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PostPosted: Thu Jun 30, 2011 10:28 am 
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A quick tip for those who are cheap (coincidently this group coincides with those who by H16's in dire need of a bottom job)

First of all, your cheap so I'm gonna assume you're using polyester resin


When I was doing my bottom job it was 60 deg F in the garage, and the resin on the hulls was taking forever to set up. Using a hairdrier I was able to heat the resin a bit and increase curing times. (duh)

Here comes the fun part. By putting the pot on ice I was able to attain a 45min-1hr pot life. By heating the repair area (to about 90deg) I was able to reduce the time between layers to 20-30min in the cold air, could be further optimized. At any rate despite the cold air in the garage I was able to get 2-3 layers per batch. To achieve these results you need to pre-cool your resin in the ice bath, then add the hardener.

If done properly (which mine ironically wasn't cause I was in a hurry). you could potentially get a pot life of several hours.

It should be noted that temperature manipulation of the curing rate does not affect all curing mechinisms equally, so by chilling the pot and heating the work area you are changing the final chemical structure of the hardened resin (for those chem savy guys, this deals with chain length, and cross linking, although I really don't have a good understanding as to how) and as a result I wouldn't recommend it for structurally intensive repairs.

Cares to share how curing rate affects the structure of polymer chains and their physical properties, that'd be swell. My guess is that fast hardened resins have shorter polymer chains with more crosslinking resulting in a harder, stiffer, more brittle material that is less strain rate sensitive than 'normally' cured resin.

-Joe


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PostPosted: Thu Jun 30, 2011 12:08 pm 
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You can control the cure time of polyester and vinylester resins by moderating the amount of MEKP you use in relation to the ambient temperature. Cold weather = more MEKP, hotter weather = less MEKP.

The other thing you can do is make sure you get the resin spread out quickly. The less resin you have sitting in your mixing cup, the less heat will build up and the longer before the resin kicks off. My first goal is generally to get most of the resin out of the cup quickly. Then concentrate on getting it worked into the glass evenly and removing excess resin.

So for a bottom job, typically I would mix up the resin, pour it along the bottom of the hull about a foot, then spread it out quick and rough, then do the next foot, and so forth. Then lay down the glass, again pour a little more resin on in one foot sections doing a quick spread just so the resin doesn't pool or drip. After all the glass is initially wet out, then go back and concentrate on really working the resin into the glass and making sure everything is evenly saturated.

Otherwise, if you try to get one spot perfect before moving to the next, you'll be working with a cup full of polyester resin and it will kick off very quickly.

sm


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PostPosted: Tue Jul 12, 2011 6:30 pm 
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My 18 needs a bottom job, but my question is do I have to lay some cloth down or can I just add some resin. I know this depends on how bad the wear is. The wear is not bad at all, there is very little fiber showing. I just want to thicken it up, and I don't want to have to lay cloth and deal with making sure the resin is deep enough to engulf the cloth.

So is it OK not to lay cloth if you just need to repair a little wear?

Also is your tip a good tip or a bad one? I Think its a great idea to control the temp like you said to save time and resin, I plan on using it. But your title says its a bad tip. Should I not do it?

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PostPosted: Tue Jul 12, 2011 6:41 pm 
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Jmecky, if you are going to add resin, why not add cloth? Cloth+resin is structural, resin alone is merely a filler.

It's really not that much more work and money to add cloth, so why not? I can't find any reason why you would not want to add a few layers.

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PostPosted: Mon Jul 25, 2011 4:36 pm 
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I'm a little slow on my replies, but the answer to your cloth question is, what do you feel like doing? On a hobie 16 where the bottom rounds a sharper corner than on the 18 it can be difficult to get the cloth to lay up right. However, per unit volume fiberglass is lighter than resin, so your repair will be lighter and stronger with cloth.

On my bottom job I used cloth by necessity (if you wear through the light fiberglass into the big heavy (1mm diameter plus) glass range you need to replace some structure) and finished the job with 3 layers of tinted resin for some UV protection. I would highly recommend doing something to protect your repair from the sun, especially if a lot of the original fiberglass is exposed to light through your repair.

As far as is my tip good or bad, not sure but it worked great laying up the bottoms and the repair is holding though beaching and aggressive sailing. On a bottom job where the structure is not really a driving factor I would recommend it. On a structural repair, test in an inconspicuous area first?

Joe


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PostPosted: Fri Jul 29, 2011 12:15 pm 
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jmecky wrote:
My 18 needs a bottom job, but my question is do I have to lay some cloth down or can I just add some resin. I know this depends on how bad the wear is. The wear is not bad at all, there is very little fiber showing. I just want to thicken it up, and I don't want to have to lay cloth and deal with making sure the resin is deep enough to engulf the cloth.

So is it OK not to lay cloth if you just need to repair a little wear?

Also is your tip a good tip or a bad one? I Think its a great idea to control the temp like you said to save time and resin, I plan on using it. But your title says its a bad tip. Should I not do it?


I am in the same situation - 2" strip of gel coat worn through on the keels but no damage or fibers. Can I just flip the boat over on the beach, sand, wipe clean w/acetone and then roll on maybe four or five layers of gel without the cloth? For that matter is is it even possible to use a paint roller with gelcoat? Can successive coats be applied while the gel still wet?

I have no idea what I'm doing but it's something I need to address while its still warm outside.


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PostPosted: Fri Jul 29, 2011 2:59 pm 
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I did a bottom job on my 18 earlier this year. The wear was bad enough that I layed down some glass in the bad areas first. Then filled in with putty, and then painted on gelcoat.

If your boat isn't worn bad enough that you need glass, then I think there's no problem going right to the gelcoat. If you have any deep scratches, you probably want to fill them with putty first.

Anyway, for my gelcoat application, I used a brush to paint it on (cheap 1" wide brush from harbor freight, you can get a box of like 3 dozen of them for $5). Pull out all the loose bristles first before using so they don't end up in your work. I got the gelcoat from west marine, it had the wax already in it, so you just mix it up with the catelyst and paint it on.

I did about three coats of gelcoat, sanding between coats. The first coat was mixed with filler (microfibers) to make a thick paste, then straight gelcoat on the next coat and on the last coat, I cut it with acetone to make it thin to minimize finish sanding.

sm


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PostPosted: Mon Aug 01, 2011 8:58 am 
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srm wrote:
I did a bottom job on my 18 earlier this year. The wear was bad enough that I layed down some glass in the bad areas first. Then filled in with putty, and then painted on gelcoat.

If your boat isn't worn bad enough that you need glass, then I think there's no problem going right to the gelcoat. If you have any deep scratches, you probably want to fill them with putty first.

Anyway, for my gelcoat application, I used a brush to paint it on (cheap 1" wide brush from harbor freight, you can get a box of like 3 dozen of them for $5). Pull out all the loose bristles first before using so they don't end up in your work. I got the gelcoat from west marine, it had the wax already in it, so you just mix it up with the catelyst and paint it on.

I did about three coats of gelcoat, sanding between coats. The first coat was mixed with filler (microfibers) to make a thick paste, then straight gelcoat on the next coat and on the last coat, I cut it with acetone to make it thin to minimize finish sanding.

sm


Thanks much, I'll give it a shot. I'm curious as to why you used such a small (1") brush? Is it because the gelcoat is considerably thicker than paint? Is the "roll and tip" method out of the question with acetone-thinned gelcoat? Also, if I mark off the work area with painters tape will I be able to peel that off when I'm finished (or do I need to re-tape for each coat)?


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PostPosted: Mon Aug 01, 2011 2:17 pm 
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I used 1" wide brushes because that's what I had. They are what I use for general fiberglass work. You can get a box of them for a couple bucks and you only get to use them once, so I buy a bunch. Anthing larger also wouldn't fit inside my mixing cup (3 ounce paper dixie cups, also a one-shot deal).

I masked the area off, but really just as a guide. I never actually went up to the tape line.

Here is the before (note the fiberglass tape added in front of and behind the daggerboard trunk):
Image


And the after. Not perfect, but certainly good enough for a beach boat:

Image

sm


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PostPosted: Tue Aug 02, 2011 8:32 am 
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Nice! That's what my hulls look like so I'll probably end up adding some tape as well. Very helpful, thanks. Your end result looks really good.


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PostPosted: Fri Aug 12, 2011 8:52 am 
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Location: Indialantic, FL
SRM, thanks for the pictures. How did you match the white? Did you add pigment to the gel-coat or paint something over the repair?

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PostPosted: Fri Aug 12, 2011 9:43 am 
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poolemarkw wrote:
SRM, thanks for the pictures. How did you match the white? Did you add pigment to the gel-coat or paint something over the repair?


Trick photography... :D

This is just straight West Marine white gelcoat with no pigment added. It's not a perfect match, but it's on the bottom, so I don't really care. It's 100 times better than a 2" wide brown stripe. Also, after wet sanding it, it blends in pretty well with the existing gelcoat, but if you look closely, there's a visible difference. White is a difficult color to match.

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PostPosted: Thu Aug 25, 2011 4:44 am 
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When you said you filled in with putty, what exactly did you use? I'm about to do a bottom job on a 16 and there are some small gouges on the bottoms that I'd like to fill in.

So your order of application was glass, putty, gel coat?


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PostPosted: Thu Aug 25, 2011 4:57 am 
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I used fiberglass resin with West 404 filler to thicken it up into a putty (peanut butter texture).

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PostPosted: Thu Aug 25, 2011 6:12 am 
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I'm assuming bondo wouldn't work?


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