I am using Prather Miracle Micro-balloons filler for the first time.

It says it can be mixed with epoxy (I used 5-minute epoxy, what epoxy is best for mixing with the Micro-balloons?) and I will see soon how it sands.

The product says it works best and sands better if mixed with Polyester Resin. What is Polyester Resin and where can I get it?

The product also says it is great at filling all dings, dents and holes. How accurate is this statement? And how heavy is it as a filling compared to regular filler and plasters?

Who has used it and at what results?
Please share your feelings towards this product.

P.S: Is it good at applying the reinforcing tape (fiberglass tape) on the wings?

http://www2.towerhobbies.com/cgi-bin...?&I=LXBH71&P=7

finishing resin.

BTW - easier to sand with more baloons, harder with less.

Where are you using this mix at?

Did I ever suggest that you experiment with new products on scraps? Shouldn't jump into ANY new product/process until you are sure result will be what you are seeking. Good way to create LARGE pieces of scrap.

You can't use epoxy with microballons with fiberglass tape. The Microballoons will keep the epoxy from soaking into the fiberglass.

You could use resin with microballoons to fill dents and dings with, but it's going to be heavy. There are other fillers available that are much lighter.

Using 5 minute epoxy you're going to find that you won't have enough working time to mix the balloons into the epoxy and then apply it to your work area. Use 30-minute (or longer) epoxy.

A quick note about microballoons, you can substitute corn starch for name brand microballoons and get the same results. This helps a lot for those of us without a LHS nearby.

Ken

Mix the balloons THOROUGHLY with the resin ONLY, then after they are thoroughly mixed add the hardener.

I frequently use micro balloons with Bondo for making fillets (cheaper than the SIG epoxy-lite ). I do my initial sanding about 10 minutes after it kicks/solidifies and the final sanding the next day. Sanding the next day takes a little more effort, but 180 - 220 OPEN COAT paper handles it just fine.

Polyester resin is commonly used for auto body and boat work. You can find it at most auto supply stores. Most epoxies mix close to 1 to 1 resin to hardner. Polyester resin is different in that only a few drops of hardner per ounce of resin is used. Polyester resin also produces a lot of vapor and is best done outside or with good ventilation and even a mask. I've not worked with poly resins myself, but have heard that it is easier to sand than epoxy.

Microballoons can be mixed with either, generally for two purposes. One is to make it lighter, the other is to make it easier to sand. I tend to use it where I need a little more durability, such as filling a ding on the trailing edge of a wing, where a softer filler could easily be chipped. Another place is where I need to do some intricate shaping, once again taking advantage of its greater durability over other fillers. I would not recommend it as a general filler on balsa, there are lighter choices.


Scott

In addition to what saramos said about polyester resin, it will also dissolve styrofoam. Epoxy is much more user friendly for a beginner and it doesn't make the whole house smell like a auto body shop.
The catylist for polyester resin contains methyl-ethyl-ketone-peroxide (MEK peroxide), something that you do not want to get in contact with, especially not your eyes.

Got my own opinion about it already. I DO NOT LIKE IT . . . for filling anyway, it will be great at fillets and gaps where you WON'T HAVE TO SAND. I sanded it smooth but then had to fill in uneven spots with patching plaster, so as bruce says - "TEST ON SCRAP WOOD FIRST" [sm=bananahead.gif]

polyesther resins are used on boats, surfboards, automotive etc. epoxy resins are stronger and more flexible and will not attack styrofoam like the poly resins will. epoxies are also used in these same applications, but are generally more expensive, so the poly is used where cost is more important than weight and results. we use the micro-balloons or corofil in some applications doing repairs on full scale aircraft on the composite surfaces. i have also used them doing fiberglass repairs like mentioned above to thicken or lighten resin (epoxy or polyesther) when using it for a filler, but like mentioned it would seem like a rather heavy filler for most rc applications especially where something else would suffice.

For dings and dents in balsa, before you add weight with epoxy and fillers, try raising the grain of the balsa. Its very simple. Heat up your covering iron. Wet the spot where the dent or ding is. Let the water soak in, then place your covering iron over the spot. The heat causes the water to expand to steam, pushing the wood grain out. When it dries in a few seconds, the dent will be nearly, if not completely gone. If there is a tear in the balsa in the dent, raise grain, then use a drop of thin CA to heal the tear (if there is a good fit).

Brad

West Systems Epoxy is my preferred product for glassing, and doing fillet work. West Systems is the primary brand used in boat building and is available in most if not all Boating Supply shops (as well as many places online) I buy mine online at [link=http://www.newportnautical.com/westsystemepoxy.htm]Newport Nautical[/link], their shipping is only $3.95 no matter how much you purchase.

When you are using micro balloons, you want to mix it up to the consitancy of thick peanut butter. This not only keeps the epoxy from running, but it also makes the final product light and easier to sand. When you apply the mixture, tape off surrounding areas to keep excess epoxy from area that it's not needed so that it wont need to be sanded away later. Smooth it out best you can, but as it starts setting, the exothermic reaction will cause it to soften slightly and smooth out even more. For doing fillets, I like to use a syringe to make application easier and neater.

I have found that if the micro-baloons are a dark color when mixed then when you cover the airframe the dark color will show thru the covering. I use balsa colored fillers to minimise the color showing thru.

There are two types of microballoon, polyester (brown in color) and glass (white in color). Either work well if properly mixed and sand quite easily (if properly mixed). What is proper mix? Use a slow epoxy, at least 30 minute or more. First completely mix the epoxy component parts well then start adding the microballoons. Keep adding and mixing until you have a paste very similar in viscosity to thick peanut butter. Apply with suitable tool then, use your finger (best if wearing a rubber glove) dipped in alcohol and smooth out any imperfections in the surface. Let cure at least 4 hours before sanding.

The glass (white in color) stuff is Colloidal Silica and is used for strengthening the epoxy joints.

Rodney does bring up an important point when working with Epoxy resins. You should always wear gloves so that your skin doesn't come into contact with the resin. Constant exposure to epoxy resins can cause severe allergies. So much to the point that you couldn't even be in the same room as an open container of resin.

Hi!
Polyester resin and brown microballoons (plastic) are best for filling dents and holes on our airplanes and boats. White microballoons are made of glass and are harder to sand.

The soft, light hobby filler you can get at hobby shops is no good as thse are very easy to sand but will leave a soft surface which is no good for if you want a nice surface on which to put automobile primer and put on a high gloss paint on.

You should never use 5min or any other glue epoxy when using microballoons as the mix will be very hard to sand. Using polyester resin and brown microballoons is very easy to sand and you see the difference in surface structure where you have sand and where you have not.

Even better than polyester resin is to use 24 hour mold making /finnishing epoxy resin. Not the hobby stuff variety, West system has a rather good product but there are much better (harder more easy to sand) finnishing resins on the professional market.

For a smooth finish when using microballoons and epoxy, use a piece of wax paper over the repair area. Use a credit card or other plastic implement to smooth it out and feather the edge. When the epoxy has cured, the wax paper peels right off, leaving a nice smooth repair requiring little, if any, sanding.

Brad

Colloidal Silica and white glass microballoons are two different products and produce different effecs when mixed with epoxy.

Scott

What exactly is the procedure for mixing the epoxy with corn starch, and how much corn starch should be used?

The reason I ask is I'm building a 100" sailplane (Skybench Oly II) which has a two piece wing. The wing joiner box which contains the wing joiner rod and brass tubes needs to filled in with epoxy. If I can substitute corn starch for microballoons (which I don't have) in the epoxy mixture, that would be great.

Coastie

The same as the others have said for using microballoons. Mix it in until it's the consistency of thick peanut butter.

Ken

Just as a note, the fumes of SOME of these resins can be quite harmful. Please use adequate ventilation/protection. Read the MSDS Material Safety Data Sheets for the products if available. Request them from your supplier or find them online.