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Home > Don't Screw It, Bond It
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Don't Screw It, Bond It by Terry Buddell
It may not seem obvious at first but one of the fastest ways to induce terrible (and indeed terminal) damage is to place screws (of any type material or size) into the hull or deck of your boat. The resulting damage can literally cause the premature demise of a perfectly good boat that would otherwise last for another twenty or more years.
SO HOW CAN THIS HAPPEN, THAT'S WHAT SCREWS ARE FOR...AREN'T THEY?
Basically we have to investigate why the whole concept is so wrong. Fibreglass is basically glass (real glass) and plastic resin. If you tried to screw a screw into either glass or plastic resin you would soon find out that the threads would smash the glass and plastic to minute smithereens all around the screw threads. The resulting hole becomes a perfect route for water, both salt and fresh, to spiral its way down into the core of your deck or into the nicely furnished interior of your boat.
OK, SO WHY DON'T WE JUST USE A BIT OF SEALER ON THE SCREW THREADS?
Initially it will work. However, sealer (which is soft) will crack, dry out, squash and degrade from UV effects. Bit by bit it will gradually decay away, helped along by pushing, pulling, kicking and general strain on the bit of hardware it is trying to hold to the deck. So, in time, the seal fails and the leaks start again!
Generally encouraged by the (initial) success of the non-leaking screws the enthusiastic owner will continue to add dozens more culprits to the first. The effects can be horrendous (in time). He will end up with dozens of unsuspecting little waterways all filling up the glass layers or the foam core interior adding water at the rate of quite a few litres per year.
CORED DECKS
As you can imagine, balsa cored decks obviously get to be the worst damaged of all when water seeps into the cores unnoticed. Eventually the decks will sag, squelch and the balsa rots away to black mush. Ouch! That hurts! Have you any idea how much that costs to repair. Often more than the boat is worth.
FOAM CORED DECKS
Most foam-cored decks are impervious to water...aren't they? Well, you would think so at face value. Apart from the fact that water softens the adhesive qualities of internal bonding materials causing eventual delaminating, water has a worse and secondary insidious effect on foam cores. Most foam boats are built from polyester or vinylester resin. When water lays in contact on these types of resins a chemical component of the resin called 'styrene' leaches out from the resin walls of the deck and hull.
Yes, you have guessed it already, haven't you? What does styrene do to foam cores?...It softens and melts them! Result: Squashy wet collapsed decks that will cost you much more than your granny will leave you when she goes......
BONDING
So, screwing into glass and foam cored decks is out. How about timber? No way! Same thing but a bit different. The timber fibres get squashed when a screw enters and eventually combines with acids contained in the wood. This rots the wood and corrodes the screw and water sucks happily down into the boat to cause destruction...so what do we do now?
There is happily, a solution. It is however a more time consuming process and is really a bit of a pain but the benefits are just great. Many years ago it was discovered that bonding of hardware to a boat was a very effective way of permanently preventing a fastener (any fastener that is, canvas snaps, screws, bolts, self tappers and wood screws) from ever leaking. And (happy days!) there are several ways of doing the job.
The actual concept is to 'bed' the fastener into epoxy and allowing it to cure solidly around the fastener curing the propensity for detaching, coming loose, shearing, pulling and leaking ever again. There are solutions for all fastener type and sizes, let us have a look at some.
WOOD SCREWS
Before drilling wood screws into timber or glass, drill a pilot hole shallower than the depth required. Coat the wood screw threads with epoxy and then fill the pilot hole with epoxy using a pipe cleaner or syringe (a printer ink refill plastic syringe is great). Wait for bubbles to appear, refill the hole with more epoxy then insert your wood screw and screw up. Wipe off excess from around the screw head with acetone or thinners. Allow to cure.
FOAM DECKS OR BALSA DECKS
Drill a pilot hole with a 'spade type' drill, drilling an oversize hole. Fill the hole with epoxy resin. Note: If working on a vertical surface, soak the hole first in unthickened epoxy then using a mixture of epoxy and high-density filler make a paste and fill the oversize hole. Insert the fastener and allow to cure.
NOTE OF INTEREST
In their initial research years ago, Gougeon Brothers of America discovered that a wood screw size 12 required a direct pull (tension load) of 901 pounds (408 kg) to forcibly remove it when inserted into a dry, standard screw hole. However, when the same screw was soaked in epoxy and allowed to cure a massive 1897 pounds (860 kg) direct pull was required to move it...Guess what? The timber broke before the glue or screw did! It has been discovered that fastener bonding with epoxy increases load capacities by an average of 70% or more by using 'self-tapping' screws. Here is the reason why:
The fully threaded shank of the self-tapper has much more surface area and is therefore better able to key into the wood/resin matrix than the humble wood screw. Furthermore, 'machine-type' screws with flat 'V' heads have even better resistance qualities when bonded into base materials.
Sadly, many modern boat manufacturers seem unaware of the superiority of these kinds of fastening techniques or simply for economic reasons don't bother to use them at all. It has also been discovered that most fasteners in use on boats are more liable to have shear loads (sideways pressure) placed upon them (for example, cleats and winches) than direct tension (vertical pulling).
Unfortunately, 'shear loads' will fail quicker than 'tension' loads, so fastenings must always be of adequate size and not skimped. It is an old but true saying "Nothing too strong ever broke"..it still holds good today.
LARGER FITTINGS
It is a well known fact that for larger fittings such as winches, cleats, windlasses etc direct through-bolting is the preferred method. Basically, foam cores and balsa is removed from inside and strong ply pads are then bolted and sealed up against the glass and sealed with a proper sealer such as 3M's 5200. There does however, exist an opportunity to use 'bonding' on these items provided it is correctly carried out. For example, a deck winch can be 'cast' from epoxy and large machine screws bedded into oversize holes filled with epoxy. It does take longer but the benefits are greater. More strength and no, repeat, no leaks! Similar procedures can be used to bed keel bolts and chain plates. If bolts are required to go through decks and cabins it is possible to bond the bolts into wooden or ply pads using the techniques mentioned above.
METAL BONDING (JUST A QUICKIE)
Yes, even metals can be bonded to epoxy provided the correct procedures are adhered to once again. Briefly, cleaning with correct acids and thorough surface scrubbing must take place so that adhesion is adequate.
The next time you have to screw something quickly to your deck...think on. The extra time for preparing fasteners in place properly can definitely save you thousands in the long run. The 'quick way' has been time tested and has no place in good marine maintenance...both you and your boat will reap the benefits if you do the job properly.
REMOVING BONDED FASTENERS
There is an easy way of reversing the 'bonding'. Heat the screw or bolt to about 121°C (250°F) with a heat gun, being careful not to cause any other damage. The epoxy will soften and the fastener can be released...refill the hole with epoxy not sealant.
Terry Buddell is a freelance writer, boatbuilder and marine surveyor who lives on board his own yacht the "Nicky J Miller" with his partner Nicky in Gladstone, Queensland Australia. Terry has designed a series of boats that he sells from his website on the net and also built his own 42' yacht which he refers endearingly to as "his filthy old lugger'. Terry writes for several boating magazines and specializes in the " How to do it " kind of article using practical ideas and basic common sense! Terry is only too happy to help people who wish to build their own boat from a dinghy to a yacht and his contact deetails can be found on his website http://www.dolphinboatplans.com
About the Author
Terry Buddell is a freelance writer, boatbuilder and marine surveyor who lives on board his own yacht the "Nicky J Miller" with his partner Nicky in Gladstone, Queensland Australia. Terry has designed a series of boats that he sells from his website on the net and also built his own 42' yacht which he refers endearingly to as "his filthy old lugger'. Terry writes for several boating magazines and specializes in the " How to do it " kind of article using practical ideas and basic common sense! Terry is only too happy to help people who wish to build their own boat from a dinghy to a yacht and his contact deetails can be found on his website http://www.dolphinboatplans.com
If you would like to read any other articles in a similar vein or would like Terry to write an article for you go http://www.dolphinboatplans.com
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