Epoxy vs polyester

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marie galante

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I'm fitting some ply 'backing pads' up under the foredeck cleats and I'll need to butter them with some well-thickened glop to ensure a proper mating of the surfaces. I've looked at the prices of Plastic Padding Marine Epoxy and P/P ( polyester ) Marine Filler....both of which should set hard.

What's to choose between them? Better alternatives....? :confused:
 
Use P40 (you can get it from Halfords).

Just mix it up and gob it on, then push the wooden pad on and screw it down.

Perfic!
 
I have always understood that epoxy will mechanically bond to old polyester better then polyester will. So I would have thought a dollop of low density filler in some epoxy will do the job.. Having said that, a quick abrade with course grit paper, a wipe over with acetone and a dollop of 'No More Nails' worked for me, two years and counting :-)
 
marie galante said:
I'm fitting some ply 'backing pads' up under the foredeck cleats and I'll need to butter them with some well-thickened glop to ensure a proper mating of the surfaces. I've looked at the prices of Plastic Padding Marine Epoxy and P/P ( polyester ) Marine Filler....both of which should set hard.

What's to choose between them? Better alternatives....? :confused:
Click to expand...

If you want to do a proper job your backing pads should be thinned at the edges so that they don't create a hard spot at their edges. Use epoxy for superior adhesion to polyester with microbaloons not coloidal silica as its too brittle. Once the pad glued on I would add a couple of layers of cloth over the back, but I do like beltand braces.
 
Interesting inputs.

In a similar requirement last year, ply blocks - well epoxied and painted - were used ABOVE the deck to lift the lead of the lines to the height of the toerails. These were bedded on CT1.
Underneath the deck, ply pads were bedded on an epoxy/microballoons mix and the assembly tightened up progressively.

There are probably several ways of tackling this, including the use of polybutyl tape.
 
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Duster said:
Thanks so far for inputs. :)

I may have been 'ambiguous' in my OP, so clarifying in case that changes anything.....

The 15mm ply pads of concern will be UNDER the foredeck, with 4 x 8mm bolts passing through to nuts and big penny washers. Up on deck, the cleats will mount onto ~40mm painted and epoxied ply pads which will raise the 'lead' to the height of the top of the toerail.

The above-deck ply pads will be sealed to the deck with CT1. I'm happy with that plan. It is the under-deck pads that need 'something' undecided as yet, and the subject of my query.
Click to expand...
Almost anything will do. You dont need anything with great adhesive power but it will be convenient if they are stuck in place while you fit the bolts etc.
PP polyester filler stets quickly esp if the surfaces are warmed so will set while you hold the pads in position.

OTOH if you are using CT 1 anyway above the deck why not use that below as well
 
Ply is not stiff enough for the bonding product to matter. Anything that fills the space. If it were GRP (a MUCH better choice), then bonding would make it function as a part of the beam.

Tapering ply is probably a bad idea. the edges will fall apart. GRP yes.

And don't forget that you STILL need a metal backing plate or at least thick washers. A common washer will pull right through the ply at max load. A fender washer will fold right up. Best to cut some out of 6mm metal stock. Done the testing.
 
Duster said:
Thanks so far for inputs. :)

I may have been 'ambiguous' in my OP, so clarifying in case that changes anything.....

The 15mm ply pads of concern will be UNDER the foredeck, with 4 x 8mm bolts passing through to nuts and big penny washers. Up on deck, the cleats will mount onto ~40mm painted and epoxied ply pads which will raise the 'lead' to the height of the top of the toerail.

The above-deck ply pads will be sealed to the deck with CT1. I'm happy with that plan. It is the under-deck pads that need 'something' undecided as yet, and the subject of my query.
Click to expand...

Use CT1 then, that's what it's for.
 
Mounting the cleats on thick blocks will mean that the force from the rope tries to bend them over. This may mean it's advisable to beef up the deck locally?
You could consider laying up a pad of grp under the deck, instead of a plywood backing piece.
OTOH you may be OK as you're using 4 bolt cleats which have a wider base. Depends how strong the deck is to start with.
If the deck is balsa or foam sandwich, take out the balsa/foam locally around the bolts and fill with resin/glass. Hollowing out a 20mm radius around each bolt is common practice.
 
marie galante said:
I'm fitting some ply 'backing pads' up under the foredeck cleats and I'll need to butter them with some well-thickened glop to ensure a proper mating of the surfaces. I've looked at the prices of Plastic Padding Marine Epoxy and P/P ( polyester ) Marine Filler....both of which should set hard.

What's to choose between them? Better alternatives....? :confused:
Click to expand...

Duster said:
Thanks so far for inputs. :)

I may have been 'ambiguous' in my OP, so clarifying in case that changes anything.....

The 15mm ply pads of concern will be UNDER the foredeck, with 4 x 8mm bolts passing through to nuts and big penny washers. Up on deck, the cleats will mount onto ~40mm painted and epoxied ply pads which will raise the 'lead' to the height of the top of the toerail.

The above-deck ply pads will be sealed to the deck with CT1. I'm happy with that plan. It is the under-deck pads that need 'something' undecided as yet, and the subject of my query.
Click to expand...
Bit ambiguous in your posting identities too...

Did you forget you had logged out as one and logged back in as the other - not so easy maintaining this double identity business is it? :encouragement:
 
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