Wet Balsa Core

[status]

My cockpit seats are balsa cored.

At time of construction (nearly 30Yrs ago) a large hole was hacked (possibly with a blunt spoon) in the side of the cockpit to fit the cockpit locker hatch combing. The edges of the hole were not sealed. The hatch was sealanted in, through bolted and glassed on the inside.

Roll on 30 years the sealant has degraded allowing water to get in but not out due to the glass internally hence wet balsa.

Hatch combing removed, rotted balsa raked out, good but wet balsa chiseled out to screwdriver depth. Air dried for two weeks, hot air gun dried for two hours but still sodden.

The sandwich has delaminated (and, I now know, has been since I got the boat) allowing water penetration I dont know how far and preventing an easy squirting in of resin to re-bond.

Due to time constraints the open end has been refilled with thickened resin filler and the hatch re-sealed and bolted, but the balsa is still wet.

Assuming I have now solved the water penetration but sealed in the water does the panel think:

a) Given polyester resin is microscopicaly water permeable the water will naturaly dry out!! (Some Hope)
b) Live with bendy seats until I can take no more (or something else happens), remove the Tekdeck, cut a panel out, rake out the now rotten balsa, replace with more balsa or ply, glass up and hide with more Tekdeck.
c) Drill holes from the underside hoping to allow to dry out, leave for a season or two then inject resin and hope.

All comments gratefully received

Status

 

[Twister_Ken]

c)

 

[Danny Jo]

You have my sympathy. I am still working on my rudder, having dismantled it to remove the wet balsa core.

Some of it was so wet you could squeeze water out of it like a sponge, and it would have taken months, if not years to dry it without removing the glass-epoxy outer lamina (skin). But the skin was still firmly attached to the core, so exposing the core involved destruction of the skin.

So I'd probably go for (c), but I'd cut the holes with a bi-metal hole cutter of, say, 38mm diameter.

 

[boatmike]

I am afraid b is the only way forward when this wet. End grain balsa does not transmit water unless it has delaminated. Ergo, therefore yours is delaminated and you won't re-bond it by injection.

 

[Noddy]

I'm doing up an old Iroquois which is famous for wet balsa in the coach roof.

I cut out the inner glass laminate. Remove all the wet balsa. I grind back to dry so don't worry about drying.

I have a 6 by 4 lump of balsa which I cut up across the grain with a bandsaw to the required thickness. Some people replace with foam - take advice and get the right foam though!

I then stick this to the deckhead with polyester / silica mix (a bit like P40). Roughly fair it and then lay glass over, thus replacing the inner laminate.

As long as you can leave the outside surfaces undamaged its relatively simple to do. It sounds as if you can get the affected part home into your garage - if so then it is simple (no glassing over your head on an inverted surface)

I vote for (b) but with more angle grinder action.

P

 

[wotayottie]

as an off the wall suggestion, the BP of water goes down with air pressure so if you can get a partial vacuum in the sandwich you could remove the water. try connecting a milking machine to the sandwich at the same time as applying heat to the inside skin

this will definitely work in theory - the question is will it work in practise

 

[luddites]

[ QUOTE ]
as an off the wall suggestion, the BP of water goes down with air pressure so if you can get a partial vacuum in the sandwich you could remove the water. try connecting a milking machine to the sandwich at the same time as applying heat to the inside skin

this will definitely work in theory - the question is will it work in practise

[/ QUOTE ]

Wotayottie, fantastic!

You have just described where the idea for the highly successful Hotvac hull drying system originally came from (not mine unfortunately).

 

[30boat]

Water mixes with acetone and also evaporates with it,It you inject acetone into the laminate and leave a number of holes on it the drying up process is greatly speeded up.This bit of knowledge comes from a book on fiberglass boats repairing,I have not tried it.
When I had the exact same problem as you I just cut tjhe seat tops off and redid the laminate wth new core.

 

[Elessar]

Can you get to the underside?
Does the underside need to look perfect?

If the answers are yes and no, you can do as I dis to my cockpit sole 2 boats ago.

Grind away the inner GRP and all the balsa.

Epoxy some ply onto the areas that used to have balsa.

Epoxy the outside of the ply if it doesn't see sun. Add some glass mat to the epoxy for bullet proof strength if desired. Varnish or paint if UV is a risk.

I did the same to a transom and that worked too.

 

[oldsaltoz]

[ QUOTE ]
Water mixes with acetone and also evaporates with it,It you inject acetone into the laminate and leave a number of holes on it the drying up process is greatly speeded up.This bit of knowledge comes from a book on fiberglass boats repairing,I have not tried it.
When I had the exact same problem as you I just cut tjhe seat tops off and redid the laminate wth new core.

[/ QUOTE ]

Methylated spirits has the same qualities but much cheaper and safer for you and your laminate.

But both are highly flammable.

Avagoodweekend......

 

[oldsaltoz]

G'day Stuart,

If at all possible do the repair from the back (Below deck). I start by drilling holes on a 50mm grid, check the material from the drill bit for moisture, marl only the holes that come up dry. Cut the glass out between the dry hole marks, remove the wet balsa and another 30mm past the cut and check the edge is dry all the way around.

You can use more balsa, ply, foam or micro-balloons to fill the gap. I would use only epoxy resins for this type of work.

After cleaning and washing with Acetone. Cut and shape your sheet of whatever you have selected and drill 6mm holes on a 50mm grid to allow the resin to escape when pushing into position.

Apply a coat of epoxy resin to the whole area being repaired, then mix some resin with micro balloons and spread this on the upper side of the sheet of material and push into place, the holes will allow the trapped air and any excess resin and balloons to escape.

Now you can fare the underside leaving a little for the glass depth and finish off.

Hope this helps.

Avagoodweekend......

 

[wotayottie]

just make sure you like your hair style before you star the job 'cos you'll have it for a while afterwards! /forums/images/graemlins/grin.gif

 

[status]

Thaks all for the responses. Sorry for ignoring everyone, day out the office yesterday.

In answer to some of the queries. The biggest problem is the bit of deck in question is right over the gas locker, so 1 1/2 inch clearance to the underside. Apart from the very back edge working from that side is impossible.

I like the idea of injecting acetone, might give that a try, meths may be cheaper but the company buys acetone in 220L barrels, terrible leak on the barrel tap though!!

As Noddy said, looks like more grinder action.

Status

 

[oldsaltoz]

Just be aware that Acetone will soften fibreglass laminate.

I would grind the gas container off the wall, and stick it back with epoxy resin and Micro-fibres mixed to the same thickness as peanut butter. About 30 minutes to complete.

Hope this helps.

Avagoodweekend.......