Question about using PL for stringers

othelloears

Petty Officer 2nd Class
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Jun 28, 2008
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I am doing my stringers and had a specific question.

I am using PL for bedding under my stringers and will then run epoxy peanut butter along all edges to round everything over for the 1708.

I was planning on doing one stringer a day (PL/peanut butter/1708 tape/1708 wrap) to keep everything wet/tacky and avoid scuffing/vacuuming/acetoning.

Is it preferable to let the PL dry or do it together so everything bonds together? I guess the bottom line is whether epoxy peanut putter will bond to uncured PL?
 

erikgreen

Captain
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Jan 8, 2007
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3,105
Re: Question about using PL for stringers

I know it will bond, but how well is anyone's guess I think.

Did you know you don't have to use anything under your stringers at all? The PL actually is meant to ensure an even transfer of force from the hull to the stringer instead of letting it happen at a few "hard spots", but you can also just suspend the stringer in place a quarter inch or so off of the hull while you glass it? The only difficult part is getting a smooth radius at the stringer/hull joint. You have to sort of drape the first layer of tape in a curve.

Some folks use nothing under the stringers (air), some use PL, some use epoxy glue, some use blue or pink foam. If you're really careful to hand fit every inch of the stringer to the hull you could in theory put it directly on the glass. Much easier to use a "bedding" compound to make a perfect fit, though.

None of this is really significantly structural... all of it is meant to make sure that you don't have a situation where the hull can press against a small part of the stringer, focusing force there and flexing, forming a hole or crack. Usually it's also formed to make a fillet so the glass on the stringer sides doesn't have to make a 90 degree turn.

Erik
 

othelloears

Petty Officer 2nd Class
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Jun 28, 2008
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Re: Question about using PL for stringers

Thanks for the detailed reply. I am actually struggling on whether to put anythink underthere as there is nothing under my original stringers which are about 1/2" off the hull. I wasn't sure if I would be able to make the turn with the 1708 without anything. Would you recommend I give it a shot without anything or would you recommend just using peanut butter for both...the bedding and the groove. The PL appealed to me because I thought it would be softer and provide more flex
 

danond

Lieutenant Junior Grade
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Jun 11, 2007
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1,118
Re: Question about using PL for stringers

Use something under the stringer. PL works. I prefer epoxy. There's no guesswork, no worry about curing if it's sealed off from exposure to air, and epoxy is a guaranteed bond and is structurally awesome.

I'd like the PL cure before applying the glass and epoxy. Epoxy bonds to just about anything solid where it can get a mechanical grip as it cures. If the PL is still drying you probably won't get as good a bond.
 

J. Mark

Petty Officer 1st Class
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Sep 3, 2008
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Re: Question about using PL for stringers

When I used the PL I let it cure 48 hours minimum before glassing over it.

Some folks have used it for the filets-I tried this and didn't like it, thickened epoxy goes on much smoother.

If you buy PL in the big tubes, you will need more than you imagine-go ahead and buy a case. Stopping work because you run out of supplies really sucks.
 

erikgreen

Captain
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Jan 8, 2007
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3,105
Re: Question about using PL for stringers

I'll agree with that.

The easiest way out is PL, it ensures a perfect fit and will hold the stringers in place while you glass, plus you can mold a perfect fillet in it with the end of a popsicle stick. On the downside if you have any moisture around it will bubble some, which may require cleaning up before glassing over it.

Epoxy glue is perfect for the job, very solid, identical to the epoxy you use in the glass so the whole thing is one piece.

I've used PL, epoxy, and foam, and I'll probably do the foam again because it's quicker (although it can be harder to do) but epoxy would be my second choice.

Erik
 

othelloears

Petty Officer 2nd Class
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Jun 28, 2008
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Re: Question about using PL for stringers

You guys are great...these answers are perfect

I am only replacing about 1/2 of 2 fo the 4 main stringers. (1/2 of the length of 2 and 2 others staying.

Given that would you be more inclined to match whats there (1/2 space)?

Have any of you guys left a space and used 1708?
 

J. Mark

Petty Officer 1st Class
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Sep 3, 2008
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303
Re: Question about using PL for stringers

If you are sectioning stringers, I would definitely try and duplicate what was previously done. PL does have some give after it is dry, but if 1/2 of a stringer is mounted in a different manner, I can't see the PL not creating a differing stress distribution from the stock set up.

I would scab some 3/8th's plywood at the joint to help hold the new wood in place. You can remove it after you get a layer of resin and glass in place if it is in a spot where you can't accommodate the extra thickness (like by a gas tank). You can also add some bracing at the opposite end to keep your new wood in position.

To keep your filet putty from flowing under the new section you may need to make a barrier of some type. I would just lay a sheet of medium weight glass on wax paper, coat it with resin and let it cure and then cut it into strips just a bit higher than your gap. Do the work with unwaxed resin if using poly and do your filet and layup before it sits too long and it will just become part of the glass. Heavier glass will make it harder to get a smooth transition-all you want is some minor barrier to keep your filet alongside the stringer not underneath it where an errant bit of your putty might turn into a hard spot. A piece of foam does the same thing essentially.
 

othelloears

Petty Officer 2nd Class
Joined
Jun 28, 2008
Messages
123
Re: Question about using PL for stringers

I think I will need to do foam strips so the fillets won't get pushed underneath...no PL

Thanks Everyone
 

cjd

Cadet
Joined
Sep 3, 2003
Messages
11
Re: Question about using PL for stringers

What Is PL?

I am looking a ta prodcut called Pettit Flexpoxy to bed my stringers. I am not confident I can do this without bedding the stringers, but the Pettit flexpoxy is pretty pricy.

Any one use it?

Is PL better and cheaper?
 

danond

Lieutenant Junior Grade
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Jun 11, 2007
Messages
1,118
Re: Question about using PL for stringers

PL is a construction adhesive.

Don't spend a bunch of money on the bedding material for your stringers. If you are, big $ alone means it's likely the wrong solution.

Use thickened epoxy or PL adhesive. Both are no-guesswork, have excellent adhesion and are cost-effective solutions.
 

cjd

Cadet
Joined
Sep 3, 2003
Messages
11
Re: Question about using PL for stringers

perfect advice. thanks
 
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