I made a mold of Camaro rear fascia. The first few castings came out okay. A recent one came out lighter in color and a little sticky and soft,pliable. I assume I may have not mixed the resin properly or not enough hardener. However the casting is maintaining its shape and is easier to trim and not sticky. Can I use the casting as is or will it deteriorate at some point.
Which resin is it? Just from that, it sounds like the mixture ratio was off (but it could also be something else) and sometimes you can salvage a casting that comes out like that. Is this a model or a full scale car part? Can you post a picture of it? Depending on what went wrong like how far off the mixture was or the environment being on the cooler side, you might still be able to use the casting depending on what you're using it for and some post-casting curing. A picture and some more information will help us figure it out.
Your mix ratio is off....I have had the same issues in the past. I scratch build 1:25th Ford,Mercury,Edsal and Lincoln dirt track stock cars. Your body part will never be usable in its present condition and it never will magically become cured. Primer and paint will not properly adhere to it and CA doesn't properly bond. 1:25 resin parts and pieces should be firm and not pliable.
Mix ratios is of the utmost of importance when mixing resin....RTV Silicone is a little more forgiving, but not much. If your plans are to do more castings, then a Gram scale is a must. Mixing by weight is very accurate...more so than by volume. Here are some links that deal with the issues that you are having....read thru them as viable solutions to the problems are provided.
alumilite.freeforums.net/thread/362/rc-3-expose I've had real good luck since I posted the expose with pouring the part "B" into a cup, weighing it to determine how much part "A" and then pouring/mixing the part "A" in the same cup as the part "B" ....the part "A" is not as thick and pours a lot easier than the "B" part.
An exert from the expose.... "I think one the biggest issue people are having is the mix ratios by being off. The closer that I can get to an absolute equal amount of both parts "A" and "B" the better results that I had. MIX NO LESS THAN 1/2 oz. OR 14.1748 GRAMS OF BOTH PART "A" AND "B"...THATS NO LESS THAN 1/2 oz. OR 14.1748 GRAMS IN THE PART "A" CUP AND NO LESS THAN 1/2 oz. OR 14.1748 IN THE PART"B" CUP. 1/2 oz. or 14 grams..thats it , no less."
If your body part mold requires less than minimum amount shown above, then you need to create some more molds of what ever you think you will need for this build or for future builds.
I'm going to be pouring some resin this weekend...I have a mold that I am working on now that is a gang mold of some dry sump oil system parts that I need for a current build on the bench. I have some other molds that I have done in the past that I will pour the excess resin in...an intake manifold for the current build and some other odd and end parts for some future builds....in other words, the 2 molds that I need poured for parts on the current build require less than the minimum amount of parts "A" and "B" ...so I'll probably mix 20g of each part just for good measure, pour the molds (4 or 5 ea.) and hopefully be done with that part of the build.
Wow thanks Brian; that's very helpful info. I may also have not mixed thoroughly enough trying to beat the short pot time and I did mix a smaller volume than usual. BTW If the mixing error involves a little more hardener would that be a safer mix error?
...In the case of resin there is no such thing as a "safer mix error" ...both the "A" part and the "B" part have to have the same amount weighed/measured out. Now with that being said, I have messed around with the mix ratios on HS-2 and HS-3 RTV Silicone and have had some decent luck with expediting the cure process some by adding 3 or 4 Grams extra of the catalyst...your results may vary depending on ambient air temps, relative humidity....atmospheric conditions that you cant control anyhow. Here's a link reference atmospheric conditions and its effects on resin. alumilite.freeforums.net/thread/384/humidity-resin?page=1&scrollTo=1419
To increase the working time with resin , refrigerate both the "A" and "B" side ....you should have finished stirring by the 30 second mark...I stir for 30 seconds vigorously and pour for the next 60 seconds....I line up my molds to be poured and have every thing ready to rock and roll before I even mix the resin. I don't refrigerate my "A" and "B" sides...don't want to hear "EEEWWW whats that in the refrigerator" from my wife...