Just finished a bottom job on my H16. A few things I learned along the way:

1. Fiberglass dust itches like the dickens. I wore a respirator, but the dust gets everywhere, particularly around the neck and in any uncovered crevices (the bend of the elbow or behind your knees) . I am glad I don't work with this stuff for a living. Even though our temps are in the 90's, I wore a sandblasting outfit to keep the dust out of my clothes. I sweated out gallons, but that was not an issue compared to the irritation caused by fiberglass dust in the skin.

2. There is a learning curve to working with polyester resins. I did a fair amount of research, but nothing replaces good old fashioned experience. I wish I had worked on a practice project before doing the hulls just to get a comfort level with the process. Everything came out okay in the end, but I did have to fix some issues like bubbles or patches of glass fabric that refused to take the resin for whatever reason. One issue in particular is the mixing of MEKP (hardener) into the resin. My tools for this were not precise enough and I would highly recommend finding something that allows you to precisely measure how much hardener is being added to the resin.

3. Gellcoat, to spray or not to spray. I used a brush application since I was only dealing with a 3" wide strip along the bottom of the hull. It was a very laborious process and added tons of sanding time due to the uneven application created by the brush. Furthermore, the new white gelcoat is brighter white than the old white gelcoat. Next time, I'll recoat the entire hull with freshly sprayed gelcoat.

But, as I write this, the boat is finished and reassembled on her trailer. Can't wait to get her back in the water.

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Karl, Captain of Stayin' Thirsty
2011 Hobie 16SE
Atlanta, GA
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Gelcote is a much higher skill level than general glass work.
By "bottom job", if you are mainly trying to restore glass worn by beachings, I would do it from the get go, before the gelcote wears away, cuts your fix by a factor of 10. Your going to have to do it anyway, spend the $100 right now & do it in a few hours.
I don't slide my Cats on sand, but I do slide them on & off a lift, so I take preemptive action. The easiest way is to flip the boat, make gravity work for you.
Lightly sand the keel, then wipe with acetone.
Snap a chalk line down the hull, or eyeball it if you have a good ey, such that you can fit either 2" or 4" glass tape,(depending on your preference for a rub strip) just inside the lines.
Wax the area outside the lines, this will make cleanup 2 minutes, instead of an hour sanding.
Go to the dollar store & get a pack of 1'-2" brushes, for a $.
Paint some West epoxy, thickened with micro fibres along the keel. (leave it slightly runny, you want it to self level via gravity), the microfibres act like glue, as well as abrasion resistance.
Start your tape at one end, then holding the end, slightly stretch it & lay it down between the lines. The thickened epoxy will now hold it securely.If you dry layup, it will want to move around, & you won't get straight lines.
Using either roller, or "tapping" gently work the entire length, to embed it & wet it out. If you have difficulty, add very small amounts of resin. USE MINIMUM RESIN TO WET OUT.
Let it set to "green", not hard, but not soft. Don't try to paint it smooth, you will just screw it up.
Using a palm sander & 160 grit, zip along the tape, especially the edges.
Now paint a layer mixed a bit thinner, let gravity level it.
You may have to paint a third layer to totally fill the mesh. Use 207 (clear) hardener. It is a slow hardener, dries clear, you will not see the rub strip from 10'.
Also the 207 does not "blush". If you are short of time & have to do it over a couple of days, you may have to sand off the "blush" other hardeners may create.

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Hobie 18 Magnum
Dart 15
Mystere 6.0XL Sold Was a handful solo
Nacra 5.7
Nacra 5.0
Bombardier Invitation (Now officially DEAD)
Various other Dock cluttering WaterCrap
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. Fiberglass dust itches like the dickens. I wore a respirator, but the dust gets everywhere, particularly around the neck and in any uncovered crevices

Have a good fan blowing behind you while you work.... helps a lot

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There is a learning curve to working with polyester resins

heck yea.... years and years of practice... fairing is a whole other art form / skill

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One issue in particular is the mixing of MEKP (hardener) into the resin. My tools for this were not precise enough and I would highly recommend finding something that allows you to precisely measure how much hardener is being added to the resin.

you have to know how many ounces of resin you have in your cup or your in trouble
West System is a bit more expensive than other resins but the pump tops make mixing the correct amount dummy proof. not to mention you can gel coat over it (some resins wont let gelcoat adhere to them)

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I'll recoat the entire hull with freshly sprayed gelcoat.

for spot repairs you can add pigment to your "White" and match it , also there are many shades of "white" gelcoat

motivated

One issue in particular is the mixing of MEKP (hardener) into the resin. My tools for this were not precise enough and I would highly recommend finding something that allows you to precisely measure how much hardener is being added to the resin.

The MEKP bottles typically come with a "dropper" tip. Just use a sharp utility knife and cut a little slit into the tip of the bottle so you can squeeze it out by the drop. Most polyester resins recommend between 8 and 12 drops of MEKP per ounce of resin. It does not need to be terribly precise and you can modify the amount depending on the ambient temperature (i.e., in 90 degree heat, err towards the 8 drops per ounce). (Note that this is in contrast to working with epoxy which requires a high degree of accuracy for the mixing ratios.)

I usually mix up small batches of polyester resin using disposable 3 ounce Dixie cups (un-waxed) and approximate the amount of resin by the level in the cup. For wet layup, you can also figure on a 50/50 resin to glass ratio. So if you're using an 8 ounce glass (that's 8 ounces per square yard), you can figure out the area of cloth you're going to lay down and calculate the amount of resin you'll need.

sm

Dogboy

motivated

One issue in particular is the mixing of MEKP (hardener) into the resin. My tools for this were not precise enough and I would highly recommend finding something that allows you to precisely measure how much hardener is being added to the resin.

The MEKP bottles typically come with a "dropper" tip.
sm

I ordered a syringe that had measuring marks on the side, sold as a precise way to measure out the hardener. The problem I discovered was that the measurements did not include the amount that was in the tip of the syringe. As a result, my first batch of resin catalyzed in about 5 minutes.

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Karl, Captain of Stayin' Thirsty
2011 Hobie 16SE
Atlanta, GA
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I have never needed to use more than the dropper top when mixing epoxy

I have never needed more than a few ounces of mixed epoxy at a time either

How big a "batch" did you cook at a time?

Here is a chart i use to measure out the correct amount of drops




Edited by MN3 on Sep 03, 2014 - 08:14 AM.

MN3

I have never needed to use more than the dropper top when mixing epoxy

I have never needed more than a few ounces of mixed epoxy at a time either

How big a "batch" did you cook at a time?

Here is a chart i use to measure out the correct amount of drops
Edited by MN3 on Sep 03, 2014 - 08:14 AM.

It was 6 ounces of resin. The poor design of the syringe caused me to put in twice as much as was necessary. I adjusted for the next batch.

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Karl, Captain of Stayin' Thirsty
2011 Hobie 16SE
Atlanta, GA
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motivated

It was 6 ounces of resin. The poor design of the syringe caused me to put in twice as much as was necessary. I adjusted for the next batch.

Gotcha, that is a larger amount than i ever work with at a single time.
glad it worked out for ya

what type of epoxy did you use?

He said he used polyester resin, not epoxy.

You can not vary the hardener ratio when working with epoxy. You have to mix the hardener in the exact proportion required or the epoxy will not cure properly. You adjust the cure time by using slow, medium, or fast hardener.

When workkng with polyester, you adjust the cure time by varying the amount of hardener (MEKP) you add.

The two resin systems are very different in this way.

sm

MN3

motivated

It was 6 ounces of resin. The poor design of the syringe caused me to put in twice as much as was necessary. I adjusted for the next batch.

Gotcha, that is a larger amount than i ever work with at a single time.
glad it worked out for ya

what type of epoxy did you use?

I was working with polyester resin from Tap Plastics company, supposedly the same materials used by the Hobie factory when manufacturing the hulls. And, as Dogboy mentioned, the catalyst determines the work time you have with the material before it starts to set up. I mixed up such a large batch since I was layering the glass (laminating) along the keels. Once I figured out the right ratio of catalyst to resin, I was getting about 20m of work time.

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Karl, Captain of Stayin' Thirsty
2011 Hobie 16SE
Atlanta, GA
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thanks!

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I was working with polyester resin from Tap Plastics company,

age and storage conditions (heat) degrade these products (and throw off cure times) as well

What he said. West Systems is the best. The pumps make so easy, exact ratio, no mess. MN3 knows what he is talking about.

911hobie

West Systems is the best. The pumps make so easy, exact ratio, no mess.

Except that West Systems is epoxy and the original question had to do with working with polyester resin, so not really relevant. Again, the two resin systems are completely different when it comes to mixing ratios and adjusting cure times.

sm



Edited by Dogboy on Sep 04, 2014 - 04:35 AM.

we got it, epoxy and poly/vinyl resin are different...

Also, there was no original question, it was a tread about what he learned.... we were just trying to impart some additional knowledge

Dogboy

911hobie

West Systems is the best. The pumps make so easy, exact ratio, no mess.

Except that West Systems is epoxy and the original question had to do with working with polyester resin, so not really relevant. Again, the two resin systems are completely different when it comes to mixing ratios and adjusting cure times.

smEdited by Dogboy on Sep 04, 2014 - 04:35 AM.

Edited by MN3 on Sep 04, 2014 - 05:53 AM.

Yes, and building something from fiberglass (via a mold) versus repairing is quite different. The processes are reversed. I ended up with a fairly decent repair, I'd give it an 90 out of 100. For perfection, I'd respray the entire hull with new gelcoat.

When I laminated the bottoms of the hulls, I did add about 1/4" of additional fiberglass to the hull bottom for strength and durability. I did a lot of sanding (of both the glass and then the gelcoat) to retain the original shape and lines of the keel. The downside is I've added a bit more weight to the hulls, but won't have to redo this project for many years.

In fact, a winter project will be to re-spray the gelcoat along the keels each year to repair any scuffs or scrapes.

Arrrgh! Now, off to the beach...

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Karl, Captain of Stayin' Thirsty
2011 Hobie 16SE
Atlanta, GA
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