Balsa core; major issue or not.

[30boat]

What's wrong with expanding foam in this application ? Is it just not strong enough, or does it not bond well enough or what ?

Boo2

Both and more.It doesn't bond well,it doesn't resist crushing loads and it soaks up water.On top of that it expands so much that you'd end up with bulges everywhere.The forces generated are high enough to lifft the skin off the core and it's very diffiult to inject just the right amount for the void.

 

[oldsaltoz]

Both and more.It doesn't bond well,it doesn't resist crushing loads and it soaks up water.On top of that it expands so much that you'd end up with bulges everywhere.The forces generated are high enough to lifft the skin off the core and it's very diffiult to inject just the right amount for the void.

30boat is absolutely correct as usual.

You will note I said 'closed cell foam' in my post above, this expanding stuff is rubbish.

You 'may' have also figured out the reason for the holes in the foam.
They not ensure no air is trapped behind the foam but close columns of cured micro-fibres also help to bond the two layers as well as providing extra support.

Good luck to you if you plan on using expanding foam because your going to need it.

 

[pcatterall]

Thanks; so thats expanding foam knocked on the head then!!
I guess that Boatmike's suggestion would be ok for small areas around chain plates/stanchions then and oldsaltoz's method for anything bigger.
Question...... what is this closed cell stuff in real life? where would I obtain it? Is it affected by fuel spills ( would it melt away around a through deck filler hole if there was any spillage/leakage)

 

[pvb]

Question...... what is this closed cell stuff in real life? where would I obtain it? Is it affected by fuel spills ( would it melt away around a through deck filler hole if there was any spillage/leakage)

See the Divinycell website - tells you all about it and has a "where to buy" link.

But don't underestimate the work involved, which can be immense. You should also note that the undersides of deck fittings are almost totally inaccessible in many boats, resulting in major dismantling if you need to get at them.

 

[stav]

Wasnt there an article in the last couple of years in PBO where a guy did the deck on a 24ft motor boat, cut out all the balsa and put back ply or the correct foam. Might be worth trying to find to give you an idea of what is required.

 

[oldsaltoz]

Question...... what is this closed cell stuff in real life? where would I obtain it? Is it affected by fuel spills ( would it melt away around a through deck filler hole if there was any spillage/leakage)

As the name suggests it made up of cells that are all closed, think of a honeycomb like structure with the ends sealed, though more often the cell are bubbles.

This means that in the event the structure is exposed to moisture they remain in tact and do not allow the moisture to enter them.

Unlike expanding foam that turns into a brown mush.

Micro Balloons and 'Q' cells are closed cells in a dust form, mixed with resin they form a paste, easy to apply and sand when cured. However they are not designed to tale a loading, for this you can use Micro Fibres, very strong as a glue as well as being great for filling drilled holes in decks and re-drilling to the required size for thru' bolting, this not only forms a seal but also load bearing column. Making balsa decks water tight.

 

[kingfisher]

Hi Oldsaltoz, thanks for the tips.
I'm thinking about doing a similar thing to repair my deck. What I do not understand of your solution:
- sandwich decks work like cardboard. The structural integrity is based on the sandwich of

XXXXXXXX GRP
OOOOOOO Balsa/closed cell
XXXXXXXX GRP

Where, whichever way you flex it, one layer is always under tension, another is compressed, and especially: the one layer which is under tension is always under more tension than the other layer is under compression.

If I read your solution correctly, you do not replace the below/inside layer of GRP?

My idea is to drill dozens of evenly spaced holes, rout out the rotten balsa (using the allen key technique) and inject epoxy mixed with microfibres, so the new structure would look like

XXXXXXXXXXXXXXXXXX
OO OO OO OO
OOO OOO OOO OOO
OO OO OO OO
XXXXXXXXXXXXXXXXXXX

Should a deck have flex or can I use a rigid solution (epoxy)?

 

[prv]

Hi Oldsaltoz, thanks for the tips.
[...]
If I read your solution correctly, you do not replace the below/inside layer of GRP?

I think you missed this bit:

then lay the original section you cut out over the repair

I replaced the core in Kindred Spirit's aft deck, completely sodden after the previous owner drilled cable holes straight through it with no attempt to seal them. That was maybe a square foot or two, as most of the area is locker lids. I wouldn't like to have to do anything much bigger.

I worked downwards from above, and used ply as the new core because it supports the mizzen mast, but otherwise my technique was much as Old Salt describes.

Pete

 

[SvenglishTommy]

Are you sure the area under the stanchions is balsa cored? My deck also has a balsa core, but the areas where the chainplates and stanchion bases are fixed are not cored at all - I've seen this on other boats too, and it makes whole lot of sense. In fact there are no holes in the cored area of the deck at all, apart from one I made to fit a vent (following instructions from oldsaltoz of course

 

[exfinnsailor]

Been there and got a t-shirt. My first FINN had a balsa cord floor just where you keep jumping up and down. First noticed a small indentation where my heals went under the toe strap. Simple job

Well it looked simple.

Used a router to cut out a panel in the floor about 300mm square and the balsa was very wet. Made a bigger hole in top piece and still wet. What looked like a small hole was now a very large hole and the balsa was dryish.

So used west and stuck a layer of closed cell foam down to the under floor. Then covered that with chop strand to bring it up to deck level and then made some 4 mm marine ply floor boards and wested then in over the top.

Painted with none slip. Sailed it for a couple of months then sold it.

You could jump on the floor afterwards. Made a really neat job. Its not doing the job its how it finishes up that is important.