Non-marine plywood prep

[Celestialsailor]

Originally Posted by pcmm

What a load of BS... What makes you think "Plywood was designed to eventually separate."?? The bulkheads of my 44 year old Morgan are Exterior Grade ACX plywood and are still intact. When do they "Eventually seperate"??

Get use to it. this guy has been on the forum for a short amount of time yet has everything to say about anything. None of it accurate or even true. I love the one he spews about poly-ester f/g boats no good after x amount of years because they are saturated with water. Of course no forum rule about trying to dazzle everyone. You can always put them on ignore. Some people have.

[Mickeyrouse]

Aside from the previous suggestions, I strongly encourage the use of an effective dust mask. Epoxy sanding dust can be pretty nasty stuff. Epoxy poisoning cases requiring hospitalization are not uncommon.

[pcmm]

Originally Posted by Celestialsailor

Get use to it. this guy has been on the forum for a short amount of time yet has everything to say about anything. None of it accurate or even true. I love the one he spews about poly-ester f/g boats no good after x amount of years because they are saturated with water. Of course no forum rule about trying to dazzle everyone. You can always put them on ignore. Some people have.

If you don't keep calling these people out on their misinformtion other new members may start to beleive the stupidity these guys spew and that does everyone a diservice!

[Pete7]

Originally Posted by wholybee

For a 1.5 inch hole in a floor (not a structural component), why use plywood at all? Why not just fill it with thickened epoxy? Tape the bottom of the hole. Fill with epoxy. After it cures add whatever paint or non-skid over it as needed to make it invisible.

Or instead of plywood, just use an offcut of GRP and epoxy that in with a backing pad underneath.

Pete

[Spot]

I like Zach's original plan updated for regular plywood and the specific forum suggestions related to penetrating epoxy. I would also try to glass the bottom side first, holding the cloth in place with some sort of pressure and release film (piece of plywood covered in plastic bag/film, jacked into place with a stick) until it cures. Then you can work the rest from the cockpit sole without things leaking/falling out.

One should be able to do the 'next' epoxy step within a couple hours, after the 'previous' step is cured to not be sticky to the touch. If one waits more than say a day between steps, some epoxy manufacturers would insist on sanding the previously coated surface to key it mechanically and/or remove amine blush.

[team karst]

Originally Posted by wholybee

For a 1.5 inch hole in a floor (not a structural component), why use plywood at all? Why not just fill it with thickened epoxy? Tape the bottom of the hole. Fill with epoxy. After it cures add whatever paint or non-skid over it as needed to make it invisible.

I’ve done several underwater hole fills, the largest being 2” transducer holes. You just need a non-structural spacer, positioned to give you room for two layers of Biax on each side. Ive used even junk foam for this application. Grind tapers on each side. This is a 20 minute job, excluding cosmetics/finish work.

[tomtriad]

Originally Posted by team karst

I’ve done several underwater hole fills, the largest being 2” transducer holes. You just need a non-structural spacer, positioned to give you room for two layers of Biax on each side. Ive used even junk foam for this application. Grind tapers on each side. This is a 20 minute job, excluding cosmetics/finish work.

This is exactly right. I would use a piece of foam, or a good piece of non-plywood, like cedar or mahogany to plug the hole. Butter it up with epoxy and glass some skins over it top and bottom. Don't use plywood at all - its inferior for a core. The strength is in the skins.

[roryboy]

When it comes to composite repairs, use as few different types of material as possible and as few bond lines as possible. Fill the hole with thickened epoxy and cover with a layer of material. If you put the material right over the wet filler and at the same time, you have eliminated a bond line and reduced the labor in the repair. With epoxy, filler can be just about anything. Talcum powder works well and is cheap and easy to obtain.

[Talbot]

The one thing nobody has addressed is preparing the hole. if you chamfer the outer side of the hull, the resulting plug will end up more as a wedge thus much stronger while still being able to sanding the outside of the hull back fair.

[zachduckworth]

I did get the piece in place last weekend. It went pretty well. The hardest part was sanding the area before and after. Actually the hardest part was taking the gnarly old non-skid down so I could fair it. I never saw so much dust from so little material. I had a lead-paint respirator and a vacuum but it was still a slog. In addition to the main hole I had to clean up some attendant holes from the Edson Binnacle as well, plus I had to drill out and repair a few spots of damage I created with a chisel when I pried the pedestal off. Anyway, I’m almost done. I got 6 or 7 layers of glass in place. I’ll post up some pictures of the process on here once I get it done.

[zachduckworth]

Originally Posted by Talbot

The one thing nobody has addressed is preparing the hole. if you chamfer the outer side of the hull, the resulting plug will end up more as a wedge thus much stronger while still being able to sanding the outside of the hull back fair.

Agreed. I did chamfer all of the holes it back quite a bit, and the big 1.5” hole the most. I used a file to create a 12:1-is angle to the plane of the deck and laid the fiberglass into it start with the smaller pieces on top of the plug and adding progressively bigger ones. The area fiberglassed was probably 4 times the area of the plug, if not more.

[team karst]

Sounds good. Btw, my 20 minute estimate uses a 5” makita and a 50 grit disc [emoji16] in lieu of filing.

[Wotname]

Originally Posted by Spot

...............

One should be able to do the 'next' epoxy step within a couple hours, after the 'previous' step is cured to not be sticky to the touch. If one waits more than say a day between steps, some epoxy manufacturers would insist on sanding the previously coated surface to key it mechanically and/or remove amine blush.

To add to this informative post. When applying the next coat of epoxy to the previous coat is - if the previous coat has cured enough to be able to sand the surface, then you must remove any amine blush (by using water) and then sand it to provide a mechanical key between the coats.

If the previous surface is too soft to sand (clogs / gums the paper etc), then it is uncured enough for a chemical bond. Likewise if you can dent the surface with your thumbnail, it is uncured and you can apply the next coat directly to it.

A chemical bond is much better than a mechanical bond between the coats.

[team karst]

No content

[Spot]

Originally Posted by zachduckworth

Agreed. I did chamfer all of the holes it back quite a bit, and the big 1.5” hole the most. I used a file to create a 12:1-is angle to the plane of the deck and laid the fiberglass into it start with the smaller pieces on top of the plug and adding progressively bigger ones. The area fiberglassed was probably 4 times the area of the plug, if not more.

Originally Posted by team karst

Sounds good. Btw, my 20 minute estimate uses a 5” makita and a 50 grit disc [emoji16] in lieu of filing.

Glad you made it through the repair.

Wait until we get you two going with a 36 grit flap wheel... The trick is knowing when to say when so you don't go too far.

I lit up an 80-grit sanding disk on an 8" (200mm) pad in the cabin/bilge of the 20-footer and I now have ground polyester and mat from stem to stern inside the boat, and I still need to chase it with a 40 grit to level it out for the new framing. Note to self to hang plastic film... I noticed that Harbor Freight sells a couple types of shrouds to mount to an angle grinder to attempt to channel the dust into a shop vac.