Bbob Posted October 13, 2015 Report Share Posted October 13, 2015 (edited) All of the molds that I make are open pour Bondo molds but I was wondering if I could have a two part mold? Would it fuse together or could I treat it like plaster of Paris? Edited October 13, 2015 by Bbob Quote Link to comment Share on other sites More sharing options...
mark poulson Posted October 13, 2015 Report Share Posted October 13, 2015 I'm sure you would have to put a release agent, like spray PAM or Vaseline, on the surface of the first part before you poured the second over it. The easiest way to tell is to make a small test, using your Bondo and whatever you have to act as a release agent. From using Bondo in const., I know it will adhere to itself if the old surface is clean, but anything that's on the old surface, like old paint, has to be completely removed before you go over it with more Bondo. Quote Link to comment Share on other sites More sharing options...
taylor1595 Posted October 13, 2015 Report Share Posted October 13, 2015 I've used bondo several times to make two piece jighead molds. Use Pam to keep halves from sticking Quote Link to comment Share on other sites More sharing options...
Ed_White Posted October 13, 2015 Report Share Posted October 13, 2015 Yup, make the halves fairly thick to keep them strong, and use pam. I used the clay base method last time, where I lined the bottom of my mold box with modeling clay, then cut into it to allow half of my master to stick up out of the clay....I also cut in to allow half of the runners and sprue, and a couple of alignment pins (I used marbles). It's important to take your time with making sure the clay is up tight against the master and everything else, to get a good parting line between the 2 halves. Spray everything with Pam, just a light coat. Mixed the bondo up, and began by applying bondo all over the master first, used an acid brush to actually push the bondo down against the surface of the master to avoid bubbles in the mold cavity, then filled the rest of the box with the remaining bondo. After it had cured a while, broke everything down and re-sprayed the master, runners, sprue and alignment pieces the made the second half. Worked pretty well, I've made hundreds of pieces so far. I've even used the bondo for small lead molds. 2 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 13, 2015 Report Share Posted October 13, 2015 I use floor tile wax as a release agent, only because I have a big tin of it. I apply with a rag and a quick blast with a blow torch to smooth it out. I never had a problem of splitting the parts, but if you forget the release agent, you will have to fight to get your masters back. Dave 3 Quote Link to comment Share on other sites More sharing options...
mark poulson Posted October 13, 2015 Report Share Posted October 13, 2015 Brushing the Bondo into the details first is key, even if you have to mix a second batch to pour over it to make the mold body. The second pour will bond to the initial detail Bondo. 2 Quote Link to comment Share on other sites More sharing options...
robn510 Posted October 17, 2015 Report Share Posted October 17, 2015 will bondo (seam filler) adhere to silicone? Quote Link to comment Share on other sites More sharing options...
Frank Posted October 18, 2015 Report Share Posted October 18, 2015 will bondo (seam filler) adhere to silicone? Nothing sticks to silicone but silicone itself. 4 Quote Link to comment Share on other sites More sharing options...
Rustyfawcett Posted July 13, 2017 Report Share Posted July 13, 2017 I know that this a old post but you can also add liquid resin to the bondo it make it more fluid like cuts down on air bubbles and flows to the details better .. when I pour a mold I always pour the bondo on to a popsicle stick in a very thin stream also helps with air bubbles and start at one corner of the mold hope this helps 1 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted July 14, 2017 Report Share Posted July 14, 2017 16 hours ago, Rustyfawcett said: I know that this a old post but you can also add liquid resin to the bondo it make it more fluid like cuts down on air bubbles and flows to the details better .. when I pour a mold I always pour the bondo on to a popsicle stick in a very thin stream also helps with air bubbles and start at one corner of the mold hope this helps I do the same, I always add polyester resin to my Bondo equivalent. It cures just as well, but flows better. Dave 1 Quote Link to comment Share on other sites More sharing options...
Baitjunkys Posted July 14, 2017 Report Share Posted July 14, 2017 (edited) Body Filler Aka "Bondo Brand" is polyester resin. with micro balloons and fillers added. Straight epoxy resin might be a better choice for mold making, takes substantially longer to cure, but is more stable in shrinking etc. Edited July 14, 2017 by Baitjunkys Quote Link to comment Share on other sites More sharing options...
goldenshinner Posted July 20, 2017 Report Share Posted July 20, 2017 On 7/14/2017 at 11:34 AM, Baitjunkys said: Straight epoxy resin might be a better choice for mold making, takes substantially longer to cure, but is more stable in shrinking etc. Wouldnt epoxi not be compatible with twmpurature range of soft plastic.. polyester or polyurea only options Quote Link to comment Share on other sites More sharing options...
Baitjunkys Posted July 20, 2017 Report Share Posted July 20, 2017 (edited) "Although there are some polyester resins that demonstrate improved resistance to high temperature, standard polyester resins offer resistance to temperature up to (HDT) +/- 60oC. At more extreme temperatures the polyester composite often becomes pliable. Epoxy resin offers resistance to temperatures of up to 300oC. Total hardening of epoxy resin products is possible after many hours baking inside a furnace. High temperatures inside the furnace provide tempering and improve a product’s resistance to high temperature. Therefore turbine air supply assemblies are made from epoxy resins." Big gap between 30C and 300C.. Or 82F and 576F Im guessing carbon fiber brake rotors on some race cars are not made with polyester resin. Sourced from a quick google search... All tho I have known that epoxy was always a better product then polyester, From my fiberglass days. Edited July 20, 2017 by Baitjunkys Update info. Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted July 20, 2017 Report Share Posted July 20, 2017 Baitjunkys - yes, that is my experience. The polyester mold (Bondo equivalent) softens when molding lead (in my case). I was still happy with the results which were non-dimensional critical, being ballast weights. If enough molds are made to allow for rotation and adequate cooling between pours, Bondo can work. Dave Quote Link to comment Share on other sites More sharing options...
Baitjunkys Posted July 20, 2017 Report Share Posted July 20, 2017 36 minutes ago, Vodkaman said: Baitjunkys - yes, that is my experience. The polyester mold (Bondo equivalent) softens when molding lead (in my case). I was still happy with the results which were non-dimensional critical, being ballast weights. If enough molds are made to allow for rotation and adequate cooling between pours, Bondo can work. Dave Agreed, it works, was offer a better alternative tho. With epoxy resin you would not need any filler like bondo. It would cast with a thinner viscosity as well. 1 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted July 22, 2017 Report Share Posted July 22, 2017 I will try that next time. Dave Quote Link to comment Share on other sites More sharing options...
stretcher66 Posted July 24, 2017 Report Share Posted July 24, 2017 (edited) actually you can use about any type petroleum product as a release agent. i have used wd-40, triflow, vaseline. they all work just make sure you get everything coated with whatever you use. i have made probably 15 different 2 piece bondo molds for saltwater jigs. i like the bondo glass (green colored) better than the standard pink (after mixed). Never had any of the molds warp on me and they save me a ton of cash on 3oz to 8oz lead jigs. the ocean is not forgiving on lures. I also use a couple of these type clamps on the mold when pouring lead https://www.harborfreight.com/3-inch-spring-clamp-39530.html Good luck..... Edited July 24, 2017 by stretcher66 Quote Link to comment Share on other sites More sharing options...
Travis Posted July 25, 2017 Report Share Posted July 25, 2017 I see bondo molds as disposable so not too worried about the longevity. That being said you can turn out a lot of baits in them. Two piece molds aren't difficult. I prefer to use vasoline or Mann's Mold Release. Have used Pam also just seams it ends up getting sticky and gumming things up over time (mold box or the legos I typically use). I use the pink bondo stuff as just quick and easy. It will pick up detail just fine from my experiences. The molds will flex once they get hot but if you make enough of them you doesn't become and issue. I have messed with putting various other things in to strengthen the mold from skewers, mesh, and other resin. Just never seamed to be worth the effort for me. I figure if I can get a thousand soft plastics out of them good enough. For foam crank baits I think I have a few that I managed to get 100 plus cranks out of before they started chipping enough on the end that clean up warranted just making another mold since the stuff sets up so quick it is really is effortless. I usually over poor the half and sand back to the midpoint of the bait so the mold is perfectly flat. I then drill 1/4 holes for keys. Devcon epoxy to seal and good to go. You can use oil and get rough finished baits also if that is the goal. Overall there are better mold material options but bondo is great for prototypes and hey I want this for the next day sort of thing. About 12 years ago was the first bondo mold I made for a guy needing some 3 inch senkos fast. The initial test pours came out fine and became useful tool to add to the mix. You can mold and use those to make molds and reduce the size of bait. Go through some bondo but some guys want some strange things...I want a 2 inch version of this bait type requests. 2 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted July 25, 2017 Report Share Posted July 25, 2017 Good post Travis. Polyester has its place, as you say, particularly for prototyping and low production runs, which is all I ever do. I use floor polishing wax, purely because it is cheap and can buy by the kilo. A blast from the propane torch smooths everything out. This is prototyping, not fine detail. Dave 2 Quote Link to comment Share on other sites More sharing options...
