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What can you tell me about fibreglassing?


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There are a couple of holes in the helm of my boat that I need to fill. The helm thickness itself is about 25mm (about 5mm of glass, then a plastic honeycomb matrix of about 12mm, then a thinner layer of glass on the underside).

I've just bought a basic glassing kit and all I need to achieve is a flat surface - doesn't need to be colour matched. What should I look out for/be aware of when attempting this? I've not done any glassing before.

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Hi Andy, I would guess that your boat is polyester resin and not epoxy. Best to repair with polyester (also less expensive). T would also guess that the core material you refer to is Nidapalst (possibly 15mm not12mm to give your 25mm build thickness). PM or phone me if you wish for more details and the best way to go about it. What size holes, access 1 or 2 sides etc. Geoff,

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Thanks Geoff.

Yes, there is access on both sides of the holes. One hole is a cable access hole of around 50-60mm diameter, the other is the hole that will be left by the HDS8 plotter when I remove it - 250x180mm with radiused corners.

Why is it recommended to match polyester with polyester? And given that I've already bought the epoxy kit, is there any show-stopping reason why I couldn't use it?

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Andy, epoxy is several times more expensive than polyester and there is no real advantage in using it if the rest of the boat is polyester! As you have already bought it, make sure that  you use powder bound chopped strand FG and not emulsion bound. If using woven cloth that is fine, but not so easy to get a good finish. I assume that you are not looking for a gelcoat finish as you are not bothered about colour match so I would guess you intend to cover any repairs with new kit. To keep your build thickness the same you could use a core of anything really - plywood, foam (not polystrene) etc. The best way to make an invisible repair would be to make the hole a bit larger from the inside, chamfer the front from the inside FG and also chamfer the internal skin, to allow nice strong and flat joints. Lay a shiny piece of melamine (well waxed to prevent adhesion) to cover the outside of the hole and tape it tightly to the dash. Apply gelcoat to the back of that melamine and wait until nearly dry then apply a second gelcoat and lay up with your mat and resin . You could at this stage apply core material and inner layers of mat or do that later. All cured FG should be well abraided in the joining areas to ensure good adhesion. The mat should be applied with each layer slightly bigger than the previous layer to get it fairly flat. Sorry if that sounds like I have been rambling on and a bit boring, but that is why I suggested a PM etc. Good luck with your repair. Geoff.

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That makes sense Geoff - thanks.

I like your idea of melamine to face into the hole from the top surface. I also have some polyester resin and woven mat that came in a car body repair kit I bought years ago. How can I tell if what I have is polyester or epoxy? Is there a way to tell when they're in situ?

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Andy, woven cloth does not have a binder. chopped strand FG needs a binder, either powder bound or emulsion bound, so if you are using woven cloth it will be fine. Chopped strand is easier to roll and stipple to get the resin and strands to integrate. Woven mat keeps its woven form. It is quite common to have a layer of woven cloth between chopped stand layers. Woven mat comes in various forms, bi axial, tri axial  etc. and is very strong. Geoff.

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22 minutes ago, Andy135 said:

That makes sense Geoff - thanks.

I like your idea of melamine to face into the hole from the top surface. I also have some polyester resin and woven mat that came in a car body repair kit I bought years ago. How can I tell if what I have is polyester or epoxy? Is there a way to tell when they're in situ?

If it is a car body repair kit it is probably polyester. If it is epoxy I think it would say so on the kit as that is more expensive. Geoff.

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17 minutes ago, Geoff said:

If it is a car body repair kit it is probably polyester. If it is epoxy I think it would say so on the kit as that is more expensive. Geoff.

I meant how can I tell if the boat is made of polyester or epoxy? I already know I've got tins of both.

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Hmm ............. sound like the Helm is made of something like nidaplast and glassed both sides .......... nidaplast here ....https://www.ecfibreglasssupplies.co.uk/category/nidaplast

 

Fixing is easy, but gel coating the surface is not so easy ........ depending on the size of the hole, put a backing board behind the helm, then put in a couple of layers of glass matt, then a piece of Nidaplast cut to the hole shape, then a layer or 2 of woven glass so it ends up about 1 - 2 mm below the surface ............. when dry, mix up some gel coat filler and fill the hole level, then cover with cling film to keep it level ............. then sand with 1000 - 2000 grit wet n dry and then polish .................

 

The last helm I fixed was full of holes. This was traditional glass coated ply .............. so I cut the holes into one big hole, glassed in a piece ply to fit and then covered the whole of the helm front panel with a piece of thick white perspex, glued on with PU adhesive, so I could then layout the helm the way I wanted .................

 

Edit : Wnter is not the best time for glassing, unless you can put some heat in the cabin  .................. ideally it needs to be 20C (ish)

 

 

Edited by GPSguru
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The point that GPS made about cold weather is very valid. If you do not heat the cabin you can of course heat the repair area using a hot air heat gun or hair drier. Gently  "waft" the area with the heat about 300mm above the surface for a few minutes, but taking care not to overheat. Gentle heat can be applied to the area prior to applying gel/resin and then after repair to assist curing. The method that I referred to is what we do in the FG works, usually to end up with an invisible repair with matching gelcoat. The reason for double gelling is to prevent "print through" of the mat, and scope to sand out any slight imperfections that may be visible in the join area. FG is a marvelous  material which  enables easy repairs and modifications, but can be a bit messy and smelly. Just as GPS covered the repair area with an overlaid sheet, when I changed the instrument layout on my boat I simply overlaid the area with a new panel, but I used a piece of carbon fibre to form the new dash panel. Geoff.

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