Questions about thinning resin.

[Mark42]

Been having good results casting emblems from my latest set of molds using fiberglass resin with aluminum powder mixed in for color. But I still get the occasional air bubble in some of the finer ridges of the mold. <br /><br />The resin pours in like honey, but I want it to pour like cheap maple syrup at room temp. I am thinking that thinning the resin will make it flow into the mold better and let small air bubbles escape easier. What affect does thinning the resin have when it's hard? Does it shrink more? Take longer to harden?<br /><br />I suspect that strength may be compromised, but the emblems I am making are not structural parts and only need to survive the occasional hull scrubbing.<br /><br />I'm using polyester resin, so I think acetone or styrene is what I should be using, right?<br /><br />Any thoughts? <br /><br />Thanks,<br /><br />Mark.

 

[BillP]

Re: Questions about thinning resin.

Thinner resin definitely lets suspended air bubbles escape better. When I used thick casting resin you could watch a bubble take all day to make it to the surface...then I would pop it with a toothpick...it wouldn't pop by itself. With thinner resins you don't see this happening.<br /><br />Are your bubbles getting trapped in corners or are they suspended? If trapped in a corner I don't think thinning will help as much. If suspended, either acetone or styrene probably work equal. Styrene gives superior bonding and you aren't concerned with tenacity here. <br /><br />Thoughts to ponder...I suppose you get less shrinkage with styrene because it doesn't evaporate out but is that shrinkage even measurable? Will evaporating acetone pull bubbles with it or make bubbles more likely?

 

[Mark42]

Re: Questions about thinning resin.

Bill,<br /><br />The bubbles are trapped in a fine groove. I don't have problems with any bubbles on the flat surfaces. I try to let the bubbles rise out of the resin before adding the hardner because I only have a couple minutes to work with it before it gets too thick to flow into the mold.<br /><br />I think the bubbles I get are from the resin not flowing into the little grooves of the mold, not from suspended bubbles in the resin prior to pouring.<br /><br />Any suggestions on how much thiner to use? How much should I start thining, 5%, 10%, 30%? I only mix 2 ounces at a time, so I'm thinking I should be counting droplets when adding thinner. Maybe 10 drops to 2 oz to start? <br /><br />Thanks,<br />Mark.

 

[Clamboni]

Re: Questions about thinning resin.

Mark, just a suggestion. If you're worried about shrinkage and strength, it might be a good idea to use a toothpick to force a small amount of resin into the grooves before you pour the resin. that way you know you'll have resin fully filling the grooves and no air between the grooves. How much alum. powder are you using? are the emblems still translucent? If you can't see into the emblems then it won't matter if there's small bubbles as long as they're inside. I have never tried to make molds with resin but it sounds like it makes sense to me.<br /><br /><br />hey by the way, the part with cows and horses? I'm guessing southern, where in jersey are you?<br />cinnaminson, burlington county here

 

[Mark42]

Re: Questions about thinning resin.

Clamboni,<br /><br /><br />I put about a 1/2 table spoon full of aluminum powder in 2 oz resin. It is not transparent at all. But you have a good idea about filling the groved parts before pouring the rest.<br /><br />This is what one looks like now, there were bubbles that left voids on the left side raised ridge under the "M". The problem is whith the raised outline of the shark, the "swish" behind it and the left and right corners.<br /><br />The letters MFG come out ok. The dimples in the letters are from pitting in the original I took a mold from.<br /><br />

<br /><br />This piece is about 9" long.<br /><br />I'm from Warren County, about 20 miles from the Deleware Water Gap.<br /><br />Edit:<br /><br />BTW, the reason I am making these is because my boat is missing them. A nice fellow boater loaned me one of his to make the mold from. So this spring, I will have two nice emblems to mount on my boat!

 

[lawyertob]

Re: Questions about thinning resin.

Originally posted by Mark42:<br /> This is what one looks like now, there were bubbles that left voids on the left side raised ridge under the "M". The problem is whith the raised outline of the shark, the "swish" behind it and the left and right corners.<br /><br />The letters MFG come out ok. The dimples in the letters are from pitting in the original I took a mold from.<br />BTW, the reason I am making these is because my boat is missing them. A nice fellow boater loaned me one of his to make the mold from. So this spring, I will have two nice emblems to mount on my boat!

Mark,<br /><br />I am still impressed! One suggestion, maybe at this point you could take one of your castings and smooth out all the pitting and other imperfections, then make a new mold. That way you can have perfect emblems when you are done.<br /><br />Okay, just thought of one more. Maybe after you thinned your resins, you could set the whole mold on top of something that would vibrate it as it settles (you could use something like a back massager to vibrate a table top for instance). Between this and painting in the hard parts first, you should be able to get them just right.<br /><br />Just my $0.02 worth,<br />Joe

 

[BillP]

Re: Questions about thinning resin.

Wow, that already looks excellent to me like it is. It sounds like you are mixing resin while in the mold? Stirring may be generating the bubbles. If you try thinning...10% will make a big change. You can mix it without hardner and see the viscosity. If too thin let it sit and the acetone will evap out. <br /><br />Can you post a pic of the mold where you pour in?

 

[Mark42]

Re: Questions about thinning resin.

Hi Bill,<br /><br />I mix the aluminum powder into the resin in a paper cup, then I add the hardener and mix more. Then I pour straight into the mold (polyurathane rubber) with no release agent because the resin doesn't stick to the mold at all.<br /><br />I'll try to get some pics of the mold and mold materials sometime next week after Christmas.<br /><br />Thanks for the tips on using acitone.<br /><br />Have a Very Merry Christmas!<br /><br />Mark