Frank Posted October 3, 2015 Report Share Posted October 3, 2015 Well there may be some air introduced when mixing too. It can be somewhat stiff at time and if mixed without regard to introducing air you could make it worse. Like Dave said a thin coat on the master and let it cure them fill the rest of the mold. When you make another one take some time and cut the bad one apart and look at it to see if bubbles are there. I would bet there are. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 3, 2015 Report Share Posted October 3, 2015 Frank - I don't think I would let the brushed layer cure. Just a quick brush-on, to ensure no trapped air and all the surface is covered. Dave Quote Link to comment Share on other sites More sharing options...
Frank Posted October 3, 2015 Report Share Posted October 3, 2015 I should have said this better, the reason for the thinner coat is so when a vacumn is turned on it won't grow to three times the size and over fill the box. Brushes can cause air too especially with such a thick compound. 1 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 3, 2015 Report Share Posted October 3, 2015 I have started looking for a vacuum setup, as I have a few applications for one; vacuum forming, vacuum molding experiments, plaster and RTV mixes, resins for casting and probably a few more that I cannot think of at the moment. I have just designed all the panels for an electric vehicle to be vacuum formed. The customer wanted fiberglass, but I convinced them to go for the vacuum forming. The aluminium tools have been cut and the first panels have been formed and looking very good. Having convinced my customer to go vacuum, I should at least have a set-up myself. Dave Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 4, 2015 Author Report Share Posted October 4, 2015 Yep, so I put the mold in the oven at 300 degrees for a few minutes and took it out to inspect it....bubbles in the silicone. The heat makes them expand. Cut it open and it looked like swiss cheese. What a waste of silicone Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 4, 2015 Report Share Posted October 4, 2015 (edited) If you can find a way to grate the faulty mold into shreds, you can use it as filler in future RTV molds, thus putting it back to work. Dave Edited October 4, 2015 by Vodkaman Quote Link to comment Share on other sites More sharing options...
rixon529 Posted October 6, 2015 Report Share Posted October 6, 2015 I haven't used silicone to create molds but I have read about /seen a few videos that say if silicone is not degassed before pouring it can be poured in a small stream from a slightly greater height to allow some volume of air to escape the silicon before it enters the mold. Just beware of cross-winds. On the other hand, the "bumpy" texture on the lure surface isn't necessarily a bad thing... Who knows - the fish may even like it! Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 7, 2015 Author Report Share Posted October 7, 2015 The viscosity of the bad molds silicone was extreme compared to the good molds silicone. The good molds si cured hard but poured amazingly and visa versa for lure crafts. I need the extra flexibility so I bought more of the bad molds si ang have made me a vacuum chamber out of a 5 gallon bucket, lid, my vacuum, and a small sealed plexiglass window to watch my silicone to keep it from overflowing. Its pretty air tight. Can't wait to try it with my si. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 7, 2015 Report Share Posted October 7, 2015 One-off baits - there won't be much of a vacuum, but it might be enough to get the job done. Please report back after the test, whether successful or not. Dave Quote Link to comment Share on other sites More sharing options...
Little Creeper Baits Posted October 7, 2015 Report Share Posted October 7, 2015 The viscosity of the bad molds silicone was extreme compared to the good molds silicone. The good molds si cured hard but poured amazingly and visa versa for lure crafts. I need the extra flexibility so I bought more of the bad molds si ang have made me a vacuum chamber out of a 5 gallon bucket, lid, my vacuum, and a small sealed plexiglass window to watch my silicone to keep it from overflowing. Its pretty air tight. Can't wait to try it with my si. If you are saying you made your own chamber from a plastic bucket and it has a window made of sealed plexiglass please don't try it. If you are actually able to get a vacuum going you will probably have a catastrophic failure and you could be badly injured. Your home vacuum won't give you enough suction to do the job anyway, but if it does somehow you be seriously hurt. You can use a steel or aluminum pot with a thick (3/4") lid. Check out Best Value Vacs. Just be careful with making your own chamber. A failure can be live threatening. Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 7, 2015 Author Report Share Posted October 7, 2015 It seems to work okay without a sample of silicone inside. It sucks the lid down and the sides in a little bit. Seems to be just a little more than normal atmosphere. The lil window is only 2 inches and is bolted down with 8 bolts. It's thin and flexible plexiglass so I don't foresee it breaking. Just figured it'd help some with the bubbles better thannnnothing. Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 7, 2015 Author Report Share Posted October 7, 2015 The under side of the lid. It's a weak vacuum. Yaw think if it's enough to suck the lid and sides down a lil that it'll pull bubbles? Quote Link to comment Share on other sites More sharing options...
mark poulson Posted October 8, 2015 Report Share Posted October 8, 2015 I don't know if it will work or not, but I would recommend wearing shoes whenever you're working on anything. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 8, 2015 Report Share Posted October 8, 2015 Mark - My guess is that flipflops don't count. When I set up my workshop again, I will take your advice Dave Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 8, 2015 Author Report Share Posted October 8, 2015 I wasn't working on said piece at the time of the pic...few days prior...with boots. Quote Link to comment Share on other sites More sharing options...
Frank Posted October 8, 2015 Report Share Posted October 8, 2015 That bucket will not take the vacumn pressure it take to get out the bubbles in silicone. You will need a pump like the ones on best value vacumn sites. Any thing less and you will be wasting time and money. Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 9, 2015 Author Report Share Posted October 9, 2015 A tad bit-o research revealed to me some stuff. I'll be getting a pressure cooker, some thick polycarbonate, and trinkets. Found a pump on harbor freight that supposedly pulls 28mg mercury so I'll be set up soon Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 9, 2015 Report Share Posted October 9, 2015 When I find a pump, I will be using an empty gas bottle as the vacuum storage. All houses cook with bottled gas here, so no problem finding a bottle. Dave Quote Link to comment Share on other sites More sharing options...
Frank Posted October 9, 2015 Report Share Posted October 9, 2015 A tad bit-o research revealed to me some stuff. I'll be getting a pressure cooker, some thick polycarbonate, and trinkets. Found a pump on harbor freight that supposedly pulls 28mg mercury so I'll be set up soon Get one that goes above 29.4 and you will be set. For a vessel get a commercial cooking pot. Winco is one you should find a lot, in the three gallon range you will get a ten inch pot. These are the same ones from best value vacs would send you. Resturant supply houses have them. These pots are about 1/4 inch thick. Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 9, 2015 Author Report Share Posted October 9, 2015 What do you mean by gas bottle? Propane tank? The pump I found was only $20 and I saw where someone else was successfully using it to degas silicone so I'm gonna give it a shot first. Can't hurt for only $20. Quote Link to comment Share on other sites More sharing options...
Frank Posted October 9, 2015 Report Share Posted October 9, 2015 Here is a parograph right from smooth on. It pretty clear how much vacumn is needed. "For vacuuming silicone and urethane mold rubber or resins (urethane, epoxy, etc.) we can suggest the following minimum vacuum pump specifications; Rotary vane vacuum pump with a minimum airflow of 8 CFM (ft3/min) or 13.6 Cubic Meters/hour (m3/h). Pump must pull 29 inches of mercury. If the pump does not pull 29 inches of mercury, you are wasting your money and time. " I know these cost more. Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 9, 2015 Author Report Share Posted October 9, 2015 What's $20 when your possibly going tospend hundreds. If it "truly" (unlikely according to a retailer) took bubbles out of the guys I read about its worth a shot. If not then I guess I'll bite the bullet. No harm done with a trial. Thanks for the cooking pot idea btw. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 9, 2015 Report Share Posted October 9, 2015 Now I remember, I built a vacuum box out of ply wood. It was only evacuated with my shop vac, but the effect/improvement was astonishing on my plaster test piece. I say go ahead and do a test block; without vacuum and one with vacuum. Cut it up and see the difference. With the viscosity of liquid RTV, it won't be as dramatic as my plaster test, but it may be enough to clear the bubbles from the cavity surface. Yes, the tanks are propane. They come in two sizes; 5Ltr and 15Ltr. The 15Ltr would be best, but I have a spare 5Ltr for testing first. For your tests, implosion is a real danger. Shards of plastic can be very dangerous. So take all precautions and be aware of the power that you are playing with; heavy clothing,at least eye protection, full face would be better. Operate from behind a shield would be a very good cautionary measure. DAve Quote Link to comment Share on other sites More sharing options...
one-off baits Posted October 9, 2015 Author Report Share Posted October 9, 2015 Frank.. is this what you had in mind? Winco winware 3 gal. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 9, 2015 Report Share Posted October 9, 2015 My new shop vac just arrived. Slightly disappointed that it doesn't pull as good as my old one. Not too shabby though, nice tidy unit. Dave Quote Link to comment Share on other sites More sharing options...
