Does a fast drying and easy to sand filler exist that adheres to epoxy?

as par said it is to do with their make up. Glass bubbles won't absorb water, broken or whole. The phenolic bubbles will absorb water. Broken ie sanded they absorb more (greater surface area etc). This absorbed water will then start to break down the polymer sphere at worse and at least will start to break adhesion between the resin and the sphere. Left long enough immersed you can get a) osmosis ie blisters b) a friable mush that will break/split.

Another problem is that the phenolic spheres are also more sensitive to solvent absorption from paint on top. Take care with film thicknesses. dry times when painting.

Adding silica makes fillers hard to sand. Use the minimum you can get away with. Silica is in effect glass.

The benefit of bubbles over talc is that you will need less resin for volume and also it will be runnier/easier to use. The down sides are mentioned.

Mix your own is fine, just be very careful with mixing. Bear in mind extra time you lose in mixing. I know people who use old dough mixers for bigger batches.

 

But I thought microballoons with resin would be less runny than talc with resin??

 

Are you saying that Qcells don't run as much as microballoons?

 

That does seem to be what he is saying, and I can't say I disagree, but of course the amount you add to the resin has a big input into how it behaves. Some say q-cell is not the best for getting a slick surface as a paint substrate, you might need an extra undercoat.

 

Exactly, use micro's for the mix and just enough qcell to stop the slump. Excessive Qcell is a ***** to sand.
Talc in resin is a polyester thing, heavy and brittle but cheap, also no fun to sand when cured up, and water absorbent.

 

Talc is a common material in premixed epoxy oriented filler products. Of course, it has it's good and bad things to consider, which is why each mixture should be tailored for the job. The biggest mistake most make, is to try to use way too much of one material, for one of a few reasons, often thinking they're saving money. A straight up balloon mix is just poor understanding of the materials, ditto a pure silica mix, etc. Using a bulking agent as viscosity control is equally lacking understanding. I know builders that do all of these things. It's all about knowing the physical characteristics of the materials, when used as fillers. Most basic formulations for home made filler, are available at the usual sources and some experimenting and experience will get you filler concoctions that work, reliably and repeatably.

 

Not to beat a dead horse, but I am trying to visualize the mechanism by which the osmosis effect will take place with the phenolic spheres. I thought that the spheres were encapsulated within the epoxy thus stopping absorption at the level of the individual sphere.

PAR, could you explain how the moisture travels through the cured resin to the next sphere? I don't doubt that it does just as you all say, just trying to figure out how.... It appears to contradict what I thought I knew about epoxies and water vapor permeability. I just cannot see how the water makes the jump from sphere to sphere to create a mush so I am obviously missing something conceptually. Help!

 

Talc is hard to sand when cured? Huh?! But I thought the only reason for using talc was because its supposed to make sanding easier?? What am I missing here?

 

This can get real complicated real quick, but . . . Epoxy isn't 100% waterproof, though it's close, so close in fact, that wood can be stabilized and other materials effectively locked down. This said, on moored or berthed craft, eventually some absorption does occur. Because of material/substrate absorption and the density of the molecules in the cured matrix, epoxy is said to be waterproof on most materials.

It boils down to a few different factors, all quite small (molecular level). Simply put, the epoxy molecule is pretty big, but tightly arranged in a cured matrix, which gives it it's waterproof qualities, but there are gaps in the lattice like structure, once the molecules reorganize with the cure. When the goo is applied to a porous substrate, it will allow a few percent of moisture (vapor) to accumulate, within the matrix, possibly also transferring to the substrate as well.

This sounds scary, but it's not as bad as it sounds, mostly because the vapor pressure isn't enough to penetrate further, which maintains the gain issue at a specific level. This is why you can use 12% moisture content wood, knowing it'll pickup a couple of percent in moisture, but still remain below the threshold of rot, mold, etc., that can cause issues in dimensional instability and deterioration. The same also applies to filler materials, though to a lesser degree, depending on the molecular pressure and size of the material used. Some materials, like talc will suck up goo, making for a heavy filler, while others, like spheres don't, but because of their shape permit a higher resin to particulate ratio (making it heavy and/or brittle).

If you use a porous filler, you can expect some weight gain and if it's a fairly big particulate or molecule also some gaps in the lattice, as it remains in suspension within the cured epoxy matrix. This can let moisture vapor penetrate the substrate, it's applied to. More scary stuff, right. Well, not really. If proper laminating procedures are employed, the substrate has been previously sealed, so any mitigating moisture, is prevented from crossing the previously seal surface barrier. For example a surface coating, like a fairing compound, in itself can gain some weight and also let in moisture, but if the surface is properly prepped, only just this usually thin surface coating picks up the weight and moisture. This accounts to ounces, in the typical applications of a fairing filler. Now, a big boat, with very unfair surfaces might pick up pounds, but this can be accounted for, by the number of gallons of filler you employ and offset to a degree, by the filler material mixture you use.

This is why you need to develop "mixtures". A pure talc mix will be heavy, can absorb a small amount of moisture and can difficult to sand (high resin content). The same is true of other materials, so striking a balance of filler materials in a specific mixture is key to application ease, durability and appropriateness.

Most of my filler and fillet mixes have at least 3 different materials in them. Silica is a viscosity control agent, so there's varying amounts, that are application dependent, but in total, even with a very stiff mix, a small percentage of the filler content. This makes it easier to work and the other materials are used for their physical attributes. On fairing compounds you'll want some talc, some spheres and possibly other things, to change, improve and control the mix for the application. Some research into fillers will provide a bit of confusion, but also alternatives, such as: pulverized or decomposed stone, lighter specific density spheres (even some super lights), spheres of different materials (use plastic, it's safer), polyethylene micro fibers, instead of silica you might try paper micro fibers, etc.

Which mixtures will work for you is application and experiment dependent. You have to test some stuff and mixtures. It would be nice if one mixture could solve all ills, but there's no such beast. Years ago I developed a set of mixtures and I've stuck to them, mostly because I know from my testing they work for their intended application. This sounds like a lot of trouble and it is for a one off builder, looking for a good fillet mix, so don't pother, just use the major formulator's recommendations or premixes. On the other hand, if you're building regularly, you need to know what each mix will do, so glue up some scraps and setup a destruction test.

 

Maybe I missed it but does talc make sanding epoxy easier or not?

 

Yes, but if you use too much talc, the resin/material ratio will be high enough to make you cuss. The same is true of most anything you put in epoxy, which is why multiple materials are used in most filler/fillet mixes. Talc really just makes the mixture smoother, so when making fillets they aren't lumpy or if in a fairing compound, it doesn't "drag" as you spread it. Talc isn't a bulking agent, like balloons, it just smooths the the mixture, for easier application, which is why you don't need that much.

A classic example of this, is the difference between wood flour and wood dust, collected from a orbital sander. There's a night and day difference if seen and used side by side. The flour particulates are much finer, so the texture is fairly smooth, especially compared to the huge particles that come out of a sander.

 

Yikes! Paint chemistry.

As stated, what seems "cooking" is actually science. And this is before technology gets involved.

PAR pretty much gets the basics across.

I am sure the West Systems site has a good intro to it all. The SP...er what are they called now? Gurit, has a good site as well. They used to have suggested mix ratios to give varying fillers. Also by weight to give you a volume. It throws most people that 1litre resin and 1 litre bubbles or talc does not give you 2litre filler.

It is a bit of experience. Every resin has different characteristics with regards to how the filler will flow/ sand. And every bubble type is different...and every talc.

Just play around with variations and you will get feel.

One point to remember/not forget! - keep an eye on humidity and temp during cure. Cool and damp is killer for sandability. It will create a sticky sweat on filler that will clog your paper and make it seem difficult to sand. Sometimes it will only be a layer enough to clog paper and underneath is fine and crisp but the toplayer removal will drive you crazy. And be expensive in paper.

Which leads on to paper types. Some papers cut better than others. You pay money and take choice. 3m green paper type 245 is good. Fave of most dutch painters. Expensive but cuts as long as can be expected. Use mechanical sanders with vacuum. It will sand way better.

You would not believe how much research goes into the ready made fillers from Awlgrip, International and Alexseal. Just to give you idea, they are made under vacuum so as to minimise air entrapment and give consistent 1/1 volume mix. They test the life out of it. As you can imagine it is big risk when you are applying x0 000litres on one yacht.

 

"Microspheres" of varying diameters to suit particular needs - glass balls - also to make road markers highly reflective... I got mine from ATL Composites on the Gold Coast, Australia 3 to 4 years ago when I was building my boat.

 

Absolutely fantastic! There is so much info and experience packed in these paragraphs. There should be some way of flagging responses such as these, in order to direct the inevitable questions that will come later.
I swear this site has more great information packed in it but it is so disorganized and mixed with garbage that it is difficult for the beginner to make his way through.

 

ok I have to ask par.....on poly people have a cow over body filler used on boats....most body filler is spheres and talc for filler....why is it absorb more water than if I blend my own. what about the finishing puttys for sand scratches and pin holes. I do bodywork by trade, what fairing compounds do you recommend? I found out as far as glass goes lol.....I was doing it wrong.....so all learned on stringers and transom repair....