I have some small hoes that I filled with epoxy thickened with wood flour. This was my first epoxy job so I need to hit these again because the fill is still low in places. The finish right now is pretty rough. Do I need to sand these spots before adding more epoxy or is there enough bite there now to bond the new epoxy? The spots that I will be going over are fully cured (about 5 days old). Thanks.
You need to wash the surface you don't need to rough it up. You need to insure that there are no surface contaminates. Wash with clear water and use a clean scrubber sponge.Â
Wood flour thicked epoxy is a beast to sand, and the surface is rough enough to fill without sanding. While cleaning epoxy is always a good idea, it's not necessary for what you describe. You won't be able to pry off the second fill from the first, much less have it "fall off" on it's own.
Dave
After a couple of times using the stuff you should become much more adept at laying thickened epoxy on and "CLEANING UP BEFORE IT SETS" School of hard knocks! :
Even though this mixture is rough, because of all the hunks of wood, particularly if you used belt sander dust instead of flour, the surface of the epoxy will have amine (as mentioned) and a slick finish. Epoxy has a great deal of "surface tension" as a liquid, including thickened, which forms a smooth, hard surface when cured. This is why it shines and this shine needs to be knocked off, if you expect the best grip to subsequent mechanical bond applications over it (more epoxy, fairing compound, paint, etc.). In other words, regardless of filler, unless you are doing a goo on green (chemical) bond, then you should always wash and abate the surface, if for no other reason then to knock the shine off the surface.
Thanks. I actually used wood flour that I ordered from duckworks.
I had hoped to varnish the rub rails but since I messed up the miter on the stem (yep, it's already epoxied in place) I will have to do some filling. I took a block plane and worked the square ends of the rails down to meet the point of the bow. Since there is obviously a gap here now it looks like I will have to do some more filling, so the varnish idea is probably out the window now. Is wood flour the best thing to use for this? Is there any way I could still varnish these rails after filling these gaps or would it end up looking like Fido's backside?
I'm trying to post a picture of this mess but I don't know if it will work or not...
Ok, it worked. As you can see, I was able to fix the chine by doing basically the same thing I am trying to do on the rails. The gap is because I couldn't get a clamp to hold due to the extreme angle. I tried to hold it with brass screws but this obviously didn't work too well.
And to think that this was supposed to be a quick project to just get our feet wet. We're going on our third week on an 8 ft long dinghy!!!
Here is another picture or two. Any suggestions (short of a fire that is)?
David,  were this mine I would fair in the fwd edges of the rails with thickened epoxy.  I like to use talic as a thickener.  If the stem didn't look right to you you could  always add an external cutwater (think false stem) to beef up the appearance of the prow a bit.  This looks like a fun build.  She's way too good for a fire.  Once you get her in the water it will take three weeks to get the smile off your face!  Trust me....8) 8) 8)
I like Craig's idea: Glue and screw a cutwater in place and fair to the rails and chines with thickened goo. The look will be classic!
Dave
What are you guys talking about when you say "cut water"? Is there somewhere that I can see a picture?