The curing of the oven is the most important phase in the construction of your wood burning oven project. It is essential over a period of several days that the oven is fired at very low temperatures to start with eg. Day one at 100°F and increasing by 100°F every day, eventually reaching 800F a week later.
Between each firing the oven should be allowed to cool down. A large amount of water has been used in the building of the oven and there will be residual moisture in the refractory dome, as well as any cladding used to insulate it. After assembling your oven and insulating and rendering it, it is good practice to leave it for several days before starting the curing process. All information regarding these ovens from Italy is slightly misleading given that the climate in the destination country may well be wet. Therefore, when you have cured your oven it is possible to get moisture entering through ordinary lime mortar over rockwool/fire blanket and entering the refractory dome. This will negate all your previous efforts at curing your wood burning oven and you will be back at square one. If you were to light a big fire in your oven now disaster would almost certainly ensue. The analogy is similar to the function of a steam engine; water is heated to a high temperature creating steam and the resulting pressure drives trains weighing many hundreds of tons. If you light a hot fire in your sopping wet oven it will destroy it, at the very least causing many cracks and fissures.
We have developed an insulating render system for wood burning ovens which is its own insulator, does not allow ingress of water and allows the oven structure to breathe.
SEGRELIME
What is Segrelime?
Segrelime is a natural lightweight insulating lime mortar and render developed specifically for wood burning pizza ovens in the northern hemisphere.
It can also be used for repairs to ovens that have been cured badly and where moisture has been allowed to enter the refractory material.
Segrelime negates the need to insulate with materials such as rockwool or fire blankets, having its own insulating properties that are extremely effective. Segrelime is specially developed to accommodate movement of the underlying refractory material during use.
What is the Segrelime System?
The Segrelime System is simple to apply, needing only basic plastering skills. The Segrelime System package comes with full instructions and email and telephone support if needed. There are two versions, one developed for use in outdoor applications, including as follows:
- Fibreglass mat
- Curing membrane (fleece)
- Aqueous water seal
- SBR based bonding additive
- Specially formulated lime mortar mix
Observations from the laboratory during testing:
“…have further tested the samples we undertook a few weeks ago. The mortar mix has been applied in two coats on to a fire brick … as you know these bricks are 25mm thick. To the reverse side of the brick that would represent the inside of the oven, propane burners have been applied at full capacity until the bricks actually glowed red, like steel. The mortar render on the other side was unaffected by the heat. Left overnight to cool down (this morning) still the sample remains unaffected.”
“…the optimum flame temperature of the propane torch would be 1990°C (3614°F), the flame directly touching the brick, until cherry red was seen.”
WARNING!
After the curing process any moisture entering through the chimney/flue or door will be a setback and necessitate the curing of the oven once again. Also, after a particularly harsh winter you should check for moisture inside the oven and decide whether you should cure it once more. If you are unsure start small fires, because if you start to produce steam you risk damage.
A complete Segrelime kit costs £48. Depending on the model purchased you may require more than one kit. However there is no need for an insulating fire blanket.
SEGRELIME INSTRUCTIONS FOR USE
Do not apply the mortar under 4c or if there is a chance of heavy rain, snow or ice falling during or immediately after application.
PRODUCT NAME: SEGRELIME Natural Lightweight Insulating Lime Mortar
PRODUCT DESCRIPTION: Natural lightweight insulating aggregates in a natural hydraulic lime base
METHOD OF APPLICATION
The product is contained in a sealed plastic sack. Inside the sack you will find the sand or aggregate and a separate plastic bag containing the natural hydraulic lime.
Find a suitable mixing vessel that will hold a full bag aprox 15kg. Open the sack and remove the inner bag of lime then empty the contents (sand) into the mixing vessel, then open the lime bag and place on top of the sand.
Mix the contents together dry before adding water, a forced action mixer or drill and paddle is recommended.
Add enough water to mix to a stiff consistency, stiffer than actually required. Leave this mix 15 minutes and
re mix adding enough water to make it into a workable consistency. This gives the sand enough time to absorb the lime and help plasticity, any water raised to the surface will be absorbed back into the aggregate and lime by the remixing process.
The mortar is now ready to be used. “DO NOT ADD CEMENT”
Drying times will vary depending upon the ambient temperature at the time of application
Method of Application:
· Prepare the masonry to be rendered by soaking the masonry in water to control suction.
On highly absorbent surfaces soaking the night before and spraying again just before application is recommended. Allow any standing water to evaporate first.
· Mix the up the insulating lime mortar as described above.
· Make PRIMER by taking a trowel full of the mixed mortar and placing it into a separate bucket. To this
add a quantity of the “Gauging Liquid” to make the mortar into a paintable slurry. This will make a
water resistant bonding coat
· Apply the primer coat and allow to dry aprox 30 mins, keep any reaming primer for the next stage.
· Apply a second coat of primer to the masonry only this time apply the 1st coat of Insulating mortar whilst the 2nd coat of primer is wet. The primer must not dry out, if it does apply more primer and immediately apply the render.
· Cut strips of the glass fibre reinforcing mesh and press this into the 1st coat of mortar during the render process each strip overlapping each other by 10mm. The 1st coat of render should be applied between 6 to 8mm thick and scratched on completion ready to accept the final coat.
· Cover the masonry with Protective Fleece. The fleece will need to be tried into position with string or galvanised wire. Leave the fleece in place for the full drying time of one millimetre per day.
Repeat the process above to apply the final coat.
· Apply the final coat to a thickness of 6 – 8mm. Finish off your final coat using either a polishing trowel of bath sponge and allow stiffening up then covering the masonry with Protective Fleece. The fleece will need to be tried into position with string or galvanised wire. Leave the fleece in place for the full drying time of one millimetre per thickness applied.
· For external applications we would recommend the application of “Aqueous Water Seal”. This will provide an impervious but breathable water repellent coating to the insulating render. Alternatively the render can be painted with a water resistant paint.
