Recore material around stanchions, rails, etc.

[jhenson]

I'm contemplating starting my deck re-core project this summer. I guess the standard practice is to cut out an area in the new core a few inches outside of load bearing items on the deck (such as stanchions, rails, and chainplates) and then glass in material in that area until flush with the core material. You then have a waterproof, non-compressable material under the bases of these items.

I just wondering if you could use a non-compressable plastic such kitchen cutting boards (polyethylene, I think) that come in 3/8" thickness. The material is relatively cheap and widely available. I'm thinking you could abrade this with 60 grit paper so it would adhere better. Is there a problem with epoxy delaminating with these types of plastics? I guess the danger would be having water flow between the sheet and the deck skin to the new balsa. This stuff seems really pretty tough though.

It seems like you could shorten some of the labor by doing it this way, but I obviously don't have any experience with recore work to know what I'm talking about.

Joe

[Tim]

Since plastics like that (which is basically what the pricey "Starboard" is) are often used to prevent epoxy from sticking, I don't think you'd get a satisfactory bond used in that application. I wouldn't choose this route.

If you want solid glass but also want/need to save time, you could use prefab fiberglass sheets, available from McMaster-Carr and other suppliers. Or, start now and laminate your own fiberglass panels with scraps or what have you.

The general concept of installing a pre-made piece of appropriate thickness to replace the coring is just fine. But it has to be an acceptable material. Prefab fiberglass would be fine here, whether self-made or bought.

[Rachel]

When I re-cored parts of my Montgomery, I didn't realize that you were supposed to use cloth in those areas. I used marine ply for the re-coring, because I had a free supply, then for the overdrilled holes and/or 4" - 5" diameter areas around the stanchion bases, I used thickened epoxy with no cloth.

I wonder now if this was wrong? I can't remember what I used to thicken the epoxy around the stanchion bases - but it might have been colloidial silica. Under the mast step (which was originally balsa - long since compressed), I believe I thickened it with "milled fibers" if I'm remembering that right.

Is this ever appropriate? Or should one always build up layers of cloth...

--- Rachel

[Tim]

It's nice to have solid material around all areas where fasteners penetrate the deck, but lacking that, oversized bolt holes filled with epoxy and redrilled are also an appropriate measure.

The whole idea is to make it so that even leaks at the fasteners won't penetrate any core material. In some areas where the deck is under compression, particularly deck mast steps, a non-compressable material should be substituted for the core, but this isn't strictly necessary for ordinary deck hardware.

[jhenson]

Tim,

Thanks,

I hope that I haven't exceeded the number of "dumb" questions allowed on this forum. I'm sure I am approaching it though.

Joe

[bcooke]

You have a long way to go before you beat my record! ... and I don't plan on taking second place without a fight.

What about using a slug of thickened epoxy under the fittings? I went the quick route last summer and drilled all the bolt holes oversized, filled them with thickened epoxy and then drilled for the correct size . That should keep my dry core intact for a while anyway. I was thinking when it came time to replan the deck layout, replace the stanchions, etc. I would use thickened epoxy under the full footprint of the fittings. Too stiff or brittle? The mast step is different in my mind though I don't know why. I was going to use (many) layers of glass there. Maybe just 'cause I saw Tim do it and it seems safe to copy the technique.

-Britton

[Tim]

What about using a slug of thickened epoxy under the fittings?

Plain thickened epoxy (assuming cabosil or other structural filler) is pretty strong, but large areas require reinforcement. I wouldn't leave large areas open in order to fill with only thickened epoxy; you need the fiberglass in there also to avoid problems caused by brittleness. I suppose you could mix in chopped fibers, but why? It's easy to throw in solid glass made from scraps left over from other jobs. You probably need not fill the entire thickness with reinforcement, but I would say about 3/4 of the thickness should have fiber reinforcement, and you could make up the last little bit with just the thickened epoxy.

Overdrilling is a perfectly acceptable way to install most hardware. Higher-stressed items are best off with full core replacement, but this isn't always practical.

It would be easy to go overboard with this sort of core replacement. Not every bit of hardware requires such serious work, but every hole should get the overdrill/epoxy technique unless you enjoy recore jobs. It takes an extra day, but is worth the effort.

I hope that I haven't exceeded the number of "dumb" questions allowed on this forum. I'm sure I am approaching it though.

No such limit! Keep asking away. They're not dumb questions anyway.

[radicalcy]

Simply due to cost factors, I would think that this would be the perfect appliction for polyester resin, since its about 1/4 the price of epoxy. Since there is no sheer involved, brittleness wouldn't be an issue, and it works well as a laminating resin. I would probably use the poly and either balsa core, or plywood, and impregnate them as much as possible. This way you retain some of the flex thats needed in these flat deck areas, and if you overdrill the mounting holes and seal them well, water intrusion shouldn't be a problem. IMHO

[Tim]

Polyester, in a repair scenario, sticks poorly to wood products and old laminates. This is why I do not ever recommend its use in these applications. You can often peel polyester-bound sheathing right off a wooden boat, or easily separate secondary polyester bonds by hand, with only a little persuasion to get the job started.

Epoxy is an adhesive as well as a laminating resin, and works well in any secondary bonding situation. Since it is also engineered and designed to be used in concert with wood products (specifically WEST System and other specific marine epoxies), it will bond wood and core products with far more success--and also is emminently flexible as part of its design function for use with wood. I firmly believe epoxy is always the right choice for repairs and additions to fiberglass boats.

I want to know that I've done all I can and used the best product for the job, whatever the end result. Polyester may seem to work, but over the longer term, I wouldn't count on it. The fact that our boats are built of polyester is not a reason to use it for subsequent repairs. Costwise...well, I maintain that epoxy is worth the premium. Any and all are, of course, free to disagree with me.

[grampianman]

To add my two cents worth in this debate - I have found from practical experience epoxy does work better and hold better that polyester. I am a Scoutmaster for a troop which has its own canoes. Boys being boys, the canoes take quite a bit of abuse which means repairs. I repaired the floors of the canoes about two years ago with polyester resin and fibreglass cloth. I have just had to re-do those repairs with epoxy as the polyester repair had started to release from the original material. If you imagine a fried egg, sunny side up, the white was releasing and only the yolk was adhering. I had to chisel some of the polyester out. I had cleaned and prepped the original surface. I have replaced the repairs with epoxy and cloth.
On the other hand, I had repaired an 8 foot dinghy using epoxy and it has seen a good bit of use (at the same Scouts hands) and so far I have not seen any evidence of repairs lifting. One thing I would mention is that I find the polyester resin far more brittle than epoxy.
I realise epoxy is more expensive, but in the long run, will provide peace of mind and in the words of the adverts, "Priceless".

Cheers,
Ian