Beware HOT resin parts attacking styrene parts

[Scott Colmer]

What we have here is a materials learning curve. The valve cover on the right is made from Smooth On resin. I have noticed that the objects made from this material sometimes feel sticky and might be soft. When I packed this project away, I had the cast valve cover in with the styrene parts. I opened the container and found the valve cover stuck to the styrene oil pan and injector hat. Both had softened areas where they came in contact with the resin part. Even left in the open air, they never hardened up again. What you see it the in-progress repair job on both parts. You can see the deep tube on the injector that is grafted in styrene. The pan has its repair piece ready to go. I am going to use another resin for future projects. 

 

Scott

[Can-Con]

Sounds like you didn't get the resin mixed exactly right.

I've been using SmoothOn products for almost 20 years and haven't had a problem with it that I didn't cause myself. ?

[Scott Colmer]

It may be me. I've using the 50/50 mix of resin and catalyst and stirring it slowly for as long as possible before I make the pour. How tight do the measurements need to be? I let it sit on the mold for about 12 hours. That was when the containers were new. 

The containers are about 5-6 years old now. The last items I cast (some cooling fans) never really hardened up. 

 

 

 

 

 

[peteski]

I agree that soft and sticky (uncured) resin is usually caused by not fully mixing the 2 parts or by  the resin being past its expiration date (or both).  5 years is way past the resin's useful life.  I'm surprised that the castings were not full of tiny bubbles.  One of the resin's components absorbs moisture from the air (even if stored in what appears to be sealed container) and that causes those tiny bubbles to form when resin is curing.  You probably live in very dry environment.

[NOBLNG]

1 hour ago, Scott Colmer said:

It may be me. I've using the 50/50 mix of resin and catalyst and stirring it slowly for as long as possible before I make the pour. How tight do the measurements need to be? I let it sit on the mold for about 12 hours. That was when the containers were new. 

The containers are about 5-6 years old now. The last items I cast (some cooling fans) never really hardened up. 

 

 

 

 

 

The product has likely absorbed moisture and gone bad. I had some that was only a year old and was no good. Get some fresh stuff.

[Scott Colmer]

Thanks for the input. Gregg, Peter, and Steve. I'll get some more resin and see how it goes. 

Scott

[restoman]

I live in relatively-humid South Western Ontario, and I've been lucky to get through a batch of Smooth On over the course of a summer without the very-last pieces being a luck-of-the-draw for softness or failure to fully cure.

I did find if I kept the bottles in a Zip-Lock bag with silica desicant packets that it did kind of/sort of help the final few pieces...

I've never trusted un-used resin more than 1 year.

$.02

[Can-Con]

The problem I've had in high humidity is the resin foaming up before it sets. 

[1930fordpickup]

Besides what the other have said, when mixing make sure you wipe the inside of the cup so you don't have unmixed resin leaving the cup. 

[Bugatti Fan]

Strange how some unlike plastics, resins, and so on can react when in contact.

Vinyl kit tyres if left in contact with styrene parts has an adverse chemical reaction. I found out the hard way when I opened a kit after a couple of years storage. I keep both separated now.

Edited January 6, 2023 by Bugatti Fan

[peteski]

Yes, it is the plasticizer in soft vinyl that leaches out and softens polystyrene.  This has been an ongoing problems for certain tires and certain manufacturers for decades.  Placing the tires in a plastic zip-loc bag isolates them from other kit parts.

[Bugatti Fan]

That is why I paint the wheels where the tyres fit eventually to form a barrier. kind of!

[peteski]

10 hours ago, Bugatti Fan said:

That is why I paint the wheels where the tyres fit eventually to form a barrier. kind of!

Often just paint is not enough (in time the plasticizer can soften the paint too, and then get to bare plastic).  Using Bare Matal Foil as a barrier works, as it is real metal and plasticizer will not pass through it.

[Bugatti Fan]

That makes sense Peter.

Foil would make the best barrier as it is metal.

BMF might be a bit expensive used in this way so I might try cutting strips of kitchen foil and using micro sol foil adhesive. It will be a bit thicker than BMF. Should work ok for this application.