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mikeb
90 Posts |
 Posted - 28 Mar 2013 : 10:40:03
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| Those prices are for EPOK 502 resin, from CFS (link on page 1), they do West 105 as well but that is even more expensive. All seems to be about the going rate online, and CFS are local to me so I can ask for suggestions/recommendations at their trade counter. |
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cliveshep
Thailand
1324 Posts |
Posted - 28 Mar 2013 : 10:48:25
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Your boat was built by lady paper-hangers in glass-fibre and polyester resin and frankly that is all you need to repair it. Polyester resin is a lot cheaper than Epoxy anyway, and both need reasonable temperatures to cure so unless you put a heated tent over the transom you aren't likely to be doing it this weekend anyway.
I would also consider bonding the old piece back in, chamfering back the two edges and taping the join with woven roving over the chamfer. Sand off and finally fill and sand with epoxy and a filler powder mix as polyester resin filler is not suitable for under water applications.
You could usefully hold the panel in place with a few screws until the resin cured bonding it to the ply, and then remove the screws and fill the holes.
The cost of boating is insignificant compared to costs of a young wife and two teenage kids! |
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mikeb
90 Posts |
Posted - 28 Mar 2013 : 11:36:30
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quote:
Originally posted by cliveshep
Your boat was built by lady paper-hangers in glass-fibre and polyester resin and frankly that is all you need to repair it. Polyester resin is a lot cheaper than Epoxy anyway, and both need reasonable temperatures to cure so unless you put a heated tent over the transom you aren't likely to be doing it this weekend anyway.
I would also consider bonding the old piece back in, chamfering back the two edges and taping the join with woven roving over the chamfer. Sand off and finally fill and sand with epoxy and a filler powder mix as polyester resin filler is not suitable for under water applications.
You could usefully hold the panel in place with a few screws until the resin cured bonding it to the ply, and then remove the screws and fill the holes.
The cost of boating is insignificant compared to costs of a young wife and two teenage kids!
Thanks Clive, I think what you describe is more or less what I had planned out in my head. Didn't realise that polyester resin was suitable, that's a bit cheaper then. On the original construction, is it the gel coat that protects the polyester?
When you say to use woeven roving over the chamfered joint, do I need epoxy resin to set that into?
How warm does it need to be for the resin to set properly? Forecast is for mid/high single digits over the next few days.
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cliveshep
Thailand
1324 Posts |
Posted - 29 Mar 2013 : 07:28:51
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The gel coat IS polyester - it is a resin that has thickeners and pigment is all, the woven roving (I should have called it bi-axial tape because that is what it really is) is less messy than CSM (chopped strand matt)and you can work the resin into it with a brush without picking up arm loads of sticky fibres. Although more expensive it does form a stronger job too although you will be relying on the chemical bond anyway. You can buy it as 150mm tape which as you are only covering a joint anyway would be ideal. You use polyester resin with it yes. Get the 450gm or 600gm weight.
Minimum temperature - ideally 60F (15C) or warmer. Polyester is exothermic with catalyst meaning it generates it's own heat as it cures but that is a minimal factor in thin layers. So you can safely "bump" the catalyst to speed up the cure reaction and also warm the surfaces before applying the resin. Keeping the resin warm before mixing also helps. So you really need either a hot sunny day - unlikely at present - or a fan heater and a tarp to tent the area so you can raise the ambient to more than 15C.
Grind back the two edges to a very long chamfer so you can spread the repair over at least 50mm on each part so your repair extends to 100mm.
Simply cut down the length of tape for the first layer with a sharp pair of scissors, reducing it to 50mm/100mm strips and apply 1st layer in the "vee" as 50mm and the 2nd layer as 100mm and that should bring the job up nearly level for filling and sanding if you get the heaviest cloth. You can buy mail order from East Coast Supplies, here: http://www.ecfibreglasssupplies.co.uk/c-958-biaxial-tape.aspx
The cost of boating is insignificant compared to costs of a young wife and two teenage kids! |
Edited by - cliveshep on 29 Mar 2013 07:51:42 |
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mikeb
90 Posts |
Posted - 08 Sep 2013 : 17:44:24
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Well, I've only just found time to start making some progress on this. This is where I've got to so far:
I've used 9mm marine ply, and cut pieces to fit in to the transom behind the outboard well, and also larger sections (on the floor underneath it at present) to fill the void where the balsa wood was. Polyester resin with woven roving has been used to fix the first piece in place. I've used two sections of the 9mm ply bonded together.
Next stage is to fit/attach the larger pieces of plywood in. The best plan I can come up with is slapping a coat of resin on the forward facing side of the ply, then stick a layer of CSM to them. Then I plan to get a coat of resin on the existing inside skin of the stern, and slide the plywood pieces into place, holding them with wedges, clamps, and possibly self tapping screws. Is it a bad idea to end up with screws in there, should I plan to remove them as it sets?
The gap inside the transom is about 15mm, so there should be some room behind the 9mm ply to get a couple of layers or so of CSM in there, and build it up level with the inside of the outer skin. The outer skin came off in one piece and then plan to glass that back in place, by bonding it to the new core/CSM layers, and then chamfering the edge and using woven roving and poly resin to build it back up.
The main problem I am envisaging is that the plywood wants to stay flat rather than follow the contour of the stern. I am worried about it trying to pull back out flat and affecting the strength of the transom. The small piece I've already fitted seemed to hold steady when I removed the clamps (although there are a couple of screws partially holding it). I'm worried that the new resin won't be forming a strong enough bond to the existing grp in order to hold the plywood in the right contour. I have the same concerns about the larger plywood sections bonding properly to the existing inner skin. Less so with the outer skin, as that will have fresh grp to bond to, and will be bonded around the edges as well.
Should I be doing something different in order to give it sufficient strength? Bear in mind that there is going to be a 60hp outboard trying to rip it off!
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mikeb
90 Posts |
Posted - 21 Sep 2013 : 10:42:23
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Now I'm at a cross roads with this repair - I've got the plywood all fixed in and have built the transom back up nearly to the level of the outer skin than I cut out. I can either:
a) Rebond the old outer skin of the hull back in place (it came off in one piece and is pretty well intact).
b) Keep building up with new layers of GRP until it becomes flush with where the old exterior came to.
Which ever way I go, I'm going to grind a chamfer along the edge of the existing hull around hole, and bond the repair section to the existing.
As I see it, the advantage of a) is that it will guarantee a good flat surface on the stern with less sanding/levelling, assuming I can get it flush with where it once was! I have a tin of 'top coat' to paint over the whole of the transom repair anyway.
Trouble is, I'm concerned about getting a good bond between the old skin and the the new internal, any gaps will adversely affect structural strength I think? It's proving difficult to get the new surface to perfectly match the required contour to get the old out perfectly flat to it.
With b), I guess it will be more difficult to get a perfect outer surface across the back of the boat. I'll have to build it up and then sand it down to get the required contour across the transom. It will also require a lot more new resin and fibreglass. But in my mind, it will be much stronger structurally?
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df
United Kingdom
5994 Posts |
Posted - 21 Sep 2013 : 12:20:33
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I believe one of the tricks to getting a nice finish with minimal sanding when laying up a repair like this is to screw a sheet of formica over it to leave a flat smooth finish and take the air away from the resin so the surface cures properly, once cured theres just the screw holes to fill and sand and the formica should come away easily (assuming you used it the right way round...).
Layup resin won't fully cure on the surface with air present, flow coat is slightly thicker layup resin with wax added(and usuallu a pigment), the wax comes to the surface to make the air barrier and fully cure the surface, not sure about gelcoat.
Sand over before the final layer so theres no glass strands coming through that can 'wick' moisture back into the layup or osmosis will set in.
Instead of formica you could probably use thin plywood with cling film or polythene sheet over it.
NBAS--The communal colostomy bag of the boating community.
Visit leomagill.co.uk |
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mikeb
90 Posts |
Posted - 21 Sep 2013 : 19:44:15
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| My supplier calls it 'top coat', but I think it's the same as 'flow coat'. |
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Steve T
United Kingdom
88 Posts |
Posted - 22 Sep 2013 : 22:04:27
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Please talk to your supplier a little more. Flo-coat and gelcoat are NOT the same, and are not for the same jobs. I wouldn't put anything with wax in it at the stage you are at, the wax additive can act as a non-stick coating, but has no idea what you want it to stick to or not!
Gel coat is the answer, agree with "casting" it with formica. I think you will really struggle to get ply+clingfilm to do the job with any success.
Cheers
Steve |
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mikeb
90 Posts |
Posted - 23 Sep 2013 : 12:05:05
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No, I didn't mention gelcoat? I was asking about top coat and flow coat being the same thing. Anyway, it's not important at this stage, first I need to repair the structure before I finish it with the top coat.
I'm still trying to decide whether to reuse the old skin, or build up new layer to the surface.
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cliveshep
Thailand
1324 Posts |
Posted - 23 Sep 2013 : 12:48:38
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I'd use the old skin, apply resin and glass to your new work and the old skin, slap both together, and clamp a ply and timber frame over it with acetate film over anywhere it is likely to come into contact with wet resin.
Leave it all to cure and then simply clean up and make good with a bit of epoxy filler to the joint. That way you'll have the bulk of the finish and only have to worry about the joins.
That presupposes of course that your work thus far is structural and not reliant on the outer skin for strength.
The cost of boating is insignificant compared to costs of a young wife and two teenage kids! |
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mikeb
90 Posts |
Posted - 23 Sep 2013 : 14:06:05
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Well... in theory the entire repair is structural, as in it's a laminate of plywood and grp layers. But the strength is going to be dependent on all the layers being bonded together properly, and that includes the outer skin.
Looking at the original construction, the outer skin is the most substantial part of the stern - the balsa wood internal wouldn't have been providing any rigidity, just crush strength, lightweight filling, and something to tie the inner and outer grp skins together. The inner skin itself is very thin (1 or 2 layers only), so that isn't providing any strength, just sealing in the balsa wood. It also looks like the molded shape of the outboard well is also responsible for adding strength.
I am worried that I won't get a good bond between the old skin and my internal repairs, as they aren't totally flat together, surely any gaps or airspaces in the joint will seriously compromise the strength of the laminate? I am planning to chamfer the edge of the outer skin as well and use polyester and woven roving to joint them back together. |
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df
United Kingdom
5994 Posts |
Posted - 23 Sep 2013 : 17:13:13
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I you use the old skin, clean it well and use styrene as a solvent as it partially re-activates the original resin for a better bond.
NBAS--The communal colostomy bag of the boating community.
Visit leomagill.co.uk |
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Steve T
United Kingdom
88 Posts |
Posted - 23 Sep 2013 : 20:43:43
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Hi
There are "bulk fillers" that can be used with Polyester (or vinylester/acrylic and epoxy) resins that will help avoid air spaces within the new structure.
Try asking your supplier for "Fillite". It is a microsphere powder, which is very, very fine and you can stir this into catalysed resin to form a paste of varying consistencies, from thick body-filler consistency right down to a very runny and messy liquid.
You can mix this into a squeezable state, as liquid as you like, which will allow the voids between the repair and the original outer skin to be filled as you clamp the outer skin onto the transom.
It will bubble and drip every where as you clamp up, but you will be pretty sure you are leaving no weaknesses in the resulting structure.
It's cheap too!
Cheers
Steve |
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mikeb
90 Posts |
Posted - 23 Sep 2013 : 21:31:12
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Good call, I have a big bag of filler/powder that I can mix in with it.
Clive, what should the ply and timber frame to clamp it look like? I was thinking of using screws (with big washers) to temporarily hold the outer in place. |
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