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Epoxy Tricks


Howard

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Fairing is mostly about technique and procedure. On plywood hulls, this can be a pretty fast thing, mostly because the panels are generally fair to start with. Most novices will want to fair twice - once before the sheathing goes on, because a fair surface that is sheathed is a lot easier to fair after it's sheathed. and the second time is after the sheathing. This might seem counter intuitive, but it's the easier way to go.

 

The "pre-fair" is to iron out seams, tape edges, screw holes, the big divot when you dropped the drill on the bottom planks, etc. I use a light mist of primer to find the low spots (cross hatched scratch thingie), then bring the lows up to the highs. The last thing I do at this stage, is to quick coat more primer and give it a cross hatch scratch, which just tells me how close I got things. If close enough, I remove the primer with solvent (the fastest way) and move onto the sheathing. Once sheathed, it's the same process, with repeated cross hatch runs to identify the surface imperfections, which will be slight if sheathed over a pre-faired substrate.

 

For the pre-fair, I'll use 80 grit and see no reason to go finer, as it'll be sheathed, so the tooth will help the fabric bond. After she's sheathed and the weave filled (use filler), I'll move up to 100 initially, but quickly to 120 or 150 grit as I fine tune the surface. Good primer will fill these scratches easily. If spraying a LPU, I'll continue with grits up to as much as 320, but no higher, as to not affect the paint's grip on the primer. If interested in a flawless, mirror surface, I'll buff and polish the top coat, not fair the primer with fine grits. It's pretty easy to get carried away with too fine a grit and have a limited mechanical tooth, for the top coats to hold onto. Simply put, if you apply enough film thickness, you can fill 220 grit scratches with paint and buff out the rest of the job, if this is necessary (drips, sags, etc.).

 

This process is different than working a car body. The primers and top coats on cars are usually thinner then hand applied paints. This means you can't take as much off and the film thickness may be too thin to fill a big scratch, like 220 grit. This is why car paint jobs will use 400 grit and higher. Don't be swayed, unless spraying, you don't want to go too smooth on the scratch.

 

I just used a simile stage LPU for a car ('67 FireBird). It's very similar to the two stage LPU's, but just no separate clear coat. It's an Eastwood product and works very well, plus saves a bunch of effort and money (about $120 a gallon). It's still an activated polyurethane (5:1), but it's ready to buff an hour out of the gun. Even without the buff it's a good finish, but the buff removes stipple and other imperfections quickly. Once the surface is ready for top coat, you can be done, ready to use in a few hours.

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Good primer will fill these scratches easily. If spraying a LPU,...................I just used a simile stage LPU for a car ('67 FireBird). It's very similar to the two stage LPU's, but just no separate clear coat. It's an Eastwood product and works very well,.

 

Paul, I really appreciate the detailed description of the fairing process but must plead ignorance of what is a "good" primer for this process, what is a "LPU" and what is a "simile stage LPU".  I've looked at the Eastwood website  ( ) and wasn't much help.  I like the idea of using a light coat of primer to expose the low spots and since it's all coming back off anyway (with sanding and solvent) does it really matter what kind/brand is used?  Help please, again!

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LPU is Linear PolyUrethane and this typically is a two part paint (hardener and resin). This is the stuff that costs a lot, but looks like a million bucks. I have a typo above and meant to say it's a "single stage" system, which means it isn't a base/clear coat type of product, like that used on cars. A single stage system means you get the finished result with application, no other coats are necessary. This types of paints can be a single or multi part paint. Brightsides is a good example of a single stage, single part paint.

 

For the novice painter the best advice is use the primer the top coat manufacture recommends (it'll be theirs, surprise). If you want to use something else, System Three has a good water borne primer and there are a number of good epoxy primers to work with.

 

Use a blocking primer (sandable) from a rattle can for the scratch coats. It's cheap, easy to apply, fast drying and comes off easily. I use Rustoleum, which has a super fast drying time and sands well. No it doesn't matter what brand, so long as you get rid of it eventually. The only time is counts is when it'll stay on the boat, under the top coat.

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A note on System 3 LPU is that it achieves a good semi-gloss finish as 1 stage or you can go for a glare back at ya finish by adding the clear coat.  I find that the forgiveness of a semi-gloss finish is more appealing than the initial wow factor that goes down hill fast with every scratch later.

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The System Three 2 pack is a WR-LPU and not the solvent base most are accustomed with.  It's not as durable, not as glossy and not as hard as the solvent base LPU's. I've hard difficulty with it, particularly bad reactions with "Fre-Cut" papers and the inability to spray it, reliability. Most roll and tip it, so it can work for you. I think a single part polyurethane is as durable as the WR-LPU's, for less cost.

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For those having trouble with clogged epoxy pumps, pulled a jug today to find 1/2" of milky solids on the bottom of the jug and the pump clogged solid. Placed the jug in a wash tub of hot tap water and the epoxy in the jug was "clear" inside of 15 minutes. That left the pump to deal with.

 

Looking around, I spotted a heat lamp with a clear heat lamp bulb in it.  Put a sheet of tin foil behind the pump to reflect the light and heat and fired up the heat lamp from a distance of about 6 to 8 inches, moving up and down to avoid any really hot spots. The white solids started melting like butter on a warm skillet......first near the metal spring, then up and down the line. I had it entirely unclogged and working normal inside of 2 or 3 minutes.

 

So, next time you find your pumps clogged, don't throw them away or mess with acetone or vinegar or any of that stuff. I suggest you apply heat and plenty of it.

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I had about a dozen gallons that were solid white.  Would have taken many hours to liquefy all of them with a hair dryer, don't know about the heat lamp.  I just put one in a pot of water on a slow cooker hot plate and left it on while I was working.  Took 4 or five hours per gallon.  One a day for about two weeks did the trick.  Just make sure the water pot never goes dry! :D

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I had about a dozen gallons that were solid white.  Would have taken many hours to liquefy all of them with a hair dryer...............................

I don't advocate heating the resin with the hair dryer, just the pump shaft.  I can pull the pump and hold it over the opening in the container, heat it to the point of liquifying the crystals and drop the pump back into the container in a few minutes.  No muss, no fuss.

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Sounds like Fishman needs a warmer place to bulk store his resins. I was wrong about that suggestion to store them in an old refrigerator with a light bulb left on being in the West Systems Epoxy Book. It was in Sam Devlin's "Stitch and Glue" boat building book.

 

And again, it is the Part A resin half that sets up.......not the Part B hardener. Mindful of Dave's previous remarks about OHSA and storing resin and hardener together, if you do store the resin in a warm place, keep the hardener somewhere separate.

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Sounds like Fishman needs a warmer place to bulk store his resins.

You're right about that Howard and I do have one..  Actually I was was under two false impressions:(1) thought it needed to be stored in a cool place which the floor of my shop is and (2) I assumed that it didn't much matter that they were crystallizing because a day or two in a warm place would re-liquify it....not so! 

 

Hirilonde, as I said in an earlier post I used a heat gun for warming the pump and I do not recommend that too hot and dangerous; I suspected all along that the resin was flammable and was very careful so it worked for me, but obviously the hair dryer is safer.  Sure enough someone on here confirmed that it is indeed flammable.

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  • 3 weeks later...

In some sources, I've seen references to using dress lining from the local fabric store as a poor man's substitution for peel ply fabric. Checked it out and I now have one yard each of a couple possible candidates. One is called Crinoline. The other is Buckram. Both are an ultra fine mesh and both are much stiffer than I anticipated. If this sounds like peel ply, then perhaps they are similar. I'm going to try some test panels to see what happens.

 

BTW, regular price is $4.99 per yard, but these happened to be on sale for $3.49 per yard. Not sure where that stacks up in relation to the cost of peel ply.

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In some sources, I've seen references to using dress lining from the local fabric store as a poor man's substitution for peel ply fabric. Checked it out and I now have one yard each of a couple possible candidates. One is called Crinoline. The other is Buckram. Both are an ultra fine mesh and both are much stiffer than I anticipated. If this sounds like peel ply, then perhaps they are similar. I'm going to try some test panels to see what happens.BTW, regular price is $4.99 per yard, but these happened to be on sale for $3.49 per yard. Not sure where that stacks up in relation to the cost of peel ply.

Do you have experience with real peel ply to compare with? If not maybe somebody here would be willing to send you some scrap in the interest of science. I love that you are trying to clear up what many of us only speculate.
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Nope.......never used, handled or even seen peel ply. Perhaps someone who has can stroll into a fabric store to check out these alternatives?

 

If not, knowing the curious nature of how I think, I'll probably order a sample of peel ply to compare it myself.

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For screw holes I use thickened epoxy in a syringe.  I'm not real pleased with this method because If the hole has no bottom, i.e. goes through both layers of ply, you can wind up with a big glob of goo on the back side of the ply.  If the hole has a bottom, it's very hard avoiding getting a bubble and leaving a void in the hole.  And it's very difficult to know whether you effectively filled the hole.  The other problem, assuming you succeeded in filling the hole,  once it hardens, it shrinks, leaving a "dimple" which can be up to say 1/16th inch deep. There doesn't seem to be an easy way to "scratch" the surface of the dimple, so:

 

1.  When I fill this dimple with another dab of thickened epoxy and a putty knife will it bond? 

 

2.  Or will sometime in the future will this little dab of epoxy pop out along with the paint finish and have to be repaired.

 

3.  Should I just ignore these little dimples and assume that the glassing, fairing, priming and painting process will fill them, and all will be ok?

 

4.  I suppose one could find a Dremel tool sanding head that could be used to rough the surface of these little boogers, but really.............give me a break!

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...

The "pre-fair" is to iron out seams, tape edges, screw holes, the big divot when you dropped the drill on the bottom planks, etc. I use a light mist of primer to find the low spots (cross hatched scratch thingie), then bring the lows up to the highs. The last thing I do at this stage, is to quick coat more primer and give it a cross hatch scratch, which just tells me how close I got things. If close enough, I remove the primer with solvent (the fastest way) and move onto the sheathing. Once sheathed, it's the same process, with repeated cross hatch runs to identify the surface imperfections, which will be slight if sheathed over a pre-faired substrate.

...

 

PAR, 1) what's the "cross-hatched scratch thingie" of which you speak? and 2) how did the Firebird tip and roll finish come out? ;-)

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For screw holes I use thickened epoxy in a syringe.  I'm not real pleased with this method because If the hole has no bottom, i.e. goes through both layers of ply, you can wind up with a big glob of goo on the back side of the ply.  If the hole has a bottom, it's very hard avoiding getting a bubble and leaving a void in the hole.  And it's very difficult to know whether you effectively filled the hole.  The other problem, assuming you succeeded in filling the hole,  once it hardens, it shrinks, leaving a "dimple" which can be up to say 1/16th inch deep. There doesn't seem to be an easy way to "scratch" the surface of the dimple, so:

 

1.  When I fill this dimple with another dab of thickened epoxy and a putty knife will it bond? 

 

2.  Or will sometime in the future will this little dab of epoxy pop out along with the paint finish and have to be repaired.

 

3.  Should I just ignore these little dimples and assume that the glassing, fairing, priming and painting process will fill them, and all will be ok?

 

4.  I suppose one could find a Dremel tool sanding head that could be used to rough the surface of these little boogers, but really.............give me a break!

Put a piece of tape on the back side.

 

Insert the syringe all the way to the bottom and slowly pull it out as you inject the epoxy, thus filling from the bottom up

 

Leave a lump on top, and when it's just in the plastic stage, slice it off. Or just sand it later.

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