Choosing and Installing Field Stone
Gathering stones from the field
Field stones can be smooth in texture and usually small in size. Stones that are of workable size are selected and moved to the construction area. If you are having trouble finding field stones you may be located in a area where there is more sand than rock.
You will find that field stones are most commonly in locations near mountain valleys and fields. It is known that farmers of these rugged terrains many times collect and pile the stone cleared from their field in one location. You may be able to catch them on a good day and collected the stones from the pile for no cost. Search for the stones that appear to be fresh out of the ground. The stones that have been recently collected should have a higher moisture content and will split better that others that have spent a good time drying out.
However a Knowledgeable stone Mason knows that a operational gravel pit sources the best stones. Typically rocky fields produce dull earth tone color stones while sandy soils hold more vibrant colors. Being able to gather and build with natural field stone is a blessing.
More typical approach to acquiring field stone is to visit the local stone yard. Even down here in south Florida where we are far from the mountains, you will find that are bedrock makes for a great stone veneer. Many landscapers use these yellow gold rocks to add beauty to the yard or garden.
Choosing the right stones
Usually you will find black, gray, green, white and red colored field stones with shades of colors in between. Many times only a certain color of stone is desired. This makes collecting the stone more difficult since pits and fields have stones of many variances.
Its best to select stones of appropriate size for your project. Know in advance what all you will need to achieve the requested and proposed design. Many times you will need straight edges, square/rectangular shapes and curved stones. Cherry picking out the right shapes ahead of time can significantly help with installation. Also be sure to know the scaling of the project and choose sizes that give a sense of balance.
Some stones will fit in the wall with no necessary trimming, these stone are few and far between. Be sure to select stones you believe will be easy to shape. You may need to split a larger stone to form a corner or other shape. Try to avoid stones with defaced or jagged exteriors. Smooth stones are easier to split and better receive the hammer strike. Since you will be cutting the stones a lot it is a great investment for you to buy stonemason hammers and chisels.
Tools of the stonemason
In order to successfully split field stones you will need a stone maul, sharp hammer, chisel, markers and a good pedestal to work on. Also you need to be sure to wear safety goggles as it is very common to have a stone chip go flying from the strike of a hammer.
Stone Mauls can weigh all the way up to 16 lbs. and can have a 3ft handle. However bigger isn't always better. One of the first things you will learn about splitting stone is that its all about finesse and striking the proper spot on the stone. The hardest hitter could be the worst splitter if his technique is off.
Stone mauls must be able to withstand a great deal of use. That is why they are made of forged and tempered tool steel. Typical steel hammers really are no good for splitting field stones since they quickly dull and lose their edge. This ends up dissipating the area of impact and causes the stone to break uneven or not split at all.
Stone Masons use a carbide tipped hammer and carbide tipped chisels to cut, trim and shape field stones. Having a selection of chisels that are one to three inches wide is ideal as there will be many scenarios. Carbide tipped chisels are the best to use on stone since they hold up there edge 20 times longer than conventional steel.
I find that marking out the needed cut is easier than trimming by eye. This way I can see exactly where I need to cut rather than try to remember.
A stone pedestal is used as a worktable for trimming stone. Mainly its function is to allow the mason to stand in a good working position while he trims the stone. It is much easier on the body than to be bent over trimming stone on the ground. A stone box is used to help position the stone for trimming and can be made from scrap wood.
Splitting the Field Stones
Before striking any stone pick it up and look it over carefully. You should be able to see the grain of the stone and maybe even a hairline crack. These are indicators of which way the stone will split easiest. However stones can be split against the grain but this requires much greater effort. Mark the spot you believe the stone will split the most easy. Then prop it up on the stone pedestal in a good working position.
When you hit the stone be sure you are striking it with the cutting edge of the stone maul parallel to the mark you have made. When you strike the stone be sure to give it a solid whack but you need not put all your power into it. If after a few blows the stone has yet to split flip the stone around and try a new spot you think it will split. With trial and error you can master this step.
To best determine how thick the wall will be split most the stone and then determine the average thickness of the stones. This way you will not have to split extra stones to make up for size differences.
Trimming Stones to fit
There are quite a few ways to go about getting your stones in the wall. First off be sure to start big. I like to try and trim very little off the first stone, cherry pick a good starting piece and flow from there. Each time a new stone is added it should be a close fit with little or no cutting needed. Mark any spots are the stone you see need trimming and set it on the stone pedestal. From here use your masons hammer and gradually chip away at the stone face. Many times a pointed hammer or chisel is used to remove bumps or high spots.
When installing Spilt field stones, do avoid laying small stones next to very large stones. There should always be a good range limit of size, however many works of art by multiple stone masons feature pebbles mixed amongst the boulders.
Facing Field Stones
Once you have trimmed your stone to fit into the wall, its time to face it. At this step you can also deface the stone and rough it up to look more rubble. Proper facing of a stone makes the back of the stone width smaller than the front. This allows masons to control the thickness of the mortar joint and help prevents the joint from becoming to wide.
To face stone place it on edge on the stone pedestal and prop it up with the stone box. When facing the stone be sure to have the hammer or chisel swinging out away from you. Strike the edge 5/8" back from the face and be sure the stone flakes off from the face side. Continue to work around the edge of the stone until the entire face has been done.
Defacing Field Stones
If a Rustic look is to be achieved a roughing of the stone face must be done. This will also help blend any mistakes or imperfections in the work.
Defacing is similar to facing except you want to completely split the stone. Never rough the stone face by striking on it directly, you will not want to leave any unsightly hammer or chisel marks.
Footings For Field Stones
Since field stones are much heavier than CMU and brick masonry units, the foundations must be stronger and able to support greater loads. For instance a field stone wall can weigh 40% more than a brick wall. Typical brick walls are 3 1/2" inches whereas split stone walls can be double that thickness.
It is best to go with a 6" thick footing if you are pouring the footer before selecting the stone. You may plan to lay a 4" thick wall but upon splitting all the stones and taking the average width measurement you find you have a majority 6" stone. It would be in your interest to have a footing to support the 2" difference.
Wall Ties for Split Stone Construction
Stone walls that veneer blockwork should be anchored by a physical steel tie. Horizontal spacing of the ties should be 16" and 8" vertically. This gives the stone wall twice as many wall ties as a brick wall. When your backup wall is wood frame construction you should use lag bolts to anchor the wall ties into the wood studs. Also be sure to have a moisture barrier between the stonewall and block.
Mortar for Field Stone and Joints
There are two types of mortar consistencies used in laying split stone. Stiff mud is used to bed the stones and a loose mix is used to fill the back behind the set stones. To help with clean up small stone chips can be inserted into the mortar fill. The stiff mortar can be dyed to achieve a desired color. For lighter colors mix dye with white mortar mix.
Three common mortar joint finishes in stone masonry used are rope, flush, raked. I much prefer the look of raked joints where the mortar is cut back exposing all of the stone edge. Flush joints tend to have a overly sized joint and rope joints are a lot of time consuming work.
Joint sizing is very important to the appearance of a stone wall and can make or break the work. A well jointed wall will have consistency and balance.