Chicken and egg

[Nessa]

Which comes first, the G4 or the epoxy? Being a £45 boa the Marauder only merits G4, not varnish. There are parts (many parts) where the fibreglass tape needs replacing. Do I G4 first, then tape, or tape first, then G4? I am asking because I do not know how well epoxy and G4 get on together and I don't want any arguments between the two.

I shall shortly be posting photographic evidence of my folly, now her indoors has relented and taken pics of what she affectionately calls 'that wreck in the garden'.

[Rupert]

Epoxy first, every time!

[roger]

Nessa definitely Epoxy first but you will need a coat of varnish or two as G4 doesnt like uv light. Having said that Merlin 36 only had G4 fr some time and didnt seem to have any problems.

Rog

[chris]

I would not think g4 and epoxy go together at all. both need to go on bare wood, not on top of anything else.

[Rupert]

I think it is epoxy as glue, Chris, not as coating.

[Nessa]

It is epoxy as glue to hold the fibreglass tape together and also to fill some gaps. Then what order ashould the layers follow? G4 then varnish? I didn't know I would need varnish as well.....

[chris]

Ah right. G4 is certainly not a glue like epoxy. I still doubt if it will work on top of anything else but bare wood. When you use g4 you need to put subsequent coats on with a very short time limit to form a unified thickness. It's designed only to go on top of bare wood (or concrete!) initially. Think of G4 as an alternative to UCP transparent primer.

As an aside; there was an interesting article in a recent Wooden boat mag abot using canvass, over ply, to make decks.

[Pat]

Half Cut's foredeck is currently G4 only, which was done as a "temporary" fix in spring 2008 as the proposed re-deck didn't happen and is still looking fine except where the top ply layer has split and a bit of damp has got in. The G4 has soaked in and kept the water out better than the previous varnish which actually ran right through the porous ply and dripped out under the foredeck! Sandy took it right back to bare wood before applying G4.

[Ed]

Yes, what Chris said about hot-coating the G4 seems very important to me.

With Jollyboat last re-build I certainly did a couple of coats and then left it for a week. Sanded down and applied another some more G4, but the second set of coats really did not adhear very well to the previous coats. it's OK.....but I would worry for the future. If you try and sand it and you go through the top coat of g4 you can start to peal it back with your nail or scraper. A bit of the issue here is that it is so hard, that it is very difficult to really sand the G4 enough to provide a good enough key for the subsequent coats.

I think Chris is right, you have to think of G4 as an alternative to UCP or Blakes woodseal. Apply 2-3 coats in quick succession and they will bond into a coherent layer of good strength. But after that you have to sand pretty well and apply varnish.

Going back to a previous thread, I said I would experiment with using G4 through a thin glass cloth to prevent de-laminating ply. I did do these experiments....and a thin glass cloth can be made to be pretty close to invisible. It may well prevent some delamination. BUT it has no where near the strength that an epoxy would give. Even months later, I found that I could quite easily peal back the cloth from within the G4. So G4 is hard....but has nowhere near the adhesive or laminating properties of Epoxy.

But anyway, Nessa, if you havn't already grasped the order, it is:

Stick any loose bits down with epoxy, don't stick down old cloth - cut it away and re-apply with new cloth or glass tape. Fill any holes with epoxy/filler. (filler = coloidal Silica for structural parts, glass bubbles for fairing).

Sand it all down and apply 2-3 coats of G4. the first can be diluted up to 25% with their diluent to really saturate the wood. These have to be hot-coated, which means the next coat applied when the previous has 'dried' but not 'hardened or fully cured.

Leave for a couple of weeks before sanding welll and applying a couple more coats of varnish. You need the varnish to provide UV protection. Do note there is a Bondamarine UV top coat, which is basically G4 +UV protection. Not used it, it is quite expensive, although G4 'Dampseal' is cheap as chips.

Can you sand between the coats of G4? I have found that you can - with care. but obviously the longer you leave it the easier it is to sand and the less likely you are to get a good connection to coat below.

You could forgoe the G4 and just use epoxy......but it is much more expensive....and much harder to apply well. Forget it unless you have a heated workshop. Personally I prefer Epoxy as a glue...to a coating system...but others would argue I am sure.

You could forgoe the G4 and use UCP or Blakes Woodseal. This may be better to be honest, but again, quite a bit more expensive.

Hope that helps.

cheers

eib

[Nessa]

Thanks chaps, I think I will follow the steps described by all of you and comprehansively summarised by Ed. I did hot coat the G4 with the MOGO, I just wasn't sure about putting it over the epoxy.

There are some gaps where epoxy filler is clearly needed, but what about the join between the two foredeck pieces that meet longitudinally down the centre of the foredeck - should that be epoxy, or would sikaflex be enough? It currently is a gap of about 3-4mm. Likewise the gap between the gunwhale and the side deck, which must only be 2mm.

Lastly, is there a cheap place to buy tape - I bought some blue gee tape at the dinghy show, but will need more.


All this is a much bigger project than I have tackled before, so I am a bit nervous!

[Ed]

3-4mm is a big gap for the centre-line of the deck....and for the edges. Ply does not normally shrink that much so I would have a good poke around to see what is happening.

But presuming it has shrunk back..

With the gunwhales, I would check to make sure they can not be pinched in a bit by screw.

A nice fix would be to take off the gunwhales, plain the sides flush and vertical and replace the gunwhale rubbing strip.

or.....get some long stips of wood, cutting of veneer? an insert them in the cracks. This does get done, but I would think unless the gaps were very uniform, you might want to run a router down them to open them up to a uniform width. If you do this, don't use a really hard wood as an insert as the gaps have a habit of closing up a bit when the boat gets used and/or damper.

OK, so the pragmatic and easy way is to fill them with some kind of filler....I wouldn't use sikaflex. It gets everywhere, stains the wood and is really hard to remove and clean. Tried it many moons ago, didn't work, nightmare.

Just make up an epoxy guk using either an appropriate woodflour ( I scouge the bottom of my bandsaw after cutting some mahogany) or take from bag of sander or use one of the darker wood coloured fillers. (West Filleting Blend). Be careful to colour match when it is wet, because the epoxy makes the woodflour much darker in colour.

You can run that into the crack and scrape excess of with a plastic scraper. Once hard it is easily sanded.
Incidentally, before you do this, really clean up the depths of the crack and run some neat epoxy into it before the filler to make sure you get a really good bond.

Best place for glass tape?

not sure....I buy when I see or need it.....try CFS at http://www.cfsnet.co.uk
or Matrix at http://www.matrixmouldings.co.uk/
or local Scott Bader stockist.

just buy a roll and avoid buying from dinghy chandler or local West supplier or you will pay through the nose.

Don't worry about it being a 'bigger' job than you have done before.

you will be fine and if you get stuck you can always ask here.

cheers

eib

[Pat]

We always find ourselves buying epoxy, gelcoat and fibreglass kit from Pro-Composites who are a small family firm based near Colchester. They do mail order (and Beaulieu boat jumble, which is where we buy) but don't seem to have a web site.
Unit 9, Edens Farm, Weeley Rd, Great Bentley, Colchester, CO7 8QS
Tel:01206 255226