"My resin is still sticky after 24 hrs?" Topic

Okay, I'm casting a little balsa wood waterline canoe I made. It's about 10+" inches long and about 1.5" wide. It's 1/4" high on the edges and 1/8" inside, so it's fairly thin. I made a latex mold of it. I cast it once in hydrocal, which I'd heard was stronger than plaster of paris, but even after 24 hours the casting broke under even minimal strain, so I decided to try resin.

I'm using Castin'Craft CLEAR liquid plastic casting resin from Michael's. It suggests 8 drops of catalyst per ounce of resin for casts of 1/4" thickness, and 15 for 1/8" thickness. I started with 8 drops. It still had not set after nearly an hour. After that, it was solid but very soft and sticky. In fact, I demolded it and was able to bend it whatever way. Several hours later, it started to firm up, but even after 24 hours, it's still somewhat sticky. I tried again with 50 drops of catalyst per 3.5 ounces of resin, or about 15 per ounce as recommended for 1/8", and got pretty much the same results. I'm trying again with 68 drops.

Is this *supposed* to happen, or is there something I'm doing wrong? I washed the mold out after casting the hydrocal, and rinsed it well. If this is supposed to happen, well yuck, somebody please recommend something better!!

In the right proportions it should not remain tacky unless it is designed to be. A few things could cause this but I think your catalyst is not working and may have exceeded its shelf life. I don't know much about this specific product but some of these chemicals are light sensitive or temperature sensitive and will lose effectiveness. Try another resin product if you didn't get good results. Smooth-On for example makes some great products including A-B resins which are equal parts. Some hobby stores or model train shops carry it or you can go to their website.

www.smoothon.com

One other factor, it's curing out in my garage (due to the smell). The temp is warmer than outside, but it's still probably 50-60 degrees.

Hey I have use that stuff before and it does not like the cold, you may have to try and let it set for 2 or more days at that temp. Because i live in the northwest and it is cold a lot of the year i switched to Alumilite it works better and hardens in 3 to 5 minutes. You can get it at somehobby stores, there webb site has a list of retailers.

Not enough hardener mixed in from my experience, or not mixed enough.

Tempreture can effect things.

If you want simplicity, try Plaster of pasis with some PVA white glue mixed in (mix in about 15-20% of mix) and it hardens up nicely.

G

Try the A-B stuff from Tapp Plastics. It like wrom tempatures (80F+) and hardens in 3-5 minutes after 30-60 seconds of pour time.

Well, I'm stuck with cold temperatures at least for the next month or so (until the in-laws leave). I noticed that the castings setting out 24 hours are still slightly malleable. This last one I definitely mixed well, and it seems about the same as the others.

I have used that stuff extensively and have tried everything and the hundreds of bases I made some are still tacky after a year. Have tried everything , more catalyst , less catalyst , left in the sun in summer , left in the cold , just about everything. The only thing I found was the more drops of catalyst the more rubbery the product. Good luck. If you find the magic bullet let me know....

I switched to Alumilite, for ease of use, easier cleanup, and less smell. It means driving an hour to a hobby shop that carries it, but it's worth it. I had the same problem with the Castin' Craft polyester - the castings stayed sticky for months.

If everything else fails, try heating the casting in the oven (somewhere between 60-80°C) untill it REALLY starts to smell. See what it feels like after it is cooled down. VENTILATE THE ROOM.

You could be suffering from any or all of several problems, some of which have been listed above.

1: Some resins do not like to set in thin cross-sections, data sheets for some polyurethanes list minimum of 6mm (1/4 inch) thickness.

2: Too much and/or too little catalyst. Too little catalyst results in a slow setting and tacky casting. TOO MUCH gives a smelly casting that may have bubbles, be rubbery, crumbly, sticky or all of the above. May also be the wrong catalyst

3: Incompatable mould making materials. Some mould RTV rubbers & some modeling clay contain chemicals that will stop resin from setting properly. If anyone has trouble with RTV not setting properly I have found painting the outside with catalyst can work. And give the clay to a small child. Klean Klay make good modeling clays that work with anything.

You may also have problems with the RTV mould being too 'Green' - RTV exudes chemicals for a couple of weeks that can stop resin from setting - this can be speeded up by heating the RTV in an oven or similar and waiting a few days (when casting metal you may notice a pitted surface from the early castings - this can be the volatiles being burnt off the surface of the mould).

4: Temperature. Lab standard is 70F & most suppliers cannot understand that you don't have a full set of laboratory gear devoted to their product. At work we have a plywood cupboard about 2'x2'(60x60cm) with a hole for a fan heater and some wire shelves that is used for curing resin castings.
All you need to do is stick a fan heater blasting into a large cardboard (or similar) box and place all your chemicals & castings inside - then everything will be equally warm. Don't forget a fire extinguisher (in case of errors), a temperature detector (cheap termometer or a roast temp. probe) stuck thru' the side and some old cake racks or similar on blocks to stack the moulds on while they set.

Come to think of it, I did try baking my CastinCraft polyester castings, and it did work eventually, but 2-part urethane resin is much easier to work with.

This may be an overly simple solution, but did you mix the heck out of your resin before pouring? I have run into what you are discussing before, and it only every happened when I didn't mix the resin adequately. You can tell if the poured product is not of a uniform color.

Rod Thomson
Flagship Games
www.flagshipgames.com

Its old tech Polyester resins (while cheap are a tough mix and shrink as they cure). The castings you have probaly will never cure correctly. try a 50-50 mix urethane resin it sets quicker and doesn't stink. Smooth on makes and orderless white. Sil pack is good , golden west isn't bad. Stay away from Vagabound smelly and it is incosistent.

Not enough hardener

I had this problem years ago with latex molds and clear resin - I had to paint the catalyst onto the demolded castings to get them to harden quickly. They did eventaully dry on their own over a couple of months though.

The latex mold is inhibiting the curing. You can switch to a different mold material (RTV for example) or to a different casting material (Alumilite 2-part resin).