Limestone Blockwork

Limestone

This information applies to limestone blockwork whether it be natural limestone (calcium carbonate) or reconstituted blocks.
Depending on availability in your area (used a lot in WA) it can be a very versatile product to construct buildings, retaining walls, screen/garden walls and as decorative features such as capping and plinths.

The main construction method that differs from bricklaying, is that generally the size and weight of a single block is too heavy to butter before laying. This is especially true of most retaining wall construction where a block may weigh between 60 - 180kg.

Reconstituted blocks will be reasonably uniform in size as they have been formed in a mould with creme cement and limestone aggregate. Basically a limestone coloured concrete block. Natural limestone will vary in size somewhat as it is mined and cut straight from the quarry floor. This limestone is more friable, can show natural blemishes and texture lines and is much more porous than its reconstituted cousin.

Gauge

Unlike bricks that are mostly uniform in size, limestone will come in various lengths, depths and thicknesses for different applications. They may range from a slimmer profile block for house construction (equal to that of 4 brick courses in height) to a denser block to be used for retaining walls.

As this is the case, simply put, use the best method to suit the situation. Once base height (bottom of wall) is established, profiles can be used to form a plumb and level line to work to. This method used if working off a slab or footing.
Alternatively, set out corner stones to be plumb and level and using corner blocks, set up a string line between the corners. Make sure that your corner stones are true to gauge, as selecting smaller or larger stones to establish line level may lead to headaches by the time you get some way along your run. This method is normally used for retaining walls. If you are careful with your plumb and level you should be able to gauge each course with a tape as you build up the corners. As brickie says, if you are any good you should be able to achieve a +/- of a few mm over a run of several metres.

Another difference from bricklaying is the size of your mortar joints. Again this is mostly applicable to the larger block sizes. Due to the variation in size of individual blocks, (+/- 5-10mm), is is advisable to gauge each course with a 15-20mm bed joint. Keep the perp ends at roughly the same size as the bed joint for a good looking wall. You can use something handy to gauge the joints as you lay if preferred - pointer finger, shaft of a rubber mallet, rounded joint striker, dead cat.........ok.ok(tip of the hat to you brickie).

Remember practise makes perfect and as you get more proficient at laying blocks generally a gauge tool will be discarded for the naked eye.

Tool Kit

Aside from your standard bricklaying tool kit, here a few other items which will help in the laying of limestone blockwork.

Scissor Lifts/Blocklifters
These things will make picking up blocks a breeze. Or at least a lot easier than struggling around with them in your own two hands. Usually a two man operation (one on each handle). Really only good for heavy blocks 400-500mm in length.

Rubber Mallet
For bashing the block down when not doing what its told.

Steel Plasters' Trowel/Float
Used for the main purpose of keeping the mud in the joints while filling perp ends.

Shovel
When using large blocks the shovel becomes your trowel of choice to apply mud for the bed and perp end joints.

Wire Brush
For rubbing back joints.

Trolley
To make carting stone over distance a lot easier.

Quick Cut Saw
A two stroke or electric wet saw using a diamond blade 14"-16". Gets through limestone like a hot knife thru butter.

Radio
Whether you like AM or FM this tool is essential to keep up the morale of the troops. Keep up to date with the Footy or cricket scores or just listen to some good old fashioned music!

Basic Tool Kit

Pros and Cons

As with all building materials there are good and bad things about them. Limestone is no different. Here are a few that i can think of at the mo.

Pros

• Most limestone constructions do not need a concrete footing/foundation to support them reducing the expense for another building process. The base of the wall acts as the footing, which in most cases should be wider than the visible part of the wall and embedded to a minimum depth. (Piers and free standing walls of height will require a footing - more on that later).
• Sheer mass (weight) of blocks makes it ideal for retaining walls - as another option where mass brick or concrete reinforced masonry walls would normally be used.
• Can make for relatively fast construction times because of the large dimension of a single block.
• Solid and thick enough to be core-drilled for a colorbond fence to be installed upon it.
• Comes in various lengths/widths for all kind of construction applications.

Cons

• Although much can be done by a single person, the larger blocks are generally easier to manage with two people.
• Natural blocks are liable to break and or chip so overordering for a specific job is generally advisable. Or use damaged blocks as backers or in a less visible area. Small imperfections are acceptable as most people choosing this stone select it to tie in with existing stonework or want a bit of 'character'.
• Natural limestone is extremely porous therefore prone to discolour over time. This is especially true of retaining walls which have soil backed up to them. The tannins in the soil will leech through the stone with rainfall/ground moisture, darkening the face of the wall. It is essential that a waterproof barrier is installed on the rear of the wall to eliminate discolouring of the face. This can be a bitumen based/cementious or plastic sheet barrier.
• Constructing tight curves can be a challenge due to the length and width of a single block. Blocks may have to be cut in half and the edges mitred to maintain a equal perp end joint through the width of the wall. If this is not done joints at the rear of the wall can become jagged and unsightly. (Not a good look if no decorative capping/bullnose is to be placed on top of the wall).

Laying Method

Setting Out
Similar to standard bricklaying, but if using large blocks for retaining, i would not suggest dry laying to see if things fit. If necessary a cut block at one end will not distract from the overall construction. (Try to make sure it wont be a tiny portion otherwise you have the horrible decision of whether you put a tiny bit in or have an enormous perp joint - both not great).

Once you have established the starting point for your wall construction - see Gauge- the process is very similar to standard bricklaying, although on a larger scale.
If laying first course on soil - in the case of a retaining wall - I will put a bed joint of mortar down to stabilise the block as well as being much easier to level. Without using a bed of mortar you may be forever digging soil away or packing the block up to maintain correct level. Remember that blocks will invariably not all be the same size!

If digging a trench to install blocks, it is strongly advised to dig wider than the width of the block to allow movement and access to a level (to check plumb). As the mortar bed squashes on the initial base course, it can fill the edges of the trench and impede you manouvering the block into plumb. As a general rule i will usually dig at least 100mm wider than the first course of blocks FRONT AND BACK.

Laying
Place mortar bed with shovel or trowel, whichever preferred, on to the ground following the string line you have set up. Leave the mortar bed plump so it can take the weight of the block being used. The width of the mortar bed does not have to be equal to the width of the block as the force of it being lowered into position will squeeze the plump bed out to cushion the entire base of the block. Unlike bricks, limestone blocks do not have a frog neither are they cored so excess mortar from the bed joint has nowhere to go but OUT! The block can then be gently wiggled or tapped with a rubber mallet to the required level and plumb. Too much mud on the bed and you will forever be beating it to get into position. It is a real pain to be taking blocks out of a trench to adjust a mortar bed that just wont work. Bit of trial and error, but after laying a few you get the idea.

As previously mentioned, perpends should be the same size. Lay the entire first couse or base of the wall, (depending of course how long the run is), then you can fill the perpends with mortar. As some limestone blocks may be equal to 4 or more brick courses high, it is advisable to, at completion of the run, attach corner blocks to a lower part of the face of the wall to recheck you have maintained plumb throughout the run of the wall. You are not laying off any lower course so this base course will determine the plumb of your entire construction. Essentially it is the most important course of blocks in the wall to get right!

Once you are happy with level and plumb, remove string lines and fill perps. You can use a shovel to drop some mud over a few perps to get started. Mortar, if a good consistency, should reasonably easily fall down the perp joints. In one hand take a plasters' steel trowel/float and hold it flat up and down on the face of the wall to cover as much of the joint as possible. In the other hand take a brick trowel and drive the mortar into the perp with the point of the trowel from the top of the block. You may need to place the plasters' trowel on the back face of the wall to fill the rear of the perp. The bed joint at this stage can be pointed or filled if needed to achieve a flush finish for now, depending on the finish required. See Finishing Brickwork.

You are now ready to build the next course of blockwork. Repeat from start as necessary ie. build corners ansd plumb and level, or if using profiles just move your string line up to the desired gauge. If the mortar on the fisrt course is still green, wiggling the second course may tend to unsettle them a little. Try to lay bed joints so that minimal force is required to manouver these blocks into position. Tapping with a rubber mallet is a good way to go. Repeat as necessary to reach finished height.

Retaining Walls

Limestone is ideal to construct gravity retaining walls due to the sheer mass that is contained within the completed structure. As the lower course creates a footing, a separate concrete footing is not always required to build upon. When building in reactive soils (clay) however, a concrete footing is usually needed.

As the height of a retaining wall increases, the base of that wall will increase proportionately to support the load. As a general rule the base of the wall should be 60% of the total height of the wall. Minimum embedment will apply to give the wall sufficient purchase in the ground to prevent forword movement or leaning. When constucting a mass retaining wall it is preffered to cross bond coursing so that there is no mortar course running through the entire height of the wall. The staggered effect of the backing blocks ensures a downward force from backfilled soil to help counteract the forward movement of the retained soil/earth.

If heavy dead loads are required to be retained ie. buildings or vehicles, extra mass within the wall construction is required. This will usually mean a thicker wall througout the entire construction. Generally buildings should not be located within a distance equal to that of the height of the wall. If dead loads are required to be suitably retained, advice from a structural engineer should always be sought. Below is an example of a typical profile of a limestone retaining wall.

http://www.brickwork.net.au/cms/tikiwiki-4.1/preview22

Finishing Blockwork

Finishing limestone blockwork is again similar to Finishing Brickwork with some minor differences. The type of finish you choose to use may be determined by the type of stone you choose to use.

Flush Joint
Recommended for either natural stone or reconstituted blocks. The flush joint has the advantage of weatherproofing the ariss of the stone, as no water can gather on the exposed edges of the blockwork. The other main advantage, especially when using natural stone, is that it can disguise any chips or blemishes that may occur on the edges of the stone which meet the joints. When filling the perpends and bed joint it is useful to smear the mortar slightly onto the face of the stone and slightly proud of the face of the work. When the mortar has stiffened (this may be 1/2 hour in summer or up to 2 hours in winter), it can be brushed off across the grain with a wire brush to achieve a flush surface with the face. A damp (not wet) sponge can then be drawn across the finished joints to remove any brush strokes.

Reconstituted stone may only require the same method as a cut flush joint to achieve the desired result.



Rolled Joints/Round or Bucket Handle Joints (all the same thing)
Recommended for reconstituted stone only. Reconstituted blocks are reasonably well gauged and will suit a rolled joint with the courses of blocks appearing to sit level. Due to the variation in the gauge of the natural blocks, a rolled joint will reveal the different sizes as well as the chips or blemishes. In other words the big blocks and small blocks stick out like dogs balls (and we all know this is not the most attractive feature of a dog). Use a joint striker to achieve a good rolled joint. See Finishing Brickwork.

Parget/Parged Joints



Recommended for natural limestone. This joint is the most time consuming and hard to master, but if done well will finish a natural stone wall the best (in my opinion). This joint in many ways is similar to Tuck Pointing.