Balsa Core

abbott013

abbott013

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I have a area 400mm X 800mm where the balsa core has completely rotted on my cockpit sole. i am going to cut back the inner skin so i can laminate in a new core, but i do not want to use balsa, what would be best material to use, help needed.
 
If you cut back the inner skin then all of your repair work will be overhead laminating (if I understand correctly?), which is not much fun at all.
Its not a terribly large panel, hence I am wondering if it would be possible to cut it out very carefully from above (ie in the cockpit), dig out the rotten balsa, put in a new foam core (such as Airex, Klegecell etc) bedded down on epoxy, clean up the fibreglass panel that you have carefully cut out, and then bed it down on epoxy onto the foam core?
The joint would be visible, but maybe you can paint the sole, and add some non skid to match what is there.
Or if you have a timber grating above, then dont worry about the visible joint!
 
I definatly want to do the job from under side, there is a large hatch in the sole so work will be tight but not impossible. Thanks for the brand names, just what i was looking for.
One more thought, would a good quality marine ply work.
 
Hello again! I am sure that very experienced folk like Oldsaltoz down under will be along soon, and he will give you comprehensive instructions re what to do!

But in the meantime, IMHO, I think marine ply would work OK as a core - it will be much stronger in many ways than a foam or balsa core, but I doubt you are worried about that, as I am sure that there is masses of strength there already.
If you use marine ply, coat it well with epoxy resin to seal it, and then bed it in on epoxy, and then overlaminate with cloth (not chopped strand mat!) and epoxy.
You will be frequently cursing Newton and his discovery of gravity while doing this though.......
It would be slightly cheaper to use polyester rather than epoxy resin, but I would strongly recommend that you use epoxy - it is a good adhesive, unlike polyester - and it is always difficult to get new polyester to stick effectively to 'old' polyester, even if you grind the heck out of it first.

Would it be possible to post a photo of the cockpit sole of your Liz 30, showing the area to be cut out in relation to the hatch?
 
G'day Martin (bananaman),

Bajansailor (another Martin) has given you some good advice, you can almost anything to fill the void left by the balsa provided it is water resistant or closed cell.

Ply that has been coated in epoxy resin would do the job but take care you are not creating a stiffer section that will result in gelcoat cracking down the track.

A closed cell foam like Klegacell would be fine, but I'm sure it comes in the thickness you require, and not cheap at all.

A closed foam would be my choice; if the area were smaller I would use an epoxy and micro balloons or 'Q' cells, you might even consider moulding a small board the right size with this material.

Most yards have off cuts of foam, just ensure it's closed cell; meaning if it gets wet it will not fall apart or turn to mush.

Cutting the underside is best done with a plunge router set to clear the top sides, very fast and easy to control.

Make sure you rid of all the bad stuff, removing even stained balsa and make sure it's totally dry, the last thing we need is trapped moisture.

Working down side up can be a bit messy but prewetting smaller and easy to handle sections of glass on a smooth surface first will help.

Remember to roll out as much of the epoxy resin as you can without starving the cloth, a ration of 1:1 by weight is about right, this will save on expensive resin and provide a good strong repair well bonded to existing standard resin/GRP.

Hope this helps, let us know how it goes or if you need further assistance.

Andavagoodweekend......

PS. I'm off to Cairns in about 2 weeks, planning to spend some time on the cat over the great barrier reef, just father son daughter and her hubby.
 
I can't help but comment as said before that upside down is going to be very difficult. The easiest way to improve the problem if not fix it would be to drill small holes from the top and inject epoxy into the void left by the rotten balsa. If you can find a way of coupling a syrinnge to the hole and provide more holes for it to come out then you should be able to get enough epoxy in to provide the stiffness you need. olewill
PS good luck to Oldsaloz on the cat up north. Keep an eye ot for cyclones though. I am sure you are aware our first has arrived on the west coast.
 
The best stuff to use is Herex, obtainable from the importers Impag in bulk but in smaller quantities from Scott Bader. Your problem in an area like that, working upside down, is to get it to bond effectively. Here is how I advise -

abrade the whole area of the repair with coarse sandpaper - in an angle grinder for choice.

Get a sheet of heavy gauge polythene (clear, so you can see bubbles etc). Lay up on it the following:

2 layers of your chosen glass fabric (stitched multi-axial fabric is best but woven roving or chopped strand mat will do). Use polyester resin and work in well with a finned roller

foam: bevel the bottom edge so the glass doesn't have to go over sharp edges and punch holes in it at 6" intervals with a small screwdriver or bradawl

one layer of chopped strand mat, wetted well with resin.

Now for the tricky bit which you'll need to practice with offcuts first. Stick the polythene using duck tape or brown parcel tape to the cockpit base with as generous an overlap as you can manage, then stick a vacuum cleaner nozzle into a fold of the polythene and tape around it for a seal. Switch on the vacuum and the laminate sandwich will be sucked onto the base. You need to keep the vacuum running until you can feel the resin has at least turned to jelly.

To avoid the vacuum overheating through lack of air flow, try to get hold of a 'Charles' - the industrial type with the face on!

The key to a strong job is the layer of CSM between the base and the foam as it ensures you get a bond across the surface, not just spots where the layers happen to touch.

Polyester is just fine for this job as long as you abrade thoroughly. My boat was built by bonding panels together and after 15000 miles there hasn't been a single trace of delamination.
 
If you have a Liz 30, then the space underneath the cockpit sole is very restricted if the engine is still in place. Whatever you do wear a suitable respirator as you "glass" things back in place. I speak from experience! I glassed extra webs into the stern of mine to prevent whip in the prop shaft which kept breaking the shaft log bolts. The fumes caused me to lose my sense of smell for over a year. Most unpleasant.
 
[ QUOTE ]
good luck to Oldsaltoz on the cat up north. Keep an eye out for cyclones though. I am sure you are aware our first has arrived on the west coast.

[/ QUOTE ]

G'day Will,
Yes I was watching the one on the West coat today on the Port Headland Radar, also interesting the met office predict it will meet up with another front further south creating some pretty stormy conditions.

We were in Cairns Last year when the cyclone hit the coast a bit to the south at Innisfail, 50% of all buildings damaged, 90% or all crops (mostly bananas) wiped out. I stayed up all night tracking the the thing an trying to work out when the tidal surge was going to arrive. by 0530 it was time to off the cat check the lines and leave her in her pen, as we made our way back we saw the yacht 3 pens down had sunk in her pen, two more had been blown onto the beach behind us, another at the front had mounted the pontoon and later broke in two, and still another, an old steel hulled sailing vessel was bashing up and down the side of an 80 foot luxury stink pot near the fuelling pontoon. The surge arrived around 0630, about an hour before low water, but the tide was rushing in, faster than ever and in a couple of hours had risen over 12 feet; we thought the marina was going to run out of piles and float away.

We were in Dampier the year Darwin was hit by Cyclone Tracey. We were hit the same year with Cyclone Trixie, the eye passed just 40 Km away. Huge seas, busted boats all over the place, no one killed, in fact only one was injured; stepped on broken glass after his roof lifted clean off.

Avagoodweekend
 
G'day Rod (Achillesheel),

Small areas can be picked up by tapping on the suspect area, however, the one we are discussing here would be soft under foot, you would feel the upper layer of glass flexing when you stepped on it.

Hope this helps.

Avagoodweekend......
 
If it is a balsa cored sandwich, and over a certain age, say three years, then it is rotten. QED.
And the moral of this tale, kiddiwinkies, is do not spend your pocket money on anything made of balsa sandwich.
 
[ QUOTE ]
If it is a balsa cored sandwich, and over a certain age, say three years, then it is rotten. QED.
And the moral of this tale, kiddiwinkies, is do not spend your pocket money on anything made of balsa sandwich.

[/ QUOTE ]

G'day Jeanne and David,

There are still many Balsa cored boats running around without any problems at all, you just need to stop water getting in, most have allowed a stress crack or other damage be left unrepaired, or have installed fittings without the correct preparation and sealing.

Nothing wrong with Balsa core as you know you have it, just look after it. It provides high strength, good insulation for heat and sound but is still very light, nothing wrong with that is there?

Avagoodweekend......
 
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