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depressions in epoxy, sanding after primed
I have a few areas where even after a few coats of primer, the area is lower than the surface around it and slightly rough. Sigh, One learns as one goes, next time more dilgnece in sanding BEFORE the primer. I dont want to move one to painting with those rough areas until smoothed out.
but now instead of just keep adding up more and more primer I would like to sand the area down aggressively, (what I should have done before the primer was put on).
Overall I have about 7 coats of epoxy, a lot I know but about half those probably got sanded away (many drips to take care of some of which still seem to be there). that that means there are a lot of coats there still and even in the places where the depresions are there should be a fair amount of epoxy laid down there too. I would esptimate that where there are depressions there are about 3 to 4 coats and eslemwere a lot more.
So my theory is that the higher areas can be safely sanded down to the level of the lower areas becasue both have sufficent epoxy beneth them. What I am getting at is that as long as I just go down to the level of the low areas I wont expose wood anywhere. It is hard to tell exposed wood ro epoxied wood once it all has the primer dust on it. Does this make sense or is the a flaw here?
I would like to move on wihtout having to sand down and remove all the primer and reapply more epoxy. but I think that agressively sanding down to the lowest level in the depressions (as long as it still is covered with primer and therefore the epoxy below it) should be okay. I will see wood around the low spots but those wont be lower than the depression so should still be covered by epoxy. Yes?
David
2 replies:
RE: depressions in epoxy, sanding after primed
What Howard said.
On varnished boats you have to fair with unthickened epoxy to be able to see the grain. On painted boats, not only should you use fairing compound to fair, you should use fairing compound to fill the weave. It's cheaper, lighter, easier to apply and easier to sand than unthickened epoxy. Easier to apply because because it's thicker and doesn't run as much.
Also, once you've applied the first layer or two and sanded the boat, only apply whatever you're fairing with to the low spots. Once a spot is properly covered there's no point in continuing to add even more stuff on top of it. Leave it alone and put your fairing material (epoxy or whatever) only in the depressions. Especially don't put any on the high spots. That's just wasting time and money. Once the surface is even, you may want to put one more very thin coat on for a final sanding, but that's optional.
Some primers are compatible enough with some epoxies that you can apply epoxy over them. System 3 Yacht Primer and Silvertip, for example. If you find a really deep depression after you primed, you can mix up some epoxy and balloons and fill the depression without sanding off the primer. Check with the primer and epoxy manufacturers if this is the case for your stuff.
Finally, you can find depressions by lightly spraying the primed boat with black lacquer spray paint. It should be basically black speckles, only. Then sand the boat all over with a fairing board. Once you're done, you only need to reprime (or fill) any speckled areas.
Or if this sounds like too much trouble, decide that if the mightiest warships in the world can sail around the oceans with a workboat finish, so can you :-)
Laszlo
RE: depressions in epoxy, sanding after primed
» Submitted by hspira - Thu, 5/29/14 » 9:51 PM
david,
if you are using primer i am assuming you intend to paint. if you have depressions that cannot be easily sanded out, you can trowel in some fairing compound and sand it fair with a fairing board that may be easier than the approach you are suggesting.
http://www.clcboats.com/shop/products/boat-building-supplies-epoxy-fiberglass-plywood/marine-epoxy-fiberglass/phenolic-micro-balloons.html is the link for micro-balloons which is what you would use for fairing. since it is mixed with the epoxy, you would take the primer off in the depression, trowel this into the area and fair it in with a fairing board.
http://www.youtube.com/watch?v=ENPIRQPSLGA is a video that, while not demonstrating on a kayak....gives you an idea about fairing.
i have used fairing approach described above for painted hulls and you can get an excellent, professional class finish. the idea with a fairing board is to get the true hull shape back. most times when we try to sand out a depression, we just create a flat.....and lose the appropriate curve of the hull. the fairing compound allows you to easily build a couple millimeters of water-proof, very sandable, light material that can be re-worked into the proper curve of the hull.
that said, your approach will work as long as the depression is really quite minor.
howard