Vodkaman Posted October 22, 2015 Report Share Posted October 22, 2015 Not sure where to post this, but it probably has most relevance here for mold making. The question is always on your mind, ‘How much hardener should I add’. I did a little research, and the recommended ratio 50:1 Bondo to hardener by weight. So, if you mix 100gm of filler, you will need to add 2gm of hardener. I just bought the Indonesian equivalent called San Polac in a 4Kg tin, but the tube of hardener just looked mostly empty to me. I squeezed the hardener into a small, lidded jar, making sure I get every drop of hardener out. The weight of hardener was 37.4gm which gives a mixing ratio close to 100:1, half that of the Bondo recommendation. If I don’t stick to this number accurately, I will likely run out of hardener and waste a good part of the can, so I have no choice but to weigh the hardener. However, now that I have transferred the hardener to a jar, this weighing process is made a lot simpler. I place the jar on a gram scale and remove hardener until the weight loss matches what I need for the mix. The other problem people have with Bondo, is the rapid speed of curing. This is almost certainly because too much hardener has been used. In my testing of the 100:1 ratio, I found that the product still hardened successfully, but a lot slower, allowing more working time. As I will be mixing 1Kg batches and wanting to paint on a layer for a bubble free surface before pouring in the remainder, then any extra working time is most welcome. I can recommend this jar storage method, especially with large tins, as all the guess work is removed from the process and you can proceed with confidence. I calculated the density of San Polac to be 1.9gm/cm³ which is a lot heavier than I thought. The significance of knowing the density, is that you can calculate the weight of product to fill a particular volume. As a rough guide, it is almost twice the weight of water. Dave Quote Link to comment Share on other sites More sharing options...
JRammit Posted October 22, 2015 Report Share Posted October 22, 2015 Good research!... I will be getting a digital scale soon (should have a long time ago!) so this will be quite useful Also a good place to post this question... What is the shelf life for this stuff? I had half a can of resin go bad so i threw it out and got a new can, but i kept the hardener and tried using it before opening the new tube of hardener... No matter how much i add, the bondo dries to a rubbery consistency... The hardener in the new tube works fine The can i threw out was over a year old, so same for the hardener... Both worked fine together when i first bought it Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 22, 2015 Author Report Share Posted October 22, 2015 The shelf life is 1 to 1.5 years. The thick layer of dust that was blown off the top of my can was not promising. This is a most informative website for answering filler questions. Dave Quote Link to comment Share on other sites More sharing options...
JRammit Posted October 22, 2015 Report Share Posted October 22, 2015 That explains everything!☺ Quote Link to comment Share on other sites More sharing options...
Frank Posted October 22, 2015 Report Share Posted October 22, 2015 I work with the stuff everyday and really think over thinking it is much of the mystery. Mixing it has a lot to do with the temperature. That said do you have a liquid or a paste? If it is truly a filler then the paste is used to make sure it is mixed well. The paste contains a colorant. Being exact might get you in trouble if it is to hot. Let's say if the temp is around 90 deg and you mix it as stated, it will cure fast and create bubbles. If it is a liquid then ten drops to an ounce by volume will be a middle ground to start. Reading this post gets me thinking that you are trying to,join two products the are very pour out. Good luck getting a good surface. The bonds you are using is much more porous than you think so beware. I mix mine on a board with a putty knife and my method is put some in the middle and with the paste start from the center of the amount needed and put a bead from the center to the edge. That is real close to what they want but not if it is hot. Then it's more like half that amount. 1 Quote Link to comment Share on other sites More sharing options...
Vodkaman Posted October 22, 2015 Author Report Share Posted October 22, 2015 (edited) Good post Frank. You know I always like to over think things. Yes, it is the paste that I am using. If anything, I will be mixing on the low side, to make sure that the tube lasts the whole tin. Yes, it is warm here, I reckon around 80F in the workshop. Bubbles at the mating face are a problem, but not of real concern at this stage. When I find a supply, I plan to mix 25% of liquid resin, to thin the mix out and give the bubbles a chance to rise under a light vacuum. The mix did heat up after hardening, but not as bad as I have experienced in the past, when I likely used too much hardener. Mixing a kilogram at a time is going to be a challenge. I will use an old 2 liter jug for the job. I have a chromed steel rod that I have sealed the ends rounded, I also have a long teaspoon for getting into the corners. Once the two halves are formed, I plan to heat the mold halves to soften slightly and then clamp together with load spreading blocks and let cool. The parts should mate perfectly after that or I will have to totally re-evaluate my plan. The first softening heat will be in boiling water. If that doesn't work, I will have another go with hot oil. I think I have all the bases covered, but it will be more than a week until I get my hands on the new mold. Thanks for the input Frank. Dave Edited October 22, 2015 by Vodkaman Quote Link to comment Share on other sites More sharing options...
