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[Trucker]

Hi, All, im about to close off the bow section of my all ply wood hull so, before doing so i need to water proof / seal the wood in side, the whole out side will be fibre glass covered, i have read just about every subject on resin coating but what i dont under stand is , why dont modelers use good old wood varnish for the inside, it seems a lot cheaper and use straight from the tin.


Trucker

[Taranis]

Whatever you choose it needs to be diluted to penetrate the wood deep enough. It may well soak right through which is fine but if you’re using resin it’s better that it’s resin meeting resin than a different product IMHO

[Capt Podge]

Hi Trucker, glad to see you didn't fall into the trap, as I did. I had to cut into the bows of my boat, resin coated and then patch the bow area.
I think you'll be fine with a few coats of exterior varnish - I used resin purely because my all ply boat won't be fibre glassed.


Hope it all goes well for you.


Ray.

[Rich griff]

Similar for me but no fibre glass skin for water to get under...


I would include some sort of water drain in the bulkhead. Sods laws says.......


I would also want to fill any "air" inside the boat with white foam, so should water get in, it has minimum volume to fill.


Foam is much lighter than water.


Remember titanic...watch out for icebergs...

[Taranis]

Water cannot get under a glass cloth coat that is resin bonded to the wood unless you put grease on it first 😂

[Circlip]

Should qualify if using white or blue foam as a filler that you use shaped pieces rather than self foaming spray in a tin which has a tendency to keep expanding.


  Regards  Ian.

[Taranis]

This is one of a few of mine that are resin coated on all inside surfaces including underside of decks etc. The outside is resin and cloth coated.
This prevents moisture from the air or direct water contact from having any effect on the size and shape of the wood which could lead to paint damage from cracking in the long term.
I see no need for foam unless you're planning on it leaking to the point it might sink or suffering collision damage.

It's common to see cracked decks on models old and new where the builder neglected the unseen surfaces and humidity has a free hand.

[SailorGreg]

Yes, a couple of coats of ordinary varnish is fine, thinned a bit so it really gets into all the nooks and crannies.  As for foam, I would steer clear - if any water does get inside it will be trapped between the foam and the hull and you will never get it out.  Then eventually it will soften or rot something important. 

I know there are experienced model builders who say they never worry about the inside of the hull.  After all, water shouldn't be in there.  But Murphy is alive and kicking, and I know all my thoroughly waterproof hulls have had a dribble or two (or more) at times.  It only takes a dripping prop shaft or a small slip when launching or recovering to get the innards wet. And if you don't realise immediately, the water will sit there for a bit before you discover it.  Like Taranis, I do all surfaces including the underside of the deck so that if I negligently leave some water inside, no permanent damage is done.  It also means you can wash the inside of the hull if you end up with a greasy streak around the hull from the prop shaft lubrication (or am I the only one who sees that?)

Happy building.

Greg

[John W E]

hi there


just to clarify a couple of things


resin/polyester based WILL absorb water over a period of time - unless it has a good topcoat of something - such as paint.


So, if painting inside a hull - it is very wise to have a hole in the bulkhead for air circulation.  This will allow any trapped water to evaporate before it soaks into the timbers.   


The best thing to do is to use an epoxy resin such as Zpoxy finishing which is a waterproof Epoxy.   


Or, if you really wish to push the boat out and spend some money - use the West Epoxy system - this is used on the 'Real I am' boats but, one has to have very deep pockets for this stuff.


Just food for thought.


John

[Taranis]

Agree John I only use Zpoxy finishing resin

[Trucker]

Thank you all for your replies, i didnt expect so much  , as this model has very little draft as the full scale version i really think i should make it as water tight as possible, it looks like the varnish i have isnt going to be good enough as it is a water based one any way, and the supply of resin i have is polyester so also probably not the best stuff to use. back to the internet and have a look at some prices for epoxy resin, better check the pockets too

[SailorGreg]

The water based varnish will be fine.  When it dries it is a good seal against water, and I don't think you are expecting a regular prolonged soaking inside your hull are you?  Also, polyester resin will be fine if you choose to use that.  After all, full size boats have been built with polyester resin for decades and they seem to manage OK.  If you were anticipating leaving a significant amount of water inside your hull on a permanent basis then you might want to make a more comprehensive job of it, but for the general dampness of a model boat and the occasional accidental spill which is mopped up fairly promptly, the varnish or polyester resin will do the job for you.  Only if you are planning to use epoxy on a regular basis in your building is it worth splashing out on that.

Greg

[John W E]

Hello there SailorGreg - yes full-sized boats are constructed using polyester resin, however, they do have what is known as a gelcoat layer which is a highly polished finish and is a barrier - which you can see on the outside of a fibre glass hull, and this is basically an epoxy style resin. 


The gelcoat style resin cures with the absence of air - and when you mould a hull or whatever, the gelcoat is applied first.    If you use gelcoat in the open, a wax must be mixed with the gelcoat and this floats to the top, thus creating an air seal.  (This is known sometimes as a flow coat).


This in turn allows the gelcoat to harden.    This method is sometimes used on the internals of boats, such as areas like bilges around the engine compartment & the stern area where the propeller shaft and rudder are located.


Yes, I have used pure resin (as in polyester) in the internals of a model hull - as we don't usually put a model in the water for 24 hours a day/7 days a week/52 weeks a year.


My point is, in my last posting, some people bring a model home after use - leave it and not bother checking the inside and clearing out water which managed to find its way into the hull from the lake or whatever.
john