Barrett, we may be getting a bit off-topic discussing building materials, but I have to disagree with you about the urethane, especially if what you had in mind is the aerosol cans of expanding foam that one can buy at any hardware store. I'm pretty sure that the urethane won't work because it is not intended to be exposed to water, sunlight, and/or extremes in temperature and thermal movement. If Home Depot or similar doesn't carry butyl, roofing supply places will. It is dispensed in tubes, just like most other sealants. For some uses it is also available in pre-formed rolls or strips, but I think the normal tube-dispensed sealant is what will be wanted. If the dome is disassembled, or at least the joints un-bolted, maybe one-at-a-time, a compressible gasket could be installed. (Patrick, maybe that's what you had in mind with "fiberglass strips"?) Butyl in the strip-form could also be installed. While either would be a good solution, it also may be too much work, and if so, the alternative is to install sealant form the exterior, using backer rods where gaps are large enough. I'm just thinking out loud... Kim -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Barrett Sent: Tuesday, March 06, 2012 10:06 AM To: 'Utah Astronomy' Subject: Re: [Utah-astronomy] Seeking suggestions for repairing RH dome Fiberglass strips won't bond to metal with good results. Even using epoxy won't give good long-lasting results. Butyl adhesive caulking will be the best bet, but only if properly pre-prepped. Among all of the "good" products for this use, butyl is among the cheapest also, though it can be a bit hard to find sometimes. Another idea for it is spray urethane foam coating. Far more expensive yes, but it does have the advantage of being long lasting and a great insulator. -Barrett