Smooth Cast Bubbles... What am i doing wrong?

[Radish]

Hi All,

I've noted around the forums and the general internet a lot of talk about bubbles occuring in smooth cast resin - and ways to combat them.

I am using smooth cast 305 in my mold, and i've used mold release, talcum powder, tapping the mold to release air, pouring slowly, mixing with metal stir sticks everything. The talcum powder sure does help to release surface bubbles - when this works it's lovely.

However, it seems like an inexact science, sometimes the molds work, sometime they are an absolute mess! I get surface pimpling (not quite full bubbles but lumpy) and champagne bubbles

I understand it could be humidity, moisture in the air, however if this was the case - wouldn't the small amount of left over resin in my mixing jug also be bubbled up too if this was the case - I have many perfect castings of the bottom of mixing jugs!

What am I missing here - i'm doing something i shouldn't be surely?:facepalm

 

[trooper]

are you degassing the resin? are you pressure casting? what type of molds, are they two pice? more info on your process would be helpful, pics dont hurt

 

[Radish]

I'm not doing any degassing or pressure casting. Some of the molds are one piece some are two piece.

General process goes that I spray on some mold release and wait a while, then dust with talcum powder. Sometimes i try without mold release and use just the talcum powder. The results are variable either way - sometimes it comes out pretty good (with some cleanup required) sometimes it's just awful! I'll try and post pictures....

 

[mslz22]

305 is funky in the humidity if you are not pressure casting it, results will partially vary depending on the humidity and the mass of the casting. The reason that the small amount left in the mixing cup is the low mass is likely allowing more time for the bubbles to work out.

If you can't pressure cast you may want to move to 310, a bit longer cure allows for the bubbles to move out even in a larger mass casting. You can go back to 305 in the cooler months IMO.

 

[trooper]

hmm, if it's an open one piece mold, try doing a sluch cast, then when that kicks fill it. the slush cast will give you the nice detail and it will not have the bubbles.

hope that helps

 

[Don Jarr]

As mentioned you could post some pictures which would also help.

You can also add bubbles pending how you pour. If you pour too slowly and to thin a stream of liquid it tends to create bubbles as it hits the surface of the resin already in the mold. If you're not degassing or pressure casting, remember to always stir with flat spatula and fairly slowly, then holding the spatula close to the inner side of the mould pour the resin onto that oppose to the mould so it runs down which helps eliminate bubbles.

However I have always found the smooth-on resin range to be way too sensitive to humidity, and only use it if I have to, then only pressure casting, and the only one I like is 310 because of its slow cure time. For me there are plenty of other resins on the market especially if you want fast cast that are far more forgiving when working with.

Don

 

[cavx]

So does pressure casting almost guarantee bubble free work? And do you still need to degas?

 

[Radish]

For me there are plenty of other resins on the market especially if you want fast cast that are far more forgiving when working with.

Don

Thanks for the thoughts so far everyone, I'll be giving it another go soon and i will post some pics... I may try the slush casting method also to capture the details

Don, what are the more forgiving resins you would recommend?

 

[exoray]

It's moisture contamination...

You have two choices, get a resin the is more tolerant of moisture or find the source of contamination and rectify it.. If the resin itself is contaminated, you will need to boil it either under vacuum at room temp, or on a hot plate outside to remove any contamination... If it's humidity you need to find a less humid place to cast...

As someone else said I too find most Smooth On resins to be very intolerant to moisture contamination and a little bit makes them go to hell, other brands of resins will tolerate it much better, actually a night and day difference in most cases...

Since you mention it only in the part you are molding, the talc you are using might very well be the source of contamination... Either get new talc or spread your existing talc out over a cookie sheet and bake it at about 200° F (95° C) for about an hour or two... Comb/fluff it with a fork every 15 minutes or so while it bakes so that it dries evenly and doesn't clump...

 

[tsenecal]

do any of you have any specific resin brands you would recommend that are more tolerant of humidity?

 

[exoray]

I personally try to do my casting when it's not humid and I regularly boil my resin to keep it fresh and containment free... So my experiences might not be the same as yours as I tend to not push the issue... But, just the same I have cast parts with Smooth On 300 series on the same day I have cast with other resins and the results were night and day...

My go to resin is AeroMarine AeroMarine Products - Casting Resin he also sells on Ebay, watch the shipping sometimes Ebay is better sometimes the website is better... aeromarineproducts | eBay

I also get a 'house' brand resin from my local supplier that works well but I don't know what brand it actually is, they tap it out of a 55 gallon unmarked drums to order...

 

[NormanF]

The only problem I have had with 300 is either old stuff or I measured wrong and the part will come out soft and flexible. Pretty sure it is me, I was getting both results from the same package.

Sent from my Apple Newton

 

[Ray22]

I stopped using the Smooth cast 300 series about a year ago, and I use Specialty Resins now good stuff I get like 2 gallons for $99 it lasts but I cast alot of stuff. here is their site they sell smaller amounts also and you can find them on Ebay to. www.specialtyresin.com Yeah if you don't mix that 300 stuff equally you'll get the rubber effect.

 

[opal1970]

I get surface pimpling (not quite full bubbles but lumpy) and champagne bubbles

I get this sometimes too, I am fairly certain that this is due to humidity as mentioned. I am not sure if a very warm and otherwise non-humid environment has any adverse effects (other than speeding up the curing process).