Superior & Seattle Railroad Build

[GPdemayo]

So John.....what are you doing when you are resting yourself? 

[S&S RR]

So John.....what are you doing when you are resting yourself? 

Fishing season is about to start.

[S&S RR]

I tried out the Star 30 mold material today that Marty and Tom recommended.  I had 6 molds that I wanted to make so I made up one big batch.  I think you get a better mixture if you make bigger pours.


So I made my pours all with hydrocal master castings. A stone round house casting that I need for a future project. Three of the castings from my C.C. Crow White Stone Church build and the Trains of Texas wall casting that we have been working with. I was very happy with the first 5 molds, even with the problems I had with one of the master castings (see the Church thread for the details). They held the details perfectly and look like the will be very durable. Then I took the box off the T of T casting. The mold looked great until I started to pull it loose from the casting. I had a mess - the rubber never cured. The mold is gooey and has lost most of the detail and the casting has this gooey film on it.

[S&S RR]

Here is a picture showing both the mold and the master casting.

[S&S RR]

At this point I'm going to let them dry overnight and see if I can save the casting.  I have 5 molds so make more castings is not an issue.


I did some research on both the instructions and on the product website and they have multiple warnings that any sulfur in contact with this material will keep it from curing. So some how the T to T casting may have sulphur on it. Or some other chemical that has the same affect. I have made molds from this casting with 4 other mold materials so at this point it could be sulphur but the trial on this casting was a failure.

[S&S RR]

Here is a picture of the instructions with the sulfur warning.  They say that sealing the casting will not help.


Tom, Marty, or anyone else ever run in to this problem.  I really like the molds I got from the other castings and would try this material again.  I just don't know how to tell if I have sulfur in or on the casting without trying it. It may ruin the master casting if you do.


Is there any chemists out there that can give me a way to test for sulfur before I pour a mold?

[martin.ojaste]

John, you are not using sulfur based priducts. If you were the sillycone would not cure.

What I was talking about is coating porous materials like wood, hydrocal, pottery, etc. This sealing process prevents the sillycone from soaking into the material and becoming as one. Also, retains the integrity of the master. If you notice there were blue specs in the hydrocal on the flats. Sealing reduces this effect and helps retain details from the master.

See https://www.smooth-on.com/product-line/superseal/




As for the gooey mold, most likely not mixing completely or inbalance of part A & B.


Also, you get the same effect using contaminated containers on mixer. To test for sulfur get a PH test strips and distilled water and test the dust of the with it. If  acidic it has sulfur.


I find Casting a constant learning experience.LOL

[S&S RR]

John, you are not using sulfur based priducts. If you were the sillycone would not cure.

What I was talking about is coating porous materials like wood, hydrocal, pottery, etc. This sealing process prevents the sillycone from soaking into the material and becoming as one. Also, retains the integrity of the master. If you notice there were blue specs in the hydrocal on the flats. Sealing reduces this effect and helps retain details from the master.

See https://www.smooth-on.com/product-line/superseal/






As for the gooey mold, most likely not mixing completely or inbalance of part A & B.


Also, you get the same effect using contaminated containers on mixer. To test for sulfur get a PH test strips and distilled water and test the dust of the with it. If  acidic it has sulfur.


I find Casting a constant learning experience.LOL

Marty


Thanks for the input - I think this one master casting had something on the surface that is keeping the rubber from curing.  I made 6 molds from this pour and 5 of the six worked great. So I think I had it mixed properly.   It is probably one of those things that I may never run up against again.  I will be buying the Star 30 product again - really like the molds that cured correctly.

[ACL1504]

John,

Yes, I have run into that very problem. I got some RTV from someone, don't remember from whom, but it didn't cure and was tacky.

I notified the supplier and they said it was probably an old mix. They sent new ones and the probelm was solved. I was also informed that the RTV has a shelf life even is never opened. Not sure they list an expiration date on the product label but it wouldn't hurt to check.

My Micro-Mark RTV says, "Best if used by date on container". Problem is there is no date stamped on the container. So, I'm guessing next time I use it, it won't be any good.

Tom

Tom

[S&S RR]

John,

Yes, I have run into that very problem. I got some RTV from someone, don't remember from whom, but it didn't cure and was tacky.

I notified the supplier and they said it was probably an old mix. They sent new ones and the probelm was solved. I was also informed that the RTV has a shelf life even is never opened. Not sure they list an expiration date on the product label but it wouldn't hurt to check.

My Micro-Mark RTV says, "Best if used by date on container". Problem is there is no date stamped on the container. So, I'm guessing next time I use it, it won't be any good.

Tom

Tom

Tom


Thanks for your input.  Non of the containers have a date stamp that I can find. I will never know what happened on this one so it's hard to tell if I will have the problem again.  I need to find a good way to clean up the master casting.

[martin.ojaste]

I have found that the stuff in the bottom of the A and B part container sometines solidifies and is not mixed up into the middle of the containers. A day or two before I use resin or sillycone I lie the container on its side or even upside down to get a proper mix.


Questions;


- The failing mold was it the first or last you poured?
- Did you mix a hold batch fir all the molds at once?
- What was the volume of one if the parts?
- Or did you go by weight?
- did you do a double pour, A in B, then A/B back into cup A?


I have found the tacky happens when one of the parts is not completely muxed, or the temperatures were too low for it to cure. I pre-cure my sillycone molds in the toaster oven for 20-40 minutes at no more than 240 F. Then let them cool fir 24 or more hours. You get less tearing.


Let me try a theory based on doing all the molds from one mix.


- you mix part A in the original container, but do not get the all solids from the bittom
- you repeat with part B but get throughly mixed
- you measure part A into a measuring cup
- you repeat with part B
- you then pour part A into the Part B measuring cup
- you mix the combination up, you think
- since part A is not 100% pure having less hardener ( or is it silicon)
- you pour one mold because the mix at the top of the A/B is in correct proportion
- you continue to pour molds the mix gets better muxed because of the pouring and lifting up and tilting the container
- the last mold fails becasue the ratios change at the bottom if the measuring cup
- then you have an incomplete cure in 24 hours, but might cure in many days/weeks.


Just curious and learning.

[S&S RR]

I have found that the stuff in the bottom of the A and B part container sometines solidifies and is not mixed up into the middle of the containers. A day or two before I use resin or sillycone I lie the container on its side or even upside down to get a proper mix.


Questions;


- The failing mold was it the first or last you poured?
- Did you mix a hold batch fir all the molds at once?
- What was the volume of one if the parts?
- Or did you go by weight?
- did you do a double pour, A in B, then A/B back into cup A?


I have found the tacky happens when one of the parts is not completely muxed, or the temperatures were too low for it to cure. I pre-cure my sillycone molds in the toaster oven for 20-40 minutes at no more than 240 F. Then let them cool fir 24 or more hours. You get less tearing.


Let me try a theory based on doing all the molds from one mix.


- you mix part A in the original container, but do not get the all solids from the bittom
- you repeat with part B but get throughly mixed
- you measure part A into a measuring cup
- you repeat with part B
- you then pour part A into the Part B measuring cup
- you mix the combination up, you think
- since part A is not 100% pure having less hardener ( or is it silicon)
- you pour one mold because the mix at the top of the A/B is in correct proportion
- you continue to pour molds the mix gets better muxed because of the pouring and lifting up and tilting the container
- the last mold fails becasue the ratios change at the bottom if the measuring cup
- then you have an incomplete cure in 24 hours, but might cure in many days/weeks.


Just curious and learning.

Marty


All great questions.  Here is what I did.


1) Added all of the contents of part B into a 16oz cup.
2) Added most of the contents of Part A into a second 16 oz cup until I had the same level of A as I did in the B cup.
3) Poured the contents of the A and B cups into a third big plastic cup.
4) Stirred until I had no streaks and the clear plastic cup showed no sign of A or B colors. 
5) Poured the Trains of Texas wall mold first (it was the biggest and most critical).
6) Continued the pour until I ran out of mold setups. I used most of the batch.
7) I let the molds cure over night.


A few facts:


All of the master castings were hydrocal.


5 of the six were being used for the first time.  The Trains of Texas Casting had been used to make 5 molds previous.


It was the only casting in the batch that didn't cure properly.


My theory is that there was a residue from one of the previous mold  materials that caused a chemical reaction with this mold material.
It was only a thin layer of material next to the master casting that didn't cure.


One of my tasks for tomorrow is to see if I can clean the residue off the Master Casting without damaging it. Right now it still has a sticky residue on it and most of the features are filled with a sticky mess.

[S&S RR]

I sure wish I knew for sure what went wrong, so I would know how not to repeat it.

[martin.ojaste]

John, alcohol, laquer thinner will help as it desolves resin if it hs not been cured. Otherwise, pick and scaping is needed, don't use any water!

[S&S RR]

I found where Micro-Mart puts the shelf life dates on their mold materials.