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

Bondo is now a word much like Kleenex, even though there are several brands and subtypes within each. The Bondo we most know is mostly talc and resin. Because of this, it's heavy and can absorb an unnecessary amount of moisture. It's density and general lack of good adhesion on most substrates, means it'll "circle" out of dents, screw head coverings, etc., particularly if much vibration or flexing is going to occur. This said, there are better "Bondos", some with better adhesion, some 'glass fibers, some have metals, etc. These are generally reserved for the pro's doing body work on a car and they don't use much of it.

Glazing compound is very similar to Bondo, except it uses much smaller particulates, so it's effective on pin holes and very fine scratches (all it's really good for really). Glazing compound is used to fine tune a Bondo'd surface. Again, these polyester products are mostly automotive use, as the resin system tends to permit moisture vapor transmission, which isn't what you want on a boat.

If you make your own poly blend of filler, you'll have the same issues as the Bondo's. It's the resin system weaknesses and material choices used.

Epoxy is a different animal, as it's not going to have the moisture vapor issue and it's bond strength is significantly higher. You can still have a crappy fairing compound, if you use too much or too little of each material in the mixture, but you do eliminate the resin system and moisture vapor transfer issues.

System Three's "Quick Fair" works well, or you can play with 407 and 410 from West System. I'm pretty sure there are other "pre-mixes" around, I just don't use them. If you do body work (automotive) then you'll have several suitable polyester choices, that work well.

 

We have the good folks at Gougeons to thank for introducing the boatbuilding world to the "amateur chemistry set" that is mixing your own glues and fillers, a huge time waster over the course of a custom build. For decades before they came along we had nice factory blended epoxy fillers and glues which were consistent and easy to use.

Steve.

 

I have consistent, easy to sand and use pre-mixes, that I've made up myself. The only element that might change with each mix is the amount of silica I add, to suit viscosity conditions for the particular job. If I have a big fairing job, I'll even pre-mix a batch with silica, for a non-sag formula.

I started doing this when I began counting the dollars, I spent on the pre-mix stuff from the formulators. I discovered I was paying 3 - 4 times what the combination of materials was worth. So if you have a need for gallons of fairing compound, instead of 1 quart tubs of pre-mix, you'd be best advised (economically) to make your own. On the other hand if you're just fixing some divots on a buddy's boat, by all means get the pre-mix.

 

I do the same when I have a big job going but I keep it to only a few basic ingredients. I use Q cells for fairing, milled glass fibers, polyethelene fibers, cabosil and various wood flours for cosmetic fillets on wood projects. I no longer use phenolic microballoons, talc, cotton, asbestos fibers etc. There are just too many to stock em all. I find that the only ones that don't require a blend with cabosil for a thixotropic mix are the PE fibers and some of the wood flours. I buy my cabosil in a big 10lb bag and empty it into a plastic garbage bin with a gasketed lid. Sometimes it is a bit clumpy when I open the bag so when i make my pre mixes i will mix them together in an old blender and then dump them into 5 gallon pails with Gamma seal lids or now ive found nice peel off lids of a soft enough plastic to be easier to use than the standard ones.
A few years, about the time that Epiglass was bought by the Azko Nobel (sp) and was introduced into the US i got excited a thinking maybe i could buy their pre mixed epoxy fillers and glue Epifill and Epifill so i called them up only to find they had bought into the amature chemistry set like everyone else for the US market, i was so pissed off i went searching for proper factory made pre mixed epoxy fillers and glues and did find a few and got samples for testing but obviously none of them were designed with any input from end users, i think the nicest filler was from Adtech, it used phenolic microballoons as the filler but if its the one im thinking of it was in the hardner. The thing is if you are going to make a user friendly epoxy filler it has to be as easy to use as bondo, if you are going to use, say a 2:1 mix, part A and part B must be of the same consistency so when you put the parts out on a palette you cant have one slump down which was the case with one i tried from a company in Florida (Fiberglass Coatings ?) You would spoon out 2 nice piles of part A but part B would just slump down before you could judge the size. So bottom line i just gave up and continued mixing my own but unless im willing to go the extra step of vacuum degassing there is no way i or anyone else for that matter, can match the consistency of good factory made stuff. The reason im so picky about this is that mixing your own is not economical when you factor in the labor cost, im quite sure that if one did a time and motion study on a large project you would find thousands of wasted labor $$$ by playing amateur chemist as well as the misery of having to be wearing a dust mask all the time or risk silicosis or worse. When West first started selling their products, one of the addatives was asbestos fibers, i used it on one project before pulled it. Yes, both West and Systems three now have pre blended products but it took them long enough, in my view West set the industry back 30 years. I realize its not the popular view with those who have not experienced more sensible products.

Steve

 

Just wondering your mixing process.. But don't worry, I don't want to know about it.
BR Teddy

 

There is some labor costs associated with the initial mixing of filler materials, but like you I do it in larger quantities, so the costs are spread across many jobs or batches of goo. I do perform a time/materials study at the time, I started this process and found I could differ the labor for a long time, justifying the initial and subsequent batch mixing. I remember asbestos as an additive, but I never considered it for obvious reasons, which at the time were relatively unknown.

 

Its not the so much the initial mixing of the powder blends as much as the actual mixing of the powders into the epoxy, you just cant do it quick or it just ends up floating around the shop. On a large project it is significant when compared to simply scooping out 2 blobs of part A and 1 blob of part B and stirring together with proper factory blended products. Sure you pay more for factory manufactured products but the extra cost is more than offset by the labor saved in a professional shop. For back yard builders where saving every penny on materials and not paying anyone for labor the West system may make some sense. When I was an apprentice in the early 70s we built a lot of cold molded as well as custom composite boats and the only product we had to mix ourselves was the fairing compounds which we made with phenolic microballoons, apart from that we used epiglue, araldite or resorcinol for gluing, epifill for filling and also had a 1:1 epoxy filler that you kneaded to mix like the stuff that plumbers use. The important thing is that all these products were available in industrial size packs so not so overpriced. We do have a few nice products available here like VC watertite but in silly little consumer packs so overpriced. If you go to a body shop supply store they have selections of really nice polyester fillers in gallon cans which are very easy to use, Epifill epoxy fillers were just as easy to use, were available in1.5 gallon kits and in white, mahogany and pine colors. They are glueing all sorts of parts on automobiles these days and the body shops are not mixing there own. I would love to see the salesman who would walk into the body shops and try to sell them on mixing up some polyester resin and then stirring in talc themselves to make there own bondo, they would be laughed out of the place.

Steve.

 

Steve, I see your point from the perspective of a large scale shop. As an amateur who builds on a small scale I have no problem hand mixing up relatively small batches of fairing compound. I like to use slow epoxy hardeners and take my time applying fairing, I realize that time is money so that might not be practical for a larger shop.

However, if I were building on a larger scale I would certainly have batch measuring and mixing equipment that would simplify and speed the process. It seems to me that if you have a mixer for your resin it would be a simple matter to add modifying agents based on predetermined formulas. If PAR has his faring compounds premixed, could he not tell an employee to mix "x" amount of faring to each quart of resin? This would seem pretty straight forward.

I've found that the biggest issue with mixing up faring material is working outside. Silica and micro-balloons in particular tends to blow around in the slightest of breezes.

In the end maybe there is no best way. Like blonds and brunettes, some guys like one, some like others. I like both.

Have a great day!

MIA

 

Mixing in the open is nuts, unless you're working with small batches. There are machines you can buy or build (put some thought into it) to solve the floating silica issue. My first mixing "machine" was a cardboard box with a clear plastic bladder glued to the top, with a slit cut in it. This bladder was quickly replaced by two flaps that overlapped, which worked better.

 

PAR. I am building a sailboat plug and need an easily sandable filler as a fairing coat for the whole thing. Could you give me a good formula to make such a fairing coat. The sides of the plug are vertical so it would need to resist slumping. So do I next mix the dry powders with resin well and then when its like peanut butter add the catalyst? I'm obviously very new to all this. Additionally, is there any specific type of resin (assuming that's what you use) that is best in your opin ion? Thanx.

 

Unfortunately PAR passed away in 2018, which was a huge loss to this forum in many ways. RIP Mr. Paul [PAR] Riccelli https://www.boatdesign.net/threads/rip-mr-paul-par-riccelli.60437/#post-831594

 

John,

PAR made that final voyage to another realm earlier this year.

You must have read this thread in its entirety.

I recumend: 80% micro-balloons, 10% talc, and 10% silica powders. The powder mix can safely be mixed into polyester resin before catylization. Epoxy resin and hardener should be mixed before adding powders. I highly recommend not adding powders before catylization. It is very difficult to impossible to correctly judge how much catalysts or hardener to add to the altered resin.