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Traditional Covering Tissue/Dope - what next?

Tissue/dope covering prone to damage- How to strengthen?

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Mike Hardy15/12/2012 21:17:02
405 forum posts
72 photos

My Spitfire (open frame) has been covered with tissue and received 2 coats of shrinking dope/thinners 50/50. I have found the wings are suffering from what you call 'dings' or 'hanger rash' and have been patched up several times. Clearly this covering technique is prone to damage. What coating can now be applied to the dope finish to toughen up without adding too much weight?

The Spit is rubber powered. will 'tufkote' add strength to the covering.

Suggestions please.

Mike.

Simon Chaddock15/12/2012 21:45:49
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Mike

In my experience you have to live with the delicate covering, Rubber just does not have the power to carry any excess weight.

Even the lightest of the film coverings are a good bit more 'ding' proof than tissue & dope but then they are also heavier!

Mike Hardy15/12/2012 22:01:10
405 forum posts
72 photos

Thanks Simon, I was hoping for a 'magic' solution to this problem - clearly there isn't one!!

Mike.

Andrew Ray15/12/2012 22:29:07
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You can use Mylar on its own or tissue cover on top of the Mylar. There is nothing you can do to make the tissue covering you have any stronger other than to add a plasticiser in the form of a couple of drops of (I think) castor oil of the medicinal variety. This gives the covering a little flexibility.
 
Mylar can be obtained from the free flight specialists such as Free Flight Supplies, Google Mike Woodhouse and you should find a wealth of information. Flite Hook is another specialist supplier.
 
I hope this helps.
 
Andrew
 
.....and then there is SAM's another specialist supplier. 

Edited By Andrew Ray on 15/12/2012 22:31:30

Radge15/12/2012 23:19:42
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322 forum posts
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After doping and painting tissue I put on a couple of coats of Amtico water based wooden floor dressing, It doen't add any appreciable weight but is a really good ding proofer. It's also an excellent sanding sealer giving a lovely smooth satin finish to wood which you can paint or cover. It can be brushed or air brushed on. **LINK**

PS I also mix the acrylic paint with it for a tough satin finish.

 

Edited By Radge on 15/12/2012 23:22:51

Stuart C16/12/2012 01:58:29
125 forum posts
4 photos

Add a plasticiser as Ray suggested. We (the old fogies) found that a level teaspoon of Castrol R in a 2oz pot of Nitro cellulose dope gave an elastic covering which could resist those multiple shock tears. Light dings would not rupture the covering, and could be restored with gentle heat. Castrol M also works, as does virtually any cooking oil. We used R because we all had stocks of it to hand. The downside is that the model looses some rigidity normally afforded by a tighter covering.

Mike Hardy16/12/2012 06:45:08
405 forum posts
72 photos

Thanks all, it looks like a bit of experimentation is required. One other question is it possible to sand down an open structure after each coat of dope without too much damage being inflicted? Should I be using none shrinking dope after applying shrinking dope?

Mike.

Peter Miller16/12/2012 08:52:37
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Posted by Stuart Coyle on 16/12/2012 01:58:29:

Add a plasticiser as Ray suggested. We (the old fogies) found that a level teaspoon of Castrol R in a 2oz pot of Nitro cellulose dope gave an elastic covering which could resist those multiple shock tears. Light dings would not rupture the covering, and could be restored with gentle heat. Castrol M also works, as does virtually any cooking oil. We used R because we all had stocks of it to hand. The downside is that the model looses some rigidity normally afforded by a tighter covering.

I am amazed at that amount of oil in two ounces of dope. We always found that more than a few drops left the dope feeling sticky.

Sanding a tissue covered open struc ture is asking to cut through the tissue on the edges.

Once you have shrunk the tissue and filled the pores adding more dope simply adds weigh and increases the risk of warps.

If you wanted a gloss finish after that banana oil (non-shrinking dope can be applied but don't add too much weight.

John Laird16/12/2012 09:09:32
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debutante finished (1).jpgthin doped tissue over mylar is supposed to be lighter than tissue on its own since the mylar effectively weatherproofs the covering from below and reduces the amount of dope needed to seal and weatherproof.

lightweight tissue applied with the shiny side out should not need sanding. I used 30/70 dope/thinners to cover my scaled up 60" span Debutante and I handle it with care. more photos in my album

The free flighters who fly in the new forest dont seem to suffer from the light models landing in the heather and gorse points to the advantage of tissue over mylar

john

 

 

Edited By John Laird on 16/12/2012 09:10:41

Edited By John Laird on 16/12/2012 09:11:40

Edited By John Laird on 16/12/2012 09:30:59

Andrew Ray16/12/2012 09:33:06
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760 forum posts
19 photos

Mike, when I have used tissue on an open structure I have applied it dry, sprayed with water but only a light atomized coat and when dry used 50/50 shrinking dope/thinners then a very light sanding to remove the roughness, taking great care on the edges of the structure as Peter says otherwise you will cut through (I never pass twice over the same point). Then I usually finish with coats of non shrinking dope. This way I achieve a finish I am happy with. Too many coats of shrinking dope will tighten the covering further and may cause warping. Some builders will apply the tissue wet to the structure, this is more difficult and requires some patience, I think it results in a better finish though.

Andrew

Mike Hardy16/12/2012 14:49:58
405 forum posts
72 photos

I found covering with tissue quite a pain! Applied dry using tissue paste any tension would tear the tissue at the paste line. Eventually I gave up with the light weight stuff and used a heavier grade which tended not to tear so much but left 'join lines' which show up more than the light weight stuff. Its taken 3 weeks to cover the 1:18 Spit, guess I have a lot to learn!!

Thanks all for all the tips - What would I do without this forum.

Mike.smiley

Martyn K16/12/2012 15:00:48
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5048 forum posts
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Silk on Tissue - with the grain in oposite directions or double cover with tissue will add a lot of strength with a small weight increase.

Add a small %age of banana oil to the last coat of dope to delay the tissue getting brittle.

Finally, learn to handle it with care.

GL

Martyn
Mowerman16/12/2012 16:49:48
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1548 forum posts
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In the past I have used Tissue from FMK Models. Applied wet and stuck round the edges with 50%dope/Thinners, a bit fiddly but tightens nicely. This tissue used to be available in light and heavy weights and a good selection of colours but now only listed as a single weight white only. A shame as obviously the coloured stuff saves the weight of paint.

Peter Miller16/12/2012 18:29:38
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First, this is your first time. Tissue covering is a skill, keep practising and very soon you will get the knack and be able to do great covering job.

Tissue is often, I would even say normally applied wet. You can colour it with food dyes perfectly. Just add the dye to the water.

How I cover. I wet the tissue in a bowl of water, squeeze it out and lay on newspaper to absorb most of the moisture.

Dope the framework and then place the tissue over the framework and apply thinners. This sucks the dope through the tissue and with a bit of care and practice you can get a beautiful finish.

This technique also works really well when covering sheeted surfaces with tissue.

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