I built an air boat and the sponsons are hot wired from thermocol to keep the weight low. Unfortunately, the edges of the sponsons are sort of delicate and they break and crumble easily. Is there anything I can coat the sponsons with, that will make it a little tough? It's got to be waterproof and shouldn't add much weight.
I was thinking of Araldite, but inquiring for better options, if there are any.

Dilute Fevicol with water to 50%. Apply a thin coat. Next, lay tissue paper on the wet coat, and apply 2 more coats. Let dry. You will have a tough, hard skin which is easily sandable

Note: do NOT use synthetic tissue

Sanjay bhai, Is that waterproof? 

Snazzy shape - you came up with this yourself ?

looks like something Annakin Skywalker would be driving

Sanjay's method is good - to waterproof paint touchwood over the fevicol tissue matrix

Saikat, yes, scratch build.

Thanks, I will try the tissue and touchwood ideas.

Yes, waterproof when dry. Then as Saikat says, touchwood, or even paint

Saikat,  very Skywalker !!! Pod Racer 

use coro for those winglets

foamybuilder, Those are the motor mount post. It's an air boat.

I prefer to cover with coloured polythene 2" Tape for smooth surface. However, this is used in free flight foam glider.

Quote from: AnjanBabu on November 08, 2013, 01:14:44 PM
foamybuilder, Those are the motor mount post. It's an air boat.

Plane or boat, strengthening method would remain same. What i mean is laminate it with 2mm coro.

KALYANPRODHAN, that works to keep the thermocol from breaking off, but it still lets the edges deform. Looking to make it hard and stiff at the edges.

foamybuilder, I used 3mm sun board for the mounting post, no strength issue there. Only the sponsons are a little delicate.

will rubber paint work or will it destroy thermocol? 

Use enamel or acrylic

Wth is rubber paint anyway?

anjan i suggest you to use thin canvas cloth dipped with fevicol glue to cover the foam.   

rubber paint is used for waterproofing surfaces. it is often used as a coating on iron sheets to prevent them from rusting.
here is a spray version demo on youtube:

OK. The rubberized undercoat. Why would you want to paint a model boat with that? Lousy stuff for finish

that is upto AnjanBabu to decide... 

Nithinraj, I already covered it with tissue and Fevicol, got to wait and see how good a job I've done.
Not a bad idea, using a fabric.

Aman, I'm looking for some easy and cheap techniques.

anjan check this out

That's not bad, looks neat.
Going to find out in the morning if i'll have to hotwire new sponsons, the tissue+fevocol coating looked very messy and uneven, it was my first time.

local tailor shop will have those canvas cloths ask for 2" width and 1 meter length.

Tried sanding the tissue coating and it didn't turn out as smooth as I expected. 
Hot wired two new pairs of sponsons, going to try using newspaper instead of tissue on one pair and Nithinraj's suggestion of using Canvas cloth on the other.