First casting, now questions... (long)

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SuperDave

SuperDave

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Joined
Jun 15, 2007
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682
Location
Sherwood, Oregon - 97140, USA.
I have three different resins that I am experimenting with to see what the good and bad points are.

I have tried two so far (using silicone moulds), with mixed results.

Max CLR:
1. mixes well with coloring agents.
2. 2:1 ratio with a 45-50 minute pot life. Need to stay on top of it around the 35-40 minute time lapse because it flashes in a hurry.
3. Easy to blend colors.
4. Lower shrinkage factor.
5. Turns, cuts and trims very easily.
6. Sands well.
7. Gloss could be better but that might be from my choice of coloring agents being too opaque. Has a higher shine than Alumilite but not the same as PR.

Mr. Fiberglass Polyester Resin
1. Mixes well with coloring agents.
2. Used 10 drops per ounce of MEK per recommendations but never did get it to start gelling.
3. Poured into two different moulds; both with WW in them. One I placed in a Pressure Pot at 80psi and the other I left out.
4. The one I left out of the Pressure Pot, eventually sat up over many hours time.
5. The one I placed inside the Pressure Pot at 80psi, never did set up or gel, so I removed it and left it on the workbench overnight and it was about 80% solidified by 10:00 a.m. next morning.
6. The shrinkage factor on the PR was at least 25% and the PR even pulled away from the WW pieces due to the shringage... I think.
7. I doubt that any of the four PR blanks will be turnable, mainly because of the shrinkage and separation from the WW.

Questions from those that are experienced in casting:

1. I know there are many opinions on "how many drops of MEK per ounce" but I know that 10 drops should have been more than ample in most of the cases. Since it didn't even start to flash over for several hours, I would like to know how long before your PR flashes and you can start to pour your blends.

2. What is your shrink % when you cast? Do you have to use much larger moulds to allow for this?

3. Those that cast WW and PR, do you have your PR pulling away from your WW? If not, any thoughts as to why mine is not bonding?

Thanks, this will be an interesting learning curve...

Dave
 
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1. I know there are many opinions on "how many drops of MEK per ounce" but I know that 10 drops should have been more than ample in most of the cases. Since it didn't even start to flash over for several hours, I would like to know how long before your PR flashes and you can start to pour your blends.


SuperDave, I'm new to this also, but, it is my understanding that PR is effected by both the ambient temp and humidity at time of casting...therefore, how can anyone accurately tell you how long before yours, or mine, should be gelling? For reference, I'm using PR from Artstuf and I'm putting 4-5 drops per oz of MEK and getting gelling in anything from 3 hours to 45 minutes...closely related to the temp and humidity we have been experiencing here.

I'm looking to purchase some gel promoter as mentioned in another thread, hoping to have a little more control on timing.

Doug
 
I made some snake skin blanks today. My shop has AC and it was set to 80. I used 3 drops per ounce in each of two jars with 8 oz each....24 drops in each jar. After stirring well, I let it set for 5 minutes before pouring in into the molds and the second jar was already jelled...too tick to pour. I waited too long. I don't usually have this problem. Into the pressure pot for two hours with the one mold and it came out hard. This works for me every time. Something is not right....old PR...bad MEKP. You said MEK, did you really mean MEKP? There is a difference. Are you stirring it in really well?

I use PR from mrfiberglass and have no problems with it.
Do a good turn daily!
Don

Originally posted by jdoug5170

[blue]1. I know there are many opinions on "how many drops of MEK per ounce" but I know that 10 drops should have been more than ample in most of the cases. Since it didn't even start to flash over for several hours, I would like to know how long before your PR flashes and you can start to pour your blends.
Click to expand...
 
10 drops is a lot of catalyst. I have noticed that when I used a larger amount of catalyst on some casts, it caused the PR to lift and cause air pockets between the PR and the medium it was filling. I think this is because of the heat involved.
Also, when my shop is cooler, (under 65F, give or take) I have found it can take considerably longer for the PR to gel.
I have only had PR pull away from wood in a couple of instances, one was a double cast, not WW. The only problem I experienced with WW was because I didn't clean the really punky wood out before I cast it. This created a situation were the PR wouldn't bond well and when I tried to turn it, the PR blew off the punky wood areas.
Obviously, be sure the wood is clean and dry. No chemicals.
I may get persecuted for this, but try lowering your MEKP and be patient while it sets up.
And of course, liquid colorants slow cure times.
Hope this helps.
 
SuperDave, I'm new to this also, but, it is my understanding that PR is effected by both the ambient temp and humidity at time of casting...therefore, how can anyone accurately tell you how long before yours, or mine, should be gelling? For reference, I'm using PR from Artstuf and I'm putting 4-5 drops per oz of MEK and getting gelling in anything from 3 hours to 45 minutes...closely related to the temp and humidity we have been experiencing here.

I'm looking to purchase some gel promoter as mentioned in another thread, hoping to have a little more control on timing.

Doug
Click to expand...

Thanks Doug,

I realize no one can tell me what times I should be getting. I was asking what other casters are getting, time wise, so I can estimate for myself what I should/could expect.

My ambient temps were mid-high 70's and low humidity. Each pour was 3 ounces with 30 drops of MEK in each. After more than 60 minutes without any hint of gelling, I poured and waited. They eventually gelled about 18-24 hours later, but the PR shrank from about 1" thick, to just over 1/2" and pulled away from the WW (which was extremely dry hazelnut root burl).

The PP seemed to delay the cure, because it was still liquid when removed and gelled over night after I took it out... still can't figure that one out...
 
Originally posted by its_virgil

I made some snake skin blanks today. My shop has AC and it was set to 80. I used 3 drops per ounce in each of two jars with 8 oz each....24 drops in each jar. After stirring well, I let it set for 5 minutes before pouring in into the molds and the second jar was already jelled...too tick to pour. I waited too long. I don't usually have this problem. Into the pressure pot for two hours with the one mold and it came out hard. This works for me every time. Something is not right....old PR...bad MEKP. You said MEK, did you really mean MEKP? There is a difference. Are you stirring it in really well?

I use PR from mrfiberglass and have no problems with it.
Do a good turn daily!
Don
Click to expand...

Don, thanks.

It was (MEKP - MEK whatever was sent with the Mr. Fiberglass PR... which is about 9 months old... because of countless delays...;)

Temps were low-mid 70's. I stirred all three cups many times over a 60 minute period.

I'm thinking the PR might be getting long in the tooth... but it was sealed well, didn't look bad and poured well...

Think I will try a plain Jane cast next and see how it work out...

Thanks again,

Dave
 
Originally posted by stevers


I may get persecuted for this, but try lowering your MEKP and be patient while it sets up.
And of course, liquid colorants slow cure times.
Hope this helps.
Click to expand...

Steve,

You just reminded me about the liquid colorants... I was using some of the liquid colors from Mr. Fiberglass... I also mixed in some of the Mica Powders...

I was also wondering if the PR pulled away from the WW because of too much MEKP which may have caused the excessive shrinkage...

Will take some pictures and post here to show what I ended up with...
 
Dave, just to be on the safe side, which Poly Resin are you working with from Mr. Fibergalss? We are assuming it's Silmar 41, but if that's not the case, then that in and of itself may be the problem.
 
Originally posted by Russianwolf

Dave, just to be on the safe side, which Poly Resin are you working with from Mr. Fibergalss? We are assuming it's Silmar 41, but if that's not the case, then that in and of itself may be the problem.
Click to expand...

Hey Mike... yeah, it's the Silmar 41.

Here is what Dave's web site says about the MEKP:

"MEKP Curing Agent
Used at a rate of 1-2 % of resin. Shelf Life: Because of the limited shelf life of MEKP, it is recommended that only enough be ordered for 2 months use."

So, I think my MEKP is slow because it's too old... I'm going to bring some home from the sign shop or get some from Michaels to test with the next batch...

but that doesn't help with the shrink rate...

Here is a photo of what I am talking about:

I actually over-filled the mold and notice the significant shrinkage from 7/8" thick to this... (what this photo doesn't show is a nearly 1/6+" gap around the WW perimeter... I can probably trim it up and get a Slimline+ blank out of it... but I don't turm Slimlines...

2008782412_WW%20Cast%20Shrink.jpg
 
Because I use only 3 drops of MEKP per ounce, I have several containers of MEKP in the shop. I never use all of a container with my gallons of PR. Most have been opened and I just grab the first I see. I'm sure the MEKP I used yesterday was well over a year old. I've been using another brand of PR for the last year and the MEKP comes in a different container than mrfiberglass's. The MEKP I used yesteday was some from mrfiberglass...and it was a year old or longer. I'm just offering information and not doubting any claim about MEKP getting old. I've been told that also by every supplier I've used.

Last month I made some casting from some PR that was well over a year old and it was the last 3 inches in a 5 gallon can. It worked great and I've been told by one manufacturer that PR has a life of 6 months from the date of manufacture.
Do a good turn daily!
Don
 
Originally posted by stevers

Are we sure the resin didn't just absorb into the punky, rotten wood???
Click to expand...

Well, it was extremely dry, but was a root burl and not in the pressure pot, so it must have used a straw!

... guess it's time to cut 'er up and see! If it did, then that wood is as stabilized as it will ever get... without any vacuum or pressure...[:p] stay tuned for the results from cutting it into something resembling a pen blank.
 
Don,

Thanks for the info.... it's helpful and confirming...

I agree that the PR is not my issue, based on what I saw when I opened the can. Hard to tell about the MEKP... so by using another batch of MEKP with the same PR, I might get different results...
 
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