MissFitz
Well-Known Member
I need to bond a bit of plywood to the deckhead as a stiffener before fitting a clutch. What would be the best/cheapest stuff to use for the job?
What to use to bond plywood to fibreglass?
- Thread starter MissFitz
- Start date
RupertW
Well-Known Member
I'm about to do something similar but as I want it as a backing plate and all removable easily then I wasn't planning on bonding at all. I'll be interested in what the experts think.
ctva
Well-Known Member
You are going to use a bit of sealant for the screw / bolt holes so just use that as a bedding compound to help spread the load and stop it falling off. 
I generally use Sikaflex.
I generally use Sikaflex.john_morris_uk
Well-Known Member
How flat is the GRP and how permanently do you want it fixed?
For a permanent job, make sure the ply is a reasonably snug fit to the GRP and bed it onto a layer of thickened epoxy. Thicken with silica or micro balloons (it’s in compression so it doesn’t make much difference strength wise).
PS. Chamfer the edge of the ply all round. Use a good quality ply and coat it in epoxy first.
I can’t imagine why anyone wants a backing plate that’s not permanent but I guess the solution might be to bed it on one of the mastics that will peel off. The problem is these types tend to remain flexible when cured which isn’t ideal in the circumstances.
For a permanent job, make sure the ply is a reasonably snug fit to the GRP and bed it onto a layer of thickened epoxy. Thicken with silica or micro balloons (it’s in compression so it doesn’t make much difference strength wise).
PS. Chamfer the edge of the ply all round. Use a good quality ply and coat it in epoxy first.
I can’t imagine why anyone wants a backing plate that’s not permanent but I guess the solution might be to bed it on one of the mastics that will peel off. The problem is these types tend to remain flexible when cured which isn’t ideal in the circumstances.
bluerm166
Well-Known Member
I have used 12mm marine ply for backing pads to spread modest loads and found that Sikaflex 292 is excellent to fix them in position,normally working overhead in small spaces,where resin would be undesirable/unpleasant to use and manage.The excellent initial grab and gap filling ability means that only a light stick or two might be necessary as an initial locating prop.Degrease the FG beforehand.
MissFitz
Well-Known Member
The GRP is very slightly curved & I do want it permanently fixed. I'm also very keen to use something as stiff as possible as the deck has had several holes drilled around that area over the years.
It is a very small area though, so I'm a bit reluctant to buy a lot of expensive materials of which I'll only use a fraction (again). Would it be a disaster to use something cheap from Toolstation eg epoxy adhesive or car filler?
Motor_Sailor
Well-Known Member
One solution is to not use clutches at all. There's nothing on a Sonata that's loaded high enough to warrant them. They are heavy and slow to use.
lw395
Well-Known Member
You could use something like 'no more nails'.
If the deck is balsa cored, then the main thing is to locally stiffen it around the bolts by replacing the balsa with filled epoxy.
But the deck may have ply in it whee they expect you to put winches and clutches.
If the deck is balsa cored, then the main thing is to locally stiffen it around the bolts by replacing the balsa with filled epoxy.
But the deck may have ply in it whee they expect you to put winches and clutches.
MissFitz
Well-Known Member
Fortunately the deck isn't cored, so that's one less thing to worry about!
True, but they are easier for feeble people to use. And there's less chance of inexperienced crew mistaking them for the kicker/uphaul/downhaul. Also, if I'm going to push off for an overnight sail, I'd be more comfortable with the halyards firmly clamped down.
Iain C
Well-Known Member
"Best/Cheapest". Pick one.
I'd disagree with john_morris on silica and microballoons in this application. I'd be using epoxy thickened with microfibres/treecell (same stuff) which has the appearance of cotton wool that has been through a blender. What you are looking for is an adhesive that bonds as strongly as possible and fills the gaps/irregularities/curve difference between the two materials. Silica makes it hard, microballoons are easy sanding and light...not what you are looking for in this application. Add as many microfibres to the mix as it will possible take, you want it so stiff that "peaks" do not fall over and the mix won't run down your mixing stick. However, before you add the fibres to the epoxy, coat both the wood and the deckhead with unthickened epoxy.
Cost needn't be high...see if your local chandlery has a small handipack that's out of date. Fibres will be under a tenner, and I'm sure if you have a poke around your local boatyard and ask niceley there will be a couple of bits of ply in a skip you can "upcycle".
Drill a couple of your holes before you bond, and use a smaller bolt covered in parcel tape to pull the pad into the deckhead (epoxy won't stick to parcel tape...means you can get the bolts out again). Don't worry about rounding off the corners of the pad, but do "fillet" the squeezed out epoxy with a wooden mixing stick. When it's all dry drill out the remaining holes and fit your clutches.
As an aside, if you are having winches too, make sure that you are putting the clutches in the correct place...try the lead angles from clutch to winch before you start. Remember a line leads into the side of a winch, not the middle!
Job done!
I'd disagree with john_morris on silica and microballoons in this application. I'd be using epoxy thickened with microfibres/treecell (same stuff) which has the appearance of cotton wool that has been through a blender. What you are looking for is an adhesive that bonds as strongly as possible and fills the gaps/irregularities/curve difference between the two materials. Silica makes it hard, microballoons are easy sanding and light...not what you are looking for in this application. Add as many microfibres to the mix as it will possible take, you want it so stiff that "peaks" do not fall over and the mix won't run down your mixing stick. However, before you add the fibres to the epoxy, coat both the wood and the deckhead with unthickened epoxy.
Cost needn't be high...see if your local chandlery has a small handipack that's out of date. Fibres will be under a tenner, and I'm sure if you have a poke around your local boatyard and ask niceley there will be a couple of bits of ply in a skip you can "upcycle".
Drill a couple of your holes before you bond, and use a smaller bolt covered in parcel tape to pull the pad into the deckhead (epoxy won't stick to parcel tape...means you can get the bolts out again). Don't worry about rounding off the corners of the pad, but do "fillet" the squeezed out epoxy with a wooden mixing stick. When it's all dry drill out the remaining holes and fit your clutches.
As an aside, if you are having winches too, make sure that you are putting the clutches in the correct place...try the lead angles from clutch to winch before you start. Remember a line leads into the side of a winch, not the middle!
Job done!
Fantasie 19
Well-Known Member
As an alternative to ply - you could use some aluminium sheet - easy to drill and work, less upkeep...
PaulRainbow
Well-Known Member
For the job you have, car body filler of the resin/chopped strand variety would be absolutely fine. Toolstation also sell a two part epoxy, same as quick drying Araldite, for about £250, this would also be suitable for the job and is good to have onboard anyway.
Rum Run
Well-Known Member
I'd use HDPE sheet (available as plastic cutting board from a home wares shop at non-marine prices), mastic gloop of choice and penny washers under the nuts. Most plywood nowadays crushes too easily and absorbs water for a pastime.
[159032]
...
https://www.saba-adhesives.com/en/p/sabatack-750-xl
Very effective. Cheaper than Sikaflex and the tube stays fresh for a long time once opened.
Very effective. Cheaper than Sikaflex and the tube stays fresh for a long time once opened.
Sneaky Pete
Well-Known Member
Totally agree. I used this method to bed in a plywood base for an additional battery. West system do a 0.25Ltr, 0.5Ltr as well as 1.0Ltr size epoxy packs. When done use bilge paint to waterproof.
MissFitz
Well-Known Member
***UPDATE*** I went to Toolstation & bought the car filler stuff plus some epoxy glue. Then, as I was passing the chandlery, popped to see what they had - which turned out to be a perfect little pack of West Systems epoxy plus filler for £18. Used that to bond the plywood to the deckhead, used a machine screw wrapped in parcel tape to hold it together, & it looks pretty damn good. (And the screw does come out, I checked!) So the car filler will be going back to Toolstation & I'll be getting in bigger pots of the West Systems stuff for various other jobs on the boat.
Many thanks for all the helpful advice as always, much appreciated!
Many thanks for all the helpful advice as always, much appreciated!
