Review of Polytek Poly 74-20 mold making rubber for brush on mold

I have finished making the mold and mother mold of my bas relief "Setting Her Sights." There is the first test casting in Aqua Resin moments after pulling it out of the mold.
You can see the full tutorial by looking at previous postings on my blog. Polytek Poly 74-20 liquid polyurethane rubber is designed for making flexible, high-performance, high-strength molds. This rubber is very liquid - much more so than many of the others that I have used. Think heavy cream instead of thick syrup.

This rubber is more often used for pouring a once piece block mold or making a blanket mold. I did not opt to do either but chose to do a brush-on mold instead. Block molds are easiest for bas reliefs, as you simply build a wall about 2" all around your relief sculpture, spray with release, mix the rubber compound and pour over the sculpture. When it cures you de-mold and you are ready to start casting.
While this mold is the easiest to make, it also requires a huge amount of rubber on a high relief such as this. If the highest point on my sculpt is 2" deep I would need to pour a mold that is about 3" deep. On an 18" x 24" sculpt at 3" deep for rubber - that's a lot of wasted rubber and the costs increase dramatically. True, if you do this pour you're done - no need to make a mother mold as the rubber holds the shape well - but the cost of material can be prohibitive - especially on a smaller run.

The next choice would be a blanket mold and it would work well too - I could have done that for this sculpture. I may do this mold for the next relief.
But I chose to make a brush-on mold. I didn't have Poly Fiber, but I did have Short Stuff, which worked well enough to thicken the rubber. I can see how pouring this rubber in a block or blanket mold would terrifically easy - it is very thin and pourable and absolutely no bubbles. I have tried pouring other rubbers and most had a thicker or gummier feel and had some bubbles which can be a nightmare, making glaring imperfections in your molds and subsequent castings.

I was pretty careful, using my postal meter to accurately measure out the 2 to 1 ratio, but my gut feeling is that this product is probably a little forgiving if you didn't have access to a scale and measured by volume instead, you'd probably have it work out just fine.
The very low viscosity of the 74-20 meant that it was very easy to stir and mix well with no bubbles and it brushed on very easily with a disposable chip brush. This was a plus for me, as the rubber was thin, light with very little weight or drag on the brush so there was no moving or distortion of the softer clay sculpture. For work with hard surfaces thick rubber or heavy -handed application isn't a problem, but for softer clays, the simple act of brushing a rubber on can cause real problems.
The first two coats were applied very thinly to pick up all the detail without disturbing the clay. Subsequent layers were thickened with the Short Stuff. It did take a lot of layers to build up the thickness of the rubber on the high points, as the rubber succumbed to gravity. Perhaps Poly Fiber 2 would have made the rubber thicker than the Short Stuff that I had on hand. I felt that the time between coats was easy to negotiate - not too fast and rushed and not waiting around eons for it to set up enough for the next coat. Overall it was very simple to use - taking 4-5 hours for me to build up the mold with very, very deep undercuts to fill.

When the rubber was cured (overnight) I sprayed it with release and made the mother-mold shell in forton and reinforced with fiberglass. I could have also added leveling legs, but instead opted to rest the open mold on sandbags as I will not be casting solid, but will casting in forton and aqua resin hollow.
Overall I am very pleased with the results. The rubber was thin enough that it brushed easily without squashing my clay and I could see that there were no bubbles. The mold that I pulled off of the clay sculpture is excellent with good stretch and excellent detail - it picked up all the detail and was easy to use.

Review of customer servive: Polytek Mold and Casting

When it comes to materials and service, I always want to hear when someone has a good or bad experience. In this case, I give two thumbs up to Polytek for there wonderful service.

I called them up with a question on one of their materials. I had used their Poly PT Flex 20 rubber for one of my reliefs. The mold process when well, in fact I was very happy at how easy it was to mix and use and how quickly I built up the mold. Peeling back an area once dry, I peeked at the mold and it looked great - really capturing the detail and had a nice give (important with my deep undercuts.) I was pleased and went to make the mother mold shell out of Forton to make it strong and light.

The problem came when I tried to remove the forton shell from the rubber - it had bonded completely - and I do mean COMPLETELY to the rubber.
The whole thing was ruined and a lot of money lost, not to mention the time and the damage done to the original sculpture. I had to repair the sculpture before making a new mold.

It was crunch time for a big show and I was under the gun - so waited until the dust had settled before calling up Polytek to ask them if the product was incompatible with Forton and what I could do to fix the problem, since I still have quite a bit of the product left and don't want to waste all the material not to mention the money.

Here's where the good customer service comes in:

1) A PERSON answered the phone! Not a robo voice and endless loop telling me to punch a number for something - love having live people on the phone!

2) This real live person handed the phone to another real live person who knew the products involved - immediately - no waiting - they walked over and handed the phone to Stan.

3) Stan LISTENED. That's not a small point - let me make this clear, he LISTENED. Then he actually asked questions. We chatted for a bit and he explained that the rubber I used is usually used for casting and not molding. True - it was an unusual choice to use it for casting but I was under a tight deadline and this set up much faster than my other choice. The store I purchased it from knew it was a different use, but that it could work and given my unique situation for time the only choice.

4) We discussed the mold realease the I used (2300....but to be fair I also had 2500 on hand....did I use the wrong one?) Stan said 2300 was preferred but both should have worked like a dream. I freely admit to being in a sleep deprived state working long hours - I could have really messed up the release prior to putting on the forton.

5) Stan didn't say it was my fault. He said it should have worked but that he felt I would like one of their other products better and would I like to try it out? Well, yeah I would! I didn't call to complain, beat anyone up or expect a free sample. I called to find out if I used the product incorrectly and if it would was something I could still use for my needs or was it was waste for what I was trying to do.

6) Stan took my information and offered to send me a sample of the product.

7) I received an email from Stan within hours of our conversation.

8) Four days later this package arrived on my doorstep.

9) The packaged was packed with environmentally friendly peanuts that are food-based and dissolve in water - Yeah!

10) I received a generous sample of their 74-20 molding rubber to try on my new relief that I'll be finishing next week.

Once the relief is finished, I'll photo the entire process of making a mold using this sample of 74-20 and will post it all on my blog.

And that folks, is how a company gives great service.