FollowupID: 760860 Submitted:
Saturday, May 12, 2012 at 09:45
The Bantam posted:
Yes, I've done little bit of fiddling with boats, a bit of a late starter for the son of a shipright.
I note that shaker is an "evidure man"...there are a couple of schools in wooden boat circles I come more from the "west system" school having defected to "boatcoat"
there is not a large difference between chopped strand and woven mat in strenght....but woven mat is available in thinner material and is better to work with.
woven mat is also better on wood in a single layer with epoxy, chopped strand is more intended for building in glass and resin alone.
the trick it not to try and lay too much resin on at once....epoxy is very much different to work with than polyester and is far far better with wood.
the trick is to use a foam roller and do several thin coats wet on tacky.
the epoxy will wet out the ply and the mat far more redily than polyester, but it takes a few minutes to do so, so ya have to be patient and hold ya nerve.
Put on too much epoxy in 1 coat and the mat will float off the surface of the wood. same if you don't wait enough between coats.
If I am working with sheets, I will tend to apply mat to one side of the board before I cut it up working on up to half a sheet of ply at a time.
The amount of strength you can get out of very thin light material is just stunning.
The optimum coverage of epoxy is considered to be arround the same weight of epoxy as glass.....so with 200GSM matt you are adding arround 400 grams per square meter total.
so adding a single layer of 200GSM mat to a sheet of ply adds arround 1.2Kg to the sheet.
Just laying up a couple coats of epoxy alone on ply improves its strength and certainly its surface stability and abrasion resistsnce...particularly in the thinner materials.
A good quality light weight ply can be half the weight of radiata or luan and just as strong...go the other way to european burch, you gain a bit of weight, but a heap of extra strength and surface resilience.
Ordinary pop rivets work quite well in plywood, the problem with any fastener as the ply gets thinner is the fastener holding in the ply.
Rivets tend to compress the ply where screws tend to chew a hole.
Pulling rivets thru ply into metal, can be quite strong and in the softer plies the rivets will sort of flush in.....100 to 150mm spacing & between 25 & 50mm from corners..... that ply wont be going anywhere
I used to use extrusion that took the ply in a slot and that was incredibly strong
A length of roadcase angle or stair nose across the exposed edge ofthe unit is a good idea...stay away from plain aluminium angle it tends to bur up when it cops a hit, and will open you up like a jam tin.
If you riveted and put a bead of sicaflex on the rails before you fix and that will be realy solid and wont rattle or drum.......hard work if you ever want to pull it up though.
no need for nutserts