David Martin Hershey on thu 14 aug 08
Hi Debbie,
Thanks for the kind words, and I am impressed with your work too!
I think my oldest master made in RU-440 is about 4 years old. I haven't
done anything special to store them, other than be sure that they are
completely clean of mold soap and plaster, and store them in a cool dark
place. I don't think ozone attacks them.
There is no apparent degradation of any kind. No shrinkage, deformation,
or weeping. The only thing I notice is that they continue to outgas
slightly. You just catch a whiff of the wet urethane smell when you open
them up. This may lead to eventual shrinkage.
I think urethane is a great material. I have surfboard leashes made from
it that are pushing 15 years old, and still look good. I even had one
stretch to almost twice it's original length in Hawaii, and not break!
(But it never returned completely to it's original length, and I retired
it in honor of it not leaving me in a very dicey situation, far from
shore...)
On a related subject, have you seen the urethane that grows 60% and
retains it's proportions when you soak it in water? Very cool material!
I assume you are casting in wax? You may need to contact Silpak and ask
them what is the right hardness of material to be using for your
application. They have very good technical support.
You could ask Joani how her molds are holding up. Her horses have very
delicate parts like some of your pieces. If there had been some
deformation of the master, she would know. But for her I would think it
is not as critical, because I know she moves the legs of her horses
around to get them out of the mold, and then re-poses them.
I don't think she's on the list right now. Contact her at Pour Horse
Pottery.
http://www.pourhorse.com/ph/information/index.html
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
D. L. Engle wrote:
>You mentioned a good library life with the RU-440 Urethane RTV. Could
you please tell us about how manyquality years one could expect? Perhaps
Joani has some molds older than yours if you've been using it for only a
few. Do you do anything special intheir storage?<
David Martin Hershey on sat 16 aug 08
Hi Debbie and John,
John, yes PolyTek has some very nice products, and it is handy to be
able to buy from them on the web. I haven't tried any of their RTV
rubbers yet, but I am intrigued with their thin shell fiber mother mold
materials, for supporting thin RTV molds. (A large plaster mother mold
can weigh 50 lbs or more!) I also am interested in some of their
casting plastics.
Debbie, I also used to use only silicones. I've found that my old molds
have all had problems, and are much more prone to tearing than urethanes.
I think you're right- the thinner the mold, the more likely it is to
shrink or distort. I used to do French molds to try to save on rubber
cost. Now if the piece is relatively small, I just do the whole thing in
urethane. Rock solid, never any problems, no false economy.
It's possible that the plaster is attacking the urethane. Is the Walco
designed to resist highly alkaline materials? Have you tried sealing the
plaster?
Re: Joani- she's a great person, I'm sure she'll be happy to talk with
you. Give her my best.
The growing urethane is a very interesting material. I've only used it
once, but had very good results. I'm getting ready to use it on another
piece, and this time I'll document the process and post something to the
list.
http://www.industrialpolymers.com/water_abs_expanding_urethanes.html
The surf leash story is one of those times where part of me was trying
to resist fear and panic, but I just couldn't help but laugh. The waves
had been rapidly building in size, as it is prone to do in Hawaii.
Suddenly we were all caught inside of a giant wave that broke 25yds
outside of us. Immediately I'm faced with 12 feet of whitewater bearing
down on me. Some of the guys panicked, lots of very big eyes...
So I dove for the bottom. Don't panic, dive, dive, dive... As the wave
rolled over, it pulled and pulled my board (and leg) until I was sure
the leash or my leg would break. Suddenly it let go of the surfboard.
When I swam to the surface I pulled on the leash to get my board back,
and it seemed like I pulled and pulled forever.
The 10 ft leash was now at least 18 ft long! And what had been 3/8's
inch thick, now felt almost as thin as spaghetti. Somehow my leash
instantly turning to spaghetti in the midst of this drama, just cracked
me up. Of course all the guys whose leashes broke, didn't see the humor
in my luck. They had to figure out how to get to shore, and were
desperately hoping that the rip didn't take their surfboards out to sea...
Behold the power of urethane! ;^)
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
D. L. Engle wrote:
>I always do contact manufacturers. They tell me conditions of usage,
storage, and other variables make that information for practical purposes,
unavailable. So I try to talk to people like you and Joanie who use such
materials and that is much more informative.
I loved your story about the surf board leash. Aside form being interesting
it tells me a lot about the material. I've found Silicones vary tremendously
in library life (and other qualities). You're right, I use molds primarily
for wax at 175 F. They are stored in plaster casings. Walco's 1065 is the
best overall I've found so far. Some of these molds are 10+ years and have
no shrinkage and are still as tough and pliable as when made. Others have
had to be replaced after 5 years due to small amounts of distortion. Not
sure what the difference is but think it may have something to do with the
size of the mold relative to its' wall thickness or maybe the amount of use
it gets.
I would like very much to talk to Joanie. I'm aware of her wonderful work
and hope she wouldn't mind comparing notes. If you don't mind, I'll mention
you sent me .
And thank you for mentioning the 60% enlarging urethane! No, I've not heard
of that and will check it out. Very interesting!<
D. L. Engle on sat 16 aug 08
Hi David,
Thank you as well!
I always do contact manufacturers. They tell me conditions of usage,
storage, and other variables make that information for practical purposes,
unavailable. So I try to talk to people like you and Joanie who use such
materials and that is much more informative.
I loved your story about the surf board leash. Aside form being interesting
it tells me a lot about the material. I've found Silicones vary tremendously
in library life (and other qualities). You're right, I use molds primarily
for wax at 175 F. They are stored in plaster casings. Walco's 1065 is the
best overall I've found so far. Some of these molds are 10+ years and have
no shrinkage and are still as tough and pliable as when made. Others have
had to be replaced after 5 years due to small amounts of distortion. Not
sure what the difference is but think it may have something to do with the
size of the mold relative to its' wall thickness or maybe the amount of use
it gets.
I would like very much to talk to Joanie. I'm aware of her wonderful work
and hope she wouldn't mind comparing notes. If you don't mind, I'll mention
you sent me .
And thank you for mentioning the 60% enlarging urethane! No, I've not heard
of that and will check it out. Very interesting!
Thanks & Best Wishes, Debbie
Valinda CA
D. L. Engle Sculpture
www.home.earthlink.net/~dlenglesculpture/
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of David Martin
Hershey
Sent: Thursday, August 14, 2008 9:36 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: making a mold w/ leatherhard clay, now urethane
Hi Debbie,
Thanks for the kind words, and I am impressed with your work too!
I think my oldest master made in RU-440 is about 4 years old. I haven't
done anything special to store them, other than be sure that they are
completely clean of mold soap and plaster, and store them in a cool dark
place. I don't think ozone attacks them.
There is no apparent degradation of any kind. No shrinkage, deformation,
or weeping. The only thing I notice is that they continue to outgas
slightly. You just catch a whiff of the wet urethane smell when you open
them up. This may lead to eventual shrinkage.
I think urethane is a great material. I have surfboard leashes made from
it that are pushing 15 years old, and still look good. I even had one
stretch to almost twice it's original length in Hawaii, and not break!
(But it never returned completely to it's original length, and I retired
it in honor of it not leaving me in a very dicey situation, far from
shore...)
On a related subject, have you seen the urethane that grows 60% and
retains it's proportions when you soak it in water? Very cool material!
I assume you are casting in wax? You may need to contact Silpak and ask
them what is the right hardness of material to be using for your
application. They have very good technical support.
You could ask Joani how her molds are holding up. Her horses have very
delicate parts like some of your pieces. If there had been some
deformation of the master, she would know. But for her I would think it
is not as critical, because I know she moves the legs of her horses
around to get them out of the mold, and then re-poses them.
I don't think she's on the list right now. Contact her at Pour Horse
Pottery.
http://www.pourhorse.com/ph/information/index.html
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
D. L. Engle wrote:
>You mentioned a good library life with the RU-440 Urethane RTV. Could
you please tell us about how manyquality years one could expect? Perhaps
Joani has some molds older than yours if you've been using it for only a
few. Do you do anything special intheir storage?<
D. L. Engle on sun 17 aug 08
Hi David,
Thanks for mentioning the thin shell fiber casing material. I tried to
locate it on their web site but couldn't find it (I'll probably give them a
call about it later). I was wondering if it is something like the FGR-95, a
fiberglass reinforced slow setting gypsum cement, that I use for large and
very thin, (1' to 4' long) casings? They are sealed with lacquer (though I
should try other sealants because of the smell! )
I'm not sure if alkalinity is a factor. The tek people are right in that too
many variable come into play for them to estimate library life. Some people
claim air quality, storage temperature even the temperature the RTV is mixed
at all affect library life. I don't know but suspect conditions of use are
the bigger factors.
I think I caused some confusion about my Walco 1065 molds. Let me try to do
this better; my French pour molds are the ones that have a thicker wall
relative to the size of the mold and are the ones that tend to distort
earlier. The large molds which are quite thin walled and made by brushing up
(adding a percentage of the viscous VRM-65 to stiffen it up) hold up the
best. Some of these molds average only about a 1/4" thick walls over a
figure up to about 20" long. But you say you've had the opposite result?
Your French poured molds are stable with no distortion for how many years?
So far at 10+ years (knock on wood) I've not had a Walco RTV mold turn
brittle and tear. Some other types of RTVs I tried earlier tore like sliced
cheese quite soon. I understand Burman's in Van Nuys has a new (pink
colored) RTV that they say is as good as Walco's 1065 and is significantly
less expensive but I haven't tried it. And as it will need at least a 10
year test in working applications I'd rather find someone else who already
has tried it .
I hope I don't miss your post when you do your next expanding urethane
project. Sounds fun and has got me thinking how I can use it. It also seems
you have a powerful "Mold God" working on your behalf in the form of your
former board strap now spaghetti noodle urethane strip.
That's what I need, gotta find me a Mold God....
Best, Debbie
Valinda CA
D. L. Engle Sculpture
www.home.earthlink.net/~dlenglesculpture/
-----Original Message-----
From: Clayart [mailto:CLAYART@LSV.CERAMICS.ORG]On Behalf Of David Martin
Hershey
Sent: Saturday, August 16, 2008 10:23 PM
To: CLAYART@LSV.CERAMICS.ORG
Subject: Re: making a mold w/ leatherhard clay, now urethane
Hi Debbie and John,
John, yes PolyTek has some very nice products, and it is handy to be
able to buy from them on the web. I haven't tried any of their RTV
rubbers yet, but I am intrigued with their thin shell fiber mother mold
materials, for supporting thin RTV molds. (A large plaster mother mold
can weigh 50 lbs or more!) I also am interested in some of their
casting plastics.
Debbie, I also used to use only silicones. I've found that my old molds
have all had problems, and are much more prone to tearing than urethanes.
I think you're right- the thinner the mold, the more likely it is to
shrink or distort. I used to do French molds to try to save on rubber
cost. Now if the piece is relatively small, I just do the whole thing in
urethane. Rock solid, never any problems, no false economy.
It's possible that the plaster is attacking the urethane. Is the Walco
designed to resist highly alkaline materials? Have you tried sealing the
plaster?
Re: Joani- she's a great person, I'm sure she'll be happy to talk with
you. Give her my best.
The growing urethane is a very interesting material. I've only used it
once, but had very good results. I'm getting ready to use it on another
piece, and this time I'll document the process and post something to the
list.
http://www.industrialpolymers.com/water_abs_expanding_urethanes.html
The surf leash story is one of those times where part of me was trying
to resist fear and panic, but I just couldn't help but laugh. The waves
had been rapidly building in size, as it is prone to do in Hawaii.
Suddenly we were all caught inside of a giant wave that broke 25yds
outside of us. Immediately I'm faced with 12 feet of whitewater bearing
down on me. Some of the guys panicked, lots of very big eyes...
So I dove for the bottom. Don't panic, dive, dive, dive... As the wave
rolled over, it pulled and pulled my board (and leg) until I was sure
the leash or my leg would break. Suddenly it let go of the surfboard.
When I swam to the surface I pulled on the leash to get my board back,
and it seemed like I pulled and pulled forever.
The 10 ft leash was now at least 18 ft long! And what had been 3/8's
inch thick, now felt almost as thin as spaghetti. Somehow my leash
instantly turning to spaghetti in the midst of this drama, just cracked
me up. Of course all the guys whose leashes broke, didn't see the humor
in my luck. They had to figure out how to get to shore, and were
desperately hoping that the rip didn't take their surfboards out to sea...
Behold the power of urethane! ;^)
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
D. L. Engle wrote:
>I always do contact manufacturers. They tell me conditions of usage,
storage, and other variables make that information for practical purposes,
unavailable. So I try to talk to people like you and Joanie who use such
materials and that is much more informative.
I loved your story about the surf board leash. Aside form being interesting
it tells me a lot about the material. I've found Silicones vary tremendously
in library life (and other qualities). You're right, I use molds primarily
for wax at 175 F. They are stored in plaster casings. Walco's 1065 is the
best overall I've found so far. Some of these molds are 10+ years and have
no shrinkage and are still as tough and pliable as when made. Others have
had to be replaced after 5 years due to small amounts of distortion. Not
sure what the difference is but think it may have something to do with the
size of the mold relative to its' wall thickness or maybe the amount of use
it gets.
I would like very much to talk to Joanie. I'm aware of her wonderful work
and hope she wouldn't mind comparing notes. If you don't mind, I'll mention
you sent me .
And thank you for mentioning the 60% enlarging urethane! No, I've not heard
of that and will check it out. Very interesting!<
David Martin Hershey on wed 20 aug 08
Hi Debbie,
Polytek's website is a bit behind the times... The thin shell plastic
material I am thinking about is shown on their video page. A nice series
of video clip on how to use their products. Look at chapters 7 & 8.
http://tinyurl.com/2sagrj If you have problems viewing the clips, let
me know.
Re: library life, hot wax has to be pretty hard on the material- but
there are silicones that are made to withstand over 500 degrees, so I
don't know. One of those voodoo deals... What hardness is your urethane?
I think the softer materials are more prone to tearing, but are easier
to get off the castings.
Interesting that you are having more troubles with your thicker French
molds. Do you think it could have something to do with how well a
particular mold is keyed into it's jacket mold? Do you store them with a
urethane master casting inside the mold?
The only time I do ultra thin rubber is when I'm making an intermediate
stage mold on the way to the final master. I usually only use them once.
I did do some thin latex molds in art school, but learned quickly how
dismal latex is ;^(
I'll cc you when I do post something on the expanding urethane.
And why not Mold Gods? There certainly are enough Kiln Gods around...
Best, DMH
David Martin Hershey
DMH Studio + Design
2629 Manhattan Ave #137
Hermosa Beach CA USA
90254-2447 310.379.6890
http://www.dmhstudio.com/
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