to have any of these today hang onto them as the are a collectors item!
- Vacuum formed plastic
Now we have gone to the complete opposite extreme with these cheap molds. They are the hard brittle plastic molds you can buy cheaply on ebay or other online stores. For the complete amateur they may seem to be the exact ticket to get going but you will soon find out that you can make 1 to 5 items before they break. The other big disadvantage is that they can only make something 180 degrees or half designs. The way they are made is that they need to have a large flat surface to form the plastic too and suck out the air. If you wish to make a circle or anything that is not flat you will have to make two halves and glue them together. Only ok for someone who wants to make a couple of items for around their own house and then toss the mold in the garbage bin. You get what you pay for !
I guess I consider these the hard rubber molds that are firm enough to stand up on their own. They work like ice cube trays, in that you bend back the rubber and pop the item out. The designs for these molds are very limited and really only work for pavers or stepping stones. Again can’t make any full 360 degree statues or planters as you can’t demould them from the stiff rubber.
- Silicon or Latex rubber
This by far is the largest category of molds and can range from a thin rubber as flimsy as a condom to a thicker 1/2″ rubber. The rubber is used to allow designers to make very detailed sculptures as well as the flexibility to pull the rubber off and around complex designs. The rubber does need a support mold around it to allow the rubber to stand up while the liquid concrete is drying. Again you get what you pay for with these molds. The cheap ones you see on ebay are usually rubber only and they tell you to set the rubber in sand or sawdust to support the mold and concrete, good luck getting it just right. On the other end is the molds that come with fibreglass casings, such as our molds on www.backyardkitz.net and www.cementmolds.com (thought I would plug myself here). These molds stand upright with not other help and allow you to fill the concrete in, vibrate the concrete, and allow to dry all in the mold. The rubber gives you the finer details and th fibreglass give you the ease of use as well as the quality you need to make very fine finished sculptures. The rubber does have a lifespan depending on the type of rubber and the care you give it.
There are other types of molds people use out there but these are the major ones available. To sum this up spend the money on quality molds to get quality finished sculptures. It will save you time and frustration trying to make some money. If you have further questions please email me or check out the websites.
When I am talking to many of my cement mold customers, both new and existing, I am often asked how to mix the concrete for pouring into our decorative molds. Below is a simple concrete mixing guide:
How to mix concrete
Safety Tip: Prolonged contact with fresh concrete will burn your skin. You should wear safety goggles, gloves, rubber boots and long sleeves when working with concrete.
Small amounts of concrete can be easily mixed in a wheelbarrow with a shovel but if you are making concrete on a regular basis you may want to invest in a concrete mixer to save time and weiriness on your back. A low end electrical mixer will work on regular household power and may only cost $300 to $600. I have also seen mixing done on a flat plastic sheet such as the Crete-Sheet which sells for about $20 in the USA.
Firstly decide how much you are going to mix up. I know how much my mixer holds and then use a bucket for measuring our equal portions of the cement, sand, and stone. For general purpose concrete, the mix can be 1 part cement, 2 parts sand and 1 part gravel.
In the wheelbarrow or mixer, add gravel and sand first to give it a stir to combine. The add the cement and combine again. Finally make a hole in the middle of the dry mix add the water in small amounts since it is hard to remove the water once it is in the mix. You can go from a too dry mix to a too wet mix very e with just a little water. The water can also very depending on the moisture content of the sand prior adding your water.
You can use either just a bagged portland cement to which you add your own stone and sand which is much cheaper or you can use the pre-mixed bagged mix such as QuickCrete. Check out my blog on Cement!
How to mix concrete in a wheelbarrow
Small amounts of concrete can be easily mixed in a wheelbarrow with a spade or small shovel.
Add the recipe as described above and mix it all together before adding water. Next add water: approximately half a standard household bucket more or less. Add a little of the water at a time. Mix with the spade from underneath and fold over. Keep doing this and adding the water until the mix is a uniform consistency making sure you scrape the sides to get all the cement stirred in.
Tip: when mixing, a smaller spade is easier to work with than a larger one.
Too much, too little water-
One problem that you will soon figure out is that the more water is added to the mix, the easier the mix is to work, and also the easier it is to place the mix into the molds. The wet mix will help get a smooth finish to your molds and should also help keep down those nasty air bubbles! Try pulling the concrete up in a series of ridges with a hoe. If the ridges slump back down and can’t be seen easily, there is too much water. If you cannot create distinct ridges, there is too little.
Make sure you have mixed all the ingredients properly and thoroughly, scraping them from the sides and bottom of the mixing box. The concrete mix should be an even color. Light or dark streaks indicate poor mixing.
Remedying a poor mix-
If the mix is too wet, it doesn’t have enough sand and aggregate for the amount of cement paste. Add 5 to 10 percent more sand and aggregate, mix it well, and test. Repeat this until the mix is correct. Keep careful notes of the added amounts; when you make the new batch, you will follow the revised figures for sand and coarse aggregate. If the mix is too stiff, it has too much aggregate. Don’t try to remedy the problem by adding water alone. Instead, add a cement-water solution that has proportions of 2 to 1. Unfortunately, in most cases even this will not work and you will have to start from scratch with decreased amounts of sand and coarse aggregate. Experiment, keeping track, of the decreased proportions, until you have a satisfactory nix. You may have to try several small batches before you produce the right mixture.
I hope you find this information helpful in producing beautiful decorative concrete garden art !!
It is comon thing to happen and is very easy to do and in most cases the glue will be stronger then the concrete around it. In all the cases below you will have to repaint the entire piece to cover up the seam or glue so it does not show.
Piece broken off – I have found Liquid nails works great to glue a small piece of concrete back onto concrete. Make sure that you clean any loose sand on both surfaces and ooze glue on both sides and then push togther. Then wipe any excess off the seam area with a wet cloth. Let dry per the instructions and try and put pressure on it if you can.
Piece broken off and missing - If I have gap that needs filling you can use som Bondo Body Filler whcih is a car body repair kit. Mix together the two ingredients and shape to fit into the space. You will have limited time to do this and best to use tools you can through away afterward as celanup is difficult.
Small holes or cracks - If you have small bug holse I have found taking a little Quickrete Concrete Patch works well. You mix a small amount of the powder with water and stuff it into the hole with your fingers and then smooth over with a damp cloth to make smooth and match the surronding area.
Ok so you have just pulled your finished gnome, angel, deer, or birdbath out of its mold and want to give it some color. Finishing the sculpture will add value when trying to sell it as well it can be fun. Anyone can produce a plain grey concrete birdbath but not everyone will paint it to look beautiful and you don’t need a lot of talent to do it.
- First thing to do is let it throughly dry, maybe up to 1 to 3 weeks depending on the weather conditions and size of your item. It should not feel cold and clamy when you grab it.
- Next clean it up. Whether old or new remove all the loose sand with a light wire brush or broom. As well, file off any rough edges or seams.
- Repair any holes, cracks or chips. (see my blog next week on how to repair items)
- Personally I like to give the whole item a coat of the thinned out white or black paint over the whole piece. You can also use an acrylic concrete primer paint. This will give the item a good smooth seal prior to applying the color. Reminder to always leave the bottom unpainted so the concrete sculpture can still breathe so your paint won’t bubble
- Finally you can give it a lacquer spray or a concrete sealer such as Thompson’s can be brushed on to help protect the paint when you are satisfied with your piece.
SO now what kind of paint can you use? You can use a good quality exterior paint. It can be an acrylic or latex paint. For small items like gnomes, you can even use a craft paint which will give you lots of colors to choose from. I even have used a paint that contains iron chips and you get it to rust so it looks like an old iron rusted piece, as well a copper and other techniques.
Reminder: If the item is a birdbath or fountain and you want it to hold water then you need to use a pond sealer so the water does not just permeate through the concrete.
Please email and I can send you out a free copy of our PDF on finishing concrete! email@example.com
SO how many of you have tried something other than plain old concrete mix in your decorative concrete molds? I am seeing and talking to more and more people creating a market niche for themselves by going green and using recycled materials in their concrete molds. They are saving themselves money on materials as well as marketing themselves as a Green Manufacturer. Customers are attracted to them and to their products.
SO what can I do to grow my business?
Papercrete: The recipe has been around almost 100 years. It is a light weight mix using 70% paper(almost any kind) with sand and cement. The paper is soaked in water and as it softens then ground or mashed up. Best to us a paint mixer attached to a drill in a 5 gallon bucket. The mix ratio is:
Recycled Concrete Aggregate: You know all those roads and buildings they tear down and haul away the concrete. How about reusing the aggregate in your concrete wet mix and put it back into a concrete bench or Buddha statue. You can even purchase pre-mixed Green cement mixes so if they are doing it why not you? You can even go as far as using rain water in your mix.
Send me other ideas that you or others are doing out there!!
Declare yourself GREEN and increase your decorative concrete sales!
- Concrete Mix
Use a Sacrete or Quickcrete Concrete Mix ( with small stone).
- Mixing Bucket, wheel barrow, or mixer
- Shovel to Mix with
- Lubricant -
You will need to use a mold release. Castor oil or vegetable oil
8 parts Denatured Alcohol & 2 parts Castor Oil
1. Prepare Mold :
Apply mold release with a fine spray on the mold and wipe
it slightly with a cotton rag.
2. Mix Cement:
Follow directions on the back of the bag. Your mix should be wet enough to a consistency of a stew. After a few pours you will find ” A Recipe” that works for you, then stay with it.
Mix very well. Mixture needs to be smooth, neither runny nor dry or lumpy but don’t MAKE IT SOUPY.
Be careful withe the last little bit of water as it can go from perfect to wet very quickly with a little water.
3. Pour cement into Mold:
Pour half of the mold first. Now shake and tap bottom & sides of the mold to eliminate all bubbles.
Fill the rest of the mold up with your cement mixture.
Shake and tap again until the top surface is flat and even.
Keep mold in a dry area for 24 hours on a level surface.
YOU CAN USE A RUBBER MALLET TO TAP THESE MOLDS
Now comes the best part as you get to see you end product. Turn the mold upside down onto a flat surface, and open up the fibreglass casing and remove the rubber. Be gentle with the concrete item as it will still be “green” and fragile. The concrete will take an additional 2 to 5 days to finish drying all the way through the item.
Keep your molds clean. Wash with warm soapy water, rinse well.
I have been in the concrete business for quite a few years and I have made latex molds and pour concrete ornaments using latex molds. Latex does not like petroleum based products as well as sunlight. Your best bet is a castor oil mixed with methyl hydrate or isopropyl alcohol (1 part castor oil and 8 parts methyl hydrate). Add the mix to a spray bottle and shake it well before each use. Just a light spray with the mixture, remember that too much is bad as it will stop the concrete from setting.
A secondary option that I hear quite often is Pam or vegetable oil. These are ok and will w0rk, but not as good. These will also get sticky and hard on your rubber unless you wash it off after each use.
A third option is a pre-packaged aerosol spray can such as Crete-Lease or Synlube 531 as examples. These work extremely well, but can be expensive in comparison.
As a warning for latex rubber molds any kind of petroleum based oil, such as (motor or mineral) is bad as it will turn your latex into soft liquid mush!
I did come across this nice headless man giving a good demo on mixing and applying the castor oil mixture: Youtube video on applying release agents. He must not like the camera much…
As for fibreglass molds, you can use almost any kind of oil as long as it does not stain your concrete. If the concrete absorbs it, there could be a layer on the outside of your finished concrete which won’t let you apply any finish to the sculpture. I find it just easier to apply the same castor oil mixture.
With the white portland cement I can control the color or just leave a brilliant white color when it dries. Being just plain portland allows me to control the mixture or sand and stone in each batch. The price might be slightly higher then the grey but I feel it is worth the cost difference. You can also use premixed cement such as Quickcrete, but unless you use the whole bag how do you know how sand and stone is in each mix. As well you are paying retail prices for the sand and stone when you can get it much cheaper delivered in bulk.
While mixing I know my mixer holds 4 full buckets of dry mixture so I add in 1 bucket of stone, then 2 buckets of sand, then turn in the mixer for a few minutes. Then I add in 1 bucket of cement and again turn on the mixture so I get a good even spread of the dry ingredients. While the mixer is still on I begin to add the water till I get a good even texture, like a stew where it jsut falls of the blades on the mixer or a shovel. This is all very easy and is just like mixing up a batch of pancakes in the kitchen!
OK so now how about some tips on handling the cement, sand, and stone….
Try not purchase more then you are going to use is in a reasonable time. Cement can absorb the moisture in the air around it so keep it sealed in the bag or even a plastic tub with a top. I periodically get comments from individuals that there cement is dry and crumbly after they demold. This could be from having some bad cement or it was not mixed well with the sand and water.
There are generally two types of sand available for building but are not interchangeable in all applications.
- Soft sand (or Builders sand) which is a smooth sand used mostly in bricklaying mortar.
- Sharp sand which has a gritty feel and should be used in your decorative concrete molds.
You can also read my blog on sand: http://gardenstatues.wordpress.com/2009/01/15/clean-sand/
Most aggregate consists of various sized small stones or gravel and is normally graded by size of the largest stones; 10mm gravel will have been sieved though a 10mm mesh to remove all larger stones. Either a sharp chipped stone or a rounded pea gravel can be used. You will want to make sure that the stone is washed and clean of any organic material as these materials prevent the cement from bonding to make a good strong concrete.
For both the sand and stone, if they are stored out side, keep them out of the dirt and keep them covered so that wind, rain, or animals do not contaminate the materials.
Concrete can be a skin irritant as well as bother your lungs and eyes. When mixing your concrete you should look to cover your arms and legs, as well as you hand and eyes. While working with the cement you also may want a mask so you do not breathe in the cement dust. So please read the cement bags for any safety measures they recommend.
Are you looking for a particular mold and can’t seem to find it anywhere. How about letting CementMold Company www.cementmolds.com make a custom mold for you? The cost of a custom mold can cost only slightly more then something in similar size.
Note: We do not steal any other artists work by taking the original and dumping liquid rubber over the master tocreate a mold. We have our own full time sculptors that use their interpretation to carve new artwork in which we can then build the mold.
So how do we go about doing this……..
- First we need a jpeg or other electronic image of your item along with the dimensions you wish the item to have created.
- Email me the information firstname.lastname@example.org and I will review the item to make sure we can make a mold of the item and a cost estimate for you.
- If you agree with the price quoted, we formalize the quotation and get the go ahead from you along with payment. Once we start the process takes 4 to 6 weeks.
- We then organize one of a expert carvers to sculpt the mold master out of plaster. Within aproximately 2 weeks I will then send you a few photos of the new item for your approval.
- You can approve or recommned changes to the master.
- Once we have your approval we then begin the construction of the mold:
- We prepare the master and spray it with our latex rubber mixture.
- A form fitted fibreglass casing is built to support the mold and allow it to stand.
- We then package and ship you it out via FedEx.
- Finally you receive the new mold to make your new concrete or plaster item.