Helifix bars, fibred and mesh reinforcement
There is some confusion over when and why to use reinforcement due to the difference in what you are trying to achieve in modern and traditional applications. Modern reinforcement is to combat shrinkage and provide extra strength. When using a strong binder like OPC(cement), the binder itself is very strong and the fabric doesn't require compaction to achieve the best performance. This means that it is perfectly acceptable to apply the mortar or plaster with reinforcement and leave it without further compaction beyond a tightening of the surface to close the pores or manage laitance with pointing tools, trowels and floats. Traditional reinforcement is different as it's primarily for extra tensile strength rather than compressive and when specified and produced correctly shrinkage shouldn't cccur in the most cases, with or without reinforcement. Or at the very least in should be managed with compaction not prevented from occuring. The difference types of reinforcement material impart different properties. As with all things lime people can struggle to produce an effective mix so often impart properties that it shouldn't have to counteract this, such a hydraulic strength. If you can find a bagged material that doesn't have fibres, pozzalons, silicates or any hydraulic binder in and is described as easy to use, I'd probably die from shock. Bullshit merchants, sorry lime suppliers seem to run around in circles doing everything other than actually learn how to make and use air lime mortars...morons.
Fibres
As with most constituents parts of lime mortar, there is a massive under appreciation for the role that micro organisms play. So preparation methods and the specification of fibres often discounts this, resulting in a reduction of effectiveness.
Fibre reinforcement also brings surface water deeper into the mortar along its length. Which is generally not beneficial. So it is advised not to use them on external finishes. As a side note; a lot of lime mortars introduce far too much water into themselves by a variety of means such as too much gauging water, unnecessarily open pored, untempered putty mixes, too many large pores from a lack of compaction, churn brush finish etc. Again the goal is to produce a mortar which doesn't let water in and dries fast as fook. The epitomy of this is probably Scagliola, which is a hydraulic air lime mortar with bio-additives like animal glue or resin. It's virtually indestructible and doesn't trap water. However, it does compromise drying action for durability so its only really suitable and effective in a limited range of scenarios. Bio-additives...be very careful you don't mess up and add too much. Eg. Linseed oil in limewash is regularly over gauged resulting in peeling.
PP - not good as they degrade and hinder the ability to compact the material as they impart compressive strength. Resulting in a weaker substrate with too many large pores to allow effective mositure transfer.
Glass - as above but more resistant to alkaline damage
Basalt - as above but stronger and immune to alkiline damage. Best choise of the modern fibres and acceptable in some stronger hydraulic applications where the use of traditional alternatives may not be an option.
Goat hair - imparts less compressive strength that pp or glass fibres so good for compaction and reducing the number of unwanted large pores. But it is often treated which reduces its lifespan and effectiveness due to weaking the hair.
Sisal - effective and imparts the right properties but susceptible to rotting in persistently damp areas. Doesn't prevent effective compaction.
Hemp - very effective and not to be mistaken with hemp shiv which is just woodchip. This is still in use in Japan and is time proven there and elsewhere. This is the hemp wonder material, not the modern waste product currently being sold and utilised in a wide array of applications. See picture.
Barley straw - a very effective reinforcement which also imparts fungicidal properties upon the mortar or plaster. Traditional, locally sourced and cost effective. Doesn't break down, doesn't inhibit compaction. Moderately more difficult to use than hair, time consuming more than anything.
Horse hair - effective when untreated as with goat hair and doesn't prevent compaction. Easy to use. Has to be coat hair, not mane hair.
Ox hair - a slightly better alternative, the most effective hair reinforcement.
Mesh reinforcement
PP - unsitable for lime, degrades. Less flexible than traditional materials so prone to cracking adjacent areas.
Fibre glass - alkiline resistant but not a great option for air limes that are specified for drying action. Less flexible than traditional materials so prone to cracking adjacent areas.
Basalt - alkiline resistant and the best of the three modern options. Less flexible than traditional materials so prone to cracking adjacent areas.
Hessian - traditional and used extensively by traditional fibre plasterers. Prone to rot in external or persistently damp applications. Flexible, cheap and easy to apply.
Reed - traditional and very effective. Less suction than lath, lower profile than wattle and fairly cheap in comparison to either.
Wattle - traditional and very effective but costly. Specific woods need to be used. Requires skilled installation and time consuming. But uber traditional.
Lath - traditional and very effective. Different woods impart different properties as does the manner in which they are produced. Needs treating with fungicide or used in conjunction with barley straw to prevent mould. Expensive and harder to work with, due to suction and two drying fronts. Although not more expensive than the stupid modern alternatives like wood fibre board.
Structural reinforcement
There is only one cost effective and safe option for this. Yes you can use stainless steel or even engineered wood in some scenarios but both are incredibly expensive. Treated steel is not something I'd recommend as it is subject to perfect installation and ongoing maintenance. Both of which are rarer by the day.
Basalt rebar. It's entirely compatible with lime and can be used in a similar manner to steel in OPC concrete.
I'm currently looking into an application which makes use of the chemical properties of the basalt in conjunction with hot mixed hydraulic mortars for an improved bond. I'm also looking into both pre-fabricated tensioned concrete and on-site tensioned with this material in conjunction with pozzalonic concretes as I'm sure that both could be very effective options which could dramatically reduce time and provide increased strength.
On a personal note; I think it may be possible to build ridiculous structures resembling something from Lord of the Rings if this can be utilised correctly with lightweight aggregates such as expanded clay, perlite or volcanic rock aggregates. Covered in Scagliola. So if anyone fancies building their own Rivendell, this is what I'd recommend you use.
Organic reinforcement
Most of these are sources of calcite forming bacteria. Some also contain strong protein chains and other nano strengthening properties. They will likely fall under two categories, aerobic and anaerobic that will depend upon local availability and application. TBC...
Blood - Ox blood most commonly, does a wide variety of things. Very, very effective all round additive.
Wheat paste - increased strength, bonding and imparts fast setting properties.
Cow muck - micro fibres, salt and sulfite resistance
Rice water - nano reinforcement, better bond.
Fig juice - fermented materials have a wide array of beneficial properties. CO2 seeding among them.
Jaggery - fermented as above
Barley straw- fermented as above
Protein - polymer chains...I think.
Starch - probably to do with colloidal shrinkage and gap filling if I had to guess, To be researched further.
Rice husk - reinforcement, the husks are very, very resilient as opposed to hemo shiv which is from the weakest part if the plant. They are protective shells. These little fellas have an eff ton of micro organisms too.
Celluslose - micro fibre reinforcement
Casein - nano reinforcement, increased bonding. Water resistance. Saponifiaction...probably.
Animal glue - not looked into these in depth, I'd say it works like glue Iif I had to guess....
Gum Arabic - see above
Eggs - protein based nano reinforcement, probably glue too.
Hemp Shiv - not a fan. Either the whole plant or the fibres were used traditionally and not chopped up mechanically. When you cut any wood like material harshly it makes it more susceptible to damage. This why cleft wood lasts longer, because you're not sawing it across the grain, you're splitting it along it's natural lines. I suspect the method of preparation for the whole plant was a combination of fermentation and milling. In which case its ripped along its natural lines with the grain, not across it. It would have jagged ends rather than flat sawn or chopped ones. The main issue I have with this is that diddy bits of wood will deteriorate with regular wet/dry periods and lime will deteriorate without them, so something is getting the short end of the stick in this scenario. But there is only so much one man can do and proving this is not high on my list of priorities, especially considering the people who like it have the Apple, Tesla, popular brands are faultless and everyone else is stupid sort of childlike mentality because they blindly believe the sales spiel. Which in this case is funded by big pharma...
Helifix Bars
Helifix bars are not suitable for lime built solid wall construction, they are a cavity wall and cement solution to expansion cracks in properties that don't have expansion joints or the appropriate design to not need them.
Why?
Resin will almost never bond well with old materials like brick, stone and lime. Nor will cement. Both will rip off the original material as the bars dilate at a different speed. The bond between lime and resin or cement is poor to abysmal on a good day. Both physics and chemistry are pissed at people attempting this.
Most lime will not bond with the bars well as its not strong enough and will debond because of different dilation speeds again.
The bars are only effective at stopping movement by dilation at the face, not structural movement and a lime built property will not have cracks from dilation. It will be caused by something else, which is almost never diagnosed. So you're fixing a symptom, not the cause. Not cool in any profession.
If you do manage to get them to take, they will stiffen up that section and potentially cause problems in other areas. So well done for that.
They will eventually rust even though they are galvanised, it just takes longer. Another win.
But if you must use these pointless and often harmful things get Basalt Fibre Rebar instead of steel and a strong NHL because that stands far more chance of actually working and not actively causing damage. But it's also a pretty stupid idea.
The joy of working on old houses is there repairability, (not sure that's a word tbh). You can dismantle entire sections with little to no bracing and rebuild them almost effortlessly. You can often source the same materials on site as were originally used. You need very few expensive tools and almost no modern materials.