balsa hull and what next?

Hi. I’ve made a balsa hull and i dont know what to do next…
This hull is from plans “Palo de agua” rg65. (Chin balsa hull)
I have some questions:

  1. How to make this hull waterproof :wink: (weight is very important)
    -maybe some epoxy with fiber coat ?
    -if yes - i have to use on balsa nitrocellulose varnish first ?
    -what g/m2 coat must use ? 50g/m2 ?
    -can i use some foil to squeeze hull from to much epoxy ?
    -what next ? some filler, paint ? (weight…)

  2. Maybe dont use fiberglass only some (3-6 ?) layers of varnish or something ?

please help me with this… i’m nooby so every answer would be like a gold to me :slight_smile:

regards. aXon (sorry for my eanglish…)

The designer’s building instructions were to use 5 or 6 coats of aircraft dope on the exterior, sanding between each coat and applying a coat to the inside as well. There shouldn’t be any need for glass reinforcent. I believe the original was still sailing last year.

yes. thats a one way. but if i decide to use a fiber with epoxy?
this will be to havy ? and what should i do next after fiberglas? use something like foile to nivelate weight of epoxy ? and what paint or something after that ?

there is everywhere different school about it. this mess with my head a lot…

personally I like a layer of glass on the outside. I use 1/2 oz glass which would be 15g/m. Just adds a bit of security and it really can not add much weight.

Stain it :slight_smile:

Then use .5oz/yd to .75oz/yd fiberglass with epoxy (West Systems 105/207 special clear hardener) to show off the wood grain.

Lay down the cloth, then using a foam roller lay down a layer of epoxy, wait an hour or two, then another coat, wait again and apply a third coat, let cure over night, sand smooth. Epoxy the insides with a brush, one coat is all that is needed.

Build the deck with wood (doing the internal mounting for fin, servos, rudder, etc.) and repeat the glass/epoxy sanding. Finish it off with a clear coat, and be the envy of your club :wink:

My glassing method is to lightly (I mean lightly) spray the hull with 3m77, then lay the cloth over the hull. Remove all wrinkles and puckers. If you dont, they will show up as soon as you wet the glass. Then once you like the way the cloth is laying on the hull apply resin. I usually brush it on, then use a squeegee to remove the excess resin. Let cure until green, then trim the glass to the hull. Once completely cured, I sand it relatively smooth. Dont sand too much as you dont really have much cloth on the hull, just enough to take of the high spots. I usually then coat with system 3 clear coat, sand, coat, sand until acceptably smooth. The clear coat is a self leveling resin that is really thin so it fills better than high build primer, but still leaves a nice surface when done. It usually takes 1 to 2 coats to get a hull smooth. Then coat with varnish or automotive clear coat. you will get a nice wood grain look even with balsa.
I dont glass the deck since I feel it just keeps out the water, so it doesnt need the same level of strength.

Hi aXon:

take a look to this threat in this forum (RG65)
Thread: Varnish for wood floors vitrify.

polyurethane floor coating its something new to me. fiberglass on balsa in my opinion will be the best. some foil on it to smooth it (only in laminating time). sanding and thats all in my opinion…

aXon, you seem to be concerned about weight – If weight is an issue you should listen well to SlotRacer’s post about how to apply resin. No matter whether you use epoxy, polyurethane, polyester, nitrocellulose, or other resin, at least half of the weight of the coting is the resin. Your idea about smoothing with foil is a good idea, but a better way is to apply resin and the either squeegee off as much excess as you can or else absorb it off with paper toweling or toilet paper. That way you remove excess resin instead of trying to smooth the excess. Extra resin is NOT you friend… it mostly adds weight and doesn’t make things any stronger.

If you will paint the boat, then use the thinnes coat of glass (or other cloth) applied with the smallest amount of resin you can. Then sand lightly and use spray-on lightweight auto primer/filler to fill in the weave. It’s way lighter than resin and made to fill and even things. Spray on a coat; let it dry; sand off the high spots; repeat until the weave is filled (usually 2 or 3 coats of primer/filler)

About resins, there’s no need to fear the polyurethane floor coating – it sounds new but it’s not. It’s just a good, tough polyurethane varnish. ( My present RG65 carries a coat of VERY light nylon cloth (no exact weight but it’s stiff under tension and WAY lighter than my .6oz glass cloth) applied with polyurethane varnish.)

all done. one cloath 25g/m2 with l285 epoxy
hull weight - 68g => 2.49 oz

next step: keel … bulb etc…

one question: i wanted to use rotor blade from heli as a keel but i have only 23cm long…
how to make some light and strong keel ? - balsa + fiberglass ? and what width and hight ?

im talking about Palo de agua but with “modern keel” :wink: (because original had 2mm aluminium keel…


I used 1/8th inch plywood, two laminates and then shaped to suit. I beleive these thicker fins help the stability of the smaller boats.