Ply-cored fibreglass repair

A plastic hatch on my new boat was knackered, so I've obtained a replacement. It's the same size, but a slightly different (stronger) design. I pulled up the old hatch the other day, and discovered that some muppet had butchered the deck in fitting it - notches have been cut out of the fibreglass and its plywood core to accommodate the hinges of the old hatch:

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black material under the notch is sound-absorbing foam in the engine bay)

The fixing holes on the new hatch are not in the same positions as the old hatch, and two of them need to go where the notches are so I need a solid repair to screw into or bolt through. I also want to seal up the exposed plywood to prevent any water getting in and rotting it. The new hatch has the hinges built into the lid rather than the frame, so there's no need for any cutouts or notches in the deck.

Any suggestions? I've never done any fibreglass or epoxy work before, but am willing to give it a go.

Cheers,

Pete

Reply to
Pete Verdon
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Oh, its all pretty easy.

First thiing is to get rid of all the (slicone?) sealer and roungh up the area to be patched. Ona dry day. Or you will seal wet in.

Then you have tow choices to make the thing good. If you want real structural strength, lay up some glass CLOTH and resin - get it from e.g. Halfords. Dont use chopped strand mat. Its vile in small areas.

All that means is laying the glass cloth where you want it to go and jobbing in the resin with a stuff brush..follow directions on using the catalyst etc. As soon as its more or less done, cover the area with a bit of tough polythene, and squish down to get the air bubbles out, and then use something like modelling clay to hold the plastic over the resin till it all goes off. Minutes only usually - then remove plastic and whilst the resin is still rubbery trim any surplus with a stanley knife. If you are trying to make good mouldings, make up a female mould out of anything useful that you can think of, and then cover it in plastic. For a better finish, apply resin by itself first then a layer of cloth and resin/.

Its smelly and messy, but even gibbons can and do do it.

As far as final finishing goes or simply prettuy strong gap filling, its the same resin and catalyst, but filled with a filler to make a stiff putty. You can buy this as liquid metal, or holts P38, or two pack car body filler, at any halfords type place or a chandlers. Or you can usually by a sensible filler to go in te resin to make it.

This type of filler sets rock hard in minutes and is very very tough indeed. You can drill tap and file it like it was a hard wood. Its probably enough for your job by itself. Its the ultimate adhesive and body putty all in one.

Used to hold rusted cars together for MOT purposes since the year dot.

Years ago I repair a wing that was hanging off one. The car was subsequently crashed by its stoopid owner. The only bit of straight bodywork on that wing was the repair...

Reply to
The Natural Philosopher

Yep, transparent silicone. At some point the previous owner seems to have gone mad squirting it around all over the place instead of fixing things properly. Very little of it is actually keeping water out.

Could be mildly problematic in the present climate - snow melting everywhere. However, the notches are underneath the new hatch which I've temporarily dropped into place, so hopefully out of the worst of it.

OK - I guess I'd have to make up some kind of mould at least for the underneaths of the notches if I were to do this. Would you expect in this case to end up with solid glass&resin the full thickness of the notch (ie plywood + two existing fibreglass skins)? I can't really imagine filling those deep notches using flat cloths.

This sounds like it might be the answer for the job in hand - should be fairly easy to mould a putty-like substance into place. Presumably it sticks to some extent while wet, so should hold itself in place? Does this stickiness make it hard to handle (stick to your hands)?

Would this be epoxy resin or polyester? I have a "fibreglass repair kit" in the shed bought for another job and not yet used, which is polyester resin + hardener, and what I think is some chopped strand and some woven cloth. Would thickening that resin (I've heard people use fine sawdust?) do the job or should it be epoxy instead? I'm not trying to do this on an absolute shoestring, but it would be nice to use things I already have.

Yes, it does sound good. The only thing to be concerned about I think is how strongly it will adhere to the edges of the notch to hold itself in place. Sticks strongly, does it?

Thanks for the advice,

Pete

Reply to
Pete Verdon

Oh yes., sticks like shit, smells like shit.

Polyester.

I have a "fibreglass repair kit"

use the polyester then., The correct filler is IIRC, mica powder. Sawdust wont be as dense or as strong, but I guess it would work. You will end up with chipboard essentially is that really what you want?

To fibreglass, immaculately. Also to wood. It struggles with olefins like polythene, and water is bad news.

Reply to
The Natural Philosopher

That's not plywood, that's balsa. Balsa is the standard core for boat decks and floors.

You have an awkward profile to reconstruct there. I'd be tempted to put some stainless screws into the balsa, protruding to the depth of grp less the thickness of the GRP moulding, in order to provide some strength in the lip. The GRP layup then has to be done "inside out". Normally one lays up in the order gelcoat, then a coating of resin then then while that is tacky glass cloth and the remainder of the layup.

First thing is to get everything really clean. Remove the old sealant, grind or sand back the old surface on all the GRP. As I mentioned insert screws to provide some mechanicla strength then lay up using either epoxy or a good quality polyester resin designed for use on boats. The cheap stuff from halfords is rubbish and has a nasty red catalyst. I'd actually use epoxy for such a small repair. Remember that epoxy doesn't work with CSM, the CSM is held together with a binder that dissolves in styrene (polyester resin) but not in eopxy which is solvent free.

Use woven glass tape to build up a strong profile. You'll need something to stop it sticking to the foam insulation and that should be polythene or melinex sheet. Personally I'd use some dense LD polythene - washing up liquid bottles used to be ideal for this but they are now hard to find (the bottles are now mostly PET). Build your core, allowing room to add a gel coat. Then when the core has cured apply a gel coat. This will need to have a melinex film placed over it while it sets otherwise oxygen in the air will cause it to remain tacky.

Then grind/sand it all back into shape.

Reply to
Steve Firth

That's shit advice for work on a boat. Halfords sell only the worst and cheapest variety of isopthallic polyester resin. It's useless for boat construction.

Reply to
Steve Firth

No, it's glass microspheres.

Reply to
Steve Firth

Oh really? what exact boat construction is being discusseed here?

Its just a very minor infill, prat.

Reply to
The Natural Philosopher

Should be applied to your gob then, tit. Oh no, that's major infill.

Reply to
Steve Firth

No it isn't. That's a completely different filler for a totally different purpose.

Its weak, but its light. That's all you can say about it.

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HD filler for decent strength (not just puffing up material is mineral - see above.

prat.

Reply to
The Natural Philosopher

Balsa is a common choice, yes, but plywood is not unknown. Some boats use both, with plywood sections let into the balsa layer under higher-stressed parts. I haven't probed deeply into this wood, but it seems rock-solid to the fingernail which is not a property I associate with balsa. The main bulkhead (between cockpit and cabin) on this boat is certainly ply cored - there are some large holes from old instruments in which the plies are clearly visible.

Yep, very awkward. It doesn't need to be reconstructed accurately though, as it will all be hidden under the lip of the new hatch. All I really need is something I can screw into or bolt through (haven't decided which yet) and which won't let water into the core.

OK. The ply is probably 12mm, plus the thickness of the fibreglass top and bottom. How do I make something so thick with glass tape - just keep adding layer after layer of glass and resin?

[...]

I take it then that the gel coat should be quite thick, to withstand sanding to shape?

Cheers,

Pete

Reply to
Pete Verdon

OK, great. I'd only read about thickened epoxy, but then most of this discussion is on American sites where they seem to be able to slop epoxy about with gay abandon.

[...]

OK. Presumably not something I can obtain from Halfords or whatever in the short term? I'm in a hurry to get the hatch fitted so the boat is finally watertight. Probably stick to the premixed putties I think.

Well, a mix much richer in resin than most chipboard, but point taken.

OK, two-pack polyester putty it is.

Cheers,

Pete

Reply to
Pete Verdon

Oh, and I like Steve's screw idea, so I'll be moulding it round a few of them just to make sure.

Pete

Reply to
Pete Verdon

No, glass microspheres are the commonly used filler material when working on boats.

It's light, but its stronger than "mineral" fills which are still not mica and tend to be whatever is cheap, such as talc as on the page that you give a URL for.

Using talc has no strength and you do not want the extra weight on a boat. If you look on the page that you give above you will see that glass microspheres are recommended for "boat fairing".

You should adopt that as a sig. It suits you.

Would you care to mention how many boats you have worked on in the past?

Reply to
Steve Firth

I really wouldn't use polyester putty for this application. If you feel you have to use it, use "bridging compound" which is stronger than talc filled polyester filler.

Also don't get your supplies from Halfords who charge rip-off prices. Go to an appropriate supplier.

Bridging compound:

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coat/glaze:
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're going to have problems getting a good colour match to the existing gel coat. Boats are all white, and no two of them are the same. You can get gel-coat matching kits from chandlers which are supplied with blue, black, yellow dyes to allow you to match the colour. It takes experience and a good eye for colour to get it right. All "white" fillers are too yellow for the job.

Reply to
Steve Firth

Yes, it's going to be a protracted process because you can't pile up lots of material as it will sag until the resin cures. it will be easier if you put a sheet of something that the resin won't stick to between the foam and the edge of the moulding. This then provides support while you work. Then build on that sheet layers of glassfibre tape and resin. Once you have constructed a "floor" across the edge of the cut then it should be easier to construct the vertical part. The difficult part is to get the cloth laminated for maximum strength. You need it laid in a continuous ribbon both left/right and then front/back in an L shape with overlapping laminations.

Given the shape of the profile you may need a couple of different widths of tape or take woven mat and cut it to shape with scissors.

For your layup to work, the glass has to be throughly wetted with resin.

Not too thick since it has no strength of its own. The finish thickness shouldn't be much more than 1 mm, though this is difficult to achieve. If you are doing epoxy layup then you don't want any of the epoxy exposed to light since it will change colour rapidly (to brown) then start to lose strength. But you also don't want a hugely thick gelcoat since it will be weaker than the GRP layup.

Reply to
Steve Firth

I thought you said itr was galss balls?

Tsk Tsk. If you are going to troll, be consistent.

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Reply to
The Natural Philosopher

West Systems small epoxy kit (under 20) lasts me about a year in the workshop. Very, very useful. Available from better woodworking outlets and boat chandlers, especially a timberyard like Robbins in Bristol that serves the boatbuilding community.

While you're about it, get a copy of the "Gougeon Brothers Guide to Boat Building". These are the people behind West Systems, and the book is a useful manual of construction techniques with epoxy, whether you're doing boats or not.

You'll also want some fillers. Buying good thin epoxy and then thickening it as needed is a much more useful technique than thinking it begins and ends with tube Araldite. Fibre fillers are used for strength, powders for general bulking and gap filling. The lightest (and generally the best) are glass or phenolic microballoons. These are hollow spheres, so they're lightweight and easy to sand. Glass are white, phenolic are brown and less wear on your tools (I often plane or scrape this filler down flush). You can get mineral powders too, but they're mostly used because they're cheap - microballoons are usually better. I also use 1/4" Kevlar fibres as a strength filler, as it's much easier to work with than glass fibres - also gives me a way to recycle my Kevlar trimmings.

If you have a Glassplies nearby, then go and talk to them about GRP (usually polyester resins rather than epoxy). These are cheaper for fabrication purposes, but for repairs I tend to use epoxy instead. Glass cloth (of several different weaves and knits, talk to the seller for advice) is useful for reinforcement. Avoid the old chopped strand mat as it tends to be heavy and uneven, unless you're careful when applying it. These days you don't even see it much. A gallon of acetone is cheap at any GRP shop and a handy degreaser before gluing with either resin.

Reply to
Andy Dingley

Are there any chandlers which don't operate a "stick another nought on" pricing policy?

Reply to
Clive George

Around Ashington / Blyth

Two towns which are also the most depressed towns I've ever seen anywhere in the UK. ...and I've lived in Hull and up the Welsh Valleys. Not soemwhere I'd ever want to live, but they were the cheapest chandlers near Newcastle.

Reply to
Andy Dingley

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