Build a Stone Barbecue 

By Charles Long

 

                                     

                                               Photo: J. Michael Lafond

 

When Prometheus stole fire from the gods and gave it to man, Zeus had him chained to a rock – not to some black metal box with tiny wheels and a propane tank. It was and remains a matter of fitting elements to the occasion. At the banal end is your quick family burger. Go ahead and black box it; Olympus won’t deign to notice. But when a cottage crowd gathers for the weekend worship of fire, water, and serious food, it’s time to barbecue on something more worthy, like stone – a solid altar for all the marinades, glasses, and elbows that gather around a flame.

Here are tips and ideas for building a stone barbecue at your cottage. To see complete plans for the Cottage Life stone barbecue, see the June 2001 issue of Cottage Life magazine.

Project Tool Box
  • wheelbarrow for hauling and mixing
  • hoe for mixing
  • crowbar for prying up stone
  • sledgehammer
  • small hammer
  • trowels: large triangular and narrow pointing
  • level
  • wire brush to clean the rocks
  • yardstick
  • chisels: one wide and one narrow
  • circular saw with masonry blade
  • steel-toed boots, safety glasses, gloves

 

Materials
  • mortar mix
  • concrete mix
  • heavy-duty mending plates
  • high-temp stove paint
  • firebricks
  • high-temp refractory cement
  • grills
  • concrete slabs
  • concrete caps
  • downspout splash blocks
  • scrap of pipe

 

Tips on Breaking Stone

The beauty of natural stone lies in the irregular shapes and rugged faces. For that reason, a crude break is bound to look more natural than a finer cut. The trick is to control the break. If you place the blade of a wide chisel on a rock and strike it hard enough or often enough, the rock will break under the chisel. The break should follow the line of the blade across the rock and follow the shaft through the rock. Should. In reality, the break will follow the line of least resistance, seeking a weak bond between two sedimentary layers, or taking the shortcut across a skinny rock instead of the longer line you wanted. Controlling the break is a compromise between recognizing the stone’s natural weaknesses and knowing that if you chisel along a straight line, holding the chisel perpendicular to the rock, sometimes the break will follow your line. A narrow blade concentrates the force; a wider blade is better at controlling the line.

A sledgehammer is often all you need to reduce one large rock to several smaller, more usable pieces. Look closely and you’ll see that the business end of the hammer is square-edged. If you swing from directly overhead to hit a rock in front of your feet, the far edge of the hammer face will strike the rock first, breaking it east-west if you’re facing north-south. As with a chisel, the break should follow the hammer’s edge. Should. Fortunately, many small rocks are as useful as one big one, and any mistakes become contributions to the rubble core.

The one place where precision counts is with the bricks. Use a wide chisel or “brick set” and support the brick evenly on flat ground or a board. Repeated light blows along a line can be more successful than one almighty whack. And if all else fails, stick a masonry blade in your circular saw. That, however, requires goggles and a mask to protect eyes and lungs.

Tips on Mixing Mortar

For a job this size, the best mortar mixer is a metal wheelbarrow and a hoe. Dump a bag of mortar mix (pre-mixed sand and cement) in the barrow, make a crater in the middle, and pour in a little lake of water. Pull the sides of the lake into the crater and hoe it around until the water disappears into damp patches and dusty blobs. Repeat with successively smaller lakes until the mix is uniformly damp and grey, with no more powdery patches. Sprinkle lightly with water and hoe until the mix is the consistency of fresh mashed potatoes. It should slide easily off the hoe and yet hang together well enough to stand up without slumping.

The trick is to add the water in smaller and smaller quantities. A dribble too much can turn an almost finished mix to unusable soup. Left in the shade and out of the wind, a fresh mix will last about an hour. If it starts to stiffen, give it a stir with the hoe, not more water.

Concrete mixes in much the same way, but is more forgiving with the amount of water. The larger aggregates in concrete help the mixing process, breaking up any lumps of dry cement and sand. Aim for the consistency of gritty pudding, soft enough to flow.

Bare-handing mortar or concrete can wear your fingertips raw. Be sure to wear gloves.

Tips on Pointing

Pointing should be done when the mortar starts to get stiff. On a sunny day that’s likely a couple of hours, so you’ll probably start pointing the lower courses long before you get to the top. If you point too soon, the soft mortar runs down the face and stains the rock. If you leave it too late, the mortar will be too hard to shape under the trowel.

Start by pushing any excess squeezed-out mortar back into the joints between the stones. If you don’t have a pointing trowel, a 1" paint scraper does a credible job. Lacking that, use a gloved finger.

Then, with the end of the trowel (or finger), scrape out the joint to an even depth. The uneven bulges of mortar fall away in a cascade of crumbs, leaving a uniform surface. Only then do you try to smooth the joint with the flat of the trowel.

Repeated passes squeeze moisture to the surface, leaving it slicker, damper, and smoother. Cut away any crumbs or ridges of excess that the trowel might have raised.

Things to Keep In Mind

There are larger grills available, but several smaller grills afford the option of cooking simultaneously on more than one level.

Since the grill layout determines the size of the firebox and the position of supports, select the grills first, and design the rest around them.

The best stones are those closest to hand. Closest is best for three reasons, and the least of these is price. More important is the natural look. Unlike quarry stone, which may be more conveniently square, stone from your own lot fits the landscape. Then there’s the labour. A stone pile for this type of barbecue could weigh about 3,600 kg. Those rocks over the fence and through the woods might seem more interesting at the start, but by the end of the day any stone closer to the job will start to look pretty darned good.

Bring the stones to the site and spread them out on the ground before you start building. You’ll want a variety of shapes and sizes from which to choose. Set aside any with straight, square sides. They’ll be useful as corners.

When finished the construction, cover the whole structure with plastic for at least three days to keep moisture in while the masonry cures. Resist any temptation to barbecue in the first week, and then stick to small fires for a month. There’s no reason to hurry something that will stand for a century of mythic summer meals.

 

Complete plans and instructions for building a stone barbecue are available in the June 2001 issue of Cottage Life magazine.