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Discussion Starter · #1 ·
Hi fella's,

I have some resin from micromark. I think I have only ever casted about four bodyshells that have come out really well. In order for me to get a good one I have to do about 6 castings. The issue is my resin tends to dry with bubbles in it, but It does not do it everytime. I'm mixing using a plastic measuring cup and a wooden spatular. Am I stiring too fast therefore making too many bubbles or do I just fold the liquid over. I'm stumped as it seems to get the bubbles during the curing process. Any advice, much appreciated.

Barrie
 

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Senior Slot Car Mechanic
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Bubbles forming after you pour, is almost ALWAYS moisture contamination.

Using a wooden stirring implement could be the culprit, as, wood does contain some moisture.

And, you MUST always stir, mix, shake each of the components even before you mix them together. Failure to do this, doesn't normally form bubbles when curing, but, will leave the resin weeping and crumbly, along with many other assorted problems.
 

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Hi Barrie, are you slush casting or are you using two part moulds?

A good way to ensure there are no bubbles on the surface of your casting is to pour a small amount of resin into your mould and then using a paint brush of appropriate size paint the inside of your mould with the resin ensuring all the bubbles are removed from the surface of your mould, once that has hardened then you can slush in the next layers until you've reached you desired thickness.

Here's a couple of pics...





 

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Discussion Starter · #6 ·
Thanks guys for the tips. I will try the paint a layer first, thats a good idea. I have also noticed that my resin casts dry white, the ones done on here are all yellowy colour. Is this just the type or brand of my resin. Reading some of the replies and looking at some of my castings, I have noticed that some are a little crumbly, these have been the bad ones and been discarded. One thing I have not been doing though is shaking the bottles before I mix, I thought this may increase the oxygen content and make the bubbles worse.
 

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QUOTE I'm stumped as it seems to get the bubbles during the curing process
All the brushing in the world won't help, as, the bubbles are forming AFTER the pour while the resin is curing.

Sounds like you have your answer. You absolutely MUST THOROUGHLY mix each bottle even before you mix them together. Failure to do this will give you all kinds of grief.

And, yes, resin does come in Beige or White. Maybe other colors, but, those are the two I have seen/used.
 

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mac pinches
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Hi Rayden.
these bubbles are a very common problem with home castings.
Here are a few tips to help you get a good final casting.
first, get the mix right, most resins are a 10 to 1 mix ratio.
An easy way of mixing is to take a straight sided container, add
an amount of resin, then vertically push a wooden probe into the
resin, mark the probe at the point the resin reaches, measure
the amount of resin on the probe, divide by a factor of 10, this
will indicate the amount of hardener required = ie
resin depth=5 cm, hardener required = .5 cm.
---------------------------------------------------------------------------
Mixing !!!! this is the point where most of the bubbles come from.
DO NOT whisk the mix as you would when beating egg,s, this just
produces bubbles by the boat load !!
If you can imagine you have a plate that just fits into the top of your
container, in the center of this plate there is a hole just big enough
to take a mixing stick, with a circular motion revolve the stick but
ensuring the stick stays in the imaginary center hole, in this way
the mix is agitated but bubbles are not produced.
It sounds a little complex but with a little practice it works well.
---------------------------------------------------------------------------
Poring.
With most resin mixes it takes 24 hours to go off.
once you have your mix ready, let it stand for a while, allowing any
bubbles to make there way to the surface
DO NOT pore the mix directly onto the model being cast.
tilt the casting box approx 20 degrees, pick a corner into which you pour
the mix, at this point take your time, let the mix run into the casting box
in a thin stream this allows any remaining bubbles to burst.
As the mix slowly creeps up the sides of the model, it pushes any remaining
bubble to the surface.
As the casting box fills lower it into the horizontal position and you should
produce a bubble free casting.
A lot of words but once you get the hang of it you should have good casting.
i have used these methods on many hundreds of casting and had very good
results
Hope this helps a little.
Cheers
Mac P
 

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Discussion Starter · #9 ·
Thanks guys, it seems so simple when you explain it. Mac, as I was reading your steps I was thinking, I dont do that and I dont do that. Lots of things to practice now. My resin is a fast cure, its rock hard in 40 mins, so I have been rushing the process, I think this is adding to my problems. Thanks for all your advice guys, always good to ask those who do it regularly.
 

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mac pinches
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Hi datto, i was talking silicone rubber and the making of bubble free moulds
If the method put forward by MAF to cast the finished shell is followed
you should get a good product
Cheers
Mac
 

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Phil Kalbfell
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Rayden how old is the resin you are using,has it been sitting part used for some months?
Some brands of resin will " go off" once opened, and need to be used with a couple of months. Check the specs on the resin you are using.
 

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Discussion Starter · #13 ·
Hi Phil, my word, can't believe the great Phil Kalbfell is answering my post, you are a god my friend. I have watched your work with amazement over the years. Actually it was you, swissracer and howmettx that got me into this casting thing.

Anyway, my resin is getting on a bit now. Its probably 18 months old, however it has been producing these results since i bought it. Like you I thought it was age, then I would say one last cast and i'll chuck it, but then it would produce a perfect cast. I bought in bulk i.e. a gallon of each, so I do have a fair bit left and was reluctant to ditch it. I'm gonna try the method mac p suggested and see what the results come out like. If I still get similar issues, then i'll buy a new batch, but its probably just me and more practice.
 

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I think your problem is definately the age issue. I normally find however that the resin I use for prototyping starts to crystalise in the bottles after a while so I end up with lumps in the liquid. Maybe buying it in such large quantities isn't the best idea. Like most casting products it does have a finite shelf life.

Graham.
 

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Discussion Starter · #15 ·
Yeh Graham, I do have some small build up at the bottom of the container. I think its time to buy some more in smaller quantities, however I still think it was my mixing process that gave me similar results when I got the stuff new. If the resin has a limited shelf life, I may aswell practice with some new stuff and make several shells from the mould until i'm happy with the mixing process, extra body shells is better than dumped resin.

Barrie
 

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H Guys,

I'm new to sratch building what resin do I need and where can I get it? Also what is the mould made of and is there a handy book that gives some guidance?

Sorry for all the questions but hope someome can help.

Alfie.
 

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QUOTE (MAF @ 20 Oct 2011, 10:46) <{POST_SNAPBACK}>Hi Barrie, are you slush casting or are you using two part moulds?

A good way to ensure there are no bubbles on the surface of your casting is to pour a small amount of resin into your mould and then using a paint brush of appropriate size paint the inside of your mould with the resin ensuring all the bubbles are removed from the surface of your mould, once that has hardened then you can slush in the next layers until you've reached you desired thickness.

Here's a couple of pics...






That car is stunning, what is it?
 

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Hi Wraith see here. The moulds were sold to OCAR and I think are available from them or Pendles now.

Alfie, the link above shows the materials I use too.
 

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Discussion Starter · #20 ·
Hey MAF, I like the way you use the lego, thats a cool idea. I always end up looking for small boxes that have to be taped. I will raid the kids lego from now on.

Barrie
 
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