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Old 11-03-2020, 07:48   #1
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Soft decks

Has anyone had any experience with injecting foam products to fix the wet or rotted core of a sailboat deck. I have read the info on a product called "Inject A Deck". This looks like a viable solution rather than pealing of the deck and replacing the core and re fibre glassing. any experience with same or similar products.
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Old 11-03-2020, 08:36   #2
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Re: Soft decks

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Has anyone had any experience with injecting foam products to fix the wet or rotted core of a sailboat deck. I have read the info on a product called "Inject A Deck". This looks like a viable solution rather than pealing of the deck and replacing the core and re fibre glassing. any experience with same or similar products.
Upcoming article in Practical Sailor.

Consider that the shear strength of end grain balsa is about 1100 psi and the shear strength of high density 2-part foams is about 100 psi. Add the mulch and dampness that's trapped in there now, and you need to be extremely realistic.

The deck will be firmer.

Re-glassing is not as bad as it sounds, particularly if you are willing to re-paint the deck at the same time. Depending on the area, you're talking a day or a few, not a month. Much depends on what the old core was and how experienced you are with glass work. It can go pretty fast.
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Old 11-03-2020, 08:38   #3
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Re: Soft decks

Who knows

I’ve seen epoxy products injected into decks via grease nipples

Does it work ?

Once again.. who knows
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Old 11-03-2020, 08:48   #4
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Re: Soft decks

I'd think the end result would depend a lot on how big an area of deck is damaged and how damaged it was. If it's totally rotted, I don't think there's much of a fix without cutting it open. If it's plywood cored and wet, but not rotted, for example, it might be possible to get it dry with a combination of heat and vacuum, then force epoxy through the wood to make it more solid and get decent results.
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Old 11-03-2020, 10:40   #5
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Re: Soft decks

Remember that virtually all of the load on the core is shear, not flex. Even plywood does NOT carry a significant portion of the load (it is to stretchy, particularly if damp, compared to glass). You need to get a bond to the top and bottoms skins, which are not prepared and are at least damp.


Expansion foam is too weak. Epoxy is too thick to soak far, so the holes typically have to be every 1-2 inches. It also does not cure well with excessive moisture (there are underwater epoxies, but they are thickened).



I started on the project after finding a paddle board on a jetty, kinda beat up.
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Old 11-03-2020, 11:00   #6
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Re: Soft decks

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Upcoming article in Practical Sailor.

Consider that the shear strength of end grain balsa is about 1100 psi and the shear strength of high density 2-part foams is about 100 psi. Add the mulch and dampness that's trapped in there now, and you need to be extremely realistic.
I'll be interested to read this Thin. Thanks again for all your good work .

Questions: How does this "inject-a-deck" stuff work? I've read here it cures using the existing water that is in the de-laminated deck. If so, does that imply the water is removed (bonded into a different molecular structure)?

What is shearing in a deck laminate? I haven't really thought much about this, but I would have guessed the deck is presented with compression loads more than shear -- no?

How much shear strength is required in a deck laminate? I have no idea if 1100 psi is needed, or is 100 psi enough.
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Old 11-03-2020, 12:11   #7
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Re: Soft decks

My guess is it's something like Gorilla Glue (GG), a liquid that foams up and cures in the presence of moisture. That stuff stick just about anything to anything but it's not magic, you still have to deal with the structural strength of what you attempt to bond.
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Old 11-03-2020, 12:35   #8
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Re: Soft decks

Injecting epoxy is done where there is delamination without any deterioration of the core material.
Gorilla glue is to brittle for this application.
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Old 11-03-2020, 13:56   #9
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Re: Soft decks

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I'll be interested to read this Thin. Thanks again for all your good work .

Questions: How does this "inject-a-deck" stuff work? I've read here it cures using the existing water that is in the de-laminated deck. If so, does that imply the water is removed (bonded into a different molecular structure)?

What is shearing in a deck laminate? I haven't really thought much about this, but I would have guessed the deck is presented with compression loads more than shear -- no?

How much shear strength is required in a deck laminate? I have no idea if 1100 psi is needed, or is 100 psi enough.

Polyurethanes (most expansion foams, Sika sealants, and Gorilla Glue) use water as a curing agent. Some of the water is incorporated in the polymer. But that does NOT mean that they bond well to wet surfaces. They don't. Only underwater epoxies (Splash Zone, WaterWeld), to my knowledge, can pull off that trick.


Yes, in most panels all of the important core loads are in shear. Bend a stack of printer paper and watch the sheets slide past each other. To make the stack stiff, you need to drive a few nails through it, to stop sheer motion. This is why drilling holes and injecting glue seems to fix the problem; the pillars of glue can resist some sheer (but not much).


How much is enough? Obviously that depends on the design. The thicker the ore, the lower the sheer, in general. But do you even have 100 psi, if the foam is hit-or-miss bonded to mulch. No, you don't.


The skins, of course, are either in tension (lower) or compression (top) when you step on them. Compressive strnegth of the core is mostly a factor only when applying clamping loads (hardware, outboards), which is why plywood is sometimes used in those places. But Coosa Board is better.
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Old 11-03-2020, 14:01   #10
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Re: Soft decks

I recored the lid to my anchor locker about 18 months ago. The balsa was so rotten I could have potted plants in it. In fact I wish I had done that and taken pictures, just to prove a point! That would have been visually funny.


With foam delamination-only is possible, although once it starts to flex, the core fails in shear and tends to get torn up a bit over time (think about what happens when it flexes). Delamination-only is probably a theoretical case. And I really doubt the epoxy is going to migrate more than 1/2-inch or so. Epoxy is viscous.
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Old 11-03-2020, 17:02   #11
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Re: Soft decks

I'm currently in the midst of recoring my bow pulpit. The original plywood core was slightly delaminated, but wet throughout. However, only spots right around the poorly sealed core penetrations were actually rotted. The rest was wet, but intact when I ripped it all out.

Given some time and effort (probably no less than a recore), it likely could have been dried out and had epoxy pulled through by vacuum and been fine for many more years. But I needed the sure fix, so I wasn't about to try it.
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Old 11-03-2020, 18:49   #12
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Re: Soft decks

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Originally Posted by thinwater View Post
Polyurethanes (most expansion foams, Sika sealants, and Gorilla Glue) use water as a curing agent. Some of the water is incorporated in the polymer. But that does NOT mean that they bond well to wet surfaces. They don't. Only underwater epoxies (Splash Zone, WaterWeld), to my knowledge, can pull off that trick.
Is that what this inject-a-deck stuff is? So it's no different than a lot of the expanding foam already out there?

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Yes, in most panels all of the important core loads are in shear. Bend a stack of printer paper and watch the sheets slide past each other. To make the stack stiff, you need to drive a few nails through it, to stop sheer motion. This is why drilling holes and injecting glue seems to fix the problem; the pillars of glue can resist some sheer (but not much).
Thanks. This helps a lot. I really hadn't thought about it before. Makes it clearer what might be going on below the skin. So these sheering forces lead to de-lamination, and then separation of skin to core. This leads to the potted plant syndrome you mentioned as things start moving. And then any compressive force will break the skin? Or a tension (pull) will rip a fitting -- Is that the failure route?

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How much is enough? Obviously that depends on the design. The thicker the ore, the lower the sheer, in general. But do you even have 100 psi, if the foam is hit-or-miss bonded to mulch. No, you don't.
It's just that I have no idea what psi is required to be "good enough." You gave a broad scale of 1000 to 100 psi. But what is good? Even 35 (the pressure in my tires) sounds like lots of force to me. But honestly, I have no idea what forces we're talking about.
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