Dope or not?

[Richard Purser]

Yes i know..ive lost the plot for sure!?.....is there an alternative to using dope on balsa sheet? to strenghten and aid finishing, (with tissue) ,or is it neccessary only to aid fuelproofing  on ic powered models etc...short and sweet this time cheers

[Doug Ireland]

Hi Richard,

In the good old days we used to use Sanding Sealer before laying the tissue. Then one coat of dope, sand off the glaze then apply a top coat. Dope on top of balsa whether coloured or not is all the fuel-proffing you need!

[Richard Purser]

thanks for that doug...im actually building a model for electric that was originally designed for ic, im just testing the water for ideas for saving weight and at the same time give model a decent overall finish, wings are foam cored fus is balsa/ply , i intend to use enamel paint with possibly water based satin/matt varnish...cheers

[Simon Chaddock]

Hi Richard

As an old doper I can tell you it is not proof against glow fuel but that shouldn't bother you. It does water proof (and adds some strength) which will interest you as balsa absorbs a lot of water and swells if you get it wet. Dope also shrinks which can be an issue on thin sheeting (as you apply it to only one side) but sheet well supported over a foam core (compatible with dope?) should not be a problem. As you are going to paint your model you are really using the dope as a sealer but dope is heavy, 2 coats thinned 50/50 will give a better finish than one full strength one. Go easy with the paint, it is heavy also. It may look good but paint itself never made anything fly better!

[Tim Mackey]

Todays much better and easier to use method is PolyC which is a water based PU type liquid that can be used with all the usual materials- especially useful with tissue on foam models, but equally good on balsa. I use it to toughen up most if not all of my foamies, and have just used it on a balsa and ply sloper - tissue on all surfaces, and fibreglass on the fus bottom to protect it on belly landings in the rough grass and gorse! POLY C

[Former Member]

[This posting has been removed]

[Richard Purser]

Thanks all for that youre a mine of information, yes eric i knew about the dope/polystyrene incompatability , but thanks for reminding me! ...you should all get together and write a few modeling tips books!! great stuff as always!...regards and thanks richard..... p.s. i'll be looking for some poly c ...cheers all

[Tim Mackey]

You can only get it from the supplier I linked to.

[Richard Purser]

i've checked it out and it sounds like good stuff to me! and ideal as it dries quickly, i may well give it a try...thanks again richard

[Bob Cotsford]

I'm substituting for Poly-C with Cuprinol indoor water soluble varnish on a small .15 model - it's stuck a layer of glass cloth onto the balsa sheet fuselage a treat - and it's left lovely satin mahogany finish!  It sands nicely and iyt feels that coats dry out quite light - whther it's fuel proof is another matter.  

[Richard Purser]

thanks for that bob,do you think ronseal quick drying stuff would do the same?

[Bob Cotsford]

try it on a piece of scrap and see!  one good thing is that it has no odour, and drips can be cleared up with a wet rag.

I've covered the wings with lightweight glass cloth  and diluted  Evostick resin W.  I think the Cuprinol filled the weave better than the PVA, but they both sanded ok - whether they would be so easy to sand after a heavy coat is another matter.  lots of thin coats works well.

Now to see if I've got any Christmas wrapping paper left for the final finish.

[Richard Purser]

all sounds good to me...cant wait to see the finished item on the cover of the december issue!...cheers for now