Bedding Fasteners

Do most of you bed transom fasteners(screws) in something (pine tar,grease, sno seal, soap,etc.) before driving? If so, why? To ease entry, prevent splitting, avoid rot, add holding power, something else? In fact, do you even drill in this age of self driving screws? If it sounds like I have a screw loose on this topic, I probably do. Any thoughts appreciated.

 

A lot depends on where the fastener is and what it will need to do.

I'm replacing the transom on a 50 year old runabout. The transom is attached to the lap strake planking with bronze screws and the knees with through bolts. The through bolts are bonded with epoxy and the plank screws just receive a dip in a lube, specially designed for this purpose, though some folks use soap or oil. The screws shouldn't cause splitting if the clearance and pilot holes, plus the countersink are the correct size for the screw AND the density of the lumber. Hardwoods require larger pilot holes then softwoods, soft screws require larger holes for hardwoods.

This technique is used for this application because the transom will need to be removed at a later time and bonding the 150 plank fasteners would also likely bond the ends of the planks to the edge of the transom or eachother, prevent them from moving. These planks need to swell to seal the lap and bonding methods would harm this required feature, meaning the planks would leak there.

Self driving screws don't work well in wood and are typically used in low load applications, in metal, drywall or other material where speed is the requirement over holding power. Ditto for self drilling screws used in wood. There are wood screws of several shapes and designs and fasteners for other stuff. It's important to use the right fastener and the correct clearance, pilot and countersink holes.

In the repair above, I'm using McFeely's square drive, silicon bronze boat screws (which are different then regular wood screws) The boat is all bronze (fasteners) and requires I do the same for this repair. The through bolts are home made from round bar stock that I threaded.

As for "bedding" the fasteners, I generally bond fasteners in applications where I can, with epoxy. I use a lube to ease driving effort and strain on the fastener other wise. Some people will dip the screw in an adhesive (like epoxy) but it doesn't help much, because the screw wipes off the goo shortly after entering the hole, as it works it's way into the wood, leaving near all of it's length uncoated.

Log onto WWW.WestSystem.com for a complete description of fastener bonding. You can also log onto WWW.McFeelys.com for more information about fasteners, hole size recommendations, materials etc.

Not knowing what you are doing (boat, construction type, etc.) I hope I've been of some help.

Good Luck . . .

 

Thanks PAR, your reply was very helpful and covered a lot of ground.I'm building a 15 ft norse pram and the builder of one we put together in a class last year used the pine tar dipped self drilling screw system in fastening the transoms( and copper fastened rivets on the laps and futtocks as he had learned it in Norway) Anyway, I forgot the tar on some and was considering removing those and replacing but am not sure what function the tar played and therefore the downside of leaving them alone or bothering with bedding in the future. I love the looks and handling of the "Fjord Wheelbarrow" And will probably use her as a pulling boat although she is an effective sailor. Many thanks for your help.

 

The tar will not help much, as I pointed out, but old timers will tell you it does. Just don't cut the transom fasteners out to show him. Let him think it works fine. It may work as a lube to make inserting easier though. Personally I'd try some wax or proprietary product for this, but we all have to make folks happy. If you feel you must, back the offending screws out a few turns and smear on a glob of tar, then re-tighten.