If you have a “chink” in the armor of a building it is usually due to different or moving materials coming together and the need for a filler that accommodates the differential in movement between the two masses. Plastics may work but many owners wanting to go green don’t want that between their logs in living spaces. Outside, the linseed oil mix we suggest breathes and plastics would tend to keep water in the wood possibly accelerating their rot. Modern caulks may do the same to historic window frames.
I. Between Logs:
- First coat: Pack the crack with some backer material. Historically mix ratios like- 1/3 clay/1/3 coarse sand/1/3 lime with enough straw to make a heavy-strawed daubing filler. Don’t forget to fill large voids with cherry-cock noggin stones or brick to gallet the void with solid material. Let it dry for 3-4 weeks. Today the backer used is often insulation such as rigid foam and placed as the back-up. Some use more organic sheep’s wool, hemp-lime mixtures w/gallets as a backer. You use fibrous daubing, whether the fibrous binder is straw or hair, and due to the suction of the natural material, (i.e. not containing any latex or Portland cement which err’s toward an impervious surface and inhibits natural keying-in (chemically) through suction). By doing this you will have a good start for a second coat especially when you create a rough surface texture to this inner backer material and create a good “mechanical bonding” surface. Today galvanized wire lath, chicken wire or the like is used over foam insulation but these metals all rust, save stainless lath and plastic lath. Great idea is to insert 1-1/2” galvanized roofing nails top and bottom of the wood, only nailed in half-way of their shank, ½” away from the back up material with the heads sticking up vertical about ¾” to increase the grab of the second coat.
- Second coat – Slightly dampen the back up and then throw on with a casting or “Harling” trowel a hairy second coat of 1 part NHL (Natural Hydraulic Lime) #2 (make sure the NHL 2 has a 50% free lime content which allows for movement and self-healing of a pure lime mortar), to three parts concrete sand which is coarse and pebbly. Note- The filling of voids with an aggregate is how a mortar, a stucco or concrete helps reduce its shrinkage. Pebbly sands help to allow the final thickness of this second coat equal three times the thickness of the largest average pebble in the mix. Good to make this about ¾” thick application. Scratch the surface in a cross-hatch pattern the next day as you will find that the mix is still pliable and you can compress the mix up against the logs and rub out any cracks in the mix within 24 hours and make cross-hatch texturing to increase the final coat’s bond. Keep slightly dampened 2-3 times a day and protected with burlap draping over it for 4 days. Let it go through a year of seasonal changes, shrinkage, etc.
- A year later- Apply with a small paint brush a 50/50 mix of Raw and Boiled linseed oil primer along a ¾” exposed edge of the upper and lower log up against the second coat just before applying the final ye alde calk flexible joint material in a wet on wet application.
Making a Fantastic “Sand Mastic” mortar, AKA “Ye Alde Calk” for sealing the Chinking “shrinkage gaps” one year later OR between wood frames and masonry which have a different rate of expansion and contraction and swelling and shrinkage rates for various types of wood: Take a small electric concrete mixer and direct a torpedo heater into the barrel ½ full of sharp well-graded sand until you get the sand to about 800F. Do this while the small portable electric machine is turning. You are doing this to dissociate the chemically bound water, which is in the sand. Then you let the sand cool down. You add 8% of sand weight in crushed rosin. Don’t buy a block of rosin used for violin bows; get powdered rosin (from tree bark) with grains the size of table salt or finer. Rosin is used as a “dryer”. Mix the sand and rosin together and keep it in a sealed drum until you are ready for the next step. The next step: Mix in a 50% boiled and 50% raw linseed oil mixture to take the place of the displaced water in the dry sand and rosin and now the oils become chemically bound to the sand.
- For Chinking add the minimum amount of Natural Hydraulic Lime (NHL 2 w/50% free lime content) or use whiting as an inert filler until the mix retains its shape and can hold together for placing into the shrinkage crack between the log and the hairy lime second or final coat which was placed over the daubing or lath and set for a year of seasonal changes.
- When pointing up that void between a window frame and brick or stonework, start from the bottom, having already placed backer rod, whether it be foam or sheep’s wool, (Even rope soaked in linseed oil or rolled up newspapers were used historically as a backer rod.) The backer material should be set back an inch from the face of the wood and stone). Point up the void. You should prime the interior edges of the masonry and the wood with a linseed oil primer mixture without the sand and rosin put in it. Put masking on the brick or stone for the faces and a little of the return so as not to stain the finished exposed masonry with darkening linseed oil.
- For repointing historic brick or stone most applications will simply require Ecologic™ Mortar in one of our standard colors. This is mixture of one part NHL 3.5 and 2-1/2 parts well-graded sands along with iron oxide pigments. The liquid and vapor permeability of Ecologic™ Mortars will allow moisture to be drawn to the cured mix and out to the atmosphere and still give a strong performing mortar in extreme freeze-thaw weather cycles. You can mix various ratios of our different standard colors to achieve a new hue to the mortar and you can add a quarter part of a different aggregate like washed coal flecks, mica or coarse sand to reproduce nuances of the original historic mortar you are trying to match. Call us with questions or to design a different mortar mix for you for a more specific application.
|Andrew L. deGruchy
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