advice - replace balsa core with ?????

[barnakiel]

There is no choice. There is foam.

Cheers,
b.

[Adelie]

Originally Posted by Moosemiester

Marine Plywood is cheap relative to balsa or foam, easily found, and easy to work with.

Like other posters have already said fix the leaks first...

As Thinwater indicates it is heavier than endgrain balsa.

Contrary to what MM indicates, plywood is not easier to work than endgrain.

When I worked with endgrain it was very easy to work with. The balsa was individual cubes bonded to a light backing mesh. It was easy to cut to shape using a utility knife and it conformed to compound curves with no need to apply significant pressure.

When wetting out the balsa I took a brush, bent each row of cubes open, painted them with resin, repeated with each column of cubes, then laid the sheet out and proceeded as normal with bedding and laminating the sheet.

This meant that each cube was individually sealed, so is there was a leak into the core just one or 2 cubes were affected and the rot did not spread.

[stormalong]

Originally Posted by Aaarrgh

Could you please offer a preferred source for the penetrating epoxy that you recommend, and maybe a preferred brand name?

Thankfully,
Aarrrgh!

Plywood is heavy and WILL affect the balance of your vessel. Don't do it.

[Jim Cate]

Originally Posted by stormalong

Plywood is heavy and WILL affect the balance of your vessel. Don't do it.

Perhaps if one replaced the entire deck, but for spot repairs, the weight difference is trivial.

Jim

[Moosemiester]

Rotted, soaked chunks of luan used in older Asian boats is much heavier than plywood. My waterline is proof... But if you have something newer then yes, it might be heavier....

West System is thin and penetrates well -with a price to match. U.S. Composites is half the price, that’s what I use. But I have only owned old Asian boats....

[MoorOrLess]

I agree with Adelie, end grain when installed correctly should only ever have a single square/rectangle damaged. Each 1/2" cell is sealed.
If you are trying to use the original deck and replace from below, then it will be much easier to install than foam or ply.

[valhalla360]

If it's a small area (few square feet) the weight is irrelevant.

That said, end grain balsa sealed up and kept sealed will last the life of the boat.

Foam can work but has some downsides:
- Wood (kept dry) has incredible fatigue resistance. Foam even if kept dry can eventually break down from repeated compression.
- Adhesion can be a bit trickier.

Plywood: If you have some small chunks the are sized right, should work OK if you keep it sealed but wouldn't be my first choice. I have a fiberglass covered plywood box for covering our portable generator in the back of the truck. Took a lot of time and effort to seal the edges but eventually, it wore thru and I didn't seal in time....The bottom 8" are now rotted as it quickly wicked up along the grain and the plys separated. I'll be rebuilding it next year.

[chouliha]

Originally Posted by Suijin

Divinycell. Some complain that it's expensive, but in the grand scheme of a recoring project it's cheap.

Would be my first choice.

[Terra Nova]

Originally Posted by MoorOrLess

...end grain when installed correctly should only ever have a single square/rectangle damaged. Each 1/2" cell is sealed...

Sounds good in theory. Too many bad examples show otherwise. Virtually impossible to seal 100%.

[thinwater]

Originally Posted by Terra Nova

Sounds good in theory. Too many bad examples show otherwise. Virtually impossible to seal 100%.

Obviously. I've owned one.

IF there is considerable curvature, this tends to be true, but if the curve is slight, the epoxy does not penetrate all of the scores, not all the way.

One the other hand, it is a myth, or at least profound exaggeration, that limited rotten core is always a death sentence. If the skins are thick, there is solid core where there are fittings, there is enough camber, and area is not too large, often there will be no symptoms for the life of the boat. I've seen boats were the core was complete mush but the deck was not the least bit soft. Without question, the sorce of the leaks should be fixed and solid sections provided, but in the absense of symptoms, a complete re-core may be an overreaction. Just sayin'.

[DerekKelsall]

Originally Posted by valhalla360

If it's a small area (few square feet) the weight is irrelevant.

That said, end grain balsa sealed up and kept sealed will last the life of the boat.

Foam can work but has some downsides:
- Wood (kept dry) has incredible fatigue resistance. Foam even if kept dry can eventually break down from repeated compression.
- Adhesion can be a bit trickier.

Plywood: If you have some small chunks the are sized right, should work OK if you keep it sealed but wouldn't be my first choice. I have a fiberglass covered plywood box for covering our portable generator in the back of the truck. Took a lot of time and effort to seal the edges but eventually, it wore thru and I didn't seal in time....The bottom 8" are now rotted as it quickly wicked up along the grain and the plys separated. I'll be rebuilding it next year.

Again - Your foam getting wet and breaking down is typical of low density Polyurethane foam - which could be two pot foam in place. Had you built your box of say H-80 Divinycell foam with glass and polyester resin and a good paint coat it would last 50 years +.
The one time I used balsa (power racing 25ft.) we kept the balsa in its packing till ready to use and we never left balsa open to the air for even overnight. The idea that you can guarantee no ingress of moisture for a whole boat with thin glass skins inside and out would be rejected by anyone who has made tanks of fiberglass. It takes more layers than on any typical boat sandwich skin to keep the tank water tight. The boat repair guys love balsa.
Nothing compares to foam for ease of use. cuts, bends, sands etc.
Happy Boating. Derek

[APKetcher]

I recored the foredeck on my 1980 Allied Princess about 5 years ago using epoxy impregnated divinicell. The repair has held up very well. I did rebed all of the foredeck hardware also.
The Divinicell and West Systems Epoxy came from Jamestown Distributors.
I avoided having deal with the deck molded non-skid and trim by replacing the core from below.

[valhalla360]

Originally Posted by DerekKelsall

Again - Your foam getting wet and breaking down is typical of low density Polyurethane foam - which could be two pot foam in place. Had you built your box of say H-80 Divinycell foam with glass and polyester resin and a good paint coat it would last 50 years +.
The one time I used balsa (power racing 25ft.) we kept the balsa in its packing till ready to use and we never left balsa open to the air for even overnight. The idea that you can guarantee no ingress of moisture for a whole boat with thin glass skins inside and out would be rejected by anyone who has made tanks of fiberglass. It takes more layers than on any typical boat sandwich skin to keep the tank water tight. The boat repair guys love balsa.
Nothing compares to foam for ease of use. cuts, bends, sands etc.
Happy Boating. Derek

Go back and re-read:
- The box in reference was plywood.
- Foam can fail without getting wet. It's fatigue strength is not nearly as good as wood. Wood can be compressed to 95% of failure millions of times and it will still be nearly as strong as it originally was. Foam won't hold up nearly as well. Properly designed and built it can be fine but much easier to make mistakes.

[ramblinrod]

My preference is plastic honey comb.

It is light, relatively inexpensive, and can never rot.

I have replaced core in J-boats with this stuff.

PS, whoever said balsa should not rot beyond one square is a little out of touch with reality. Yes there is a gap between squares that in a perfect world would be filled with resin to prohibit moisture migration. Alas, moisture migrates extensively in more balsa cored decks.

[ramblinrod]

https://www.plascore.com/markets/marine/performance/