RipLip Posted June 24, 2008 Report Share Posted June 24, 2008 I finished making a silicone mold and there was like little air bubbles under all the baits when I pulled them out. Now when I pour them it looks like a couple have a wart problem:lol:. I'm sure its not going to effect the way they fish but it doesn't look right. Am I supposed to do something different when pouring the silicone or does humidity play a role in the silicone. The last couple molds I poured didn't have a problem so I'm not sure where I went wrong. Any thoughts would be great. Thank you Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted June 24, 2008 Report Share Posted June 24, 2008 (edited) A tip I received here on TU (thanks) is to paint a layer of the RTV onto the master first, just before pouring. This "wets" the surface and gives the bubble nothing to attach to. Also, pour slowly, away from the master and allow the RTV to find its own route across the master pattern. Ideally, you should invest in a vaccuum chamber. This would definately solve the problem. I have read on suppliers web sites that the chamber is recommended. This causes the bubbles to expand to many times their normal size and they come to the surface very quickly. Not sure how long the vaccuum operation is, not more than a minute is my guess. If you make a lot of molds, this is the way to go, but if you just make the occasional mold, like me at the moment, method 1 works for me. Obviously, find a mixing technique that does not whip too much air into the mix. Most instructions (I always read the instructions!) suggest a figure 8 motion. What ever! Some of the RTV's have a very small working time before they start to go off. My next purchase will buy me at least fifteen minutes of working time, even if it is at the expense of set time. Whats the rush! Edited June 24, 2008 by Vodkaman Quote Link to comment Share on other sites More sharing options...
Spike-A-Pike Posted June 24, 2008 Report Share Posted June 24, 2008 (edited) Did you take your time and mix it good and slow? The silicon we used to use on the flight line was used as potting compound inside cannon plugs and electronics and communications equipment. The newer guys used to get impatient mixing it up and would get air trapped in the process leaving the same type of bubbles, That was back in the early 80s; so I don't know if its still a problem these days. Vman - Would an automotive vacuum brake bleeding system provide enough vacuum to draw the bubbles out? There are some pretty inexpensive models out there. Edited June 24, 2008 by Spike-A-Pike Quote Link to comment Share on other sites More sharing options...
RipLip Posted June 24, 2008 Author Report Share Posted June 24, 2008 I may be mixing it to fast because I wasn't aware that would cause a problem. I also pour it fast for this type of mold because I set the master in after the silicone levels. The weight of the bait sinks itself in level. I have not tried coating them before setting them in and I may try that. Just like you Vodka I may make a different mold every other month, so I don't think I would need a vacuum system. When I had masters set in place and I poured over them I poured those slow and they came out fine. I'll try doing everything slower this next time and see what happens. Thanks for the input Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted June 24, 2008 Report Share Posted June 24, 2008 I think most people bottom mount the masters, rather than floating. I think bottom mounting gives more control over the split line. But I had trouble finding a technique for the bottom mounting. It would be interesting to hear how everyone else does this. Quote Link to comment Share on other sites More sharing options...
MDC Posted June 24, 2008 Report Share Posted June 24, 2008 The RTV that I have used recomends 10lb of vacuum, it also takes about 12 hrs to cure, so there is plenty of time to mess with it. I always set my masters on bottom and pour over like Vman said when using RTV. If you don't have a vacuum chamber, another trick is to punch a small hole (I used a phillips head screwdriver) in the bottom of your mixing container and let the RTV run out over the masters. Just remember to pour in a corner of the mold box and let it self level Quote Link to comment Share on other sites More sharing options...
