homecrete

Just starting a type of hempcrete  project for a large shed , its being filled/spread  into the floor ,walls and roof  ,and i have been fine tuning the mix recipe and technique to this process, i have also been trying to establish the silica content of hemp shiv but info is evading me , most sources simply state this as being very high and the majority of sources just seem to be quoting from each other back and forth with no real figures. My quest for this percentage level of silica is in response to justify my  alternative bio source for hemp shiv , but in the meantime i will carry on ,heres a batch i mixed up.

I have been reading some studies done in sweden relating to grass and reeds, some of its based on alternative sources for hemp in building products but mostly as an alternative for use in burning for producing electricity , growing bio mass on large scale to supply it chipped and dried as a renewable energy sounds good but here in ireland it fell on its arse. Farmers were encouraged--the usual way--by subsidies--to plant miscanthus grass to supply the furnaces ,which in most cases were not new or updated plants and had been built to burn coal with a percentage of dried milled peat , but these soon ran into problems with the build up of a silica clinker blocking the grates. The reeds and grasses have  low melting silica content in their ash that forms a glass like product clogging things up ,this apparently is made up of SIO2 and K2O and in the case of miscanthus its about 70% of the ash content. These furnaces stopped taking chipped and dried m/grass after trying to sort out a solution failed and most of the projects envolved farmers were left to sort out what now became their problem , themselves , not all of them grubbed up and round up sprayed --three times - to get rid of it.

Some farmers held onto their miscanthus and found some alternative uses for it , well here in eire , there are only 2 other uses so far , its dried and chipped then plastic baled for pet bedding ,chicken sheds and horse stall use and some garden centers use it as a mulch  .When looking to start my project using hempcrete the prices of hemp would have made it a non starter as although you can obtain the bales it is all imported from Europe via the UK , its mostly used on a few historic building restoration or adaption for insulation of these old stone buildings and as first choice of bedding for race horse /stud farms ,and although its possible to obtain a permit to grow your own i would not be able to grow 10 hectares of it and a delay of months  and months of paperwork. So i started a read up on both plants and a few others to find out if it was possible to substitute the hemp in hempcrete and why or how hemp was the only suitable plant source.

The hemp shiv or inner core is the waste of the plant left over once the outer layer of fiber has been stripped away for other uses , hempcrete made from this chipped up  by-product has been trialed and tested  back to back  with crete made from chipped dried stalk with fibre still on it ,findings have shown that  too much fibre in the mix was not an improvement or of much benefit and it was found that the lower the fiber content the better the end product/result was. Then the very high level of silica contained within the plant stalk has been referred to as being as major factor in causing a reactant or setting-up  effect on the hydrated lime used in the crete recipe , whilest this is fact , hemp does have high level of silica ---but this varies from 1% to 7% of total mass from variety to variety and season to season and the ground its grown on . Then hemp as a species does not have the highest level of silica in or on it , there are several other species that score equal to or higher such as bamboo , reed grasses and grain stalks with rice husk being very high , but still with variation as all are natural products.  Silica does have a setting effect on hydrated lime but most hempcrete binder recipes have hydraulic lime added to them for this to ensure that a reaction occurs and the setting process happens ---the silica is an added free bonus if in high enough % . The commercial binders mixed up for crete rely mostly on  NHL5 limes  or the better naturally  occurring hydraulic limes found in a few quarries to achieve this , because these are trademarked products they may have tweaked this mix by adding in silica .

My doubts about the silica content in hemp or other plant material as being a major reactant to set up the lime is that the percentages vary too much to be relied on , and the silica in plants is water soluble --so in the case of hemp being processed for fiber  which takes a lot of soaking , leaching and rinsing plus some chemical exposure this must play a part in reducing this further . But in any case , the lime binder seems to be bonding to the lignin , cellulose and hemicellulose of these plant materials , which miscanthus  ,and reeds ,plus grasses have,  the open cell sponge material in their stalks holds water which is released or taken by the lime binder as it sets up just as hemp shiv does

I had seen and done a little  working with hempcrete  just helping out on a project, but all on small scale small batch and using a brand name bagged binder so following the recommended  steps of the suppliers you do get a good result and after a bit of experience even better again, my own project requires about 10 metric tons of baled material possibly 12 , so i soon calculated that  that hemp was out of my budget , before i even bought in hydrated lime and hydraulic lime. I decided to try miscanthus and bought 10 bales of it from a pet bedding supplier to trial a few runs of it and cast up some test block samples---nothing too scientific or noteworthy , and following the many internet sourced recipes of which no 2 are the same  --they are mostly still within a similar ratio of ingredients -- had varying results .Firstly to dry and crumbly ,then too much lime , but the hardest of the process was mixing it. The good thing with this biocrete despite making mistakes  you can recycle all of it back in to later batches ,drop a bucket  or spade full on the ground ---no bother let it harden off ,pick out the stones--not that they upset the mix --they would just cause some grating noises in the mixer i built, then crumble it up into the next batch . My first mixing was done in a small half bag mortar machine , but involved too much measuring on a small scale, so too much faffing around and variation when trying to make a decent amount , so next up was in an old bathtub which works quite well but more manual of course. It would be my choice for a small project as it holds a bale (25kg) of m/grass  or 10 x a 20 liter bucket in volume wise, and if you got inventive a simple frame work on wheels could be done to move it around. I wouldnt make it too high off the ground as you need to work the stuff at just off ground level was comfortable enough for me.

Mixing in the old bath i found using a spade or shovel was too much hard work ,biocrete needs to be handled like hay or muck , with a pitchfork , mines an old 4 tine  and this makes the process much easier to churn and lift into the tubs as well , i first mixed the water and binder into a slurry ,mashing any lumps smooth ---heres where a drill mounted mortar mix blade would help  , then i would add the grass in a bucket at a time, surprisingly over mixing even by hand  can be done ,which results in the lime binder separating and to start balling up instead of staying coated onto the grass . The recipe i settled on was gleaned from some studies done in sweden , 19% binder  31% grass  50% water by weight of what ever amount you mix , the binder is made from 2 parts hydrated lime and 1 part hydraulic lime---mine is NHL5 purely because thats what i have to hand , but i will be trying out some NHL3 . The study done substituted some of the binder with flyash about 5% of the total mix by weight. I did try some ash from my wood/turf burning stove as an added ingredient but not as  a part substitute for the binder in 2 batches , both did set up but i cant prove in any definite way if for better or quicker, and i cant see the point in using it for my purposes , i only produce about half a bucket of ash per day at most usually less. There is a large coal burning power generating plant about 30 min drive away they supply to several cement producing plants, but flyash from coal is considered a heavy metal contaminant waste material and you require a permit of sorts to handle and transport it ---so i wont be going to the added expense or trouble for my small scale

its okay remove the entire posting from the beginning , i dont mind , cheers tony

Tony, how did this end up working out on your final project? I'm thinking of using something similar for infill in an outdoor kitchen build.