Minwax Helmsman or other spar varnish for waterproofing

[David W]

I'm in the process of putting the Amati Fifie together for radio control. Of course that means it will get wet. I thought I had done my homework before purchasing but afterwards found that besides the bulkheads being MDF, the keel was as well. OOPS! MDF does not like water. I want to fully, or as much as possible waterproof that material. I am considering a good couple of coats of spar varnish on the inside as well as the entire keel. It will then be fully painted with, probably, Humbrol red on the outside bottom and at least to the waterline then a full coat of spar varnish or other paint

 

 I could use a resin overall or something else as years back, a model 'dope' paint worked too.

 

Any comments on what I should/could do to keep water away from MDF and thin woods?

 

 

 

 

[Ian_Grant]

The custom for RC is to use thinned epoxy resin on the inside. You'll need to fiberglass planking on the outside with light cloth and resin.

 

[David W]

15 minutes ago, Ian_Grant said:

The custom for RC is to use thinned epoxy resin on the inside. You'll need to fiberglass planking on the outside with light cloth and resin.

 

Thanks -

I considered using 'glass already but will not be using it for this model. I want to maintain the visual planked look of an early 1900s Scottish fishing boat.exterior along with keeping the weight down a bit. Most of its life will be on static display. I will reconsider using a thinned resin on the inside and keel instead of spar varnish plus an overall thinned resin exterior coat before final color painting.

[Ian_Grant]

Having said that, I don't know what to thin epoxy resin with. 😄

 

Could you clue me in? Thanks.

[David W]

51 minutes ago, Ian_Grant said:

Having said that, I don't know what to thin epoxy resin with. 😄

 

Could you clue me in? Thanks.

Usually there is a suggested chemical on the container but I have usually used a good grade of acetone, not the low end stuff sold in a big box store, when working on fiberglass components on after market car bodies. A few drops at a time usually works up to your desired consistency.

 

Since our last discussion, I've spent a good part f the morning looking at different resins and what keeps coming up is ZAP Finishing resin. That's a "sanding" resin and can be painted. Of course the world seems to be out of stock of any but a 4oz size until mid Jan 2023...

[Roger Pellett]

I know virtually nothing about RC models but I do have experience working with Epoxy.  Epoxy can be tricky to use.  It must be mixed in accordance with the specific resin/hardness ratios specified by the manufacturer.  Different manufacturers use vastly different mixing ratios.  If you add hardener beyond the specified ratio to “speed things up,” the mix will not cure, and you’ll wind up with a sticky mess.  Since chemical formulations between brands vary,  under no circumstances would I suggest trying to thin the resin.  Use it as it comes from the can!

 

Epoxy cures with an Exothermic reaction- it gives off heat.  A large batch can get quite hot.  A thinner can effect this too in an unpredictable way.

 

Like most other things, you get what you pay for.  The marine brands; West, System Three, etc IMHO are worth spending money on compared to the hardware store bands.  West System requires a 5:1 resin to hardener ratio that can be hard to measure correctly.  West System sells calibrated pumps that are foolproof or you can weigh out the materials with a scale.  Other brands, such as I believe System Three feature an easier 1:1 ratio.

 

Epoxies now are available in a bewildering array, all with different specialized features.  You can surely find a low viscosity one.  OR. At least one high quality brand- West System is “modular.”  The basic Resin/hardener mix results in a thin mix; about like maple syrup.  West then sells different additives that allow the mix to be thickened to the consistency of peanut butter.

 

It’s your model to finish as you see fit, but working with Epoxy you have one and only one chance to get things right.  Once you have coated your model, the outcome is in the hands of the Epoxy Gods.  If the mix does not cure, you will wind up with a difficult if not impossible to remove sticky mess.

 

Roger

[Jaager]

5 hours ago, David W said:

besides the bulkheads being MDF, the keel was as well

OK,  if you have not started, go back to this initial step it replace these components with something that is waterproof.  I would skip any plywood replacement and go straight to hardwood.

For the price and ease of cutting Yellow Poplar is difficult to better.  You can even use thicker material for the molds and center spine.  The outside keel can be a separate timber if the spine is thicker than the actual keel.

 

Valente Lumber in Averill Park looks to have what you would need, and probably can or knows who can do the necessary resawing.  It looks like there is a possible valuable resource there.  There is probably a local woodworkers club in your region and those guys are good at being helpful - especially to a weird duck like a ship model builder.

 

I suspect that Roger's suggestions bear very close attention.

[David W]

45 minutes ago, Roger Pellett said:

I know virtually nothing about RC models but I do have experience working with Epoxy. 

 

Roger

Thanks Roger. I have looked at the West epoxies as well as theZAP products and haven't purchased anything yet. My experience is with fiberglass car bodies and have leaned a few lessons but am for sure NOT any kind of expert. I'll at least use the ZAP on the inside and see what happens since it will be out of sight

12 minutes ago, Jaager said:

OK,  if you have not started, go back to this initial step it replace these components with something that is waterproof.  I would skip any plywood replacement and go straight to hardwood.

 

Jaager - even closer is Curtis Lumber at ~5 miles away vs 30+ to Averill Park and they handle many sizes of poplar along with many exotic woods. As to pulling this model apart - can't be done at this point and remanufacturing bulkheads and a keel from Amati's drawings would require a scroll saw which at this point, don't have nor do I have room for without giving up other tools that are regularly used. It could happen but not yet. Thanks for that tip about another kinda local wood source as they have an interesting web site

[Jaager]

16 minutes ago, David W said:

remanufacturing bulkheads and a keel from Amati's drawings would require a scroll saw which at this point, don't have nor do I have room for

A good quality hand fret or coping saw with one of those gangplank "V" opening base would not take up much room.  For the first time, the slow and up close and personal aspect is fun.  

I prefer using my 9" bench top bandsaw for scroll cutting.  With the Carter products blade guide, it will twist and turn as much as I need.  Eats thru 1/4" Hard Maple quickly - just as long as I keep small scrap from jamming the blade.  The blades have too much set to get more than sorta close to the line.  My purpose built scroll saw is junk and the up-down chatter was too irritating. 

 

Backing up and redoing - it allows you the opportunity to see just how close full on scratch building is.  Doing the step into scratch opens up a magnitude larger world of possibilities.  The intimidating virtuoso projects in our scratch forum are the exceptions.  They are way more complex than it needs to be.  I wonder if Jean Boudriot had any idea what he was unleashing with the publication of his 74 gun series?

[Ian_Grant]

I've used West System to build a cedar strip canoe and repair my fiberglass dinghy. I love the stuff and the results. The resin is a constant but you can buy hardeners with various cure times, and also cellulose filler to thicken it up.

 

I've never thinned it; the reason I mentioned it is I've seen several mentions in RC forums of painting the inside of a hull with "thinned epoxy" hence my question. I will need to waterproof my current RC build (first in 40 years), when I get to that point, and I thought "thinning" might reduce the coating's thickness and hence added weight, which is a concern.

 

Here is what West System has to say about thinning their epoxy:

 

https://www.westsystem.com.au/wp-content/uploads/2019/07/thinning_epoxy.pdf

[David W]

Ahhhh, scratch building!!!! I'm just getting back into modeling after many years of doing other things. I'm not ready  - yet and why I'm doing the Amati Fifie instead of something like a multi masted 1700s ship. Gotta crawl then walk before I run a marathon. But, with that said, I do have the Amati full size drawings and there are many others available. It may happen someday in the future as I get comfortable again doing models

 

Speaking of band saws - my little one had to go off to a new owner when we moved to this (very) much smaller house with no space for a real workshop after having over 750 square feet of shop and an oversized 2 car garage.

[Ian_Grant]

I take it you looked at my log. 😄  I'd love to have a big shop, mine in the basement is about 15ft x 16ft. If my dad could see the mess in it right now he'd have a fit.

 

I debated doing an RC galley or a square rigger; I thought the galley would be an engineering challenge but tedious to sail after a while, while a square rigger would be easier to build (many plans available) but a constant challenge to sail (multiple sail winch servos). For better or worse I opted for the galley this time but I would still like to do a full rigger if not a 4-masted barque. I have the catalogue of Harold Underhill's sailing ship plans.

 

Happy modeling!

[David W]

I haven't found your log yet- I'm still a newbie here and floundering through a few folks postings/threads each day.

 

I do have a little space (~6'x12') in the UNHEATED garage and my 'man cave' in a loft in this tiny house we have moved to for my wife's destroyed back. That man cave has at present only a 27x54 inch table to work on and a floor for my modeling tools and odds and ends. It is what it is and wont get better anytime ever.

 

I did take a look at that West info. Good information. When I said thinning epoxy, that was only to lower the viscosity a little bit for flow into tight spaces, not for wood penetration as West alludes to in their paper. My original comment was to only add a few drops of acetone, probably less then one percent. Strength - wont matter interior wise nor will color though that has never been a problem for me in  the past. Exterior - that ZAP paintable finishing epoxy really sounds good and may not need thinning. You apply, sand, prime (I have 2 unopened quarts of epoxy auto primer) then paint the desired color

 

 

[Ian_Grant]

Sorry, I thought you had seen my log as there was recent mention of a bandsaw in it.

[Bob Cleek]

17 hours ago, Ian_Grant said:

Having said that, I don't know what to thin epoxy resin with. 😄

 

Could you clue me in? Thanks.

I have used a lot of epoxies over the years and, as others here before me, would not advise thinning epoxy. They aren't all the same, chemically speaking, and you've got to carefully experiment when deviating from the manufacturer's directions. There's nothing worse than a partially-cured coat of epoxy resin.

 

For the application described here (i.e. we're not talking about epoxy and glass cloth sheathing,) I would suggest using a product called Smith's Clear Penetrating Epoxy Sealer, also known in the trade as "CPES." . This an epoxy sealer, not an epoxy adhesive base as are the products mentioned here above. This is an epoxy sealer carried in a volatile solvent. It mixes easily with a 1:1 ratio of "Part A" and "Part B" and is sold in kits as small as a quart of each part. It's not cheap, but has a long shelf life. A (2 part) "quart kit" would serve to coat many models inside and out. It has the consistency of water and penetrates the wood surface easily. It soaks in and does not build up on the surface. It has some flexibility to it when cured which resists cracking when the wood expands and contracts. (No epoxy resin is moisture proof, actually.) It cleans up easily before curing with acetone or vinegar. Oil based or acrylic paint and varnish may be applied over it. It sands reasonably well. It can be purchased at most chandleries or from the manufacturer. Clear Penetrating Epoxy Sealer (smithandcompany.org) (It's also repackaged at a higher price by "the Rot Doctor." CPES™ - The Rot Doctor )

 

Or... you can also consider applying a generous coat of thin shellac ("two pound cut" out of the can.) Shellac is probably one of the most effective moisture barriers that exists. It's also completely safe to use and is thinned with alcohol. ( It's safe enough to eat. "Food grade" shellac is used to impart a shine to apples and jelly beans.) Shellac also soaks into the wood well and does not obscure detail so long as you don't put too many coats on. I dries very quickly and any paint or varnish can be applied over it without any problems. It's also a lot less expensive than epoxy of any type.

[Ian_Grant]

Thanks Bob for this recommendation. CPES sounds ideal for my RC project; I was dreading the race to coat the inside before setting starts, and also trying to keep the coat thin and light.

[David W]

Smith's is interesting but my oh my it is pricey on AMAZON for the 2 quart size. The 2 pint size is available elsewhere for about half the price.  As a note, AMAZON also lists other similar products as well as rot repair

[Bob Cleek]

6 hours ago, David W said:

Smith's is interesting but my oh my it is pricey on AMAZON for the 2 quart size. The 2 pint size is available elsewhere for about half the price.  As a note, AMAZON also lists other similar products as well as rot repair

The two-pint kit from Smith's directly is $68.00. Yes, that may be costly, but you get what you pay for. For a much less expensive sealer at $21 a quart, shellac works very well. Zinsser Bulls Eye Clear Alcohol-Based Shellac (1-Quart) in the Sealers department at Lowes.com

 

Others sell "thinned" epoxy for "rot repair" products, but Smith's CPES(tm) was the first and claims to have a unique recipe. It's been around for almost fifty years now and it seems yet to have been equaled by imitators.

[Roger Pellett]

I haven’t bought any for a long time but I suspect that West System Resin, Hardener, and pumps would cost about $60-70 too.

 

Just checked- 1qt West Sysrem 105 Resin, 7oz 205 hardener, and a pair of pumps:  $86.60 on Amazon.

Edited December 19, 2022 by Roger Pellett

[Dr PR]

I have used several types of epoxy for decades and have never had a curing problem because I am meticulous about getting the mixture exactly as the manufacturer recommends.

 

I have used a thin two part epoxy "paint" that model airplane builders use to seal the wood on motor mounts so fuel cannot soak into it. It has the consistency of house paint (thicker than water but thinner than honey. I seal the interior of planked hulls with it. It penetrates into the wood, between individual planks, and between planks and bulkheads. This prevents cracks from appearing between planks years after the model was built. It makes a very solid hull!

 

You can also find epoxy paints. We used them in the magazines on a ship I was on. They are similar to the epoxy sealer mentioned above.

 

I also advise caution about thinning epoxies. The mixture ratio is critical for a good cure. Rather than try to thin a thick epoxy it would be much better to get the epoxy sealer or the model airplane epoxy.

[Bob Cleek]

5 hours ago, Dr PR said:

I have used several types of epoxy for decades and have never had a curing problem because I am meticulous about getting the mixture exactly as the manufacturer recommends.

 

To this sage advice I would add that the tolerances operative in working with epoxy, i.e. the proportion of resin to hardener and temperature and humidity, become increasingly critical as the amount of epoxy mixed gets smaller. With the relatively small amounts of epoxy generally mixed for modeling purposes, the amount of tolerable error becomes smaller as the amount mixed becomes smaller. Measuring small batches has less margin of error. Additionally, the use of measuring pumps is advised, but a single stroke of the pumps, the minimum amount measured by the pump is more than is often needed, which contributes to the waste of an expensive material. For mixing "dime sized" or "quarter sized" amounts of epoxy for modeling purposes, one would be well advised to use graduated hypodermic syringes or a suitably sensitive scale. 

[Roger Pellett]

My current modeling project requires extensive fabrication of sheet brass. Where possible, I prefer soldered joints but there are cases where this doesn’t work; wood/brass joints or joints where soldering would damage other soldered joints.  In these cases I use Epoxy, usually in the dime to quarter amounts that Bob mentions.  I would not try to mix these using tiny quantities using the Epoxies that we have been discussing.  Instead, I use the Epoxies that come in tubes.  My favorite is J.B. Weld Original Formula.  I have found that with these formulations, the eyeball is able to judge the 1:1 proportions accurately enough to get a mix that cures with adequate adhesive strength.  Since stress is force/area I wouldn’t use Epoxy to join very small parts such as those made from wire.  I would solder these.

 

Roger