Intro: Brick Press From a Block Splitter
This article shows how to turn a hydraulic block splitter into a brick press or block press suitable for making concrete blocks or natural clay bricks by changing the splitting knife to a mould box.
For a recent landscaping project we saved a lot of money by making our own concrete blocks. The materials in the blocks were about ¼ the price of buying ready made blocks. We poured concrete in plywood moulds and while pouring the concrete is quick, assembling, disassembling and cleaning moulds between each pour was slow and laborious, so it got me thinking of faster ways to mould a block.
Searching online found that there are companies making hand operated brick presses using a lever to press clay bricks and large large hydraulic block presses are also made for commercial block production but little in between. It seemed pointless spending a lot of money on a block press - you mid as well just buy the blocks.
After seeing a friends blocksplitter in his shed, it seemed like it had everything needed to make a simple hydraulic block press in it minus the block mould. He gave it to me to experiment with as it didn't have enough power to split the large blocks that he had bought it for and it was much more efficient to cut light blocks with an axe.
The blocksplitter was a horizontal design and had an electric powered pump and hydraulic controls built in. These 4 ton block splitters are available new at our local hardware for under $500 but you should be able to pick them up for a fraction of this second hand. The block press modification design is fairly obvious just change the splitter to a moulding box.
If you already have a hydraulic blocksplitter then a modification to change the knife to plate with four bolt holes would allow you to interchange the knife with a block mould and still retain the original bloccsplitter functionality.
This hydraulic press is suited to moulding concrete blocks using a relatively dry concrete mix with a small amount of clay in the mix to help hold the block together while it is wet. A dry concrete mix is more economical as it uses less cement for a given strength compared to a wet mix. Normally a wet mix is used to make it possible to pour the mix into a form however the use of a hydraulic ram makes it possible to press a dryer mix into the mould that will hold its shape without support (if you are careful) while the mix cures.
The 4 ton hydraulic ram of this small block splitter is not powerful enough to mould a reasonable sized compressed earth block. To make a compressed earth block, minimum moulding pressures of 5MPa (N/mm²) are recommended, thus this would limit the compressed earth block size for a 4 ton press to 70mm x 110mm which is very small for an earth block.
Step 1: Bricks & Blocks Basics
There are many types of bricks and blocks. The broad categories of bricks and blocks are:
Concrete blocks are made with mix of cement, aggregate and sand. The strength of the block is dependent on cement content, proportions of sand and aggregate and the water/cement ratio. A lower water cement ration gives a stronger brick but is harder to form, but this can be overcome with a hydraulic press. While the typical strength of premix concrete is 20 - 30 MPA (3000 - 4500 psi), concrete blocks are more often 10 - 20 MPa (1500 - 3000 psi).
Concrete blocks are usually made with large cavities that are suited for placement services and steel reinforcing with concrete grout to fill the cavities where extra strength is required for cyclone prone areas or ductility for earthquake prone areas.
Fired clay bricks
The most common building brick in my part of the world. They come in a huge range of colours finishes but there are a few common sizes typically 230 long x110 thick x76 high for face brick and 300 long x 160 high x 90 thick larger hollow core units that are faster to lay, usually rendered and common in low rise construction. They are made from a mix of sand and clay that is fired in a kiln at high temperature like pottery. There is a wide range in the strength of fired clay bricks with 10 - 20 MPa (1500 - 3000 psi)
Unfired clay blocks
These blocks are usually made onsite or close to site using local soils and various techniques such as hand ramming a moist clay and grit mix in forms (rammed earth), hand forming wet clay with straw reinforcing and baking in the sun to dry (mud brick) or a compressed earth block using a manual lever press such as a Cinva press or a hydraulic press such as a Vemeer BP714. They can be stabilised with cement and lime up to about 10% and polymer additives. (Greater quantities of cement are more suited to a concrete block)
Given the wide variety of natural materials used and the varying techniques, there is wide strength range with building codes typically requiring block strength of 2MPa (300psi), tested after soaking in water.
Strength of a Masonry Wall
The design strength of a wall constructed from masonry units is a lot less than the individual strength of the brick or block. The strength of the wall is reduced due factors including mortar strength (should be weaker than the blocks to avoid cracking problems), reduced mortar area (allowing for joint raking), tolerance in the wall construction and buckling and bowing of walls under load. A wall constructed from masonry units that have a strength of 15 MPa may be only designed for an allowable compressive stress in a load bearing wall of 1MPa.
The weight that a wall or an individual brick can carry varies not only with the strength of the material from which it is made, but also on the size of the wall or the brick, so instead of weight or force, the strength of materials is usually given as stress which is determined by force÷area. In engineering applications the units are usually MPa, megapascals (same as N/mm² ) or psi pounds per square inch.
There are standard test procedures for measuring strength of different materials such as concrete which uses a standard size moulded cylinder cured under water for a set period (typically 7 or 28 days) and also standards for determining what stress to record for example steel can stretch a reasonable amount before it breaks so it is common to record the yield stress when a sample has stretched by 0.2% as well as the ultimate breaking stress.
To measure the strength of a compressed earth or concrete block without special testing equipment, a hydraulic shop press with a pressure gauge could be used or a smaller sample of the concrete or compressed earth can be loaded up under a pile of bricks using a couple of planks to stack the bricks on and keep the stack of bricks stable
Step 2: Making the Mould
The mould is made from heavy steel plate, 10mm thick. Thinner plate could be used but you will probably need reinforcing bars welded across the plate at regular intervals to reduce flexing of the plate. I had some 120mm x 10mm flat bar, so I welded two lengths together to make a section 240mm wide to give a block 220mm long allowing for the internal width of the mould.
The mould used on this project has a top lid that hinges open to load the concrete block mix, one end that is open for the ram and the other end is open but has a loose endplate that is secured by pins and can be released quickly after pressing the block to eject the block from the mould. The mould needs to be 1.5 to 2 times as long as the height of the block two allow space to add loose mix to the mould and to allow for compaction when the block is pressed.
The length of the mould needs to than the stroke of the ram as you will need to use the ram to eject the freshly pressed block from the mould. While compressed earth has enough strength to handle straight from the mould, the reduced clay content and lower moulding pressures for a concrete block make it more difficult to handle.
To overcome the problem of handling uncured concrete blocks, the mould is constructed with the floor of the mould extending at least one block length out from the end of the mould. The ram pushes the block out of the mould and onto a thin steel plate sitting on the extended floor of the mould and the block can be lifted and set down for curing still on the plate. An even better solution would be to have the extended floor of the mould stepped down by 12 to 16mm to suit the thickness of available plywood and plywood plates cut to receive the blocks as they are ejected from the mould. A cheap and stiff material for these drying plates is required as you will need about as many plates as the number of bricks you intend to make in a day so that the concrete can be left to cure for at least one day before lifting off the plate.
Step 3: Using the Press
1. Remove pins from top lid, open top lid.
2. Place pins in end lid and place end lid.
3. Place earth and cement mix in mould. Use a standard measuring scoop to load the mould for consistent size blocks. Weigh the mix or take care to use consistent density of material in the measuring scoop for greater consistency.
4. Close the top lid and place pins to secure lid.
5. Operate the ram to compress the block.
6. Place a metal plate on the end of the mould ready to receive the freshly pressed block.
7. Remove the end pins and operate the ram to press the block out of the mould.
Before starting to make blocks you will want to experiment with different proportions of sand, gravel, clay and moisture to achieve a mix that holds together ok after it is pressed out of the mould. A good starting point is 10 to 15% clay and 15% cement. Clay content can be approximated by half filling a glass jar with the sample soil, filling with water, adding a pinch of salt and shaking the jar to mix up the soil. When the soil settles after a few hours, the soil will be sorted from coarse aggregate and sand at the bottom of the jar to a clay layer visible on top. The thickness of the clay layer can be used to approximate the clay content. You will also want a soil without a lot of fine sand in it. Fine sand has a much larger surface area than coarser sand and will need a lot more cement to coat the sand particles thus it will not be as strong for a given quantity of cement. It will also be stickier to eject and harder to compress.
A good starting point for moisture content is to mix water into the soil until it holds together when squashed as hard as possible in one hand. It should stick together but not be wet. If it holds together when you drop the squashed handful, it is too wet and clayey.