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Old 08-02-2012, 19:52   #46
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Re: The Science of Soggy Decks

I've been here too. We found as noted that the meters are not always reliable and in our case, the filler used to fair the deck after the teak was removed gave a false wet reading over a huge area. I took down the headliner and checked with the meter from inside. The real area of wet turned out to be localized near a port and was less than 10% of the area indicated on deck. I drilled a couple exploitory holes where it was wet on deck but dry below. It was totally hard and dry.

As noted above, you will not dry out with heaters. You really have to expose the core and/or remove and replace the core. I chose to use a hole saw from inside and remove 3" diameter glass washers on seversl inches centers and then dig out the wet balsa in-between. You can keep drilling and digging until you reach solid materials. Let it dry and then prop up glass mat soaked with epoxy using wood struts cardboard and polyethylene plastic sheet. You could do all of this from above much easier and you might prefer it if you plan to repaint the decks.

I happened to have a convenient exposed area along a hatch to be able to pour my replacement material filler in. I used US Composites low viscosity epoxy and microballoons filler. I made a dam on deck and poured the stuff in. The dam needs to be sealed well enough to prevent the mix from running out of control. I use gray tape folded double along the middle of the strip with both edges stuck down. I drilled a couple of vent holes at the extremes of the repair and inserted a 1/4 inch hose from below so that its end was against the inside bottom of the deck. Suck on the hose and the resin mix nicely fills the void. You could see it advance from the dam to the vents because the round patches were clear. windows.

I continued with the microballoons to fair around the hatch.
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Old 09-02-2012, 08:03   #47
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Re: The Science of Soggy Decks

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Originally Posted by colemj View Post
Really? You got that much epoxy penetration across the cell structure of the epoxy? That is unusual. Balsa readily soaks up epoxy (and water) from the endgrain, but generally not much from the sides of the "long grain" (I don't know the word for that).

In fact, it's resistance to soaking up things "sideways" is one of the reasons endgrain balsa is used and not, for example, quarter-sawn balsa.

Mark
No, no. Across the top of the core into the end grain. We had pulled this mess in more or less one piece. The only way I've found to get epoxy to spread into balsa without pulling the top laminate is by hydraulic injection, which forces it through the core. I'm not even sure that really works but the spots we did were really solid afterwards.
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Old 09-02-2012, 08:03   #48
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Re: The Science of Soggy Decks

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I've cut open and properly repaired decks which were "scabbed" in that way. The job always ends up going south sooner or later, it is a temporary stopgap measure, not a permanent fix. When I peel a skin off a job which has been epoxy injected, it's immediately apparent how far the epoxy did or didn't penetrate. I'm never impressed. In fact, it's such a PITA for us to grind out all the crap which has been injected to make room for a nice clean, fair, core replacement, that we charge substantially more to fix the amateurs mess than we would to do a normal core replacement. A few times I've seen jobs where a great deal of injection was done, in one case thickened with cabosil, which is almost impossible to grind/chisel out without destroying the delicate inside skin. It was a serious issue and probably cost several times as much as a proper job would have. A deck needs to be lightweight, strong, flexible, and fair. Injection is exactly the wrong answer for all of those issues. Personally I think a deck core replacement job can be a boon in disguise; it is an opportunity to get all that organic rotting crap that never should have been in the layup in the first place out and replace it with something worthwhile, like a foam core or coosa board. Once done right the boat is good for at least the life of the owner in that regard, no more ticking timebomb in the deck. And injection will certainly not guarantee that you will pass survey, especially with a surveyor who clearly knows how to use a moisture meter. I guess this is the case, since his meter said it was wet and you didn't believe it, but now you are slowly being convinced he is right as you look more. The meter never lies, you just need to know how to spot false readings.
Yep, nothing like trying to pull soggy core with hundreds of little epoxy pillars getting in the way.
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Old 09-02-2012, 11:06   #49
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Re: The Science of Soggy Decks

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I do most of my deck core replacement jobs in poly. Next time try Core Bond Core-Bond / Poly-Bond Instead of regular bondo. It has a very slow potential cure time, though you can mix it hot, and it weighs half as much as regular bondo and is more flexible without cracking. Cheap too. Specifically designed for this app.
Thanks, I dont remember if I used the green marine version of bondo or regular at the time. Oh.... and I dont intend for there ever to be another go at one!!
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Old 09-02-2012, 11:44   #50
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Re: The Science of Soggy Decks

[QUOTE=colemj;881679]If you truly have wet decks, over large areas and delamination, the only way to fix this is to cut it out and recore it. I have tried just about every way to fix wet decks and the only one that works for good is recoring.

you could always do like I did with my first boat. Separate the top and bottom, dig all coring out from inside and reglass to 1/2" thickness. Felt like walking on concrete slab afterward but oh how I suffered through the process, Then to finish it off I glassed the two pieces together inside and out and finished the outside so there was no seam visable. Groan
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Old 16-02-2012, 07:03   #51
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Re: The Science of Soggy Decks

Hey so just an update. We did find a small section that had a soft spot under the stanchion. I cut the skin off {about 7 X7 inches} with a dremel tool and dug out the rot. The only problem is that the surrounding plywood is really wet, not rotten, not delaminated, just wet. I am have tried to dry it out with a heater and acetone but it doesn't seem to be working. I hate the thought of ripping up the deck just becasue something is wet but I will have nothing for my patch to bond to if I don't, ugh.

So I am sorry I lied and said my deck was "bone" dry. It is hard to tell the condition just by taking a small core sample.

On a side note it looks like the builder used a combination of balsa and plywood on the deck. weird huh?
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Old 16-02-2012, 07:12   #52
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Re: The Science of Soggy Decks

The major problem with fiberglass is that it is osmotic. In time everything will become wet in the inside unless shielded by an impermeable coating. All polyester resins are in principal osmotic. Vinylester the least. Therefore: a sandwich construction in a FRP laminate is not such a great idea, balsa cored being # 1.
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Old 16-02-2012, 09:52   #53
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Re: The Science of Soggy Decks

It amazes me that builders havent improved this problem that much. Maybe some have, I dont know. I understand how small builders might never get to the point of defining where all the deck "bolt on" items are. But you would think production builders would get those areas defined as a priority, eliminate core in those areas leaving solid glass to bolt stancions, cleats etc through. It's just sloppy manufacturing by companies that dont care..
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Old 16-02-2012, 10:06   #54
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Re: The Science of Soggy Decks

I know acetone penetrates, but does it absorb water?

If not, use high-proof alcohol. It absorbs the moisture and then takes it out as it evaporates. Saok, cover, let marinate, then let evaporate. Or put a cover over the area and rig a small low-pressure vacuum pump to help suck it out, maybe aided with a ring of 1/4" holes drilled a foot or two further out, to let dry air in behind the moisture?
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Old 16-02-2012, 10:13   #55
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Re: The Science of Soggy Decks

In the beginning nobody knew that fiberglass was osmotic. Even now, builders use thick balsacores nota bene under the waterline (Contest). Complete useless and unnecessary.
A stiffer hull, yes for now and a stiffer wallet for the future.

I worked in my spare time on an old AC, a big brute of a boat and discovered that the deck came loose from the underground what came out as being plywood. I knew the builder and asked why he did construct the deck this way.

"Had I known at the time of building, I would not have done it, but we didn' t know (at that time, 1972) that polyester was osmotic."

Because the fiberglass let waterdamp through, the whole deck was more or less infested with black rot. Again, any core in a fiberglass laminate will cause sooner or later delamination of the inner layer of laminate. Though this might take some 20-25 years after building. Beware of the older ships, specifically those with Kevlar inside.
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Old 16-02-2012, 10:13   #56
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Re: The Science of Soggy Decks

Any alcohol has a hydrogen molecule attached which will bond with other water drops and will speed evaporation

I havent had time to read all this thread but a few yrs ago, Kristian modified an old microwave oven by removing the door and then fixed it up against the underside of his deck heads to heat a wet core.

Might be worth looking out that thread?
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Old 16-02-2012, 10:26   #57
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Re: The Science of Soggy Decks

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Hey so just an update. We did find a small section that had a soft spot under the stanchion. I cut the skin off {about 7 X7 inches} with a dremel tool and dug out the rot. The only problem is that the surrounding plywood is really wet, not rotten, not delaminated, just wet. I am have tried to dry it out with a heater and acetone but it doesn't seem to be working. I hate the thought of ripping up the deck just becasue something is wet but I will have nothing for my patch to bond to if I don't, ugh.

So I am sorry I lied and said my deck was "bone" dry. It is hard to tell the condition just by taking a small core sample.

On a side note it looks like the builder used a combination of balsa and plywood on the deck. weird huh?

Cutting it out is the only option. I would not try to dry a ply core even with the Hotvac, it just can't be done in an efficient manner. Ply has no end grain exposed like balsa and so just won't dry. Balsa or foam at least wick moisture efficiently and are therefore dryable, though in the case of balsa I don't think it's worth doing because it will rot anyway. So will ply. Once it gets good and wet theres no saving it, even if you did dry it it will probably dry rot, it'll just take a little longer to happen. Suck it up, cut it out and replace it. No fun but you'll feel much better about it when it's done. Replace the balsa core with 5lb. rigid urethane foam core, and replace the ply with Coosa board of a matching thickness. You'll never have a problem again, and the cost is about the same. Faith in the moisture meter comes with experience, I have clients question the meter all the time. They are always wrong.
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Old 16-02-2012, 10:30   #58
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Re: The Science of Soggy Decks

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It amazes me that builders havent improved this problem that much. Maybe some have, I dont know. I understand how small builders might never get to the point of defining where all the deck "bolt on" items are. But you would think production builders would get those areas defined as a priority, eliminate core in those areas leaving solid glass to bolt stancions, cleats etc through. It's just sloppy manufacturing by companies that dont care..

Many builders have greatly improved the problem. In fact many of the basic innovations in fiberglass yacht construction in the last 20 years have been a result of addressing these problems. Techniques like SCRIMP and infusion are much more common now, as are foam or hexcell cores, solid deck block outs in way of hardware, etc. etc. Newer boats are much better built. The problem is there are a great many more old boats on the market than new ones. So retrofitting to solve these problems properly is important.
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Old 16-02-2012, 10:33   #59
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Re: The Science of Soggy Decks

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Any alcohol has a hydrogen molecule attached which will bond with other water drops and will speed evaporation

I havent had time to read all this thread but a few yrs ago, Kristian modified an old microwave oven by removing the door and then fixed it up against the underside of his deck heads to heat a wet core.

Might be worth looking out that thread?

Acetone functions in the same way but evaporates much faster. Once it has had time to mix with the water it is generally safe to apply heat. I do it all the time, even though I am often questioned on the safety of it. I have been doing it for many years and have never acheived ignition when drying something with acetone and a heat gun.
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Old 16-02-2012, 10:45   #60
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Re: The Science of Soggy Decks

There are modern methods of building but those are intended to reduce waste of resin and to keep resin/glass ratio within certain limits. Injection moulding and vacuumbagging helps but cannot prevent osmosis in the final end. Only the use of epoxies can do that but that makes a boat much more expensive because of some unpleasant habits of epoxy when drying out. Prepregs (epoxy) might overcome those technical issues but do not solve the financial ones.
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