Deanna 9/2/08

I have just ordered a sample pack of sorbothane ultra soft polyurethane sheet for possible use under some large objects.  Has anyone used this stuff before?  what hardness would you recommend?

Jamie Hascall 9/16/08

Hi Deanna,

Sorry to take so long to respond on this.

I've use Sorbothane in a couple of different ways. While at Seattle Art Museum, we used some sorbothane under a stand to both give it a cushion and possible energy absorbtion in the event of a quake. When we later removed the piece, we found that there was a lot of transfer of some sort of extractive from the Sorbothane that stained the floor pretty well. In the end, we decided that it was a better tactic to not use it so that the stand could absorb energy by skating across the floor, as opposed to being absorbed by the elastomer but possibly toppling due to the stickiness of the Sorbothane. a layer on the floor that might allow sliding might give the best of both.

The other way I used it was as a thick energy absorbing layer in a steel support for a large mineral specimen. In this instance, 1" thick Sorbothane of about a durometer of 60 was used to absorb shock and limit movement in the event of a quake. To try to describe it in words would take a while, but suffice it to say that I think the concept was sound, but I had no way to test it to see if it would perform in the fasion I'd planned and would absorb enough energy to be worthwhile. I know that The Getty folks have tried various elastomeric solutions but have found that only a full isolation/decoupling is really effective for true seismic stabilization.

What are your plans for the Sorbothane? We might be able to give other suggestions with more info.

Jamie Hascall Chief Preparator Museums of New Mexico

Deanna 9/17/08

Jamie, In addition to being in a seismic zone, we are getting ready to break ground for a new wing of the museum here in St. Louis.  We have a two large seated Asian figures.  One is bronze and  the other is ceramic. Both are seated on furniture that is bolted to the floor just outside the construction vibration zone.  I was thinking of  using the sorbothane under the bases of these works to absorb the vibration at the base, and reduce the potential of it from traveling through the sculptures.  This sounds similar to the first application you described.  Both figures have a low center of gravity and the furniture has two or three tears the top tear is only three or four inches in height.  I was thinking about detaching the top tear from the rest of the furniture, blocking it into position and using the sorbothane as a barrier between the blocking and the lower tears of the furniture.

What durometer created the residue on your furniture?

Thanks

Deanna

Jamie Hascall 9/17/08

RE: [mountmaking-forum] Re: Sorbothane Deanna,

It's been many years since those original experiences, but I would imagine that the durometer of the Sorbothane used was in the 40-60 range. I will say that all the Sorbothane I've worked with has had a very oily feel and I would never recommend placing it in contact with anything that might be a sensitive surface.

In terms of the reduction in vibration from the construction, this sort of ongoing higher frequency/lower amplitude motion is what I feel Sorbothane excels at. A buffering layer should be able to interrupt the flow of vibration if that's what you desire.

On the other hand, Sorbothane by itself probably won't do too much to dampen larger seismic movement. Your concept of decoupling the top layer and giving it padded stops has been used and was the essence of the second example that I cited. With the low center of gravity, the danger of toppling is reduced and the freedom to move can help absorb the ground movement. It must be remembered that the P wave at the onset of seismic movement can provide enough upward force to really throw things, so keeping things retained vertically is still a necessity. Also, as one gets further up in the object column, the forces and thus the motions are often exaggerated. Support for appendages etc. needs to still be considered to keep things safe. The sort of de-coupling you have described can certainly help the latter, but I know that the Getty's work has concluded that things need to be fairly sophisticated to be truly effective.

I'm now hoping that sharing these thoughts will get the conversation going and that Getty and other folks who have had the resources to do the real research on this will now add their thoughts as I know mine are incomplete at best and may have some very real holes in their logic.

Jamie