Setting stringers with PL poly construction adhesive

[Paul Bell]

I have read a few posts previously in some threads that talk about the idea of PL poly const. adhesive as an alternative method to set stringers.The flexible yet structurally stable bonding characteristics of this product and ease of application are appealing.
I understand it is important to not have direct contact of wood to hull.
I would be very interested in hearing about experience others might have with this method.
If I go that route once the PL is dry would there be any problem to then cover the wood with fiberglass matting and epoxy to complete the job for stability and integrity of the rebuild?
Would epoxy and PL poly be compatible?
I have attached a photo of my rebuild that shows a few new stringers as well as "sister board" reinforced stringers. The PL appears to be a great means to bond the wood reinforcements before screwing them together.
Advice on these ideas would be greatly appreciated.

 

[oops!]

Re: Setting stringers with PL poly construction adhesive

cant say about the epoxy......but let the pl fully cure before you glass over it.....

 

[ondarvr]

Re: Setting stringers with PL poly construction adhesive

Whatever?s used between the stringer and hull makes little difference, its just used to keep the wood off the hull, not really aid in the bonding and should not be the only thing attaching the stringer to the hull. The stringers need to be glassed in place (epoxy or polyester) and depending on the design, much, or most of the strength is supplied by the laminate. Some people use foam spacers between the stringer and hull, all you need to do is prevent creating a hard spot by having just a small area of the wood in contact with the hull.

 

[tashasdaddy]

Re: Setting stringers with PL poly construction adhesive

i've been using PL poly for years, for transoms, bedding strigers, etc. never a problem. i have even used it like marine tex, to fill a scratch, or gouge, that is going to be painted.

 

[jonesg]

Re: Setting stringers with PL poly construction adhesive

I'm gonna try that construction glue, sounds great.
I've seen instances where guys put down 4-5 small foam spacers first, then the glue, to keep the stringer from pushing down to the hull, makes sense.

My stringers are ready to go in, but we got 10 inches of snow last nite.

I glassed my stringers first, then sealed edges with poly , then sanded then they are ready to install. Its easier to do all that on a sawhorse.

The bottom edge of the stringers which will be most likely to meet moisture were soaked with poly resin thinned with acetone, soaked in continually until the resin started to thicken on the brush.

Through bolts and angle brackets are used to connect stringers to the main cross braces on mine, the old ones were still good since 1974, I'll re-use the angle brackets. Screws will tend to loosen methinks.

 

[Stoutcat]

Re: Setting stringers with PL poly construction adhesive

Ondarvr wrote,

Whatever?s used between the stringer an hull makes little difference, its just used to keep the wood off the hull, not really aid in the bonding and should not be the only thing attaching the stringer to the hull. The stringers need to be glassed in place (epoxy or polyester) and depending on the design, much, or most of the strength is supplied by the laminate. Some people use foam spacers between the stringer and hull, all you need to do is prevent creating a hard spot by having just a small area of the wood in contact with the hull.

OK... Now I'm absolutely, thoroughly confused. (Granted I come from the wooden boat world, and my understanding of the functionality of stringers is probably different from FG guys... I apologize right up front.) But I thought a key element to the strength and functionality of stringers was that they had some sort of mechanical/chemical bond (aside from the goo/mat that encased them) to the hull itself.

Truly confused and trying to catch up...

Alan

 

[Paul Bell]

Re: Setting stringers with PL poly construction adhesive

Were buried in snow and cold here in Northern Ill. I love a winter project this is a little more than I ever expected.I plan to pull all this wood that is just placed there after cutting and bring to my heated garage for a few coats of epoxy then place the epoxied boards and set with the PL poly. My 89 Celebrity did not use angle brackets but an extra piece of wood blocking at every point where a 90degree angle meets another. Lots of stainless screws then fiberglassed wood to the hull. Previosly the fiberglass ran up the sides of the boards but left the top inch exposed.They rotted then from the top down once the foam became saturated.Screws will not loosen after covered with layer of fiberglass. Through bolting with SS bolts of the sister boards in a few spots might help but the PL poly will hold the sandwich together after clamping and screwing.
This all started just because I wanted to remove my carpet and fix a soft spot in the floor!!
Thanks for the thoughts.
Nice to know I am not the only one taking on a job like this.

 

[BillP]

Re: Setting stringers with PL poly construction adhesive

Ondarvr wrote,



OK... Now I'm absolutely, thoroughly confused. (Granted I come from the wooden boat world, and my understanding of the functionality of stringers is probably different from FG guys... I apologize right up front.) But I thought a key element to the strength and functionality of stringers was that they had some sort of mechanical/chemical bond (aside from the goo/mat that encased them) to the hull itself.

Truly confused and trying to catch up...

Alan

Wood boats are a totally different animal. Glass boat stringers are what darvarer said (iboat historical event...we agree). The glass is load bearing on the hull no matter what the stringer material. The stringer is captured by the glass and doesn't need to touch the hull. Foam spacers are typically seen on boats that use ply for stringers and bulkheads because the ply has such a small footprint. I wouldn't worry about it when using 2"xX dimensional lumber on the typical trailer boat.

bp

 

[oops!]

Re: Setting stringers with PL poly construction adhesive

stoutcat, what ON-THE-RIVER....(ON-DA-RVR) is referring to is that the fiber glass hull's of boats have some flex in them.....stringers dont have the same flex.....if you put any style of stringer directly on the hull....and cee-ment it down. the hull would flex and the stringer would not. that means the glass and gellcoat would generate crazing aroung the outter hull flex points.

so as long as there is "somthing" between the srtinger and the hull......the issue is resolved.

some common bedding compounds are "peanut butter" pl and 3m 5200

 

[jonesg]

Re: Setting stringers with PL poly construction adhesive

Celebrity did not use angle brackets but an extra piece of wood blocking at every point where a 90degree angle meets another. Lots of stainless screws then fiberglassed wood to the hull. .

you have a lot more cross bracing than I do,
I only have 2 main formers going from hull side to side in a 20' heavy glass boat.
More bracing spreads the load better.
You can't go too far wrong following the original build.
Nuts, bolts and brackets are a pain compared to screws.

Almost 20 inches of snow the last 2 days here. The boat cover is starting to sag. bah!

 

[Bondo]

Re: Setting stringers with PL poly construction adhesive

what ON-THE-RIVER....(ON-DA-RVR)

Duh,.......................

Nevermind......:redface:

 

[JorgeE]

Re: Setting stringers with PL poly construction adhesive

Gents,
At the risk if taking this thread slightly off-course...
The Rptdoctor.com website suggests using PL Polu (they specifically recommend Dymonic FC) for setting the plywood floor over the stringers. This seems to make sense. They call Dymonic FC a "low modulus - high strength" adhesive. This would allow sllight movement between plywood and stringers, but keep them from separating.
Any experience in using this between floor and stringers?

BTW, Paul and I are doing essentially the same work, on same model/year boats - spooky? Naw, just happen to both own 20 year old boats. Thankfully for me, he's about a month or more futher along

Thanks for any words of wisdom...

Jorge

 

[ondarvr]

Re: Setting stringers with PL poly construction adhesive

I haven't used it, but like what was said before, it really doesn't matter what you use. By the time any stress would be put on the adhesive spacing the stringer off the hull the laminate would need to have completely failed, at that point the strength of the adhesive wouldn't be enough to hold it in place.

 

[James R]

Re: Setting stringers with PL poly construction adhesive

My Son and I got into removing the rotted portions of the deck and stringers on our 16ft Cobia Monte Carlo. What a shame that the manufacturer used what I consider junk wood for the stringers which probably rotted because it was wet to start with. The main area is the box which surrounds the fuel tank. The fiberglass shells are strong and we have carefully removed all the rotted wood. we plan to make new stringers out of quality ply, seal them in resin and slip the stringers into the slots created by the fiberglass shells. We will use resin and clamps to attach the new ply to the shells and cap the ply with cloth and resin. Our main concern is which adhesive to use to attach the new marine ply decking. My thoughts are to use heavy duty construction adhesive and stainless screws. I have seen many references to PL? If this is the best approach can you please advise where this may be obtained.
Any help on this project would be appreciated.

 

[jonesg]

Re: Setting stringers with PL poly construction adhesive

home depot sells it.

 

[Mark42]

Re: Setting stringers with PL poly construction adhesive

Whatever?s used between the stringer and hull makes little difference, its just used to keep the wood off the hull, not really aid in the bonding and should not be the only thing attaching the stringer to the hull. The stringers need to be glassed in place (epoxy or polyester) and depending on the design, much, or most of the strength is supplied by the laminate. Some people use foam spacers between the stringer and hull, all you need to do is prevent creating a hard spot by having just a small area of the wood in contact with the hull.

Maybe I've misunderstood something. So I have to ask:

- Once the stringer is glassed in place, hasn't a hard spot been created along the entire length of the stringer by connecting the stringer to the hull with fiberglass?

- Boat manufacturers have been glassing the stringers to the hull with no cushioning since the advent of fiberglass boats, but stress cracks along stringers doesn't seem to be very common at all. Whats different between what you suggest and what manufacturers are doing?

Not trying to start an argument, I just want to make sure I understand the stringer spacer/cushon concept.

Thanks!

Mark.

 

[PaulyV]

Re: Setting stringers with PL poly construction adhesive

stoutcat, what ON-THE-RIVER....(ON-DA-RVR) is referring to is that the fiber glass hull's of boats have some flex in them.....stringers dont have the same flex.....if you put any style of stringer directly on the hull....and cee-ment it down. the hull would flex and the stringer would not. that means the glass and gellcoat would generate crazing aroung the outter hull flex points.

so as long as there is "somthing" between the srtinger and the hull......the issue is resolved.

some common bedding compounds are "peanut butter" pl and 3m 5200

Perfect sense now..

 

[Mark42]

Re: Setting stringers with PL poly construction adhesive

Perfect sense now..

How does any cushioning under the stringer prevent hard spots when the strigner is ridigly attached directly to the hull with fiberglass on either side?

What does the cushioning do once its encapsulated in glass?

 

[ondarvr]

Re: Setting stringers with PL poly construction adhesive

Mark

You?re correct, there are probably far fewer boats made with spacing than without it and it affects a thin hull far more than a thicker one and then only sometimes.


The typical laminate over a stringer extends out about 6? on both sides and the edges sort of taper off, plus the laminate has flex similar to what the hull has, so this spreads the load. Plywood has very little flex when turned on edge and the contact patch may only be the size of a dime, so the whole load is concentrated in a very small area. The other thing that takes place is the laminate over the stringer will shrink as it cures, this forces the stringer against the hull before any stresses from it being used are applied, so it pre-loads the plywood. You can often see bulkheads, cores, backing plates, or anything that?s glassed into a hull, just look down the hull side, it can affect larger boats more noticeably because there are more of these items, plus there is much more surface area with little contour to hide them. If the hull flexes more than it should, or the laminate over the stringer (or anything else glassed in place) is too stiff, then it may form stress cracks whether it?s spaced off the hull or not. Using putty (peanut butter) under the stringer just spreads the load over much more of the surface so it?s less likely to form stress cracks, it would probably be more likely to crack or show than spacing it off the hull would though.

After the stringer has been glassed in place the cushion or spacer does nothing, that?s why just a couple chunks of foam will work as well as the best construction adhesive.

 

[James R]

Re: Setting stringers with PL poly construction adhesive

Thanks JonesG. Based on much input, especially Tashas it looks like Pl is slated for the job.
Thanks a bunch guys and Happy New Year!