Replacing wet balsa core

[Nicholson58]

Originally Posted by svtrio

Bonding issues with epoxy are often created by neglecting to water rinse the blush from cured epoxy. I've learned that removing the blush sometimes requires some vigorous scrubbing with a 3m kitchen pad.

The blush is water soluble, so acetone isn't a substitute for water. And sanding before the water rinse forces the blush into the surface making removal more difficult.

Except for a special laminating hardener, all the West hardeners blush, with varying degrees dependent on temp and humidity.

Blush removal is a pita, but I've learned to live with it during my refit. However, I now generally use the non blush hardener (and still often rinse; some habits don't die).

And yes, I learned this the hard way.

This forum has been a great resource for me, and I'm grateful to those folks who take the time to share their experiences, especially those employed in the marine trades. They deal with a depth and breadth of issues - and resources - that I'll never encounter in my more focused project.

In the end, I mix the varied comments here with my own experience and research and take my best shot.

Roger


Sent from my iPhone using Cruisers Sailing Forum

PLEASE read my posts above; follow the links to US Composites for 635THIN resin. It is ZERO BLUSH. You can layer build any thickness with no wash or scrub. It is user friendly Epoxy. It is soap & water clean off your hands until it begins to cure. (3 to 6 hours). Epoxy is the O-negative of resins. It sticks to polyester and vinyl ester as well as any other boat materials. OH- it costs less than any other epoxy options. I use no other resin for any major projects and for most minor jobs. Fiberglass , Epoxy , Composites, Carbon Fiber - U.S. Composites, Inc.

[phorvati]

Originally Posted by minaret

No, Coosa will not crush. Not anymore than marine ply would. It is built in a hydraulic press at 60k PSI.

Few more questions...Balsa squares are loosley tied so they will conform to the deck. Deck is moslty level along the genoa track, but there will likely be some dips and peaks in an area as large as mine 12" by 12 feet. How do i get coosa to conform to avoid possible voids beneath.
How many layers of 1708 to get to 3/16? I read on another forum that no more than 2 1708 layers at a time due to heat buildup. Is the first glass layer supposed to be the largest, closest to outter bevel edge, and then subsequent layers are smaller. Some articles say to do it hat way, but isnt there going to be bunching of fiberglass at the corners?

Thanks

[minaret]

Originally Posted by phorvati

Few more questions...Balsa squares are loosley tied so they will conform to the deck. Deck is moslty level along the genoa track, but there will likely be some dips and peaks in an area as large as mine 12" by 12 feet. How do i get coosa to conform to avoid possible voids beneath.
How many layers of 1708 to get to 3/16? I read on another forum that no more than 2 1708 layers at a time due to heat buildup. Is the first glass layer supposed to be the largest, closest to outter bevel edge, and then subsequent layers are smaller. Some articles say to do it hat way, but isnt there going to be bunching of fiberglass at the corners?

Thanks

Apply Corebond with a notched trowel and lay your Coosa into it. This will fill all possible void areas, as long as you use the big notches. It's what it's made for.

For a full 3/16 I'd do two DBM 1708 followed by two CSM 1.5 oz. The CSM on top will give you something to grind/fair on without hitting your structural lam with anything. It will also roll out fairer and nicer. Finish with a peel ply if possible.



First glass layer largest only on new construction. For repairs, always small ply first to match the bevel on the grind.


I commonly do up to 7 plies of 1708. But it's cool here!

[phorvati]

thanks, that's helpful.
Here are few progress photos. Man, grinding fiberglass inside is a pain. Ive done keel joint but that's outside and you can always angle it so that wind takes it away. I don't know how some of you folks do it from inside. That must be a disaster. I decided to stop chiseling healthy balsa. Also you can see that ply was somehow offset from the centerline of genoa track. Also you can see the extent of the damage. I can tell that water did not come in from the chainplates. Windows are suspect. I re-bedded those in 2010 and i know water does not come inside the cabin from the windows. Cabintop has no sandwich. Perhaps water makes its way between laminate and headliner and then saturates the deck. I will look into this further. As I was chiseling away, some CSM was coming off (attached to balsa). After sanding it with random orbit, I plan to add 1 layer of CSM. It was 10F at the time I was doping this. Everything was frozen. I can see how boats with no shrink wrap(me for 5 years in a row) get in to this predicament. Any little moisture will freeze and work the cracks. Then the problem compounds the following winter. It was not my original intend to spend winters up here. Family circumstances are making it difficult to bring this boat away from ice. I don't think boats belong this far north. Season is too short and winter always wins. If i had my choice, I would rather deal with UV then ice.

[minaret]

Looks great. You'll probably have to pull the one stanchion. And, for future reference, always make your cuts at least 2" inside of the edge of the nonskid and decore from there if possible, even if it takes a lot more effort. This allows you to do the whole repair in nonskid, with the smooth gel taped and protected for the whole job. It reduces finish work dramatically. But it's a bit late for that here. Also layout and make straight fair cuts if possible, even if it means removing a little good core. It makes glassing and fairing much quicker. Laying a CSM first is fine, just don't lay so much glass on the lower skin that it throws off your core thickness. High core is bad.

In this case, it's possible that the cabin side is cored as well and tied into the side deck, resulting in the rot from porthole leaks. If that's the case, you may need to decore under the portholes as well. I'd open them up and take a look before you get into glassing. Just in case.

[phorvati]

I only see 5 gal buckets for Core bond B70 I don't need that much. Does anyone know a source if less than 5 gal.

[guyrj33]

Originally Posted by minaret

No, Coosa will not crush. Not anymore than marine ply would. It is built in a hydraulic press at 60k PSI.

Here's a link with the technical data for Coosa Panels
http://coosacomposites.com/images/Co...ata-052914.pdf
the compressive strength is a lot lower than 60k PSI.

[minaret]

Originally Posted by phorvati

I only see 5 gal buckets for Core bond B70 I don't need that much. Does anyone know a source if less than 5 gal.

No. But I pay $80 for a fiver of CoreBond. Catalyze and toss what you don't use.

[phorvati]

Its more like 208$ for slow and 230$ for regular plus 20$ catalyst at
Merritt Marine Supply. ATC Core-Bond B70 Polyester-Based Adhesive 5 Gallon

Does anyone know if you need a commercial account to order from composites one or can you order from Scott Bader directly?

[BigSmile]

Originally Posted by minaret

Looks great. You'll probably have to pull the one stanchion. And, for future reference, always make your cuts at least 2" inside of the edge of the nonskid and decore from there if possible, even if it takes a lot more effort. This allows you to do the whole repair in nonskid, with the smooth gel taped and protected for the whole job. It reduces finish work dramatically. But it's a bit late for that here. Also layout and make straight fair cuts if possible, even if it means removing a little good core. It makes glassing and fairing much quicker. Laying a CSM first is fine, just don't lay so much glass on the lower skin that it throws off your core thickness. High core is bad.

In this case, it's possible that the cabin side is cored as well and tied into the side deck, resulting in the rot from porthole leaks. If that's the case, you may need to decore under the portholes as well. I'd open them up and take a look before you get into glassing. Just in case.

Question: Can you elaborate a little more about "High core is bad"? What is considered high core, and what are the negatives?

2nd Quote: "Apply Corebond with a notched trowel and lay your Coosa into it. This will fill all possible void areas, as long as you use the big notches. It's what it's made for."

Question 2)what if after the core is removed, as in the picture, the exposed open deck is walked on, and a "crack" is heard?

[minaret]

Originally Posted by BigSmile

Question: Can you elaborate a little more about "High core is bad"? What is considered high core, and what are the negatives?

2nd Quote: "Apply Corebond with a notched trowel and lay your Coosa into it. This will fill all possible void areas, as long as you use the big notches. It's what it's made for."

Question 2)what if after the core is removed, as in the picture, the exposed open deck is walked on, and a "crack" is heard?

To answer both questions at once:

If you add laminate to the top side of the inner skin, it will throw of your core thickness. That is, if you have 3/4" core which you have removed, and you replace it with 1/16 of glass + 3/4" core, your core will sit 1/16" higher than the surrounding core. If you rebond the top skin this way, the whole deck repair will be high by this amount. High is bad; it is relatively easy to add material and fair in a low, but it is much harder to fair in a high, as material cannot be removed without taking out part of the upper skin. Therefore, if the inner skin is damaged in the core removal process(common), you must either repair it from underneath if possible, or back grind it, glass it, and rough fair it from the top, to avoid high spots in your repair.


Don't get carried away, though. Just the act of bonding in Coosa with CoreBond will fill and bond together all possible cracks and voids, if done right. The very long open time makes a huge difference.

[Scott Fuller]

I am 3/4 of the way through this exact process on our O'day 34. I spent a lot of time debating core materials, and considering things like G10 for under the genny tracks. In the end, I went back with balsa core, and marine plywood under the tracks - just like the original. I coated the plywood with thinned epoxy, and installed it in 2' long sections with a small margin of thickened epoxy between. I also potted all the fastener holes to insure water doesn't get to the plywood. I used scored balsa core, and flexed it in both directions and brushed epoxy between each block prior to installing it. I used three layers of 1708 for my layup. I did as Minaret suggested and cut a couple inches inside my non-skid so that I could keep my repair off the smooth gel coat. I will be using KiwiGrip for my nonskid. Removing core under those margins was a huge pain. I used a Fein MultiMaster for removing the old core, in the field and under the margins. It is amazing how well adhered my very wet core still was! The Fein tool was not great at getting all the core out of the margins and I ended up making a 24 grit abrasive disk "sandwich" by peeling the foam velcro pad off a hard rubber backing plate for my 7" polisher, then using double sided tape to adhere the 7" abrasive disks to the top and bottom. I ran it on very slow speed as going to fast was both too aggressive and caused the tape to heat up and not hold the abrasive disks. It fit under the margins well, and did a great job of removing the remaining bits of core in relatively little time. Midway through the job, I became concerned about water getting into the core from the port light area even though I pushed a lot of thickened epoxy in ahead of my core under the margins on the cabin side. (I had already re-cored the cabin top and knew I had no water problems coming from there). I removed all the port lights and discovered the cabin sides are hollow - hull liner inside, external cabin side outside. My initial plan to seal the gaps was untenable due to the varying thickness of the layups - both cabin sides and liner, so I ended up making some"U" shaped temporary spacer blocks to create a consistent thickness to the cabin walls, then injected urethane spray foam insulation in the void all around the perimeter of all the port light openings. A few days later I carved out the foam at least a half inch deep around the perimeter and filled this area with West Systems thickened with 406 to a very stiff consistency. After this was cured, I used a Dremel tool with a coarse burr to route out the rain channel grooves for the port lights, and to smooth out any rough areas around the perimeter. I have detailed this process with photos on another forum. I realize the method I chose is not the only way, and in the opinion of many may not be the best way, but I felt given my abilities and for my boat it was a good method that should last at least as long as the original method, if not longer!

Scott

[minaret]

Originally Posted by Scott Fuller

I am 3/4 of the way through this exact process on our O'day 34. I spent a lot of time debating core materials, and considering things like G10 for under the genny tracks. In the end, I went back with balsa core, and marine plywood under the tracks - just like the original. I coated the plywood with thinned epoxy, and installed it in 2' long sections with a small margin of thickened epoxy between. I also potted all the fastener holes to insure water doesn't get to the plywood. I used scored balsa core, and flexed it in both directions and brushed epoxy between each block prior to installing it. I used three layers of 1708 for my layup. I did as Minaret suggested and cut a couple inches inside my non-skid so that I could keep my repair off the smooth gel coat. I will be using KiwiGrip for my nonskid. Removing core under those margins was a huge pain. I used a Fein MultiMaster for removing the old core, in the field and under the margins. It is amazing how well adhered my very wet core still was! The Fein tool was not great at getting all the core out of the margins and I ended up making a 24 grit abrasive disk "sandwich" by peeling the foam velcro pad off a hard rubber backing plate for my 7" polisher, then using double sided tape to adhere the 7" abrasive disks to the top and bottom. I ran it on very slow speed as going to fast was both too aggressive and caused the tape to heat up and not hold the abrasive disks. It fit under the margins well, and did a great job of removing the remaining bits of core in relatively little time. Midway through the job, I became concerned about water getting into the core from the port light area even though I pushed a lot of thickened epoxy in ahead of my core under the margins on the cabin side. (I had already re-cored the cabin top and knew I had no water problems coming from there). I removed all the port lights and discovered the cabin sides are hollow - hull liner inside, external cabin side outside. My initial plan to seal the gaps was untenable due to the varying thickness of the layups - both cabin sides and liner, so I ended up making some"U" shaped temporary spacer blocks to create a consistent thickness to the cabin walls, then injected urethane spray foam insulation in the void all around the perimeter of all the port light openings. A few days later I carved out the foam at least a half inch deep around the perimeter and filled this area with West Systems thickened with 406 to a very stiff consistency. After this was cured, I used a Dremel tool with a coarse burr to route out the rain channel grooves for the port lights, and to smooth out any rough areas around the perimeter. I have detailed this process with photos on another forum. I realize the method I chose is not the only way, and in the opinion of many may not be the best way, but I felt given my abilities and for my boat it was a good method that should last at least as long as the original method, if not longer!

Scott

Don't tell anyone I told ya, but a circ saw blade will chuck right in to a heavy duty 7" grinder if you pop out the center diamond. Super dangerous though! Count your fingers first, it may be the last time you see them. If you use a dull 1/8" kerf blade on a variable speed set pretty low, it removes core in a big hurry without messing up the glass. If you like your fingers too much for this, there is much to be said for a long spade bit on a right angle drill, followed by clean up with a double sided grinder as described above, which by the way can also be pretty dangerous.

[Scott Fuller]

Originally Posted by minaret

Don't tell anyone I told ya, but a circ saw blade will chuck right in to a heavy duty 7" grinder if you pop out the center diamond. Super dangerous though! ...

I thought long and hard about that and probably would have ended up there if the disk sandwich hadn't worked!

[Scott Fuller]