I am re-coating the hull of my ski with West System Epoxy and 207 Special Coating Hardener. According to them, in order to avoid sanding between coats, I should re-coat within the same day, but first, it must cure firmly enough to support the weight of the next coat.
Ok, how long is cure firmly enough? Any of you that has already build boats, how long do you wait between coats to recoat?
Thanks in Advance,
Iceman
PS: Any tips are well appreciated…
recoat time
There is no specific time that works for all situations because of differences in epoxy formulation, especially the hardener, and because of varying temperatures and other weather conditions.
Basically what you are looking for is a point at which the epoxy is no longer tacky (sticky to the touch). That is the soonest you will want to recoat. The instructions for the particular epoxy/hardener blend should tell you the maximum amount of time you can wait to recoat without sanding first.
As far as technique is concerned, I normally roll the epoxy out with a foam roller. Although I will roll in different directions to spread the epoxy, I finish off by rolling lengthwise on the boat (from bow to stern or vice versa). Don’t overdo the rolling or you will work extra bubbles into the epoxy. After rolling the epoxy on, I then tip it off with a disposable brush. By tip it off, I mean lightly drag the tip of the brush over the area you have just rolled to knock off the bubbles/slightly foamy look that the roller will leave. I go from the dry edge of the epoxy back into the wet area, and I always work lengthwise on the boat.
I always manage to make it sound harder than it is, but the general process is roll it on, then run the brush over it.
Ice…
I usually waited over night…
tell us why are you doing this… do you not have gelcoat?
not tacky to the toucg so it won’t …
come up when you put on the next coat.
Don’t apply or let cure in direct sunlight. You’ll get lots of bubbles.
Test first!
I recoated an old kevlar and the resins beaded up like water on a waxed car. If you ever waxed or otherwise treated the ski, test first or you will regret! Cleanliness of the hull is critical. After what I went through, I would test on the topside where it doesn’t matter before making the bottom worse.
Be ready to sand sand sand.
When I use West system, a thin coat is a good start. Think thin thin. then tip off, remove all lost brush hairs (Hair patrol) and recheck in 1-2 hours for the runs. It won’t run until after you quit for the day. Then in unison, off it goes. Be ready to rescue with brush, roller, or automotive squeegee for body work. Pack of 3 hand squeegees for $2.
In S. FL, should be ready to recoat in 6-8 hours, overnight is a good sequence. Wash with ammonia water, sand lightly, dust off, and 2nd coat.
Keep us posted, g’luck.
I rolled on four coats in one hot day
using 505 hardener. I am sure each coat WAS a teensy bit “tacky” when I put on the next coat. The wetness of the next coat of resin on the roller was QUITE sufficient to keep the tacky quality of the previous layer from causing problems. The whole point of putting on layers with little delay is to allow the amine blush on the previous layer to COMPLETE rising through the previous layer and to rise through the next layer, while allowing the new layer to bond chemically to the previous layer BEFORE that layer has completed bonding to itself.
I recommend contacting West for advice as to how to judge when the next layer should go on. You should not be waiting for long periods, or you defeat the purpose.
ICEMAN CALL ME … AHHHHH
WHY ARE YOU DOING THIS ???
as soon as possible
I put succesive coats on as soon as I can. 2-4 hrs usually. If the surface is a little “tacky” that’s alright with me, as long as I can apply another coat without lifting the previous.
You want the first coat to be “green”, not fully cured. Every epoxy and every hardner is different but with a medium hardner 12 hrs is the longest I would wait for a chemical bond. If it is over 75 degrees more like 8 hrs maximum.
Do you have their epoxy manual?
My System Three epoxy came with an excellent guide to using it. This might not be the same for your epoxy and hardener, but they say recoating without sanding first can be done within the first 72 hours of the previous coat.
I always wait till the previous coat is at least tack-free before re-coating. That provides a window of time from about 24 hrs to 72 hrs, in my dry heated work area.
Make sure your coats are thin, even, and smooth if you are going to dispense with sanding between coats!!! Sanding in between gives better results.
Thanks a lot to you all!!!
– Last Updated: May-13-05 12:43 PM EST –
I was able to see the responses, but I could not write a that time, now, I'm waiting for the last coat.
c2g, the brusing thing works great! Rolling lengthwise is not that easy because the hull is quite rounded, but it is coming out good.
Why am I doing this, in a boat practically new?
The boat came from the container with a couples of little dents of about 5mm2, and during the last 7 or 8 months I did two or three more :D, so I wanted to fixed them. However, I also discovered a couples of blisters (maybe hydrolysis) that weren't there several months ago. I fixed them all, so they bacome invisible. Don't forget, the boat does not have gelcoat.
At that moment, I realized that the abrasive resintance of Epoxy was unsurpassable compared with the vinilister the boat broght, maybe 4:1. For instance, with a 320 sandpaper, the vinilister sand like if nothing were there, on the other hand, the epoxy is a pain to sand.
Therefore, looking forward to the long term of the boat, I decided to re-coat it with a couples of very thin coats of epoxy. It should become way more abrasive resitant and minimize any future hydrolysis problem.
By the way, if I went-sand 600-grit or more, am I going to get a glossy finish, or I must have to varnish no matter what?
Thanks again,
Iceman
Yes, I do have it
and I read all the info. from West System; however, I found it not very clear the difference between cure firmly enough but not fully cured. Now, I think I am having an idea 
Regards,
PS:
I was forgetting. For better of for worse, at the end, I’ll post a couples of pictures to show how it went
You need to varnish it
Even if the epoxy comes out looking real pretty you still need to varnish it to protect the epoxy from UV damage. Using a good quality marine spar varnish like Captain’s or something similar will not only protect the epoxy from sun damage but it will make it that much nicer looking and is quite hard in itself.
Varnish the Hull
– Last Updated: May-14-05 10:52 PM EST –
If I varnish the hull, I am sure this will be the only surfski in the world to be varnished :D :D :D
I have worked with gelcoat and epoxy, but I have never used varnish. How hard is too apply it? Is it easy to handle?, and how long after the varnish is applied I have to wait to use the boat?
Thanks for your inputs...
varnish
If you’ve worked with gel coat and epoxy, you know how to varnish. Its easier to work than either of those two.
Varnishing
You need varnish or paint to protect the epoxy from UV deterioration.
True, if you have worked with epoxy you can work with varnish. However, they do not behave the same so it would be good to read up on varnishing techniques (Rob Macks and Nick Schade have posted some great advice on this; check the archives at www.kayakforum.com).
In short, varnish’s main advantage (in terms of ease of application) is that it is used straight from the can. You do not need to measure and mix Part A and B as you must with epoxy.
BUT varnish is much less forgiving than epoxy, IMO. It has a shorter working time so you must brush quickly yet not be sloppy. With epoxy, if you have runs/drips, shaving them flat using a scraper after the epoxy has green-cured works beautifully. When I did the same with varnish drips, the excess did come off, but the scraped area was sticky and nasty, unlike with the epoxy. The sticky part takes forever to dry, for some bizarre reason. And trying to smooth it by sanding makes it really messed up.
Sanding uneven surfaces of epoxy, then coating again with more epoxy fixes the surface flaws. Not necessarily so with varnish. Any hairline edges of scraped drips WILL show up even after being coated with more varnish. It shows every little flaw in your underlying work.
The weirdest thing is that varnish’s surface dries very quickly and feels dry to the fingers, yet the varnish remains soft for days, even weeks. The longer you can let it cure, the better. Drips that are left alone for months harden and can later be sanded without getting the goo effect. Yet even though they are dry on the surface within hours after varnishing, don’t even think about trying to sand them after a week.
Best thing about varnish is how glossy and beautiful it looks when you get it right. And getting it right will take practice. I have had people admire my kayak’s varnish but it is definitely flawed, and I’m hoping to get it right next time.
paint not varnish
Unless this is a wooden boat with a clear finish varnish is not the way to go for UV protection. I would put white pigment in the last coat of epoxy and/or paint the hull with a marine over the epoxy.
Pain Vs. Varnish Vs. Nothing at all
– Last Updated: May-16-05 11:36 AM EST –
I understand your point, and I thanks your inputs. If I want the maximun UV protection I can get, I must use the white pigment from West System (which I have), and then, paint the hull.
However, I still do not want to paint the boat for several reason:
1. This is a racing boat not a touring one, so by not using gelcoat/paint, its weight is way below average even after recoating with epoxy this last weekend.
2. I don't leave the boat on the sun, and when I travel, I cover it.
3. It is too pretty to paint it :D :D
Even though it is not wood, the clear carbon/kevlar to my eyes (don't kill me for this wood lovers) looks as pretty as it were.
4. I found very easy to fix the clear hull because I don't have to deal with paint and/or gelcoat, and any minor repair looks invisible.
5. I think that the blister were principally due to a poor vinilister, and UV played a minor roll. However, in a couples of month I might be proven wrong, so at that point I might have to consider painting the hull.
Regards,
Iceman
Varnishing
– Last Updated: May-16-05 11:33 AM EST –
You described most of my fears of varnishing, and for you personal experiece, I don't think this is a job to be done in a weekend and paddle on Monday. It might take me several weeks to have my boat ready to go.
At this moment, I don't have the time to stop the ski for so much time. We are a couples of weeks from the State Games, and less than 3 months from the Nationals. However, after the Nationals, I may take two or three weeks of paddling the ski, and do the job. I also think that might be a good idea to varnish during summer time in order to obtain a faster cure.
As I did with a epoxy and gelcoat before (and you said it), I think I must do with varnish, research, research, and more research...
Regards,
Iceman
paint/varnish
I see your point. I like the color of the clear resin/kevlar, too. If you want to maintain that look then varnish is the only way. I have several decade + old wood strip boats that I keep varnished( every 3-4 years) and have seen no deterioration of the resin at all. I don’t take as good care of them as you seem to with yours.
There are lots of varnishes out there and you will pick your own, but here is what I have learned works for my situation. Polyurethanes are clearer, Oil-based spars are soft yellow and will impart a bit of their own color. Polys are harder. They are easier to sand to refinish because they don’t gum up abrasives so much. They are also less flexible finishes and more brittle and prone to crack or check if your hull flexs a lot. Spars are softer-not much- are a little harder to sand for refinishing and are flexible. I use spar on canoes and paddles. Poly on furniture.
There are very expensive spars out there and some cheaper ones that do as good a job for your use. I use a cheaper one with great results. Benjamin Moore Impervo 440 Spar Varnish. I think it is still less than $10/quart.
Make sure you let your resin cure for a week before sanding and varnishing. I wash my hull with clear ammonia and warm water before sanding to get any amine blush/waxy stuff off.