Adding layers of fiberglass to deck

I have soft decks on my flybridge and it got me thinking that on my particular boat the fiberglass on the decks is too thin(imo) and wanted to sand off the gelcoat/paint and add some layers of fiberglass..

I know the correct way would be to remove the coring(there's little to no coring left)and replace but obviously adding layers would save me from having to cut the deck and the boat is in the slip with haulout very far away(making debris removal a problem).

It's boating season and I want to get on with it..

in the end if I need to recore I can inject the deck or cut out like I would but salvage the top layer.

I honestly think that adding 2-3 layers of fiberglass would essentially solve the problem but add some weight(not concerned much there).

I'm just trying to talk myself into it and at this point

It's the "sandwich construction" that gives the deck strength. You really need to replace the wet,rotted core then re-glass to get the strength back.
You can do that in smaller sections and knit it back together with the layers of fiberglass.

Adding layers of fiberglass will not solve the problem. It will only make it that much more difficult to actually solve the problem when it finally has to be done. Fix the core problems now, or wait until the day when your foot goes right through the flybridge floor, and THEN fix it.

The hassle is GRP is strong but not stiff.

You could consider rebuilding a new deck on top of the older deck, with a fresh new core. Just ignore the old rotten crap, and use the deck surface it as your form.

Would add about 1 inch to the deck height and about 3 lbs per sq foot of deck.

+1 on all the responses. You really need to address the coring issue. It is similar to an I beam in the strength versus a layer of plywood without the I in the beam, the plywood will sag and so will the deck without the core. Sorry, not the news you want to hear, but just adding a couple of layers of glass probably won’t do the job. If you were to add enough glass to make it say a half inch thick then it would work, but that is why the coring is there to add strength without the weight of all the glass.

Been there, done that on a Mainship mk1. Your bridge deck is full of water and balsa mush. For details use the search function on here or go to the Yahoo Mainship site. Sorry Mrwesson. There is no short cut.

I agree with all of the above. While I'm not against half-measures, in this case adding a few layers of glass mat won't gain you much and isn't all that much more work than cutting the deck, taking out the balsa and replacing with a synthetic core. Not saying that isn't a lot of work, but not a lot less than doing what you are suggesting.

dhays said:

I agree with all of the above. While I'm not against half-measures, in this case adding a few layers of glass mat won't gain you much and isn't all that much more work than cutting the deck, taking out the balsa and replacing with a synthetic core. Not saying that isn't a lot of work, but not a lot less than doing what you are suggesting.

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What about solid fiberglass hulls? They seem pretty strong.

Mrwesson said:

What about solid fiberglass hulls? They seem pretty strong.

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They are, but they are also a lot thicker.

I totally agree with all that has been said above.

There are lots of ways to do this job, but one way to approach the repair is to completely cut away the top layer of glass at the edges. Pull up the top layer in one piece or at worst a couple of pieces cut on the smooth surface lines. Then you can scoop out the balsa mush, replace it with new balsa core and epoxy it to the bottom glass layer. Then epoxy the top layer back down to the new core.

This way you reuse the non skid pattern and the only patching required is along the edges.

With heavy, thickened epoxy troweled over/under the new core top and bottom, the deck will be stronger than new.

David

David, would you replace with balsa or use one of the synthetic core materials?

dhays said:

They are, but they are also a lot thicker.

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Never drilled more than 1" through a hull and even solid fiberglass sailboats are under 1.5"...

Mrwesson said:

Never drilled more than 1" through a hull and even solid fiberglass sailboats are under 1.5"...

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If you want to add fiberglass to your decks, you certainly can. If you decide to do it, let us know how it works out.

You need to do both. Maybe put in a foam core rather than more wood to rot out.
My understanding is that if you remove the teak planking, you have to restore "stiffness", I suppose strength too, and to get a good waterproof seal. On my boat when I had the teak removed, we put 2 layers of fiberglass mat where I opted for a painted finish fwd, and one layer where we put fresh glued not screwed teak sides and aft.
I only had to repair my core in 2 small squares where teak had been used in the sandwich,it was replaced with foam,as was used everywhere else.
But, if you opt to just lay more glass without touching the core, that`s probably still an improvement.

dhays said:

David, would you replace with balsa or use one of the synthetic core materials?

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Balsa has superior structural properties to anything else typically used for coring: it has higher sheer strength at the core to laminate bond and it has higher compression strength. Anything else you might use will be weaker.

And if balsa is installed properly, and any penetrations are sealed properly, it will last forever.

David

djmarchand said:

Balsa has superior structural properties to anything else typically used for coring: it has higher sheer strength at the core to laminate bond and it has higher compression strength. Anything else you might use will be weaker.

And if balsa is installed properly, and any penetrations are sealed properly, it will last forever.

David

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Good to know, thanks. The key of course is making sure that any penetrations are sealed properly.

dhays said:

If you want to add fiberglass to your decks, you certainly can. If you decide to do it, let us know how it works out.

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Don't favor one way or the other but just can't wrap my head around the logic of it all rather than just saying because.


"You shouldn't because it'll add weight up top" or "you'll use more resin than you need to" I can see but fiberglass is pretty strong on its own unless you use 1 or 2 layers for waterproofing the core material in which it gets it's overall strength.

Mrwesson said:

Never drilled more than 1" through a hull and even solid fiberglass sailboats are under 1.5"...

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Then lay on 1” of glass and let us know how that works out.

Or, cut open the deck, dig the core out and lay the glass in there.

Because its a waste of your time and your money. Covering a water-soaked rotten deck with more fiberglass isnt a fix or even a patch.
If you were to cover the decks like you mentioned, you would still need to remove the hardware & flybridge. Thats a big chunk of your labor right there.

I think we have pretty well explained the reasons why it is a bad idea to not fix it properly. However, his boat, his choice.

I use the information I glean to make my choice. You can't have too much information.

We have soft decks, part of the reason we got our boat so very cheap.
Ours are 17mm ply over frames and epoxy was a dirty word.

2 ways it can be fixed.
Version one from a boat builder mate who had a timber trawler is, as you fall through a soft spot chop it out and scarf back in a fresh bit of ply that's had a good drink of resin and glass over.
This has been our method thus far, a few hours here a few hours there, patchwork quilt and use the boat.

Version 2 which we will start implementing soon is to get nidaplast, polycore, whatever you want to call it and start cutting it to shape and laminating up panels at our leisure and marking them so later, we can simply remove a large matching section and replace it with plastic.
Done.

Mrwesson said:

What about solid fiberglass hulls? They seem pretty strong.

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Yes but not horizontal decks that get walked on. Sandwich construction is what makes them stiff.

I did many of the decks on my "ex" Mainship I. I cut the skin and trashed it, then scraped out all the wet core material and let it dry. It was completely soaked in some areas.
I consulted a local fiberglass supply house and followed their suggestions.
5/8 exterior plywood for a core. Cut into pieces so I didn't have t build the contour out of plywood. Prepped all plywood surfaces with poly resin mixed with 25% acetone to allow penetration. drilled 1 inch holes in several places on each ply piece. Used "Bondo-lite" (regular bondo will work) to stick the ply to the base (bondo is compatable with poly resin). Used bricks to hold the ply till cured (10 minutes). Scraped off the bondo that ozzed thru the holes.
One payer of 1 1/2 oz mat material with resin, then woven roving over that to stitch the ply pieces together into one. Then 3 more layers of mat/resin.
After allowing the week to cure, we ground the contour back onto the flybridge deck with a 7 inch disk grinder.
Followed up with 2 coats of vinylester gelcoat tinted light gray with non skid mixed in.
Came out mint.

The job took 3 weekends. 2 of the days I had another couple help us.

Mrwesson said:

What about solid fiberglass hulls? They seem pretty strong.

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Hulls have BIG Strong stringers spaced fairly close vs flybridge decks.
Agree w others the core gives the outside layers stength due to the ctoss section.

I redid a cored swim deck as others suggested but omitted the core anywhere there were pentratipns and built up w glass & resin NO worries about future sealing or leakage.

The Mainship balsa was ruined by know nothing dealers allowing ignorant riggers to finish out the boats drilling into balsa cores improperly mounting seats, hardware and so forth. A shame really, they started the clock on the water intrusion problems that appeared after any hope of warranty adjustment

There are post that can be found using the search option on here with many suggestions as to what works, what does not and what might.

Suggest that you not do as a friend of mine that had ground out blisters, sanded hull and after he had done much work painted the bottom (against All advice and protest) in a rainstorm to meet his schedule because he just had to git er done.

I bet you can guess rhe rest of the story. Don’t be that guy.

We recently purchased a trawler with a teak covered sun deck (which I swore I would never do). The Admiral liked the boat and I couldn't find a good reason not to buy it (I tried) my only condition was the teak had to come off because it was soft in several spots and not worth the effort to save it. Covering it only delays the inevitable removal and increases the likelihood of even more costly repairs.

We've lived with it for two seasons but she goes in this month to have it all removed and replaced with anti skid fiberglass. The fly bridge deck was re-cored and re-glassed the year we got it. The two pictures are the same fly bridge with a lot of improvements.

Mrwesson said:

What about solid fiberglass hulls? They seem pretty strong.

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That is a good question.

The answer is that hulls are never flat.
If they were, they would have to be much thicker. Their shape gives them the strength they need, along with the keel and stringers.. A flat piece of thick fibreglass will still flex and sag.

I’ve done it on decks before and it’s worked great ...it was on a cockpit deck that was removable ..about 8’ x 7’ ... added the glass underneath... worked great

"Sandwich construction is what makes them stiff. "

Sandwich construction is a way to make then thick (therefore stiff) at lower cost and weight than solid GRP.

Most of the early glass boats had solid decks and PH , and do not suffer rot.

Plywood core was chosen for most TT as there was no deck or cabin mold so it was a cheap ez method to create needed surfaces .


Vessel structure longevity was never a consideration for TT builders, 30-40 years ago.