Balsa core; major issue or not.

[pcatterall]

I am considering buying a mid 70s yacht. I have seen a 2009 survey which is generally positive.
It was noted that many of the stanchion and chain plate fittings needed resealing and that the coach roof area around the tabernacle had high moisture readings.
The surveyor suggested that the side decks and some other areas had a balsa core.
I recognise that, in the case of the stanchion and chain plate bolts, I scrape out any soggy balsa, fill with epoxy and redrill the holes.
My concern is what to do if there are larger 'soggy' areas. Lots of holes and expanding foam comes to mind but I supose this needs to be well controlled.
I will be having a new survey so guess that I should mention my concerns to the surveyor and get his slant.
Question.... major issue for a DIY guy or not??

 

[Searush]

Not my area of expertise, but it could be a big DIY job if it needs extensive "re-coring". I suspect it all depends how confident you are as a DIY'er. It's a good price negotiating ploy, but do you want to do the work or just sail her & see how it goes? Even a surveyor is only giving his opinion unless you start drilling cores out - and I can't see any seller agreeing to you doing that before sale!

Try not to get stuck, focussing on just one option - think of as many options as you can before evaluating them & homing in on a decision.

 

[noelex]

Balsa cored decks are very common. If they get significant moisture penetration it is a major problem requiring the skin to be cut away and the rotten balsa replaced. The area is usually much larger than first appears because end grain balsa can wick the water a considerable distance.
Small areas can be treated with epoxy injection, but I afraid the survey does not sound promising and personally I would keep looking for another boat.

 

[Bobobolinsky]

If a deck or coachroof is a bit spongy in places, is it so great a problem? After all a few years ago osmotic blisters were considered terminal and a boats value was decimated. Many if not most seventies boats with balsa core decks and coachroof have some form of water ingress within the laminate. So long as safety critical areas are not affected, i.e. deck steps, stanchions etc, there should be no great issues. On wooden boats, we very often accepted the odd deck seam that leaked, the odd soft bit of plywood.

 

[pvb]

Question.... major issue for a DIY guy or not??

It could easily turn into a major issue for you, either imminently or certainly at resale. There are so many boats for sale that I'd be tempted just to walk away and look for another one.

 

[fergie_mac66]

balsa is a no no in any form in my book . Its so soft and absorbent . one step up from loo parper

 

[chrisedwards]

balsa is a no no in any form in my book . Its so soft and absorbent . one step up from loo parper

Agonsied before buying my current boat - a freedom 30 cat-ketch. Not only were the decks balsa cored but also the hull to about two feet of the long keel. Plenty of research followed -Why was this - originally so expensive - boat built this way? - particularly as it was far more expensive for Freedom to do so. The balsa does not meet any fittings - from stanchions and push/pulpits to aluminium toerails. Through hull fittings pass through the solid bit referred to above. Extensive survey showed perfect hull/deck after 30 years - not sure how confident I can be with the measuring of this.

Boat is quiet and condensation free however

Chating with a club member who was putting a bowthruster on his Southerly. He was under the impression that the balsa core just extended to the waterline - it didn't!

Bottom line? - the boat will outlast me and at 30 years old went for a song and love is blind.

 

[fergie_mac66]

Can understand that.
The method of construction is as good as the workers using it. If they did a good job and any potential leaks, stanchions hatch covers etc, are kept on top off then will be ok. Its just so many builders were rushed by targets that slippage in standards occurred: Probably still does!

 

[Quandary]

balsa is a no no in any form in my book . Its so soft and absorbent . one step up from loo parper

You don't know a lot about yacht construction, perhaps? The majority of boats have balsa cored decks and coachroofs,ultra light single skin exceptions like the SJ 320 are like a springboard to walk on.

 

[boatmike]

I am considering buying a mid 70s yacht. I have seen a 2009 survey which is generally positive.
It was noted that many of the stanchion and chain plate fittings needed resealing and that the coach roof area around the tabernacle had high moisture readings.
The surveyor suggested that the side decks and some other areas had a balsa core.
I recognise that, in the case of the stanchion and chain plate bolts, I scrape out any soggy balsa, fill with epoxy and redrill the holes.
My concern is what to do if there are larger 'soggy' areas. Lots of holes and expanding foam comes to mind but I supose this needs to be well controlled.
I will be having a new survey so guess that I should mention my concerns to the surveyor and get his slant.
Question.... major issue for a DIY guy or not??

This is a common fault and should not put you off buying an otherwise sound boat at the right price. In fact it gives you something to negotiate over. How easy it is to correct is a matter of how far it has spread and how accessable the underside is. get your surveyor to check carefully around to indicate the spread. Often it is local to the holes if they were not properly sealed in the first place and as balsa is end grain does not spread far unless the outer skin has delaminated extensively which is a different problem. If the area is local to stanchion and chain plate bolts only and the area underneath is easily reached the easiest solution is to cut away the inner skin and remove the local area affected entirely leaving the outer skin intact. If the area is flat then replace with ply bedded on a good thick resin which can be held in place temporarily with through bolts while it cures. Then layup the area inner skin with plenty of overlap and refit your stanchions through with a nice big aluminium backing plate inside if possible. Simples!

 

[pvb]

The majority of boats have balsa cored decks and coachroofs...

I'd agree that cored decks and coachroofs are common, but many builders use Divinycell polymer foam core material, which doesn't rot and has low water absorption.

 

[fergie_mac66]

You don't know a lot about yacht construction, perhaps? The majority of boats have balsa cored decks and coachroofs,ultra light single skin exceptions like the SJ 320 are like a springboard to walk on.

I know real a lot about wood and quite a bit about construction. Build a couple of smallish boats plus a foam sandwich 25 footer . If something is going to be cored would much prefer it to be a closed cell non absorbent foam, not as stiff trueas balsa, but water is the ultimate element at finding a way in/ through.The use of a wood that soaks water up like a sponge is a conflict in something that floats . Great for designers and builders. Not so good for the unfortunate consumer.

I have seen quite a few boats where the water has got into the balsa and the remedial work involved in replacing it is massive . More than the average second hand smallish boat owner on a finite budget can undertake , the disappointment and disillusionment that results from a wrong purchase can cause several years of heart ache to a new boat owner.

 

[fergie_mac66]

I'd agree that cored decks and coachroofs are common, but many builders use Divinycell polymer foam core material, which doesn't rot and has low water absorption.

thats the way to do it . said in mr punch voice!

 

[Bosun Higgs]

Question.... major issue for a DIY guy or not??

Major issue - avoid like the plague unless so cheap you have nothing to lose. Far worse than osmosis.

Expanding foam wont do the job.

 

[30boat]

Major issue - avoid like the plague unless so cheap you have nothing to lose. Far worse than osmosis.

Expanding foam wont do the job.

I had a boat like that and it took me a huge amount of work to fix .The decks were rotten and had to be redone. The hull was delaminating from the balsa core.I had to inject epoxy resin into the hollows until it passed the hammer test .You can't use foam for this problem.Unless you know what you're doing stay away,that's my advice.

 

[oldsaltoz]

My advice.

You need to establish the total area/s that need treatment then estimate the cost of materials and double this figure.

Take at least this amount off the asking price, if the seller will not agree, walk away.

I have a number of repairs on balsa and foam cored boats, it's messy, dusty dirty work, and sometimes almost impossible getting yourself or a tool into an area to work.

I have developed a system that works for me and have had no failures in 20 years.

When ever possible work from bellow decks, this preserves the finish on the outside and often means you can continue working in bad weather as well.

It also helps to control air temperatures and can reduce emissions like dust on other boats in the yard.

The procedure:
Working from below deck, identify a soft area above deck and go below with 6 mm drill, drill into the suspect area and collect the dust and shavings that fall away, check them for any sign of moisture making sure you have reached the underside of the deck/hull but not though it.

Now move the drill 50 mm in any direction and repeat, keep doing this with a 50 mm grid till all the outer holes are dry.

Now use a 4 inch angle grinder and run it just outside the outer line of holes, use a sharp scraper to remove the fibre glass, this normally meand cutting in about 75 mm around the outer edge and the whole thing will come away.

You now need to hollow out the dry edge of the balsa/foam along the cut.

I find an old Allen key in a drill with the short bits tip ground sharp is good for this, cut away about 25 mm and check for any sign of moisture, re cut and extend the area if any moisture is found.

Next clean and sand the exposed inner side of the deck/hull and wash with Acetone.

Now make a template of the area the balsa has been removed, I just draw a line with a marker pen then use thin paper and sticky tape and trace the line.

Use this to mark a section of 'closed cell foam' of the required thickness, you can glue thin sheets together or cut/sand thicker sheets. and curved areas can be made by using a timber saw and cutting within 10mm of right through allowing the gap to close will let it bend, you may have to make several cuts 10 mm apart to get the bend required, this method also works for compound curves.

Cut the flat section first, then cut this section in half, this will help when fitting as you need to get the foam over the lip you left after the Allen key around the edge.

Offer one half into the repair area and check it fits properly making any adjustments for curve and edge fit as required; when you are happy it will fit, mark a line along the cut edge you made when you cut the foam in half. Remove this half and do the same for the second half making sure the marked line is on the edge cut earlier.

Next drill through the foam with a 6 or 10 mm drill on a 25 mm grid making sure each hole is clear and clean.

Now mix enough epoxy resin to give the whole area 6 coats and apply only one coat to the underside of the deck, then mix the rest with Micro fibres, spread this around the outer edge of the balsa with a brush just to coat it and apply the rest on the top side of the foam, fill any saw cats as you go.

You should have 6 to 8 mm of layer all over the top and be ready to offer it up one section at a time by using the line between them you marked earlier.

When both halves are in place bush up on them and allow the excess mix and any trapped air to escape through the holes drilled in the foam.

Use this material to finish filling around the edges then lay the original section you cut out over the repair, adjusting the level with packers if required but make sure there are no cavities, then add a sheet if plastic over the area and prop it into position with ply pads on the props. not not too hard though or you will have a dome on deck, so check.

Let this cure overnight at least then peel and clean up any dags and using a grinder grind around the gap between old and new then wipe with Acetone and class over in the normal way, you will find a small timber off cut handy to level the new class.

When all the repairs are completed a coat of low sheen over the whole area will it look as good as new.

This is not the full version, I am working on that on my Blog Page, coming soon.

Good luck.

 

[pcatterall]

Thanks guys for all the advice, Oldsaltoz has come through as usual and I wonder where we can find a proper 'library' containing all his tips plus, of course the contributions from VicS pvb and all our other experts.
Two points on this particular issue:-
'Walking away' when something is wrong is always an option and easy advice to give; in this case the boat ticks all my boxes and is cheap, also what 35 year old boat will not need some work?
This particular boat uses balsa as stiffening only over limited areas, the areas of high moisture readings were just around the through deck fittings along the side decks and around the tabernacle.
My plan now is to take advice from the surveyor who I know to be practical and thorough, if the work required is within my ability then I will use it as a negotiation tool and get stuck in by following the good advice supplied.
Thanks again!!

 

[Poignard]

My plan now is to take advice from the surveyor who I know to be practical and thorough, if the work required is within my ability then I will use it as a negotiation tool and get stuck in by following the good advice supplied.
Thanks again!!

An even better 'negotiating tool' would be a couple of boat-builders' estimates for carrying out the repairs. The owner may end up paying you to take it away

 

[Boo2]

Expanding foam wont do the job.

You can't use foam for this problem.

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

 

[MASH]

I'm guessing, but in my experience expanding foam's structure is deformed and damaged when crushed. Think Crunchie Bar. So with the ineviatable flexing of the deck from footfall or sailing loads the expanded foam crushes a little and leaves a new void for water to enter which it then soaks up. Balsa doesn't crush under normal loads and closed cell foam always expands back to its original size so neither suffer this problem.