Thread: Metal Fastenings - yes or no?

Howdy Simon,

Epoxy is certianly not compatible with traditional building methods. The water is kept out because the timber in the planks (clinker or carvel) swells up to create enough pressure for a watertight seal.

So fastenings are the only way that will work - to allow the planking to swell and shrink without breaking the pieces of timber.

If you take a boat built this way out of the water, the planks shrink a greater or lesser extent and it will leak when it goes back in the water to a greater or lesser extent.

So you can't mix the methods. If you try to glue without dealing without dealing with the shrinking and swelling the boat will tear itself apart ... quite quickly.

Or waterproofing a traditional structure will mean that it will leak between the planks.

Best wishes
Michael

Possible exception to the rule is plywood over frames MIK ?
Seems to be a sort of a half-way stage between plank-over-frames & monocoque epoxy/ply.
Can be built fully sealed, *or*
'traditionally' with screws & paint.
But not mix'n'match methods.
cheers
AJ

so where does glued lapstrake fit in to all this, it's traditional clinker builing just with epoxy and not the copper rivets and roves, plus it has a lot les frame work.
my yellowtail could be built using 8mm cedar or 9mm ply, i chose ply due to cost but if i had gone for cedar it would have been glued along the lap just the same

Howdy,

Neither ply over frame or glued lap rely on the timber swelling to keep the water outside the hull. So they are completely compatible with keeping the water out of the timber too. with epoxy coating.

So then it is swings and balances to decide whether to keep the water out and leave out the fastenings too.

There are two main reasons for fastenings.
1/ non gap filling glues .. like everything except epoxy (please don't clamp epoxy hard) ... rely on close fits and good clamping pressures ... so if the close fits and higher clamping pressures are not available then there is good to have a backup of fastenings. Anyone who has repaired an older boat built with non gap filling glues will know about this one. Often the glue join can be cracked in places, but if there are fastening there it will just leak a bit ... and if the boat sits in the water for a few days the leak might stop as the wood takes up. This was the behaviour of almost all ply racing dinghies in the 60s and 70s. Dry as corks for the first couple of seasons, then they would start leaking and take on weight.

2/ the non waterproofness of paints or varnishes that use solvent thinning .. the water does get in always. So the wood will swell and shrink a bit whenever it wets and dries - ever seen paint crack over a join in a boat .. or over the top of a fastening .... that's this one. These swelling and shrinking cycles will eventually start breaking down the glue joins and the paint covering allowing more water to get in.

Quality epoxy systems don't have thinners ... called "high solids" so there is nothing to evaporate out and leave wormholes for water to find its way through. Water still goes through quality 'pox .. but the rate is so slow it tends to balance with the relative humidity of the environment.

So ... if you think it worthwhile to epoxy coat ..

You avoid the shrinking and expanding by coating with epoxy ... then there is little reason to use permanent fastenings. Use temporary ones which will save you money and they marry nicely with cordless drivers to save more time (or staplers or temporary nailing or stitching).

You won't see a moved joint between two pieces of wood or a crack over a fastening again. If you do the epoxy job properly!!!

For those of us who were building and sailing raceboats before the days of epoxy ... it is sometimes a bit like a revelation ... just how different the boats are ... so some of us get a bit religious about the 'pox.

In the USA they can get timber and plywood at about 1/6 or 1/8 of the price we can ... so a legitimate question they have is whether it is better to go cheap with everything and extra $200 for epoxy looks out of proportion .. they talk about $60 boats .. and ignore epoxy all together and accept that the boat will not last as long ... it is a legitimate approach too.

Actually ... any boatbuilding approach that the owner likes is legitimate for them!

But properly used epoxy can help remove the pain of being a wooden boat owner.

MIK

Used correctly, epoxy is only effective within two methods: as an adhesive in a joint or as a coating. The adhesive part is self explanatory.

As a coating, it must "embalm" the piece. Other wise it's just an expensive paint. Encapsulation with epoxy resin is quite a bit different then coating part of something with epoxy paint.

First of all, the paint, if it's a true epoxy is two parts (if it's a one part paint, but says epoxy, it's actually a polyurethane) and more importantly it uses a "vehicle" to commute paint into and onto the substrate. This means the epoxy is thinned, usually fairly dramatically with solvents, making it very weak, much less waterproof and rubbery.

Don't get me started on thinning epoxy, but an example would be a laminating resin, lightly thinned, say 5% by volume with alcohol will loose about 2/3's of it's compressive strength. That's a huge change in the physical abilities of the resin, so trust me, you don't want to do it, no matter what your "uncle Joe" might have said.

On the other hand, the rubbery, breathable, weakened epoxy, just might be a perfect base for a paint coating on things that move (like wood). Personally, I've tried the epoxy paints, and though they apply nice, they don't last, chalk up quickly and cost nearly as much as better paints.

With a taped seam build (stitch and glue), the structure becomes a homogenous whole, literally one giant epoxy molecule when cured, if encapsulated properly. On the other hand a traditionally built craft is an amalgamation or assembly of parts. Each relying, sometimes heavily, on it's neighbors to help share the stresses and loads. This requires a level of "movement" not permissible with epoxied structures.

Removing fasteners requires some practice. I've removed tens of thousands and have little tricks and custom tools to deal a blow to every little sucker that gives me a hard time.

The only way to avoid metal fasteners in traditional building, is to employ wooden trunels or pegs. These serve the same, acting in sheer or resisting pullout in most cases. They also have the benefit of not rusting, snapping off or stripping either. Unfortunately they're also not as strong as metal fasteners, by a considerable margin and can swell from moisture gain possibly splitting the plank or frame it's in.

A wealth of info, thanks. In many fibreglass boats where wooden reinforcing pieces have been "embalmed" in the epoxy, the wood has rotted due to penetration from screws to attach travellers, cleats, blocks and the like. These screw holes have been the entry point for water, which can't evaporate as the epoxy doesn't breathe. Presumably the same happens with Stitch and Glue.
How do you get around this?
Maybe this is where the wood should be rot-proofed! (oh no Simon not again, I hear you say)

Originally Posted by Simon Purser

(oh no Simon not again, I hear you say)

questions questions but this is how we all learn and leave info on this forum for others to learn, there is some great stuff posted on this thread that will be of use to me with my next build

on my yellow tail for the smaller screws i just filled the screw holes and the surounding area with sikaflex and screwed the fitting home, but on a few of the larger screws i drilled out a 10mm hole and filled it with epoxy so in effect i had an epoxy plug then pre drilled the hole for the screw.

Not sure if this is the correct way of doing it but i happy with the results

Originally Posted by Simon Purser

A wealth of info, thanks. In many fibreglass boats where wooden reinforcing pieces have been "embalmed" in the epoxy, the wood has rotted due to penetration from screws to attach travellers, cleats, blocks and the like.

If you mean fibreglass production boats ... they don't use anything to protect the ply used to stiffen up that flexible fibreglass stuff. Just glass and polyester resin. But over time the polyester resin allows water into the ply and often the subfloor area or the bottom edge of the transom never really dries out because there are only a couple of bungholes at the back. They could use one of the polyester compatible epoxy resins to seal the ply that goes into the structure - would cost them about $50 in materials and add a couple of hours to the building cost, but they reckon most people will sell the boat within a 5 year period so it will never be a problem.

Screws are not necessarily a liablity in an epoxy built boat. I don't like to have heaps of them ... but that is a personal preference ... part of my methodology. I know some very good boatbuilders who just leave the screws in because they can save more time that way. Their boats last well too because they countersink the screws and make sure there is a good thick epoxy bung over the top.

LIKE AJ (BOAT) said ... it is matter of understanding how the system works then really sticking with it - whether it is 'pox or trad.

With Wood Epoxy boats, I can't say what the reasons are for them deteriorating .. I have not seen many that have. And the ones I have seen it is usually because some component of maintenance not being carried out. A boat at anchor with a lump missing out of the epoxy for a long period (the wetness that can create deterioration is not instant by any means), varnish that has broken down in UV, someone who does one coat of epoxy thinking it is enough, unsealed end grain.

Those are much more likely than a particular screw causing a problem.

PAR has MUCH more experience repairing boats over a long period than me so he might like to comment on modes of epoxy failing to keep water out.

The only literature I am really aware of was WEST going back to look at some of their very early projects and finding most in rather good condition. They did not have many good things to say about plywood rudder blades though! (Racing people know that one already)

Best wishes
MIK

Oh Simon,

Just realised the second part of your question. We do often have to use screws to attach fitting to a boat. Or bolts.

With small boats it is common these days to glue the screws and bolts in. Means you need a soldering iron to take them off again, but you know they are really going to stay put even if you tow the boat across the nullabor!

On bigger boats you can either use something sikaflex under the base or a method developed by WEST called "hardware bonding" where the whole fitting is glued to the surface of the hull or deck as well as fastened.

Originally Posted by honkongphoie

on a few of the larger screws i drilled out a 10mm hole and filled it with epoxy so in effect i had an epoxy plug then pre drilled the hole for the screw.

Seems a neat way to isolate the wood from water

you can use the same method for centreboard pivots and mast step pins and all sorts of places too.

Drill an oversize hole where you want the pivot pin to be. Fill with glue mix, redrill to the correct size. Glass if the plans call for it.

You get a hard wearing ring around the pivot hole.

MIK

Originally Posted by Simon Purser

A wealth of info, thanks. In many fibreglass boats where wooden reinforcing pieces have been "embalmed" in the epoxy, the wood has rotted due to penetration from screws to attach travellers, cleats, blocks and the like. These screw holes have been the entry point for water, which can't evaporate as the epoxy doesn't breathe. Presumably the same happens with Stitch and Glue.
How do you get around this?
Maybe this is where the wood should be rot-proofed! (oh no Simon not again, I hear you say)

The object with stitch & glue is to either remove the stitches prior to epoxy encapsulation,
or encapsulate the stitches as well. Either way, nothing pokes out through the pox.
Fittings & etc have already been answered by MIK & PAR.

It is possible to have failures with epoxy covered wood. I've seen failures, but none have been epoxy related if applied properly.

Again, the key is encapsulation or literally embalming the separate pieces, including fastener holes with neat epoxy. This continuous plastic membrane will keep out moisture.

The problems come in when folks decide to make a change and drill a hole or drive a fastener without putting epoxy in the hole. Eventually the moisture will get past the fastener (threads act like a moisture wick) and it's trapped within the wood, with little avenue for escape. Rot doesn't start right away like an uncoated piece, but it does eventually. Rot needs food (wood), fairly warm temperatures, air and moisture. With the small entry point, air and moisture will be limited which starves off rot, some times for a long period. Rot needs all four things to survive.


I have some standing rules about fasteners in an epoxy coated piece. All are bonded below the LWL, no exceptions. It's not a difficult thing to do and it dramatically increases pullout and sheer strength of the fastener. I usually do every other fastener, then the other ones, once the first round is bonded and cured. Above the LWL, but exposed to the weather bonding is very common, but often, particularly if the piece needs to be renewed, removed or serviced in some fashion, I'll coat the threads with a mold release so it can be easily withdrawn. A bedding is placed under these elements.

Some will just put a drop of goo on a screw and drive it in a hole. This doesn't work, as the glue coats the top two or three thread rings, then is wiped off as the screw drives down. This will glue the head down fairly well, but not for long. I use a squirt bottle and fill the hole, then drive the screw, Yep, goo oozes out, but this is what you want, not a mostly dry hole.

I've also switched to using machine bolts and screws (mini bolts) instead of wood screws. When bonded, with or without mold released threads, they have a much higher pullout strength then regular screws. They're also easier to drive and you only need one pilot hole, no clearance hole is necessary.

In the failures I've seen, attempts to epoxy over size timbers or coat planking have been tried. Without encapsulation, the wood will not stabilize and will change dimension with moisture content changes. This will test any coating, including epoxy and eventually something gives up. Other failures were also related to incorrect resin/hardener mixtures, application errors, improper surface prep, etc., none of which is the fault of the epoxy.

As a system, epoxy has brought wooden construction and restoration back from the brink. By the 1980's most had written wood off as a novel material to make coffee tables out of. With the wide spread acceptance of epoxy, many old wooden things are being restored and preserved, but if it's not done right, it can lead to issues just like anything else.

yap ... so you can epoxy fastenings in, recess/countersink them and put a plug over the top or remove them and plug the hole with goop.

I pull 'em out and have also moved to machine screws (metal threads in OZ) to hold down fastenings instead of self tapping screws that i have used for decades. Usually use bolts for high load fittings though ... rudder!