Sealer for solid hull

[bigcreekdad]

I'm at the sealing stage of my Smuggler build. Before moving on to deck work, I need to seal the hull to protect it from stains,dirt etc until I paint it later on.

 

First...any thoughts on sealers? I have some water based Varathane Poly. Is this OK? Also, it is water based. As such, does this limit me to water based paints?

 

Sorry if this is stupid question...it's my first ship that I will not plank, and I don't paint my planked models.

 

Thanks/John

[Jaager]

A safe sealer is shellac.  The first coat or two should be half strength. 

The more purified the shellac flakes, the lower the saturated solution in alcohol.

What I mean is =  I think orange shellac is 20% at full strength and 10% at half.  I prefer super blonde and with it, 10% is full strength and 5% is half.

There is a grade more purified than super blonde, but super blonde is close enough to water clear for me.

The solvent is alcohol.  Methanol (wood alcohol) is the traditional type,  not sure how easy it is to get.  Ethanol is what is usually available, the main factor with it - the best that can be had is 5% water - ethanol forms a special attraction with water - it requires expensive and energy requiring steps to remove the last 5% and even when done, if the 100% ethanol is exposed to the atmosphere, it pulls in water vapor and quickly becomes 5% water again.  That 5% does not seem to make it not suitable for shellac.   I had my pharmacy order a gallon tin of 100% isopropyl alcohol, it drys more slowly, so is more forgiving on finish coats, but even then, it was costly, and by working there I got it at cost.  The stuff out front in bottles has too much water.  I like the 91% iso for removing wood dust from sanded surfaces.

The traditional dissolving of shellac flakes in alcohol is "pound cut" - pounds of flakes in a gallon of alcohol. This is not even close to being practical for us. As rough as this is, a little rounding makes it easier.  Call a lb = 500 g  and a gal = 4000 ml  and the math is easy.  

There are low cost small battery scales - that measure grams - and a graduated cylinder in ml need not cost much.  Once mixed, shellac has a limited shelf life,  but by using % - any volume can be easily made up.

For what you want, premixed orange shellac and a tin of shellac thinner will do.   I like shellac as a finish and super blonde does not darken the wood very much.  As an undercoat, it is compatible with most everything.  I even use half strength as a first coat before applying a 50-50 base coat of Tung oil when I want an oil finish.

[Bob Cleek]

Jaager beat me to it and then some. Shellac is a great all purpose sealer and not a bad model finish for "bright work." It will yield a gloss finish if it's built up with multiple coats, but one or two coats will yield an excellent representation of varnish brightwork on models. I've never used anything but plain alcohol from the hardware store to thin it and that's worked fine. I buy it premixed in a can from the paint or hardware store. It may thicken in the can, but a bit of alcohol added brings it to whatever "cut" (thickness) you want. I love the way it is so easy to clean up brushes with alcohol, too. I save the alcohol I use form brush cleaning. (Alcohol evaporates very quickly, so you'll probably find you do a lot of thinning to keep the solution diluted like you want.) As the shellac builds up in the "first rinse" alcohol, it can be used for thinning thicker stock or for very light sealing. Shellac is also excellent for stiffening line coils and card stock. It should be considered an essential modeling material.

Edited November 18, 2018 by Bob Cleek

[Bob Cleek]

6 minutes ago, Y.T. said:

Hi, could someone explain why need to seal? What is the problem painting straight on wood?

Sometimes nothing. Sometimes a lot. Particularly, water-based paints tend to raise the wood grain, preventing a smooth surface. A good soaking of shellac will permit sanding with very fine paper and the painted surface will be perfectly smooth. It also saves on paint, which tends to soak into bare wood, often requiring many more coats that way. Good sealing also retards ambient moisture causing swelling and shrinking of wooden parts which eventually may break glue bonds and cause splitting and cracking of wooden parts. Proper construction and finishing techniques require sealing before finish coats. You'll be amazed at the difference it makes.

[Jaager]

Your way works. 

Those who do finishing for a living, do it differently?

Sealer was/is less expensive?

If you wish to remove the paint, a sealer layer above the wood makes it easier and less damaging to the wood?

Paint is difficult to sand, it tends to be a sticky film rather than fine particles, it gums up sand paper?

[bigcreekdad]

Way confused guys...argh!!

[Bob Cleek]

On ‎11‎/‎17‎/‎2018 at 5:43 PM, Jaager said:

Paint is difficult to sand, it tends to be a sticky film rather than fine particles, it gums up sand paper?

Sanding difficulties with paint are primarily limited to water-based paints containing latex and some acrylics. If the solids contain rubber (latex) or "rubbery" type material, you have trouble sanding it. (Sanding rubber isn't advised.) This is another reason, among several, that experienced painters prefer oil-based paints for modeling. There's really no comparison between the two types of paint.