Model Boat Mayhem
Technical, Techniques, Hints, and Tips => GRP & Epoxy => Topic started by: clockworks on May 21, 2019, 05:33:10 pm
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I'm building my first RC boat kit - an Aeronaut springer. I've got 3 more kits ready to start, but I thought I'd build something relatively simple first, and practice some of the techniques that I'll need to use on the more complex kits.
Something that's probably not essential for the springer, but will be needed in future, is finishing the hull with epoxy and glass cloth. I bought some Z-poxy and lightweight cloth, along with some polyester resin and mat for beefing up the inside around the propshaft/keel. The inside is a bit messy (but solid), and I discovered that glass mat doesn't really "do" corners. I've not worked with GF and resin since I built a Westfield kit car 30+ years ago.
Struggling a bit with the GF made me read through a lot of posts on here before I started on the outside of the hull. For sharp corners, the best way to work seemed to be in sections - lay the cloth slightly oversize on an area, wait for it to cure, trim the edges back, then lay the next section?
I figured I'd do the smallest panel first - the transom - just to get an idea of how epoxy works. Once that's cured, the bottom of the hull & bow, then the sides.
Does that sound like a good plan? I hope so, because I've just done the transom. Brushed on the epoxy, laid the cloth, waited for it to "wet out", then gently over the surface with a credit card. Seems to have gone OK.
My question really is how to tackle the bottom of the hull. I assume that I can do the front panel at the same time without the cloth lifting off the plywood? What do I do about the keel/skeg? Lay the cloth in one piece, with a slit cut to go either side of the skeg, or in 2 pieces?
For the skeg itself, do I try and use cloth on that (one piece or 2?), just brush on some epoxy with no cloth, or just use a few coats of sanding sealer? I've already run a fillet of tube epoxy between the bottom panel and the skeg, and around the prop tube, so it's pretty solid.
Like I said, I probably didn't need to use epoxy and cloth on this kit at all, just want to get the hang of working with it before building my Boothbay lobster boat. I really don't want to mess such a nice kit up by practicing new things on it, so the next build will be an Aeronaut Mowe 2. A bit more complex than the springer, but still relatively flat hull surfaces.
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This might be of use to you https://www.modelboats.co.uk/news/article/finishing-and-sealing-of-wooden-hulls/18771 (https://www.modelboats.co.uk/news/article/finishing-and-sealing-of-wooden-hulls/18771)
I think it's also somewhere on Mayhem but that's incidental. Don't mix finishes e.g. sanding sealer and epoxy. Wetting the surface before laying the cloth on can be a pain if you get wrinkles in it, because you're bound to open the weave of the cloth by trying to lift and reposition it. The Spraymount trick has worked well for me since I began using Z-Poxy a long time ago.
Also don't go for the very lightest cloth for much the same reason. I use the 34gsm De Luxe Materials stuff and it's just the job. I covered my Midwest Lobster Boat hull in three pieces; one each side from the keel to the gunwales and the third on the transom. Note that the manual specifies two thicknesses of the cloth supplied - that works fine.
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Great advice Dave I will be asking questions this weekend O0
For my recent Lobster rudder which is only a small flat area I found that dots of superglue worked effectively to secure the cloth. This was in the instructions.
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Thanks for the link - clears up most of my questions/issues. I'll get some spraymount, that sounds like it'll make life a lot easier.
The cloth that I have is 17gsm, which is quite fragile. I'll get the next weight up on my next order for future builds.
I've got a big can of 99% isopropyl, which I think is the same as rubbing alcohol? Does this also work for cleaning epoxy from brushes and scrapers? I used acetone today for cleanup, didn't thin the epoxy. I suppose I could just use cheap brushes and bin them, but I didn't want to risk loose bristles getting stuck in the job. I'm using a Harris 1" synthetic brush, which I didn't get on with for decorating, but seems to work well with epoxy.
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Great advice Dave I will be asking questions this weekend O0
For my recent Lobster rudder which is only a small flat area I found that dots of superglue worked effectively to secure the cloth. This was in the instructions.
Did you do both sides with one piece of cloth wrapped around the rudder?
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Yes :-))
I veered away from the instructions though in that I did not round off the edges first.
I clothed and resined before trimming the edges back to square then rounded off before applying second coat of resin
(https://photos.smugmug.com/Midwest-Booth-Bay-Lobster-boat/i-3gjRM3M/0/0c8c3ea2/X3/42CF697B-8981-4EA0-A061-897D1F0BF84D-X3.jpg)
(https://photos.smugmug.com/Midwest-Booth-Bay-Lobster-boat/i-Nz2nrF2/0/7a1466dd/X3/E0DFD18F-A611-46EC-B508-97F66FCF1231-X3.jpg)
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Thanks. Good to know that it'll lay OK around the edges
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I buy these in bulk for best price
These rarely lose a bristle
https://www.nexusmodels.co.uk/great-planes-3-8-10mm-disposable-epoxy-brush.html (https://www.nexusmodels.co.uk/great-planes-3-8-10mm-disposable-epoxy-brush.html)
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I-PA (aka rubbing alcohol) is a bit expensive for cleaning up! I buy a 5L can of Standard Thinners from our local motor spray shop - about £9 once every three years - and use that for cleaning up just about everything. I also use cheapo brushes but, being 50% Yorkshire, I can't bear to throw them away after just one use. Even squeegeeing off the surplus resin brings tears to my eyes... What a waste. You'll find that thinning the epoxy about 10-15% makes it a lot easier to apply and scrape off again, and you'll be throwing away a bit less expensive resin on the kitchen roll mop!
I tried the trick of using dots of superglue to tack the cloth along the keel line but found it left hard little lumps, so I reverted to the Spraymount technique. Helluva price but it works for me.
DaveM
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Is the spray mount applied to the cloth after it’s positioned ?
Cancel that :embarrassed: Better to read your link O0
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That’s in my favourites now thank you :-))
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Is 3M77 at around £17 really better than all the other repositionable spray adhesives which cost from around £4 on Amazon?
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£13.89 delivered
https://www.ebay.co.uk/p/3M-Super-77-Multi-purpose-Spray-Adhesive-500ml/1505718719?iid=112730921702&chn=ps&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=112730921702&targetid=594652397000&device=m&adtype=pla&googleloc=9046321&poi=&campaignid=1782815976&adgroupid=70885939162&rlsatarget=aud-629407025025:pla-594652397000&abcId=1140486&merchantid=101774645&gclid=Cj0KCQjww47nBRDlARIsAEJ34bn5c0J1H9MR0vgCn-q-btkjymXCd73MmWeSIyHXkZbti-peXDsgAu4aAsi6EALw_wcB (https://www.ebay.co.uk/p/3M-Super-77-Multi-purpose-Spray-Adhesive-500ml/1505718719?iid=112730921702&chn=ps&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=112730921702&targetid=594652397000&device=m&adtype=pla&googleloc=9046321&poi=&campaignid=1782815976&adgroupid=70885939162&rlsatarget=aud-629407025025:pla-594652397000&abcId=1140486&merchantid=101774645&gclid=Cj0KCQjww47nBRDlARIsAEJ34bn5c0J1H9MR0vgCn-q-btkjymXCd73MmWeSIyHXkZbti-peXDsgAu4aAsi6EALw_wcB)
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Is 3M77 at around £17 really better than all the other repositionable spray adhesives which cost from around £4 on Amazon?
I really have no idea. The can I have says '3M Spraymount' on it and Googling that name will reveal many sources, most of which seem to be less than £17. I do know that it works fine for me every time I use it. If you do find an alternative on Amazon then please let us know what it is and maybe I'll get some when this can finally runs out. At the current rate of use that will be sometime around 2028.
DM
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Interesting
We’re did 3M77 raise its head %%
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Interesting
We’re did 3M77 raise its head %%
Er yes. I have heard of 3M77 being used & I thought that it was Spraymount but apparently they are not the same product.
3M77https://www.amazon.co.uk/3M-Super-Multi-Purpose-Spray-Adhesive/dp/B002BB9A4S/ref=sr_1_1?keywords=3m+77&qid=1558510004&s=gateway&sr=8-1
3M Spraymounthttps://www.amazon.co.uk/3M-SprayMount-Adhesive-Spray-Transparent/dp/B000SHR4ZE/ref=sr_1_4?keywords=3m+77&qid=1558510004&s=gateway&sr=8-4
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I've ordered some 3M spraymount, 2x 400ml cans for £23.99 on eBay. Also some 35gsm cloth.
I'll keep an eye out for some of those Great Planes brushes.
I've been using isopropyl alcohol for years as a general cleaner and degreaser when working on clocks. I buy it in 5L cans, and decant it into a smaller bottle. I like it because it's not too flammable (can have a ciggy in the workshop without setting fire to myself!), doesn't smell too bad, and doesn't irritate my skin. Not keen on using thinners indoors, but appreciate it's cheaper.
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French tin
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F254229836295 (https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F254229836295)
Listed here as same stuff
https://www.etilux.lu/en/product/adhesive-sprays-195/3m-spraymount-7043-4507-php (https://www.etilux.lu/en/product/adhesive-sprays-195/3m-spraymount-7043-4507-php)
Don’t use the brushes from hobby craft they lose bristles big style
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Top Tip, apply cloth using De lux meterials Eze-coat, Ebay. Its water based so no mess or thinners .
You can then either epoxy, using stiff card spreader or carry on with the Eze-coat.
Safe no fumes easy clean win win id say :-)) :-)) :-))
Jim
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Hi Guys,
I have used West Systems, SP Systems and recently Easy Composites (cheaper/slower setting options) epoxy resins
and lightweight glass cloth over the past 40 years + as the base coating to finishing large balsa glider fuselages and
balsa/ply boat hulls etc, followed by Halfrauds aerosol paints.
I think its wonderful stuff giving a firm foundation soaking into into the wood, stiffening the surface especially when used with cloth,
once dry and flatted down you have a great surface to paint or use as a clear gloss coating over wooden planked decks etc,
this can be burnished to a high gloss finish with the cloth disappearing beneath the resin.
My favorite weapon of choice for applying glass cloth is a mini stiff foam roller (usually sawn in half to make it more manageable)
I quickly roller on a coat of epoxy, then drape the pre cut glass cloth onto the wet surface, roller over to lay the cloth out and it goes on
perfectly without Spraymount etc and disappears into the resin, depending on what weight cloth you use.
Rollers allow you to push very fine cloth around corners, I have wrapped a complete large scale glider fuselage using one piece of
lightweight cloth to cover the whole model in one session, forcing the cloth around the complex 'egg' shaped fuz with a roller.
Very lightweight (0.9oz per sq.metre) will disappear into a single application of resin (check my Swordmans deck at Mayhem this weekend).
Recent experience with slightly heavier Easy Composites 100gm cloth requires a second coat of epoxy to fill the weave,
applied while still 'Post It Note' tacky to prevent blushing.
Having related the above about the wonders of epoxy resin - I am in the process of finishing a small free sailing solid balsa yacht for this weekends event
using Wilko's water based floor varnish (aka. EzeKote?) to apply fine glass cloth and it worked very well.
Simply applied by a soft half inch flat artists paint brush the hull covered in one piece nice and flat, no wrinkles,
will be interesting to see how it stands up to the test of time and dings etc, certainly a much cheaper option,
easy to apply, cleans up with water and no nasty fumes. regards Paul
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Interesting statement before about smoking round chemicals which I think needs taking with a pinch of salt. Most if not all the alcohol/solvents mentioned carry explicit warnings on the MSDS sheets regarding fire, and there should be the regulatory CLP pictograms on the suppliers cannisters. I'm a smoker myself, but never around solvents or alcohol (unless its the pub beer garden). 2 reasons: fire, and smoking is a very easy way to transfer contaminants from your fingers to your mouth.
A few years ago now I politely suggested to someone that smoking on a garage fourcourt right opposite a couple of cars filling up might not be a great idea. I was chased into my own car and threatened!
Wasn't that long ago I started using the little bottles of hand sanitisers. I made a schoolboy error of using some gel and when my hands were dry (or so I thought) I lit-up a cig. I din't have to worry about plucking any nose or eyebrow hairs for about 4 weeks after. Silly mistake of course. Duuh!!
Just saying because not everyone, particularly beginners are aware of the hazards of some modelling products. They might come in small bottles, but actually some of them can be quite dangerous. I'm not meaning to be patronising, but when your tub of stuff says flammable, toxic, poisonous or irritant etc, please heed the warning if youre a beginner.
Rich
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Accepted £5.01 so £8 delivered
https://ebay.us/BAXvku
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A quick note about setting times may be of interest - I've found West and SP resins WILL set off in their recommended,
short, around 15 minutes working time - requires one to get a wriggle on before things starts heating up and setting !
The heating up is real folks - early experiments with West resin - I used too much hardener in a mix,
minutes later the plastic mixing pot was smoking and eventually melted,
the heat generated by the catalytic reaction has to seen to be believed.
I've recently switched to using Easy Composites (Stoke on Trent) epoxy resins because -
a) its a cheaper than the above + great next day service from helpful knowledgeable staff.
b) they provide a SLOW SETTING HARDENER option, which stays workable for up to an hour in cooler weather,
allowing you to take your time, possibly cover the whole model in one session !
Update re the floor varnish (ezekote) - FOUR coats applied and allowed a day to dry in a hot conservatory,
a quick sand down - sounded like playing a musical wash board,
varnish had not filled the cloths weave, coat of grey primer revealed the surface to be covered in pin holes,
not amused. Paul
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...............................I've recently switched to using Easy Composites (Stoke on Trent) epoxy resins because -
a) its a cheaper than the above + great next day service from helpful knowledgeable staff.
b) they provide a SLOW SETTING HARDENER option, which stays workable for up to an hour in cooler weather,
allowing you to take your time, possibly cover the whole model in one session !......................
not amused. Paul
Which Easy Composites resin?
My ex supplier of West System has 2 different hardeners. I wonder if you have only tried the fast one.
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Update re the floor varnish (ezekote) - FOUR coats applied and allowed a day to dry in a hot conservatory,
a quick sand down - sounded like playing a musical wash board,
varnish had not filled the cloths weave, coat of grey primer revealed the surface to be covered in pin holes,
not amused. Paul
Not EzeKote then...
Colin
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The 35gsm cloth turned up this morning, so I've just done one of the hull sides. Much easier to work with than the 17gsm. I'll do the other side tomorrow, but leave the curved bottom until the spraymount gets here.
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Hi Tug Fanatic,
Yes have used all the West permutations over the years and in my opinion its the best of the bunch -
dries rock hard and crystal clear, ideal if you want a glass like surface over natural timber decks etc,
just very expensive for the small amounts modellers require.
I use Easy Composites EL2 Epoxy Laminating Resin and AT3 slow setting hardener -
now states between 90 -115 minutes working times.
https://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/epoxy-resin/EL2-epoxy-laminating-resin.html
Hi Colin, unfortunately thinks I'll be sticking to what I know works in the future,
great shame it was highly recommended by aeromodelling friends who swear by it,
plus since recently contracting a rare blood cancer (Polycythemia Vera Rubra)
I now have allergic reactions to epoxy fumes resulting in blisters and swelling around my eyes,
I hoped the water based would be the answer to this problem.
My concerns are how many coats of the stuff do you need to apply in the first instance
to fill only the tiniest weave of the lightest glass cloth on the planet,
and its long term strength etc.
Many of my boats are now approaching 30 years old and look as good as the day they were built surface finish wise,
I put this down to the stability of the epoxy/glass foundation under the paint,
I find it hard to believe that a water based product will do the same job long term.
regards Paul
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In ye olden dayes my hulls, and those of others were planking in balsa and then 'plated' with gumstrip paper using a weak solution of Cascamite instead of water and sealed with a couple of coats of shellac before painting. Totally green, durable and organic! Easy to rub down and a lovely finish.
Nothing like beetle juice really.
Colin
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In ye olden dayes my hulls, and those of others were planking in balsa and then 'plated' with gumstrip paper using a weak solution of Cascamite instead of water and sealed with a couple of coats of shellac before painting. Totally green, durable and organic! Easy to rub down and a lovely finish.
Nothing like beetle juice really.
Colin
I had not heard of that one but I wonder why gummed paper rather than just heavy brown wrapping paper.
Over recent years I have been amazed at the variety of hull coverings used which have included tights, garden fleece, dressmaking fabic etc and the glues which have included both pond waterproofer and indoor polyurethane varnish.
By the time I am not sure about the uv, & other, stability of the alternative materials and have doubts about some of the glues I will not be trying any of them.
There are times when trying to save a few quid makes little sense to me.
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I had not heard of that one but I wonder why gummed paper rather than just heavy brown wrapping paper.
Making a gummed paper hull over a mould pre dated GRP moulding. The gumstrip is of course sticky backed and requires water to activate it. When it dries it shrinks slightly giving a very smooth surface and as long as what you are sticking it to is smooth then that is what you get on the outside, no awkward ridges that have to be sanded down as with resin on cloth. I just used to add a bit of Cascamite to the water mix on the belt and braces principle.
One other advantage of this method is that it also lends itself to simulating plating. My Granada below had 5 years hard use on the MPBA regatta circuit in the 1980s and is still in one piece although long retired now.
Colin
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"...no awkward ridges that have to be sanded down as with resin on cloth"
Admiral
You ain't doin' it right, m'duck.
DaveM
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And nor are most of us Dave, we don't have your years and years and years and etc. practice. Resin of either the polyester or epoxy variety has never endeared itself to me.
Just tested my Huntsman on the bench for Mayhem and the motor extracted itself from the mount as the vibration had loosened the securing screws. Now replaced with Loctite and all other screws, nuts etc. checked for tightness.
Colin
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Spray mount arrived this morning, so I did the hull bottom. So much easier than laying the glass over epoxy!
The hardest part was cutting the glass cloth. The stuff is so slippery that I'm finding it next to impossible to get anything close to a straight edge. Just as well I left a few inches spare on all sides.
Oh, and I kept catching the cloth on the rough skin on my fingers. Reckon I need to start using hand cream, or wear disposable gloves when handling cloth.
Got a couple of small ripples where I wasn't thorough enough with the squeegee credit card.
I'll sand off the excess tomorrow, and give the whole thing a second (thinned) coat to fill the weave, then sand it back a little before glueing the deck in place.
Does thinning with IPA affect the curing time?
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I find cutting lightweight glass cloth is easier using a scalpel. Lay it out on a flat surface and use a metal ruler to cut against. You need to use a bit of pressure to cut it cleanly and a fresh blade is best as they will blunt relatively quickly.
Jim
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Does thinning with IPA affect the curing time?
I can't answer that because I've always used it thinned. It's usually ready to be feathered around the edges after three or four hours at room temperature, though.
As regards cutting the stuff I concluded that a decent pair of dressmaking scissors is the best method, so I bought Liz a new pair and nicked her old ones! I can also sympathise with the catching of the weave with rough skin. Been there and done it. I now rub my hands with 400 grit silicarb paper before handling the stuff. Hand cream would almost certainly infect the resin.
DaveM
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I think I need to sort out a larger work surface for cutting and building. Main problem is trying to cut a partially folded sheet of cloth. Probably find it easier if it was opened out and laid flat.
I meant to say working time rather than curing time. It was just starting to thicken as I was finishing, so I hope thinning won't reduce working time.
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Second coat of finishing epoxy applied this morning. I thinned it with IPA this time, which made brushing a lot easier. It did seem to extend the working time quite substantially, as well as the curing time. I will definitely have to leave it to cure overnight.
I'm wondering what to do next - sand it down then prime and fill, dust on a guide coat first, or just prime it as is before sanding?
I'm planning to use Halfords car paints, and Holts Cataloy knifing putty to fill any imperfections.
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Leaving it overnight is never a bad option. Like I said somewhere else, the two biggest enemies of a decent finish are dust and impatience.
I simply sand it again (240 silicarb, followed by 320); dust off well; use a tack-rag, and then apply Halfraud's yellow high-build primer/undercoat. Don't forget the 'sniff test' to check that the stuff has set. Works every time for me.
DaveM
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I'll pick up some yellow primer, could save a lot of time over using knifing putty.
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This might be of use to you https://www.modelboats.co.uk/news/article/finishing-and-sealing-of-wooden-hulls/18771 (https://www.modelboats.co.uk/news/article/finishing-and-sealing-of-wooden-hulls/18771)
I think it's also somewhere on Mayhem but that's incidental. Don't mix finishes e.g. sanding sealer and epoxy. Wetting the surface before laying the cloth on can be a pain if you get wrinkles in it, because you're bound to open the weave of the cloth by trying to lift and reposition it. The Spraymount trick has worked well for me since I began using Z-Poxy a long time ago.
Also don't go for the very lightest cloth for much the same reason. I use the 34gsm De Luxe Materials stuff and it's just the job. I covered my Midwest Lobster Boat hull in three pieces; one each side from the keel to the gunwales and the third on the transom. Note that the manual specifies two thicknesses of the cloth supplied - that works fine.
Thanks for this. Great info.