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Typical Email inquiry
from an Architect and My Answer
First Message
Robert,
I understand that ___ at ___ Church
in ___ has spoken with you about a labyrinth for their church.
My partner, UUU, and I are the architects for an addition currently under
construction that will add a Fellowship Hall/Gymnasium and church classrooms
to their existing sanctuary. I have attached a site plan showing a 30'
diameter labyrinth in the courtyard. The labyrinth we've shown is based
on the one at Chartres. We'll need about 10" of slope across the
labyrinth to maintain a slope of less than 1:20 between the new entrance
and the existing sidewalk along the street. The project Substantial Completion
date is ___. This is a downtown site and we have limited open space around
the church for staging of the construction project.
The church has asked us to submit
a fee proposal for design of the labyrinth. ___ has proposed that we follow
your specifications for the concrete pad and ask you to come to the site
to do the cutting of the design, staining and sealing. We will have our
General Contractor pour the concrete pad. - What do you need from us?
- Please send us your specs. for the concrete pad -
- conc. strength 4000 psi?
- 6x6 welded wire fabric or other reinforcing?
- 4" or 6" deep concrete over 4" crushed stone?
- Can the slab be sloped 10"?
- No 'cure & seal' when the slab is poured?
- What type finish on concrete slab? broomed or smooth?
- Are there other things we could have done locally to reduce the cost?
- What would be the timeframe for your work? I understand we would need
to have the slab poured 28 days in advance to allow the concrete to cure.
We look forward to working with you.
Sincerely,
___
My Reply
Greetings,
Thanks for your inquiry. I have attached two pdf files that explain our
polymer concrete technique and that give some guidelines for concrete.
Please note, we are not concrete contractors. Therefore, we do not give
direct specifications as to what needs to be done, as we take no responsibility
for the underlying concrete. There are some things that help us, however,
as far as installing the labyrinth, and so we have our guidelines. Here
were your questions, for example:
- conc. strength 4000 psi?
Unless you are going to be driving vehicles on the concrete, "normal"
concrete (which is at least 3000 psi) should be fine. The polymer concrete
that we use reaches upwards of 5,000 to 6,000 psi. Still, psi is really
abut compression, which shouldn't be a factor with foot traffic.
- 6x6 welded wire fabric or other reinforcing?
We have had concrete with 4 x 4 wire mesh and also 6 x 6. We think that
rebar around the perimeter is a good idea for stability. These days, there
are some fibers, especially metal fibers, that bind the concrete so well
together that there isn't even a need for control joints. Perhaps no need
for mesh either. So I leave this kind of decision to the concrete contractor,
assuming that he knows concrete for his area.
- 4" or 6" deep concrete over 4"
crushed stone?
In concrete school we were told that a compacted base is the best. It
should be thoroughly wetted down, so as not to pull the moisture from
the concrete. I personally think 4" is enough concrete, with a perimeter
footing of 8" to 10". If the soil is clay or unstable, piers
can be added throughout the labyrinth. However, most concrete that we
see is 6" at least. We have seen some pads for concrete that was
10", which I think is rather excessive, but should be strong. Including
a water vapor barrier is another important consideration, if the conditions
require it. Moisture coming through the slab is harmful to the polymer
mixture.
- Can the slab be sloped 10"?
No problem. That's not extreme at all. We have had some domed slabs with
the center 5" above the perimeter, which would be the same angle.
- No 'cure & seal' when the slab is poured?
Absolutely no sealer or other surface coating. The polymer must be a concrete-to-concrete
bond. If there is a coating, it will need to be removed. We have had it
done chemically (a real mess) and by sandblasting (hurts the concrete).
Plus it is a lot of extra cost. So, no coating. That means the concrete
will be exposed topossible stains, etc. So, it may be good to cover it
with paper or plastic after the curing period, to protect it.
- What type finish on concrete slab? broomed or
smooth?
We prefer a heavy broomed finish. I used to say "medium," but
they were always too wimpy. The guidelines probably still say medium,
but you should say heavy. The direction of the brooming is important.
So is taking care with the overlap in the middle of the labyrinth. These
are discussed in the guidelines.
- Are there other things we could have done locally
to reduce the cost?
The biggest cost is for re-doing or un-doing things that have been done
wrong, or having to clean or otherwise prepare the labyrinth (beyond the
normal power washing). No matter how much you tell the contractor to do
a good job on the finishing because this isn't just a patio or sidewalk,
in the end, the boss leaves and the workers do the same thing they've
always done. There will be color variation and birdbaths and all kinds
of things. But still, we try for the best we can get.
Our current job (Ruston, LA) had a problem with the concrete because the
aggregate was too close to the surface. First time that has happened.
It is tearing up all of our tools, as we are cutting stone as much as
concrete. Any normal finish job would push the aggregate down and leave
the "cream," the high-cement layer that is very strong, on the
top. Apparently he didn't do that. When we mentioned the problem, he said,
"I wish you had told me." Told him what? Told him that we wanted
it done like concrete should be done? Hm-m-m-m.
Let me now give you the news that we are booked up next year until ___.
We have jobs in ___. Of course, with construction, there can be delays.The
time for installation depends on which technique we use. We have a less-expensive
alternative that involves masking off the labyrinth and shooting the polymer
concrete with a hopper gun. That is the one that takes about a week. Our
usual technique is to cut the pattern into the concrete and color it by
hand. That takes 12 days. Our prices for 2007 are as follows: Basic cost
of a masked labyrinth is $20,000 and the basic cost for a cut and hand-colored
labyrinth is $25,000. (These are for the Chartres pattern.) To this are
added soft costs, which vary from job to job, including transportation,
lodging, and per diem for meals and expenses. The soft costs are still
usually several thousand dollars, and in some cases can be considerable.
For California, for example, the soft costs are often $7,000 because of
the drive, driver's wages and per diem..
To reserve a date we need to sign a work agreement. I can send that when
you are prepared to make a commitment. I look forward to hearing from
you.
Best wishes,
Robert
Attached: Polymr concrete description, concrete guidelines
The Response
Dear Robert,
Thanks for all the information about your company and process. Based
on your extensive experience with labyrinths (and our inexperience) we
will recommend to the church that we locate and size the pad for the labyrinth
and pour the pad based on your recommendations. We'll also forward the
information you sent us to the church and recommend that they contact
you directly for the labyrinth work and arrangements about the cost and
your stay in ___
.
Thanks,
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