Balsa hull and tissue paper problems

[NickN NParticipant @nicknn70130]

I hope someone can offer some advice here with a problem I am having with a balsa hull and tissue paper covering.

I am attempting Vic Smeed's Tiddler tug at the Model Boats plan size of 20" or so, and I am using the suggested balsa hull construction, at least as far as the deck. I have what is a satisfactory hull complete albeit with a few areas filled with the green putty stuff. I then attempted to cover the hull using aircraft tissue paper but have run into problems. This is my first attempt with this method and clearly the practice pieces I tried were not representative of what happened when I moved on to the hull.

I sealed the balsa with several coats of 50-50 thinned non-shrinking cellulose dope, rubbed down between coats. I then applied an over-size sheet of tissue paper to the main side chine from the deck down, with an overlap of 1/4" to the next chine, snipped along the edges to fold over the curves. This was applied with more thinned dope. I did the same for the bottom sheet, overlapping to the middle chine again. The problem has been when I added the middle chine and added, in effect, an overlap to the overlaps. Specifically, the overlaps tended not to stick and I ended up with a lot of very uneven, bubbling and/or loose edges. Sanding did not really help and, rather than slap filler everywhere and cover it all up, I have spent some time removing the tissue paper (with thinners AND paint stripper – it was stuck down well in places).

What went wrong? I have seen somewhere the idea that one uses thinned sanding sealer rather than dope, and that the tissue is smoothed immediately with rolled kitchen towel to flatten the covering and to remove excess sanding sealer. I had thought also that if I followed the same procedure as above for the first two chines, I should then add an under-size piece of tissue paper to the last chine so that it only lays on the overlaps, rather than creating further layers over the hard chine edges.

Any thoughts or suggestions gratefully received.
Nick

[NickN NParticipant @nicknn70130]

[Chris FellowsParticipant @chrisfellows72943]

I am a relative newcomer to model boat building but I've never come across using dope and tissue paper.

The usual method is using a lightweight glass cloth and resin. I've been using Eze-Kote resin as it is water based, no fumes and brush is cleaned in water so a quick wash and ready for the next application.

I've had to overlap the cloth at the bow and once another coat of resin has been applied it sands down a treat, so no steps.

See my Fairey builds in the Build Blogs where I've just done some.

Chris

[ashley needhamParticipant @ashleyneedham69188]

Ah Chris. You have never looked any of Glynn Guests builds! It is his preferred method of hull covering.

Nick. Firstly….sanding sealer is more or less dope with a filler powder added, so using dope only is the thing to do. I have not used the method before, but I could see the merit of using sanding sealer in the last few coats.

Overlaps in any material are tricky, and I would imagine that applying a coat of dope might tend to soften the underlying layers if plastered on too thickly or brushed in too much. It may be that you could soften the offending overlaps and trim them to become butted joints.

The covering is only meant to toughen up the balsa, not to add strength (like layering glass cloth and resin) so a lack of overlaps should not matter.

Coverings on boats are personal things. I use Eze Kote Acrylic resin, which dries to a tough finish, and is not softened by applying further coats. If the boat is small and light, my preference would be simply to apply dope or sanding sealer/Eze-Kote to penetrate the balsa and help waterproof it, and then just slap on the paint.

There is no right or wrong method, all are valid.

Ashley

Edited By ashley needham on 05/05/2019 19:15:12

[Dave MilbournParticipant @davemilbourn48782]

Nick

Shame you resorted to paint stripper. My experience says that when in doubt just leave it to set hard for a week and then sand the beggar until there ain't no more gunk left – then start again. There's an article written by some boring old geezer about finishing wooden hulls somewhere….ah, yes! Here it is! **LINK**

I'd recommend you now sand the whole thing down to bare wood as far as you can. Then use a layer of 34gsm glass-fibre cloth with Eze-Kote, as Ashley suggests. If you allow the stuff to dry hard first then any overlaps should be easily sanded out. The worst enemies of a decent finish include impatience.

Dave M

[Ray Wood 3Participant @raywood3]

Hi Nick,

The key to tissue paper is wall paper paste, cut your pieces to shape, paste the hull put the tissue on and brush more paste through the tissue, soaking the tissue gives plenty of repositioning time, the trouble with dope and sanding sealer are trying to dry fast, let the hull dry then a couple of coats of dope, then your ready for primer.

This is my +20% Tiddler, super little tug.

Regards Ray

[NickN NParticipant @nicknn70130]

Hi All,

Many thanks for the replies, comments and suggestions — Eze-Kote and lightweight glassfibre cloth seems to be the people's favourite. The only tiresome element there might be the right angle under the rubbing strip. I cut the tissue paper to fit that line rather then risking an ugly fillet of paper and gunge, and I guess the glassfibre could be cut in the same way before layering on.

But using wallpaper paste instead of dope sounds an interesting idea. I guess I need to experiment with some test pieces.

As to simply going from a sealer to undercoat, my limited experience has suggested that that approach works fine if using solid balsa, ie, bread-and-butter construction, but when using a sheeted hull like the Tiddler it is not long before the finish develops hairline cracks, although not necessarily directly in line with the grain. This could of course be my layering on too much sanding sealer or not allowing enough drying time between coats or finishes.

Nice model, Ray. I am intending to go for a wartime outfit in grey and more grey, but I rather need to get the hull done first. At least a day's worth of cleaning, sanding and doping has about got me back to where I was a fortnight ago.

Thanks again,
Nick

[Ray Wood 3Participant @raywood3]

Hi Nick,

Sanding sealer 1 coat to lay the grain is all you need, multiple coats just crack 😮 tissue is fine on your little balsa hull & cheap 😀

Regards Ray

You will need a barge to tow 😊

Edited By Ray Wood 2 on 06/05/2019 20:02:09

[Tim RoweParticipant @timrowe83142]

It's all in the name – sanding sealer.

It is not a good coating because it is filled with talc and is fairly brittle anyway. One coat should be plenty and in exceptional circumstances, if the would is porous it might accept two before it stops being a sealer and becomes a coating. Get to the primers and undercoats as soon as you can.

Tissue will stop the cracking and on my Galileo project, the inside and the deck was completely lined with tissue and epoxy which does actually provide a significant increase in strength as well as ding resistance. Epoxy is also an adhesive as supposed to dope and sanding sealer so that helps keep things stuck down like Ray's method with the wallpaper paste and Dave's method with spray mount.

By the way. It seems that there aren't any boats that Ray has not built

Tim R

[Ray Wood 3Participant @raywood3]

Unfortunately Tim is right but seldom the same type of craft twice , I'm a serial model builder, the problem is what to do with them? Anybody in the market for a boat, let me know

Maybe being on a screen, clicking a mouse for a living has something to do with my modelling , and there are plenty left on the list to build !!

Regards Ray

 

Edited By Ray Wood 2 on 07/05/2019 14:44:08

[Tim RoweParticipant @timrowe83142]

Ray

I think that last post is not quite true. You are a parallel builder

Tim R

[Ray Wood 3Participant @raywood3]

Hi Tim,

Let's hope your right with my new Super 60 wings 😀

Regards Ray

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