Warning, this got long, rambly, and potentially boring :wink:
Jake B":ms4b4afc said:
Its good to know I can mix filler and hardener brands just not of the same thing.
Just to make sure it's clear, you shouldn't mix hardener brands (at least not with marine epoxy), although you can mix fillers. In other words, the resin and hardener should "match" and be of the same brand and type; but the filler (collodial silica, structural filler, microballoons, wood flour, etc.) can be of any brand as long as it's the type you want.
If you would like one cookbook approach that will work, here is an example that I might use for filling a hole or around the edge of a hatch opening (once you read the epoxy books and get some experience, you may invent your own subtleties and tricks, as many folks do).
1) Buy epoxy and hardener, probably a medium or fast hardener for PNW (will "kick" faster but that can be good up to a point as you can then trim off things in the green stage without having it be 3 a.m. or some other awkward time/day). System 3 is an available brand that you can mix without pumps (1:2); WEST is an available brand that you can mix with pumps (1:5).
2) Buy some filler. For the job you have mentioned, colloidial silica alone will work (be careful not to breathe it in as it is very "flyaway" before you mix it).
3) Assemble things such as acid brushes, tongue depressors, squeegees (I make them from plastic milk jugs cut up for these small jobs), syringes (WEST make them), pipe cleaners, nitrile disposable gloves, protective clothing, masking tape, cups, Sharpie marker, plastic/dishpan/etc.
4) Prep the area to be filled. Once all is ready, wipe down the area to be epoxied with denatured alcohol or acetone for a final cleaning, and tape off/mask/etc. I find it *much* easier to take more time, care, and planning before epoxy work rather than clean up errant epoxy afterward. Think of it like a stir-fry, where it's 90% prep and 10% actual cooking.
5) Think about all the steps you'll be taking in your mind so you know you have everything you need to hand.
6) Once you're sure all is ready, mix up the epoxy (just the resin and hardener). If mixing in cups I mark them to receive resin first and then hardener, so that the more critical hardener is less likely to get "stuck" on the bottom and sides of the cup and not get mixed in. Mix the resin and hardener very well (stir). Any plastic container that's clean works well for mixing (pre-measured cups, beer cups, yogurt containers, etc. I guess you could use metal too, like a tuna can, if it was clean, but I usually use plastic ones (because I make my own mix cups from beer cups).
7) Now I paint on the neat (no fillers) epoxy to all areas that I will be filling. (If you are using separate batches for this stage and the next one, you can let this coat set up to the tacky stage without worry.)
8 ) Then add the filler(s) and mix well. I just "guess" and start adding and mixing until I get the texture I want. It's not super critical if you are working on a horizontal surface (hole), and you can mix it up a little bit runnier to flow into areas. On the other hand, for something like a hatch edge, where you don't want it to run back out, you have to go more to a thicker, peanut-butterier consistency. I think for either of these things you can keep it simple and just use colloidial silica, although you could also add structural filler if you wanted to (not that colloidial is not structural, just that there is another one called "structural filler," that is even stronger for certain applications).
9) Now you can use a syringe if you are filling a hole (soupier consistency), or just "pack" the thicker filler into an edge spot like your hatch opening with some variety of spatulas, tongue depressors, milk jug pieces, etc.. You can either try to get it just right (but it may sag or change anyway as it cures), or you can leave it proud and go back while it's in the "green" stage (you can test for that: you can still dent it with a fingernail but it's not "soft" anymore - more of a hard-but-slightly-rubbery) and chisel any excess off pretty easily. In the green stage you can also add more epoxy (say something slumped) and get a chemical bond without any prep. (After that stage, if you want to add more, you have to let it cure thoroughly and then wash off blush, sand, prep, and go for a mechanical bond. Not that the mechanical bond is inadequate for these things, but it's more work.)
10) Once the epoxy cures, wash off any blush (waxy feeling substance that isn't actually wax). Just use water and a 3M scrubbie, then dry with clean towels.
11) If you are going to gelcoat or paint over it, then you want to wait a good while for a full cure (I would give it days to weeks); but if you are just filling in an edge like your hatch opening, you don't need to wait past just a "normal" cure.
A few miscellaneous tips:
First of all, try to practice "clean" working techniques. One's skin can get sensitized to epoxy (some people sooner than others), so it's important to keep it off your skin. You also don't want to breathe any sanding dust. I just go ahead and put on a Tyvek suit and my respirator, and then I know I'm covered, but there is a great variety in how people approach this.
* I will don three to four disposable gloves on each hand; that way I can just peel off a "dirty" glove without the inevitable epoxy mess of trying to put on a clean glove mid-project. I also tape the first glove to my Tyvek sleeves because I found I would often get epoxy on my wrist at that gap.
* You can cut the syringe tips to whatever diameter you want (larger makes it easier to get the soupy epoxy in and out, obviously).
* When using wooden tongue depressors or popsicle sticks, I cut one end off square which allows it to scrape the mixing cups easier when stirring up or getting the last bit of epoxy from them.
* As I mentioned above, plastic milk jugs, cut up, can provide scads of cheap, handy squeegee/scrapers (for lightweight jobs; for bigger jobs the yellow body shop ones are sturdier).
* A plastic sheet over cardboard makes a good layout/mixing area and is disposable (also once epoxy cures it peels right off plastic - I use dishpans over and over for some smaller cloth jobs).
* In addition to masking tape (blue or otherwise), clear packing tape can be handy and epoxy peels right off it (and vice-versa).
* If you are filling a deep/wide/large area, be aware that epoxy heats up as it cures, and you could distort the fill or your fiberglass - or even potentially start a fire - if it gets too hot. The epoxy would also foam and not be as strong. Sometimes you may need to fill deeper/larger areas in layers (stay in the green stage and you can just keep adding without more prep). In a cooler climate and/or with slower hardener it's not as pronounced. It's good to have an area near the boat figured out to where you can throw a potential "epoxy bomb" (i.e. a cup of epoxy that starts to kick). On that note, once it starts to kick don't try to use "just a bit more." It's better to just give it up, throw "the bomb," and make up a new batch. If you are using hardener that may be just a bit faster than you might like, know that flattening out the mixed epoxy (wider, shallower cup, cold, ice, etc.) will make a noticeable difference over having it in a deeper, narrower, cup, because of the way it cures chemically and heat affects it.
Sunbeam :hot
PS: This is just one possible way to go about it. Even though I wrote it out this way, there are actually a variety of ways I might go about a given epoxy task; and others will have even more ways. Although there are definitely wrong or poor ways to do it, there are also lots of "right" ways. And/or little tricks you might develop. For example, when I'm fairing with microballoons, I find that adding a touch of collodial silica to the mix makes it go on better. Etc.
PPS: Although it's tempting to just go buy a container of 5-minute epoxy at the hardware store instead of getting into the "full catastrophe" of supplies for just one job, I think you may find that once you have epoxy and supplies on hand, you will get "handy" with them and use them again in future.
PPS: On fillers: There are structural fillers, and fairing fillers and then variations and combinations. But basically, fairing fillers are "light," and (relatively) sandable, and they are used to smooth out a surface and make it more cosmetically flat for painting or finishing. Microballoons is one of these. Structural fillers provide structure (obviously). Otherwise the epoxy would actually be sort of brittle in a way (why you don't just fill with neat epoxy). Colloidial silica and "structural" filler fall more into this category. I haven't used wood flour in a while, but I think it's sort of somewhere in between (could look it up in epoxy book).
