Big project

Ross · May 31, 2009

If you go to Noah's boat building supplies and get some Corecell in the same hickness as the original core you can't go wrong. As to redoing the non-skid areas I will leave that to others.
be sure to check the sale items before you order.

http://www.noahsboatbuilding.com/noahusa/index.asp?FSCat=2&url=IND&iFromFeatured=1

sailingdog · May 31, 2009

SoSound said:
The big project is redoing a soft (likely de-laminated) cockpit seat where there had been teak slats attached. I've done some fiberglass work in my life, but I've never had to do anything with a core before. I've seen several books and how-to papers on the topic, and lots of detailed posts on this forum that I'll return to before I start the work...

My first question is on core material. Should I replace what damaged core that I remove with the same type of material, or are there other coring materials available with improved properties compared to what was most likely used in original construction in 1989? I'll be working from the outside of the seat inward, do I still need to be vacuum bagging?

If you're working from the top down, vacuum bagging isn't necessary since gravity is working with you—not against you. Using the similar type of core material would be a good idea.

And once I've finished the fiberglass work, then it's time to refinish the non-skid surface on both cockpit seats and the sole as well. What's on there now is a sanded paint (scratchy seats), and a dry-deck matting on the sole (scared me big-time on our test sail when it slid out from under me). I've seen and read the posts on Kiwi Grip. I was originally considering a composite material that looks like teak (specifically Tek-Dek), but heard that there may be problems with "bubbling" (another word for de-lamination). I don't mind the minimalist grey surface on white get coat, but also wouldn't mind an occasional compliment if I manage to do a good job of installing something a little more sophisticated.

Thanks,
Dave

Kiwi Grip is good, as are some of the paints, like InterDeck. However, KiwiGrip, Durabak and such finishes are probably longer lasting than a paint-based one.

Ross · May 31, 2009

I have a question. If compression strength or weight is not a factor to consider in a cored structure wouldn't any core material of the same thickness be adequate? If I needed only a couple of square feet of repair core material, what would be the objection to simply slicing the same thickness off the end grain of some dry pressure treated pine?

Dan H · May 31, 2009

what would be the objection to simply slicing the same thickness off the end grain of some dry pressure treated pine?

Weight. I think balsa was used because it was light.
If I ever do a re-core again, it won't be wood. I'd follow your first sugesion and use foam. My two cents.

Dan H · May 31, 2009

Are you sure it's core and not just a piece of plywood glued and tabbed to the under side of the seat? I've seen a few instances where that was the case.

Dan H · May 31, 2009

You are going to re-install the original fibeglass piece you remove to access the core? That would be the easiest way if you can.

sailingdog · May 31, 2009

Pressure treated pine would be a lousy core material. For wood to work well as a core material, it usually is best to have it end-grain, rather than having the grain running the length of the laminate. This is to help reduce water migration and helps a lot with the resin adhering to the wood properly.

End Grain balsa and Foam are the best core materials, with end-grain balsa having a slight edge in mechanical properties, while foam edges out balsa with rot resistance. Marine plywood is the worst of the commonly used core materials, since it has the weaknesses of balsa—it rots; and the weaknesses of foam—it allows water to migrate long distances and allows large areas to delaminate quickly.

Ross said:
I have a question. If compression strength or weight is not a factor to consider in a cored structure wouldn't any core material of the same thickness be adequate? If I needed only a couple of square feet of repair core material, what would be the objection to simply slicing the same thickness off the end grain of some dry pressure treated pine?

tsmwebb · May 31, 2009

The usual way to test for delam is by tapping. If you get a hollow sound in one area it probably has a void. For steps or seats that get stepped on (or anywhere else with high point loading) you will need a high density core (balsa, ply or one of the high psi foams). From worst to best fixes might be of the following types:

1) drill some small or medium sized holes in and around the area of delam and inject a low viscosity glue (epoxy is good glue) until it comes out all of the holes. Dab a couple of layers of Kiwi Grip over the holes and try not to think about it...

2) carefully cut around the delam area and peel off the top layer. Remove any very badly damaged core. Make a batch of moderately stiff (peanut butter) glue (epoxy + filler eg. 90% micro balloons 10% silica). Sandwich it all back together. Again, cover the joins with Kiwi-grip and see your confessor...

3) Cut away the bad area and some ways into the good. Rout out the bad core. Bevel the top laminate (around 6:1 to 12:1 or so). Dry fit a new core. Then seal the core with glue and let it kick and then make a batch of paste (thick pancake batter) glue and lay in the new core. Laminate a new face. You can build the new laminate up quickly using a stitched cloth (1808 might be good). Ideally you want a layer of CSM over the core and then the first layer of "good" glass to the top of the bevel with later layers moving in towards the center so it all lays flat... Some folks like a layer of CSM on top, too... YMMV. With a stitched cloth you can remove some of the csm and then sand off the bevel when done... However you do it you will have to bog out the area and fair it (again because it is high loaded you'll need a pretty stiff bog). Then high build primer (probably twice with sanding) and then you can try to match the deck paint/non-skid... A big job, but you'll sleep like a saint when it's done...

Working from the top, and assuming a non-structural problem, there is no need to bag or infuse. If you go for the big fix it can save time and help to get better laminates to put a layer of peel ply on the top, but remember to peel it off before you add a new laminate or start to bog! I like epoxy (though it is a nasty poison so treat is as such) because it is very good glue and it has a working period where it is tacky which can be invaluable in fitting things by hand... A downside is it will take longer to do the job with epoxy.

Good luck!

--Tom.

Ross · May 31, 2009

Dog, I specified end grain pine. That is easy to get just a piece of 2x4 laid on a table saw or a miter saw and chop off pieces. Alot heavier than balsa but otherwise similar. If the gaps between the blocks were filled with resin water migration would be kept to a minimum.

sailingdog · May 31, 2009

So you did. But any water that did get in would be leaching out heavy metal toxins (which are used to treat the pressure treated wood.

Ross said:
Dog, I specified end grain pine. That is easy to get just a piece of 2x4 laid on a table saw or a miter saw and chop off pieces. Alot heavier than balsa but otherwise similar. If the gaps between the blocks were filled with resin water migration would be kept to a minimum.

Ross · May 31, 2009

Would that be harmful to the resin/glass structure?

sailingdog · May 31, 2009

Don't know, but it wouldn't be good for people if it got into the boat...

Ross said:
Would that be harmful to the resin/glass structure?

Dan H · Jun 1, 2009

You'll need to find a way to support the lower skin while doing the repair.

After you glue the original fiberglass skin back in place, bevel the edge and put the FG in there, you can sand it smooth and spray gelcoat on it. After that, you could put a gelcoat non-skid surface back on.
A painted non skid surface is surely faster and cheaper but then you have that sanded seat surface again.
I think figured out a way to put a new non-skid gelcoat surface back on the seats and the cockpit sole, but I have a few more tests to do.
email me at catalina0029 at yahoo.com if you'd like more info.

William12213 · Jun 1, 2009

Ross said:
Dog, I specified end grain pine. That is easy to get just a piece of 2x4 laid on a table saw or a miter saw and chop off pieces. Alot heavier than balsa but otherwise similar. If the gaps between the blocks were filled with resin water migration would be kept to a minimum.

The biggest problem I would see with doing this ( I have thought about the same thing) is that slicing the end grain on the 2x4 to a 1/2 or 3/4 inch almost always causes the piece to break up. I guess this really isn't a problem just more time consuming.

As far as the leaching of water....well if you have water in there then you really didn't fix the problem. Once it is glassed in, it should be water tight. You also have to make sure the wood is very dry before you start. Treated lumber holds a lot of moisture.