Hello, I have a few low areas on the hull. I put 3 coats of epoxy and am sanding down to get low areas out. This process of sanding is getting down to the fabric around the low areas. My question is how to apply the next coat to fill the low areas and stay thin on the rest of the hull? Maybe use a large flat edge to spead the epoxy rather than a roller or brush... any advise would help. Thanks!
Calvino I need to ask a couple questions over your statement “This process of sanding is getting down to the fabric around the low areas.”
By which I get the idea you’re sanding the high spots and you’re finding the ‘glass fabric is beginning to show up?
Have you had much experience with epoxy & fiberglass prior to ‘glassing your hull?
When you ‘glassed your hull perhaps your ‘glass tended to float in some areas. (I’ve heard that’s possible but never encountered it myself.)
To my mind that’s why those spots are ‘high’ in the first place, why sanding them now is showing ‘glass cloth that ended up with too much epoxy underneath.
There’s nothing wrong with applying more clear epoxy over the lower areas you’re seeing, as long as what’s already on there has cured fully then been abraded by light sanding or breaking the gloss with ScotchBrite & water.
If ultimate lightness is your primary goal you need to determine whether the total area of high spots is significantly greater than the low areas.
With more epoxy underneath the cloth than what’s needed to bond it to your hull, adding more now to fill those low areas’ll just add more weight.
Your only recourse is to pull all the ‘glass off then scrape / sand away any excess epoxy before applying a new layer. Tedious at best, but with a heat gun and lots of patience you can soften the epoxy then pull the ‘glass off.
The trick to getting a fair, even coating is to not sand and fill everywhere every time. Ideally, you want to be putting epoxy only into the low spots and sanding only the high. Eventually they merge into one even coat.
What I do on my boats is once an area has its weave filled, I stop putting new epoxy on it until I've taken care of the deep low spots. Importantly, I also stop sanding it until all the low spots are taken care of.
So it goes something like this - base and weave filling coats all over, sanding to smooth the coats and expose the low spots, then coat and sand only the low spots until there are no more.
Once this is done, there's still a bit of large-scale variation even though the local low spots have been taken care of. At this point I switch back to overall coats and sanding.
I like to use lots of very thin coats, sometimes building up 5 or more layers between sandings. This is the best way I've found to avoid drips and sags. My best success for thin layers comes from short nap rollers and tipping out with a disposable foam brush.
Whatever tool you're using for sanding should also be large enough to span the low spot you're currently working on. If a quick sanding of a low spot is only removing epoxy from the edges and not touching the center, you need to add more epoxy in the center. If you have the patience, a 2 to 3 foot long fairing board will give the best results in exposing the low spots and smoothing them into a fair hull shape.
When you finish this way, you start with a long sanding session at the beginning, then lots of short fill/sand cycles in the middle while you take care of the low spots and finally a couple of long sand/fill/sand cycles at the end getting the final fairing done.
Remember, too, that this is your boat. For waterproofing and hull integrity you only need to fill the weave. Getting it smoother and fairer is optional. If you're happy with how it looks move on. You can always refinish it next year if you want it slicker and shinier,
Have fun,
Laszlo
I'm also working on finishing a Kaholo. The panels on the Kaholo bottom are pretty thin, and can flex between the bulkheads and stringers. I'm not sure exactly when/how, but I have a couple areas on the bottom where you can run your hand with a very light touch over the bottom and feel a slight dip and rise that's the panel dipping a bit. I don't know if it was always that way, occurred during stitching when I put a little tension on everything to pull together and maybe pulled down bulkheads too hard, or after the glassing, the extra weight of cloth and resin causing the panels to droop under gravity. I was intending to use a longboard for sanding, and used it some on the sides and deck, but I'm avoiding it on the bottom so I don't get into the cloth. I've gotten down to cloth in a couple of high spots, but haven't gone through it, so I'm stopping. I still have the last skim coats so that'll seal everything up. I would also locally smooth things and not try to fair out longer scale lows associated with the egg crate ribs. I did use some phenolic microballoons to fair out some messy epoxy runs on the sides that were all my own fault, but not to try fairing the panels.
Thanks for the feedback!