What size balsa wood do you use?
2 mm, as said in the plans.
The boat today:
First polyurethane hand:
I wanted to tell you how I’ve done with polyurethane. Someone suggested me to use a fast-drying polyurethane to work faster, I found a floor vitrification polyurethane fast drying that requires no more than two hours waiting between hands and need not to be diluted, which seemed very appropriate. The balsa wood absorbs much the polyurethane, so the first coat dried within minutes and hardly covered the surface, but strongly adhered the boards. Applied ten hands of this polyurethane and not filled the gaps between boards as well despite being careful with the brush was a lot of bubbles, and the resulting layer was very thin, so it did not fill irregularities.
With these results I decided to change strategy, I visited the manufacturers’ web sites and found one that claimed to be self-leveling, so I figured it would be much more viscous than that used previously. The difference is remarkable, in just two hands filled almost all the irregularities and the surface was much smoother.
But before using this second polyurethane fill larger spaces using thick cyanoacrylate, which I think was a good idea.
I’ll give a hand over the hull and I will continue to build the boat.
That’s good to hear. It’s a surprise to hear that some of the coating needs to be diluted. I have never seen that in a product.
I decided buy a jug (4L) of the Parks Pro Finisher polyurethane, which is expensive ($40 per 4L) but It worked as well as yours did. It is also a thick and fast-drying product. I will try some experiments with heavier glass cloth (up to 1 oz.) and even some regular cloth from an old shirt, to see if there is a difference in the final weight and strength.
Don’t worry about the strength, I can promise you that the polyurethane is more than enough. My hull suffered hard stress when sanding without problems, I was very rude intentionally to be sure if the hull is strong or not.
I’m sure it is strong enough for protection of the outer hull, but I would like to look into the possibility of using it inside the hull like you would do with epoxy resin and fiberglass cloth.
I’m building the Minitux 2, and I started paining on the polyurethane today. I have 3 layers on so far today, and will put on one more before sleep. I only had to wait about 2 hours before painting the next layer.
I also painted some onto a small piece of cotton cloth and I will see how it finishes tomorrow. Maybe it will be good enough to use inside to waterproof the keel box.
Do you have a scale that will weigh one coat? I am curious about the weight of this versus epoxy, especially when you have to use 10 coats. Maybe someone has done some comparisons?
Thanks
Don
Don -
not sure there is any gain/loss in using a polyurethane of 10 coats versus only 2 coats of epoxy. Personally (I) would use the epoxy since it not only seals the wood pores, but also acts as a strong (much stronger) adhesive than polyurethane in keeping all the strips attached to each other and really no need for glass reinforcements - insdie the hull or outside on a boat that weighs around 2 lbs. or less total weight.
I don’t think that would be a good account of each coating. Intead I’ll try to weigh the hull after so-many coatings and calculate the average weights.
Maximo Lange said that a hull build with polyurethane weigh around 50-60 grams.
My Minitux is about 110g, but I haven’t cut out the stations yet. The stations are made with basswood. There is no keel box either. That should be another 100g at least. :indiffere
Hi friends:
When I said 50/60 gr. is only the hull, no keel box, no deck, no sections. only the hull.
cheers
Happy new year!!!
Hi all.
and what about Acrylic-urethane varnish ? (marine varnish for wooden bridge and boats)
this will be good for balsa hull ? strengthening and waterproofing ?
Yes ! so far you d’ont use to many layers otherwise the weight will go up.
Fiberglass/epoxy outside and paint inside is also a good idea.
Cheers
Claudio