Fixing a damp balsa cored deck.

[Brucekav]

The tank fillers on my boat were fitted by just cutting a hole through the balsa cored deck and screwing them down with a bit of sealant. Unsurprisingly the sealant eventually failed and water got into the balsa core. I've removed them and cut out the wet rotten balsa. One is fine but on 2 of the others although I've been able to remove all the soft rotten balsa through hole in the deck for the fitting the balsa I've got back to about 3-5cm from the edge of the hole is still slightly damp (feels colder than dry balsa but my finger is pretty much dry after pressing it) however it isn't much dryer after a couple of weeks left to dry. It is however firm not rotten, and there's no sign of flexing of the deck. Trying to work out what to do next. I don't really want to be removing the lower skin completely to replace the balsa as that sound like a big messy job and it's in a locker with poor access, but filling the the void to seal it up with moisture still in there doesn't sound great. I was considering drilling some holes in the lower skin and then hoping it would dry out through them once we get some hot weather to heat up the deck from above. Once dry I'd then fill those holes with thickened epoxy or similar. Is that likely to work? Any better suggestions? The fittings are close to the edge of the deck where it goes to single skin to join to the hull. Also any suggestions what to use to fill the void where I've removed the rotten balsa once the rest has dried? I figure I can fill that volume through the hole in the deck before refitting the tank filler fitting. Many thanks, Bruce

[mike d.]

drilling holes from under neath will work ! we had areas about 4 ft long by 14 inches tapering to about 8 inches. not rotted just wet ! I did cut out the lower skin ! I ripped out the balsa, used heat lamps for a couple of weeks to make sure all was dry,used a moisture meter and redid it then, re-glassed it ! I then got a hole saw that was about an 1/8 larger than the fuel and water fills and the deck drains ! I cut into the deck glass the depth of the fills, then sealed it with epoxy ! the fittings are flush, and bedded with butyl tape !

[wingssail]

Originally Posted by Brucekav

The tank fillers on my boat were fitted by just cutting a hole through the balsa cored deck and screwing them down with a bit of sealant. Unsurprisingly the sealant eventually failed and water got into the balsa core. I've removed them and cut out the wet rotten balsa. One is fine but on 2 of the others although I've been able to remove all the soft rotten balsa through hole in the deck for the fitting the balsa I've got back to about 3-5cm from the edge of the hole is still slightly damp (feels colder than dry balsa but my finger is pretty much dry after pressing it) however it isn't much dryer after a couple of weeks left to dry. It is however firm not rotten, and there's no sign of flexing of the deck. Trying to work out what to do next. I don't really want to be removing the lower skin completely to replace the balsa as that sound like a big messy job and it's in a locker with poor access, but filling the the void to seal it up with moisture still in there doesn't sound great. I was considering drilling some holes in the lower skin and then hoping it would dry out through them once we get some hot weather to heat up the deck from above. Once dry I'd then fill those holes with thickened epoxy or similar. Is that likely to work? Any better suggestions? The fittings are close to the edge of the deck where it goes to single skin to join to the hull. Also any suggestions what to use to fill the void where I've removed the rotten balsa once the rest has dried? I figure I can fill that volume through the hole in the deck before refitting the tank filler fitting. Many thanks, Bruce

I work from above (removing the top skin) but that may not be easy if you have a molded or gel coat deck. I fill the void with small blocks of soft wood (pine) before filling with thickened epoxy, then replace the the top skin (which I saved) and finish and paint.

Here is a link to some project photos which includes just such a deck repair. <Wingssail Images-Cruising Photos from Around the Pacific>

[Jon Hacking]

We ended up peeling off our entire deck, removing the balsa, replacing it with structural foam, & rebuilding the deck, but that was a HUGE job & you don't want to go there.

If the balsa feels soft or damp, remove as much as you can through the hole, & then hit the area with a hair-dryer or heat gun until the balsa is dry-dry. We put an Allen-key in an electric drill to pulverize the balsa so we could remove it easily, but if you've got a big hole then a screwdriver should also work.

Once the balsa is dry, then yes, epoxy mud should work fine. If you want excellent adhesion, you can paint the inside surfaces with epoxy resin first, then push the mud in.

If they didn't de-core that filler-hole, then they probably didn't de-core other holes. We had to de-core over 100 holes on our boat.

• Remove all fittings that are bolted to the deck or hulls, including winches, sail-tracks, deck-blocks, hatches, air-vents for tanks, thru-hulls, etc.
  
• Stick an Allen-key on a drill into the hole & pulverize the balsa.
  
• Remove all the balsa.
  
• Put tape over the inside/underside of the hole.
  
• Inject thickened epoxy to fill the entire void.
  
• Re-drill the hole once the epoxy has hardened.
  
• Re-mount your hardware.

Good luck!

[Bunji]

Originally Posted by Brucekav

The tank fillers on my boat were fitted by just cutting a hole through the balsa cored deck and screwing them down with a bit of sealant. Unsurprisingly the sealant eventually failed and water got into the balsa core. I've removed them and cut out the wet rotten balsa. One is fine but on 2 of the others although I've been able to remove all the soft rotten balsa through hole in the deck for the fitting the balsa I've got back to about 3-5cm from the edge of the hole is still slightly damp (feels colder than dry balsa but my finger is pretty much dry after pressing it) however it isn't much dryer after a couple of weeks left to dry. It is however firm not rotten, and there's no sign of flexing of the deck. Trying to work out what to do next. I don't really want to be removing the lower skin completely to replace the balsa as that sound like a big messy job and it's in a locker with poor access, but filling the the void to seal it up with moisture still in there doesn't sound great. I was considering drilling some holes in the lower skin and then hoping it would dry out through them once we get some hot weather to heat up the deck from above. Once dry I'd then fill those holes with thickened epoxy or similar. Is that likely to work? Any better suggestions? The fittings are close to the edge of the deck where it goes to single skin to join to the hull. Also any suggestions what to use to fill the void where I've removed the rotten balsa once the rest has dried? I figure I can fill that volume through the hole in the deck before refitting the tank filler fitting. Many thanks, Bruce

I removed as much of the top laminate and balsa as I needed to and sanded all of the bottom laminate then poured a epoxy glue and 411 low density fillet powder mix in and waited for it to tack off then laid some 450 d/bia cloth over it, bog and fair then paint

[Tetepare]

Be careful with the Allen wrench in the electric drill. The end of that wrench hits good core and it will crank you around instead. Modern drills have enormous torque. Though I agree with the technique

[psk125]

We had a similar problem with rotted balsa around a solar fan vent. As do you, we had access to the balsa core between the inner and outer layers of the deck once the vent was removed. We took out all the wet and rotted material we could by going at it without cutting into the fiberglass top or bottom, until like you we got to firm, if perhaps damp, balsa core. We let the hole dry out for about a week in summer sun, making sure to keep it covered from any rain or spray and fanning it as much as possible. We then tried to fit as much new core material back in as we could. Not much fit back in because the remnants of the fiberglass resin between the original balsa core blocks kept us from sliding the new balsa in very far. We could have perhaps done a better job clearing the remnants out, but that would have been tricky, finicky, and slow work. We ended up with some balsa and some air spaces in the cleared out area. We mixed microfibers with epoxy and injected it (syringes are great) into the space around the vent hole, after drilling small holes in the inner layer at the far ends of the air spaces. When epoxy started coming out of the holes, we stopped injecting and taped over the holes. Deck is not spongy now.

[zstine]

Flushing the balsa with alcohol will help dry it out. Perhaps injecting into a drill hole. also put heat on it with a ceramic heater, hair dryer or spot light, whatever.. the epoxy mud is fine to fill around the hole once dry. I would not remove the skins.

[MikeDofFreo]

This correspondence just makes me speculate as to what joys await people as the balsa cored topsides get older. Boats like the current Moody 54 look fantastic but, with balsa cored topsides? I think I read that even Oyster use balsa topsides and so it must be allowed by Lloyds.

[wingssail]

Originally Posted by MikeDofFreo

This correspondence just makes me speculate as to what joys await people as the balsa cored topsides get older. Boats like the current Moody 54 look fantastic but, with balsa cored topsides? I think I read that even Oyster use balsa topsides and so it must be allowed by Lloyds.

Well Mike, Balsa cored decks (hulls too) have many advantages, and if properly built and cared for, are not a problem. When they are a problem they are not difficult to fix. When you get a boat I am certain it will have a solid deck, no core, since you feel that strongly, and at some time you may begin to appreciate the balsa core of your friend's boats.

My boat is 43 years old. It has been sailed very hard for those 43 years. The balsa core was not well done at the original build, nor was it cared for when I first acquired the boat. But even so, it has served me well, it is light, quiet, strong, cool, and durable, and repairable.

[Manateeman]

Please read the wiki article on balsa. It covers all the good points and bad points.
I began Boatbuilding in wood and learned which wood would be best for each part of the vessel. There were adjustments for the vessel design, intended use of the vessel, cost, availability...on and on. Cork had its place in wood boatbuilding but the use of balsa was limited to rafts.
How to repair balsa core has been well discussed.
We do not believe balsa is a suitable material for vessel construction. We feel the disadvantages out weigh the advantages. Like many new ideas in boatbuilding, end grain balsa began as an experiment and time has proven, it was a very costly failure in far too many vessels.
We hope your repair goes well and that you do not become discouraged with the cost and time spent. There is no perfect vessel design, builder, method of construction nor material.
There are however...perfect sailing days.
Happy trails to you.
Captain Mark and the manatee crew.

[MikeDofFreo]

Well "Wingsail", you are partially right. I have had four solid decks. However, I was never envious of balsa cores. Indeed, I was sublimely ignorant of the problems with using balsa until I had a balsa cored deck on a Southerly. It was then that I learned the problems that others, as above, have experienced and which taught me that a hair dryer is much more important on a yacht than I had previously thought. I was surprised by the extent that that the wetness would travel even with just the camber and slope of the deck.

I dread to think what it would be like in a vertical or near vertical structure such as under the beautiful hull ports that we see on modern hulls with balsa cored topsides. However, I expect that I am being pessimistic and all builders who use balsa have absolutely perfect systems for ensure perfect seals. Of course, there will be no problems such as so many of us have experienced with our decks!

[sinnerman]

Originally Posted by Tetepare

Be careful with the Allen wrench in the electric drill. The end of that wrench hits good core and it will crank you around instead. Modern drills have enormous torque. Though I agree with the technique

Practical Sailor came up with the recommendation to take a roofing nail and cut some slots into it. Use it with a drill and it acts like a mini saw without the dangerous reverse torque being mentioned.

the article:
https://www.practical-sailor.com/sai...ving-out-cores

https://s30384.pcdn.co/wp-content/up...vq566.jpg.webp

cheers

[wyb2]

Originally Posted by Brucekav

…about 3-5cm from the edge of the hole is still slightly damp (feels colder than dry balsa but my finger is pretty much dry after pressing it) however it isn't much dryer after a couple of weeks left to dry. It is however firm not rotten, and there's no sign of flexing of the deck. …

You’ve already gotten some replies talking about peeling skin (top or bottom), but in my opinion that would be crazy to do for the issue you’ve described. Peeling skin and replacing core is the fix for a soft, rotten deck core, so wait until it’s soft and rotten to go through that.

Originally Posted by Brucekav

….Any better suggestions?…

If you have access to AC power and some spare time, you could pick up a rotary vane vacuum pump to help dry it out. Whether or not you can pull a sufficient vacuum will depend on the deck construction and will take a little dumb luck, but if you can it will completely dry out the area in a day or 2.

You can buy vacuum pumps on Amazon or similar. At 29 inHg vacuum water boils at room temp. Getting it to work may be a bit of a science experiment, but if you can, it’s guaranteed to dry out

[Cheechako]

Originally Posted by Brucekav

The tank fillers on my boat were fitted by just cutting a hole through the balsa cored deck and screwing them down with a bit of sealant. Unsurprisingly the sealant eventually failed and water got into the balsa core. I've removed them and cut out the wet rotten balsa. One is fine but on 2 of the others although I've been able to remove all the soft rotten balsa through hole in the deck for the fitting the balsa I've got back to about 3-5cm from the edge of the hole is still slightly damp (feels colder than dry balsa but my finger is pretty much dry after pressing it) however it isn't much dryer after a couple of weeks left to dry. It is however firm not rotten, and there's no sign of flexing of the deck. Trying to work out what to do next. I don't really want to be removing the lower skin completely to replace the balsa as that sound like a big messy job and it's in a locker with poor access, but filling the the void to seal it up with moisture still in there doesn't sound great. I was considering drilling some holes in the lower skin and then hoping it would dry out through them once we get some hot weather to heat up the deck from above. Once dry I'd then fill those holes with thickened epoxy or similar. Is that likely to work? Any better suggestions? The fittings are close to the edge of the deck where it goes to single skin to join to the hull. Also any suggestions what to use to fill the void where I've removed the rotten balsa once the rest has dried? I figure I can fill that volume through the hole in the deck before refitting the tank filler fitting. Many thanks, Bruce

I think you can probably fill the area where you pulled out damp core and be fine if it's nearly dry.
I would probably just use "kitty hair" ....it's fiberglass strands in resin. It dries hard and solid.
-A better solution would be to temporarily replace the fitting... caulked well, leave the core open for summer, then remove the fitting later after it's good n dry and fill the space.
-Another option is to heat the boat and have a small fan on for a few weeks directed at the repair area. Air movement dries things out fast.
-And another more tedious option is to buy or rent a small air conditioner and mount it on the boat leaving it on for a week or two. AC air is very dry and will dry it out.