Talking Shop with Alex Sparrow

Alex Sparrow is repairing centuries old buildings across the UK, and in doing so, laying the groundwork for a carbon neutral future. As you may have guessed, he’s doing it with HempLime. Alex literally and figuratively wrote the book on HempLime construction and we were lucky enough to Talk Shop with him.

Take a listen as Alex shares his wealth of experience from across the pond in the UK to help us understand what might be possible to grow the superstar HempLime material building industry right here in the US.

Transcript

Burgess Brown: Alex Sparrow quite literally wrote the book on hemp/lime construction. Back in
2014, Alex, along with William Stanwix published The Hempcrete Book:
Designing and Building with Hemp-Lime. Alex is widely regarded as the go-to
advisor for all things hemp/lime in the UK. And we were fortunate enough to be
able to pick his brain. His wealth of experience across the pond helps us
understand what might be possible here in the US. This is Trace Material.
Jonsara Ruth: Alex, we're so glad that you can join us today from Darbyshire, England.

Amazing what these pandemic times allow us.

Alex Sparrow: Yeah. Thanks for inviting me.
Jonsara Ruth: Yeah, well, we're thrilled to have you, and your expertise is, you know,
something that so many people follow and we all have your book and have been
digging through the pages for years. And it's just really great to be able to talk to
you face-to-face today. You know, I guess we met each other almost a year ago.
Was it?

Alex Sparrow: Yeah, kind of October, wasn't it, in Idaho?
Jonsara Ruth: That's right. In Idaho at the the first US Hemp Building Association Summit.
Alex Sparrow: It's been really nice to see the progress that the US HBA has been making over

the last nine months, I guess. So yeah, nine, nine, 10 months.

Jonsara Ruth: Yeah, hopefully. I mean, there's so much enthusiasm and optimism about this
industry really picking up speed in the United States. And, you know, obviously
we're lagging behind all of you guys in England and all over Europe, but but
we're, we're hoping to learn as much as we can and really make it a viable
industry, building industry in this country.

Alex Sparrow: Yeah. Yeah. And it's nice to see you know, some, some hemp growing and
processing, 'cause you guys have been ahead in terms of well, various states
have been ahead in terms of recreational and medicinal cannabis which is
something that we don't have here in the UK, but I think it's taken a little while
for, for industrial hemp to, to catch up if you like, but it's nice to see that
happening finally after the Farm Bill, I think.

Jonsara Ruth: Yeah, exactly. So, yeah, we've sped up since the 2018 Farm Bill, you know,
things are really taking hold, you know, it'll be great to see the processing
following the, the farming develop here. So yeah, so, you know, I think we
would like to just get started by hearing the beginning of your beginnings, really.
Like if you could might just remember, or kind of recount the first time that you
worked with hemp and lime and what that experience was like, and maybe how
that differed from building in the, before that?

Alex Sparrow: Yeah, sure. So going back about 10 years, little over 10 years my colleague Will
Stanwix, who I used to have a company with Hemp-LimeConstruct had... I'd
given him a hand building a straw bale building and a friend of ours in Sheffield
in England, wanted a small extension building on a Victorian terrace house.
Alex Sparrow: And so he'd– the ground was an old riverbed and he was looking for a low
density material to build with, because he'd been he'd got to have a huge
concrete foundation, which was going to cost more than the extension. So Will
was looking for something that was environmentally friendly, but not as wide as
straw bale because the size of the extension was so small that if you were to do
it from straw bale, that there wouldn't be much space inside the building.
Alex Sparrow: And there was a company at the time called Lime Technology who were
supplying Hempcrete as a material in the UK. And that was the company that
supplied the materials for that job. And then from there, just went on and
started building bigger and bigger buildings. The first– I guess the first big job we
did was a kind of retrofit project, a listed timber frame building. An old tithe
barn, 16th century. So kind of 1570s and it was an infill job where the historic
building fabric was actually an elm frame with wattle and daub, which is a kind
of mixture of earth and straw and a bit of animal dung and a little bit of lime
maybe as a kind of dogged material over a hazel lattice structure within the
frame. And that original material had lasted for a few hundred years until it was
rendered with cement and then that degraded and disappeared. So the job was
to, to re-replace that walling material with hempcrete and that's actually what
hempcrete was developed for in the first place in France. It was for adding–for
repairing historic buildings with a material that would sort of be loose fill
material that would set and hold its shape and add a bit of insulation to the
building whilst also allowing moisture to pass through the fabric.
Jonsara Ruth: It wasn't originally a material to build with, but instead of repair material?
Alex Sparrow: Yeah. So it's exactly the same type of building in France. So historic timber
frame buildings where the original fabric has degraded beyond repair. So they
were looking for, for something that you could use to infill the timber frame and
then almost as soon as, as it was used for that people started saying, Oh, hey,
we could, we could use this as a, for new build eco homes. But yeah, the, I think
the first... my first experience of the material was really just, and I think
everybody feels this when they first start using it is how simple it is and how low
tech. So it's really this kind of mixing together of the hemp stalk with with a lime
binder and water, and then pouring is not really the right word, but tipping it
into the form work. Cause it isn't as you can, you know, it, isn't a liquid material
it's like a damp solid. And so you tip it into whatever form work you've
constructed and then spread it around and a gentle pat down. And then once
when you take the form work away after, depending on the binder that you're
using after an hour, or maybe overnight 24 hours, and you take that form work
away and the materials set and it holds its own shape and binds very closely to
the frame that you're casting it around. And that's it.

Jonsara Ruth: And so had you been building in other ways before hemp and lime, like you
mentioned straw, but were you, were you interested in other natural building
materials or were you building in conventional ways?

Alex Sparrow: Yeah, so I wasn't a builder by training, but I got into working, building, repairing
old buildings actually through living in old houses and finding the... finding out
about the best way to repair them. So using lime and stone and, and sort of
learning about traditional construction methods which is, which should really,
when you're repairing an old building, it's all about maintaining the vapor
permeability of the structure of the building so that you, by allowing the
building to, to breathe, to let moisture vapor out, then you maintain that
building fabric in you know, as a healthy structure because moisture isn't being
retained inside the, inside the building where it can cause damage. So it, from
that just it's a small step really into, into hempcrete because all of those themes
run through hempcrete construction.

Alex Sparrow: Typically in a domestic context that the frame, the structural frame in a
hempcrete building will be timber, either a traditional timber frame or a stud
frame. And so one of the things that you'll want to do is maintain a vapor open
wall assembly because not only to keep the timber frame itself healthy, because
you're not trapping moisture in the, in the wall that could lead the frame to rot,
but also the wall itself is made from thousands of tiny pieces of plant aggregate,
the hemp. So although the lime in the mix is a powerful antifungal, so it will
inhibit rotting of the hemp or the timber frame. If you, if you maintain that fully
vapor open wall, then there's, there's just never any chance of moisture getting
trapped within it.

Jonsara Ruth: It's kind of, I mean, it always sounds like such a superstar material when you talk
about it, you know, in all of its properties, but tying it back to traditional
building methods is really interesting. Just in thinking about like how, how much
you've learned really from repairing traditional materials, traditional buildings
and and historic buildings that might have informed how you might, how you
build with hemp lime for new buildings.

Alex Sparrow: Yeah. And I think, I think old buildings, traditional architecture or even maybe
traditional vernacular buildings. So those buildings that were built by the
communities that lived in them without the, without the assistance of architect,
you know those, those buildings have the most to teach us about sustainable
construction because wherever, whatever type of building you're talking about,
wherever you are in the world, those, kind of, that traditional construction had
evolved over centuries within that landscape, with knowledge that was passed
down through the generations. And, and all of those, wherever you are in the
world and whatever kind of structure we're talking about, all of those were built
with natural materials, because that's all they had. Local materials, because they
weren't– didn't have the sort of infrastructure to transport construction
materials over long distances. So and they were built with thousands of years of
knowledge in the community about how best to provide shelter using in that
local climate using those local materials. So I think we've got to, you know,

there's a lot we can learn from traditional construction in terms of sustainable
construction for the future really.

Jonsara Ruth: Yeah. That's, what's so inspiring. Is, is that exactly, and that you, you, you just,
as you stated that there's, you know, centuries and centuries of development of
these natural building methods that developed and got better over time.
Alex Sparrow: It's like the work that you guys did also in India, you know, the natural paints

and finishes out there.

Jonsara Ruth: Right. And then it's so extraordinary that it lasts, you know, hundreds and
hundreds, eight up to 800 or even a thousand years, you know, the lime just
lasts and lasts and lasts. So were, was there evidence of hemp in buildings?
Hemp and lime. I know lime was, was in England for a very long time. And was,
was there evidence of hemp/lime in Sheffield when you started that project?
Alex Sparrow: No. I mean, so this is an interesting one, cause I was reading something else on
the internet the other day that was referencing hemp that's been discovered
within Roman mortars which is kind of it's an oft-repeated fact on the internet.
But I, I still have yet, I don't know if you've ever seen any, any kind of reference
for that.

Jonsara Ruth: No, I, yes, actually I have, you know, I mean, they talk about– what I read was
about that it was about cellulose and not specifically about hemp cellulose, so it
could have been wood or, or, you know, another kind of plant material, but, but
that's very exciting. So was there, is there a hint that in your local area that
hemp was once grown or, or not so much?

Alex Sparrow: Everywhere in the UK. Yeah. So there's, there's lots of– well, there's lots of place
names, road names. So you, you quite often have Hemp Lane you have various
various towns with hemp in the title that, but more than that, in the more
recent sort of architecture kind of going back to the 1900s and 1800s, there's
still quite a bit of existing industrial architecture in certain regions. So rope
walks where, where they stretched out the fibers to make rope. And so there's,
there's kind of evidence of it everywhere. It was such an important crop in the
UK going back hundreds and hundreds of years, but the particular areas, the
South coast going into the southwest in Dorset, was a huge hemp growing area.
Alex Sparrow: And they have, you know, there's records of King John then, you know, 1215
putting in a huge order for hemp for the Navy and, and even into, you know, it
was, it was such a big part of the economy there that even when it was starting
to, hemp production– hemp was starting to be imported from other areas of the
world, which, you know, towards the end of the 19th century you know, there
was still hemp production there. And in fact, I think the Navy bought out the last
hemp processing plants and have their own rope making.

Jonsara Ruth: So you're in a large part reviving this historical material for your area, because it

still is a local material.

Alex Sparrow: Yeah. All over the UK. It was, it was so important because we're a small Island
and we're a seafaring nation. So, so just for the rope and also for the sail cloth,
you know? So the word canvas comes from the word cannabis. It's and it, you
know, it's, it was strategically so important to the UK in terms of you know, our
Navy and our sort of I guess you know, exploring the world.

Jonsara Ruth: Right. That's, that's amazing. And then, you know, obviously the UK became a

great leader in the world, maybe because of hemp.

Alex Sparrow: Yeah, yeah of course.
Jonsara Ruth: That's amazing. That's amazing to tie those things together, that the ships could
sail to other parts of the world because of this plant, you know, because of,
because of hemp and, and that, you know, we could have breathable buildings
because of hemp and lime also.

Alex Sparrow: Yeah, and just getting back to what you were saying before. I don't think, I don't
know of any evidence of hemp being used in building in the UK or anywhere
really. But I would be amazed if it hadn't been. It's just that with so many
natural materials you know, they are low-impact materials, that's the whole
point. So they, they I'm sure hemp will have been used in the same way that
straw and other cellulose fibers have been used. But if it, if you're not
specifically analyzing old wall samples, mortar samples you know, to find, to find
hemp, then it, it will just eventually go back to the earth.

Jonsara Ruth: Yeah. Right. Exactly. So there's evidence of lime, of course, because it's the final
layer and it's the plaster, it's the mortar, it's the stucco, it's everything, but the
hemp itself is, is less obvious maybe.

Alex Sparrow: Yeah. And it may be that hemp was used less than straw because it was more
valued for other purposes. So I'm not sure what the... I'm not sure what the
stalk was until, or the the woody core of the stalk. The hurd, if you like, that was
originally a waste from the fiber crop. So I'm not sure in, you know, going back
800 years in the UK it's quite to, to process that material into the form that we
need it for, for construction was quite is quite... it's either a high-tech process or
it's a very labor intensive process. So it, I'm not sure how communities would
have dealt with the stalk at the time. If they were, if they were growing a long
variety, maybe it would have been used in thatch, you know, using it as a long
stem instead of breaking it up. But yeah.

Jonsara Ruth: That's great. So, so we've just thought deeply about the past, and I feel like I
could talk to you for hours about the past. It's so interesting how much the past
can inform the future and how much we've lost, really. Like when you say high
tech, you know, we somehow in the building industry took this leap in the

1950s, around the Industrial Revolution where synthetic materials became, you
know, kind of invented and then replaced all these natural building materials.
And now you're reviving this process through the restoration of historic homes.
So your path is super interesting. You know, I wonder if you could talk a little bit
about your work today with hemp and lime and what you do with it.
Alex Sparrow: Yeah. So we use the material as a walling, an insulation material. So we, my
company specializes in constructing the structural and thermal envelope of
buildings from bio-based renewable carbon sequestering, and often recycled
materials. So of those materials hempcrete is one or hemplime, as it's also
known. And but we use other bio-based construction materials as well as
alongside hempcrete. But in a new build context as I said earlier, it's not a load
bearing material. So there's always a frame, which is typically a, just a stud
frame and then hempcrete, can be– it's most commonly used for the walls of
the building, but it's possible also to use it as part of an insulated floor buildup,
and also as part of a vapor permeable roof insulation. So one of the things about
the use of hempcrete in new buildings, you can construct the whole thermal
envelope of the building from this one material.

Alex Sparrow: And in fact, when you're wet mixing and casting the hempcrete on site, you're
essentially casting the whole building or the whole thermal envelope in one
piece of material which gives all sorts of, sort of extraordinary advantages in
terms of not only the thermal performance of the building, cause it's very easy
to design out any thermal bridging through the envelope, but also in the ease
with which you can make the building airtight because you've got a single piece
of material. And so the only openings or the only breaches in that one piece of
material are the openings in the building.

Alex Sparrow: Obviously there were, there were other materials applied to it, but typically we,
you can use different finishes with hempcrete, but the typical finish in the UK is
with a lime plaster on the outside of the building. So once you apply that lime
plaster to the surface of the hempcrete, then the whole hempcrete wall
becomes airtight because it closes up the surface. You need to apply that plaster
or render as we call it to the outside of the building before the wall becomes
airtight, because within the hempcrete wall, there are lots of pockets and
channels of air. You hope, because that's, what's trapping air inside the wall to
give you your insulation. But apart from the stud frame, the timber frame,
you've got a solid monolithic hempcrete wall. And that, that wall is providing
your insulation, your walling material, your thermal mass heat storage, all in one
material. And then once you close up the surfaces with a lime plaster then that's
a really airtight efficient building.

Jonsara Ruth: So the plaster render is on the outside. And is it also on the inside?
Alex Sparrow: Yes. So in the UK, we have two words for it. I think we're about the only country
that has two different words. So for us, plaster is the internal surface and render
is the, the external, but it's essentially the same thing. So it's a coating that's
made from sand and lime. And it's important to use lime because that gives you

a much more vapor open finish. And because the, as we said earlier, because
the wall's made from a plant material, we need to keep that vapor open
performance right through the assembly. So lime plaster, especially as applied
to the outside of the building is actually very similar to a cement stucco. And it's,
it's probably more similar. The application of it is more similar to stucco than it
would be to Egyptian plaster. It's just that with the lime instead of the cement,
you know, it will take a little bit longer to set and it needs some kind of specialist
knowledge really about how the lime works and you know, how you apply
consecutive coats and the timings.

Jonsara Ruth: So great. And so, you know, you have a team of people who are working on

these projects daily.

Alex Sparrow: Sure. Yeah. So we have, we have a couple of, well, a few teams. So we, as a
company, we can we're kind of like a specialist subcontractor. So we work all
over the UK. If you're close enough to where we're based, which is in the middle
of England, we can do the whole job really from the ground works up. But more
commonly we'll, we'll travel to different parts of the UK to do the timber
framing, the hempcrete installation, the lime finishes.

Jonsara Ruth: So you do the whole gamit.
Alex Sparrow: Yeah sure, and sometimes we work quite closely with other firms, you know,
around the country. And more and more we're getting approached by other
building firms around the UK who are coming to us asking to be trained up so
they can do hempcrete. And over the last few years we've started supplying the
materials to other builders. And we do a lot of consultancy and design work. So
yeah, it's, as we were saying earlier, I don't get my hands dirty very much
anymore, but it's, it's...

Jonsara Ruth: You're managing these teams who are building, you're training other people to
build, you're writing and talking and training people to how to adopt hempcrete
you're really pushing this industry forward from all different directions. You
must think about it all the time.

Alex Sparrow: Yeah. And I do. I had a... there was an event this weekend that I've been, I've
been doing a lot of thinking about hempcrete this week with one thing and
another. I had an event at the weekend that someone said, Oh, yeah, there's no
tickets left, but why don't you arrange, you know, like a small speaking? And I
was like, nah, I just I've had enough of talking about hempcrete this week. I
think I'll give it a rest, but no, it's great. It's I, I think it's really exciting. It's an
exciting time at the moment. I think, especially, I'm doing a lot of work with
people on your side of the pond, because as we were saying earlier, it's really
taking off at the moment and there's this real buzz about hemp, the
possibilities.

Jonsara Ruth: So, you know, in all of this work that you're doing, is there anything that keeps
you up at night, anything that keeps you spinning or that you worry about in this
industry or about this kind of construction?

Alex Sparrow: Not about the construction. I mean, I think hemp/lime, hempcrete is, it's hard
not to sound like a complete crazy evangelist for it because there are so many, I
mean, we have hardly touched on the benefits of the material, you know, it's,
it's, the thermal performance is fantastic. It's a carbon sequestering material
that is actually essentially a net negative carbon emissions material. You know,
as the material, it sequesters more carbon than is used to produce it. And it
creates healthy buildings that have no sort of added chemical treatments to
stop the hempcrete from burning or rotting or being resistant to animals. So it's
completely, non-toxic because of the vapor permeability, it kind of regulates
moisture within the building. So it prevents damp and mold growing inside

homes. So it's, you know, I think it's a hugely exciting time in terms of the take-
up. Hempcrete has always been a material that has crossed over quite well into

the kind of mainstream construction industry, because it's recognizable.
Alex Sparrow: It's something that you mix and you build formwork and you apply it. So they
can kind of see the hemp is different, but they kind of understand the process.
And that's been shown in the amount of, of sort of kind of commercial builds
that have been done with it in the UK. And there are lots of firms that have used
it when it's required. I think the scale up is, is, needs to be rapid from this point
on because the construction industry is responsible for such a huge proportion
of our carbon emissions.

Jonsara Ruth: That brings me to my next question, which is like, if we were to shoot forward
10 years, 2030, what is in the ideal world? What is, what is your vision of 10
years from now in this industry?

Alex Sparrow: Well, I think hempcrete is one of the tools that we have for changing, for
bringing about that systemic change in the construction industry which has to
happen. You know, I think globally the construction industry is, is sort of
probably responsible for around 50% of our carbon emissions. And, you know,
we, we need to build another it's like another 200 million homes between now–
in the next 80 years, between now and, you know, 2100. So there's a huge
amount of a built environment that's going to be built this century. And I've, I
don't think hempcrete is the only answer, but I think we have to build that in a
way that is carbon sequestering rather than carbon emitting and hempcrete has
a huge role to play in that. And it's an existing technology that's proven. It's
quite easy for mainstream industry to adopt it.

Alex Sparrow: And I think we just need to push forward with it. And I think, you know, recent
events like, you know, w maybe one positive thing from the pandemic that
we've all been dealing with over the last few months is I think that argument of,
oh, it's too difficult to effect, you know, a big change and for everyone to
change their behavior all at the same time, I think that argument doesn't hold
water anymore, you know, cause we've just seen how everybody can change

their behavior when they have to. So maybe that gives me a little bit of hope for
what we've got to do.

Jonsara Ruth: Yeah. That's a great point. It's a great point if we– yeah, I think, I think we're
coming to the end here, but you know, I think just if we think about, you know,
you've made this great point that we can reverse or not reverse, but we can
really help the help to, to challenge this, the increasing climate change by
building differently. And, and this is a great roadmap. Do you have any last
comments about how we might get there? You're doing so much already, but
you know, you must have visions of how we get there more quickly.

Alex Sparrow: Yeah, I think, I mean, I think one thing is to be, to be confident in what we do. So
we are– all of us who work with bio-based construction materials. We are a
challenger technology to the existing you know, the status quo. But the status
quo can't continue. Like we've already said that, it just, we can't go on with
business as usual. I was involved in a presentation earlier today where we were
looking at some slides you know, showing the rough cost in the US at the
moment for hempcrete building versus cellulose wall build up or you know, a
glass fiber wall build up. And the, the comment was, you know, how do we close
that gap? Because hempcrete is more expensive at the moment. And, and I was
saying, you know, we can always, you know, we should be trying to make it as
cost-effective as possible, but when you look at, I would throw it back to them
and say that they need to close the gap on performance, and they need to close
the gap on carbon emissions.

Alex Sparrow: Yeah. Conventional construction, you know, the way that we've been doing it
for so long is, is highly is contributing in, in a really big way to, to climate change,
to carbon emissions. And there's such a huge performance gap in how existing
construction methodologies are supposed to perform and how they actually
perform in, in situ. And with hempcrete, you know, it's there's a performance
gap in the other direction. So when you look at the R-value of a hempcrete wall,
you can, you can say, okay, a hempcrete wall a foot thick will get you R-24, but
when you actually apply that on site, it performs like an R-35 wall because the
thermal mass in the wall as well gives you an extra performance of heat storage
and, and kind of buffering out temperature changes inside the, inside the
building. So you get this steady internal temperature, which is not to do with
the insulation it's to do with the mass that's in the wall as well. So, you know,
it's about getting industry to change what they're doing and being confident
that they need to change to join us, not the other way around.
Jonsara Ruth: It's great. You've offered so many great, great insights in just this last 30
minutes. I have so many more, we could talk for hours. If you wanted, if there, if
there's any little thing that you would like somebody to take away from this
transition that we need to make, what would that be? Or is there, is there any
parting words?

Alex Sparrow: I think, yeah, I think, I think, you know, we're, we're– at the moment we make
up a tiny, tiny fraction of all of the construction that's happening and that

applies to us in, in the UK, as well as you guys in America, it's even more true.
Because you're, as you said earlier, you're, you're a little bit behind us in terms
of taking this technology forward, but I think it's never too soon to start. There
are, both here and increasingly in the US, there are people around, who are
starting to use, hempcrete starting to set up companies that specialize in it. So
there's that, that kind of expertise is there to tap into. And I would just really
encourage anybody, whether they are, you know, someone who's just
personally interested or wants to build their own home or their own you know,
workshop or or whether they're a construction industry professional, is really
just to, to find your nearest training course go, and your hands on the material,
see how easy it is. And it, and just kind of take the mystery away because it's
such a nice material to work with. Such a low tech method of building with such
a high performance that once you start doing it, you'll never go back to building
with any other material.

Jonsara Ruth: That's great. That's great, Alex, thank you so much for your time. It's been really

great talking with you.
Alex Sparrow: You're welcome. It's a pleasure.