etching for fiberglass repair prep?28' Offshore rebuild

[levi_tsk]

So I'm in the process of converting my 28' Offshore Custom Yachts ( OSY ) cuddy cabin into a center console I got the hull for a song and have pretty much stripped it out to the stringers and transom and now I"m looking for something besides sanding that I can do to the existing fiberglass that will help bond all the fiberglass components and layers to the hull. there's some mildew in the compartments below where the deck is along with the other usual bilge trappings and suspects that I know fiberglass won't bond to. There's LARGE areas on this boat that will need to be prepped and I know there will be a lot of sanding but if there's anything else that I can do to the existing glass to help ensure a good bond I want to do it.
Some possible solutions I've found by internet research and asking questions in the marine store :
TCP? helps clean the hull will it etch it as well?
Prep Magic? This is supposed to be for etching your fiberglass pool to cut down on sanding before painting
De-glossing agent ? this is a sovent based compound meat to take the sheen off a painted surface i fifgure it will soften the surface layer of resin to allow a hot coat of subsequent fiberglass and resin to stick better than sanding along would do.
I'm open to other sugestions so by all means fire away?
Again this if for bare fiberglass inside the boat on what will be unseen areas so appearance is not nearly as important as getting a good PERMANENT bond between layers the outside of the boat is bare white gelcoat and will only be wet sanded and buffed because its in fairly good shape. i want to do this ONCE and CORRECTLY
Thank you for the help and suggestions
-Levi

 

[Scott Danforth]

It's actually grinding. There is no substitute for 24 grit discs and the angle grinder. Unfortunately there are no shortcuts for this step. If someone comes up with one, they will be an instant billionaire

 

[levi_tsk]

Yea I got a bunch of heavy gritted tiger paws and a nice 4 1/2" grinder I was just wondering if there was anything else I should/could do to help the bond besides a quick wipe down with a solvent.
Here's a few pictures of where I'm at so far :
The day I bought it :
Cabin removal started

 

[levi_tsk]

Midway through removing the cabin top:


Cabin completely removed:

 

[levi_tsk]

Deck is completely removed :

Offshore Custom Yachts apparently didn't make many of these hulls and mine is the only one I've ever seen with the big stupid looking cuddy. Here's a picture of the "normal" setup for this hull :

 

[jbcurt00]

You may want to scrub the interior w TSP and give it a good rinse before you grind on the hull in prep for glass work. Cleans all the crud off so it isn't getting into your sanding disc and being spread all over the areas you're grinding.

Then a good rinse and wipe down w/ acetone in prep of glassing. If the ground areas sit as you work your way around the hull, and collect dust and debris, an additional scrub down w/ TSP might be helpful before the acetone wipe down.

So yep, TSP is part of the prep glassing prep.

You mentioned alternate materials instead of plywood in another topic, do you plan to use those on this build? Used them before on a boat build?

Did you build a cradle to support the hull and sides of the boat before cutting out the cabin and deck?

Good luck w/ the conversion to CC. The factory CC is nice looking, the factory cuddy, not so much....

 

[levi_tsk]

Thanks thats what i figured dont wanna keep smearing all that bilge nastiness all over the boat.

Yes I have used them on a Mako deck replacement I did last year and I like them and will DEFINITELY use them on this project and hopefully you guys will follow along and guide and critique as I do.
I have not built a cradle yet but I will once I get it moved to where I will be replacing the transom and stringers for now I was concentrating on getting the hull most of the way stripped out but I left the old cabin bulkhead and forward v- berth bulkhead to help the hull keep its shape until I move it and I haven't removed any structural members I have however removed AT LEAST a thousand pounds of weight from the hull by way of the cabinet,s cabin roof, doors, drivers seat, deck, and the teak plywood they used for a large majority of the interior which I kept BTW and WAS trying to sell it but I'll give it to anyone who wants it and is willing to pick it up in Jensen Beach, FL. I need to make some more room in my garage
Both boats are cuddy cabins but I think on my boat the owner wanted standing room and a walkaround style boat so Offshore cut the top off their existing cuddy model and raised the roof so that you could stand up and in the process they added a TON of amenities it was built for overnights for sure because it had a full galley and a stand up head and shower.
I'm sure the hull moved some but I'll be taking TONS of measurements and levelling it up on a cradle before II start putting anything else back in or taking anything else structural out.

 

[ondarvr]

There are products that will enhance the bond, but that's after all the grinding and cleaning is finished. Products like Atprime can be applied to even hard to bond to surfaces and help get a better bite, but they are rarely used and pricy.

Most any resin will do the job, but you could upgrade to VE. it may not make a noticeable difference used on the inside though.

Coosa Board works well as a replacement for wood, but is costly, which is why it isn't used more often.

If there's a lot of grinding to be done you may want to step up to a full sized grinder, it makes the job go much faster.

 

[levi_tsk]

For where stiffness and screw holding is concerned the lightweight PVC board is KING in price and workability.
You can shape it with a grinder or router its about 2/3 the weight of marine plywood and it has better compression strength than coosa. And the price is HARD to beat at $125 for a sheet of 3/4" (they make it up to 1 1/2" and down to 1/4"). And the plascore is a DREAM to work with and also available from 3/4 to 1 1/2" thick. Just painting the scrim with resin makes this stuff INCREDIBLY stiff and once there is a layer 1708 on both sides HOLY COW.
There's alot of grinding but I can cover a pretty large area with m y 4 1/2" er and not be NEARLY as tired as when I break out the 7" I also have a metabo that I can put a bigger tigerpaw on that's light and covers a large area. I'm waiting on my fuel tanks to arrive via UPS today so I won't get much done besides hopefully completing the mold for my center console.
I just priced out the Atprime and that isn't too bad in the scope of things and i have a local place where i already get my resin from that carries it.

 

[Georgesalmon]

FWIW, I have had very good bonding by sandblasting the surface. I've only used silica sand for this, not any of the fancy soda blasting or iron oxide, etc. Sand blasting with silica sand will leave a nice clean rough surface. However it is very easy to actually blast right through so be careful if tried. I paid a local guy about $125 to do the whole inside of a 20 footer but I opted to do the cleanup myself to save money. Took him about 1/2 hour. There were a few corners in the back I still had to grind but he did about 90% of it. Glass is still bonded after 4 years.

 

[ondarvr]

PVC and honeycombs can work, but they don't have the same durability as Coosa, so depending on where it's used one may be better than the other.

I put a honeycomb floor in one of my boats about 15 years ago and it's holding up well, but it doesn't work for everything.

 

[levi_tsk]

Yea for the deck I'm planning do a 1 layer of 1708 on the bottom of 1/2" layer of pvc then a layer of 1708 then plascore then three layers of 1708 and I MIGHT do kevlar on top of that and carry that up the sides of the hull to right under the gunnels for a little extra stiffness and I MIGHT substitute the top layer of 1708 for the kevlar. This should make the deck like a rock and keep it fairly light.
Im going to do three layers of 3/4" pvc for the transom with 1708 between each layer and two layers of 1708 on the inside.
I'm not sure what to do with the stringers though they're in pretty good shape but a little flimsy and I'm tempted to scab some 1" plascore to the side of them and wrap that completely in glass. Any thoughts on that? Would you use pvc for that? Coosa?

 

[ondarvr]

1 You don't need to mix and match core for the deck, there won't be any benefits, only the cost will go up. Honeycomb can work well, but it doesn't hold fasteners and the compression strength can be low, so mounting things creates a little more work. PVC can work, but depending the exact board and the resin used, the bond can be iffy, plus it's not considered a structural core. In some situtations it works though.

2 Kevlar won't help in making it stiffer, and really adds no benefit in this application. Kevlar is of limited value in most marine applications.

3 PVC isn't really considered a strucural core, just looking at the data sheet for one PVC board I sell stipulates it's for "non load bearing" applications, so for a transom it's not recommended.

4 Honeycomb doesn't work well for stringers, the strength is not on that axis, so you end up using more glass to compensate for the lack of strength.

The Coosa Bluewater 26 works well in all these applications, it's not perfect, but is designed for this type of use.

A single layer of the correct thickness of honeycomb can make for a very strong and light deck, you just need to fill the cells in locations where you want to put screws or through bolts to mount stuff. It's a bit of hassle, but works. My dock is made from 4 layers of 1" Nidacore bonded together, it was a test panel used for temporary bridge applications for heavy equipment.

For the transom use a solid layup of glass where the motor(s) clamps onto the transom, but no bigger, then use a core in the rest of it. This solves the weight, rot and compression strength issues.

If you're going all out on the rest of it, you might as well do the stringers too, Foam, PVC board, or Coosa can work, They require varying amounts of glass to make up for strength though. My favorite stringer is a hollow one, it's lower in cost, plus it won't absorb water or rot.

 

[levi_tsk]

On my Mako deck I did this where I needed fasteners to go and that's why I wanted to underlay the 1/2" pvc so I would have something for the pvc to rest on.
My buddy screwed up a whole panel of plascore trying to use a router to take out one side of the plascore to insert a piece of pvc where his trolling motor mounting area was.

For the transom I planned on closing it in and adding some large knees from the sringers to the the top of the transom and hanging a bracket off for a more updated look. Would coosa be OK there? What about two layers of coosa 26 and then a layer of pvc on the inside to spread the load ?
I like the idea of boxing the stringers.
I don't have any plans for the space between the two stringers on each side would that be a good place for them? I saw that's the way Aquasport did it for several DECADES so must have worked pretty good or they'd have changed it up?
How thick would the glass have to be if it was going over 1/2" pvc?
Thanks again for your help and advice.

 

[ondarvr]

PVC won't help to spread the load on the transom, it has no strength when used in that way, the glass is where all the strength would be located. PVC boards aren't designed for use as stringers or anything that carries a load. The trim boards you can buy at the big box stores are the same type of product, they work well for light duty applications around the house, not studs or beams. While you can wrap the PVC in glass and get the needed strength, the PVC is heavier and higher in price than a traditional 5# density sheet foam used as a core, all you gain is the better screw holding ability of the PVC board. PVC deck boards used on your house are very low in strength compared to wood, check the warning label and maximum recommended span without support.

Here's a copy and paste from a PVC marine board manufacturer website

• Wood Replacement (Non-Load Bearing)
• Marine Seat and Bottoms
• Cabinetry
• Shutters
• Instrumental Panel / Consoles
• Case Goods


Adding a layer of PVC to the deck doesn't fix the low compression strength issue of the honeycomb, while it will hold a screw better, the honeycomb is still under the same compresion load and can be crushed if you through bolt the center consol down (just an example). The cells of the honeycomb need to be filled, or removed and replaced with a solid laminate anyplace there is high compression loading. If you glass the center console in place you don't need to fill the cells though.

I like to have a solid laminate anyplace I have extreme compression loads like where the outboard bracket will be bolted to the transom, while there are cores that will work, knowing that it will never be crushed no matter what load is applied makes me more confident in rough seas with big motors. It's the same for motors bolted directly to the transom. These solid laminate areas don't need to be much bigger than the bolt itself

 

[ondarvr]

I'm having a customer do some bond testing on my current PVC product and see if the standard laminating resin will bond adequately to it. I should have the results tomorrow.

 

[ondarvr]

Well, I need to change my opinion for the current PVC boards I sell. I tried to pry the laminate off the PVC and there was no way to break the bond, the laminate sheared internally and left fibers and resin on the entire surface of the PVC. The prep was sanding with 36 grit on a small grinder.

So with this PVC board bonding is not an issue.

 

[levi_tsk]

What do you think about arjay nidabond or seacast? The back of the hull will be wide open so access won't be a problem.

 

[levi_tsk]

Well, I need to change my opinion for the current PVC boards I sell. I tried to pry the laminate off the PVC and there was no way to break the bond, the laminate sheared internally and left fibers and resin on the entire surface of the PVC. The prep was sanding with 36 grit on a small grinder.

So with this PVC board bonding is not an issue.

Yea the guys at Raka ( they are my nearest pvc board distributor) said that a quick sanding to get the sheen off makes for an INDESTRUCABLE bond with polyester resin because the polyester melts the surface layer of the PVC TO the wet resin. He said that with epoxy he didn't think it wouldn't bond as well as with polyester.
Do you think that after a layup of 3 layers of pvc with glass and resin sandwiched between via vacuum bagging that it would still be too flexible for a transom?
The guys at Raka ( who supply MANY boat manufacterers their materials her and all over south Florida )were saying that there are alot of boat manufacterers that have transitioned from plywood to pourable compounds and now have gone to the lightweight pvc because its as strong as plywood and you don't need an inner dam like you do with the pourable compounds. I'm open to debate the merits of the three but its HARD to justify $400/ sheet for coosa when arjay would do the same if not a better job for less money.

 

[ondarvr]

My only concern at this point would be the impact resistance at lower temperatures and overall durability. Without more testing I can't say I would recommend it for a transom, but it could possibly work very well. Coosa and the pourable products have been tested and used a great deal.

As a supplier of these products I can't recommend unproven applications without taking on some liability for the consequences.