Well I have used mineral spirits/paint thinner (for oil based paints, not urethanes) on Acrylics for 40 years on countless boats without any obvious negative effects but that is the only testing that I have done. I always tape to keep the worst of the caulking off. Scrap the bulk of the material off with something soft like the soft plastic spreaders used for applying bondo and then finish cleaning with rags and the paint thinner. Also, if you only clean up a small area at a time, your caulking will be easier to remove. Once you disturb the bead and spread it out thin, it cures much more quickly.
Bill R. is definitely right that if you use a lower strength silicone that the future removal will be much easier. My reasons for using the 3145 is because the caulking can last the life of the new plexiglass without leakage and I would rather fight with the removal aspect at the end than to deal with leaks and having to redo the caulking. There seems to always be a piper to pay! (grin) The 3145 btw is also non corrosive so the stainless screws fair a bit better than if you use the more common silicones with the acetic acid in them. I think that there are other non corrosive silicones with a lower strength than the 3145 out there but don’t know of any that are clear or white off hand. Perhaps others can help.
Best of luck with your project.
Silicone RTV. If you get any squeezed out when screwing down, cut it with a razor and peel it off. Let the screws do the securing and the RTV, the sealing. The next owner will be thankful.
CW Bill Rouse
Admiral, Texas Navy
Amel School www.amelschool.com
720 Winnie St
Galveston Island, TX 77550
Pat and Ian, that might be a workable idea, but it would be a lot of work. Getting the masking tape right to paint the edges (to cover the sealant) was a huge job, and this would be the same again.
James, both of your ideas seem like much less work. I had not considered using longer screws. That still leaves the problem of getting the butyl tape into position, and it's very frustrating to cut... so I think perhaps I'll go the silicone route. I also was not aware silicone could be easily wiped off acrylic. I thought I would have to use a solvent (like acetone) which would attack it. I'm surprised mineral spirits is safe; I usually consider that harsher than acetone.
Does anyone have a recommendation for a silicone?
SM 233 Iteration
Boston, MA, USA