HMD 21 starting - help

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TomW1
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Re: HMD 21 starting - help

Post by TomW1 »

You really need two fairing boards, one stiff for the flat areas and one flexible for the rounded areas. Like Evan said I used black spray paint but I shook the can back and forth as I was spraying it and got dots and not a solid coat. I used a fast drying Krylon brand available from Lowes. It dried in about 30 minutes so I could get right to work sanding.

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duysall83
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Re: HMD 21 starting - help

Post by duysall83 »

Evan_Gatehouse wrote: Tue Mar 02, 2021 4:28 pm I use cheap black spray paint. Shows the highs and lows easily.

Sand off drips. You will use a LOT of fairing compound to cover them if you try that.

Use 60 or 80 grit sandpaper (quite coarse) for initial fairing.

Use a long board (~30" / 800mm or so) with long sandpaper glued or stapled to the ends for fairing. You can't fair with a small sander. You can make things SMOOTH but smooth is not fair.

Got it. Thx Evan, we'll see what i can.

duysall83
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Re: HMD 21 starting - help

Post by duysall83 »

Hello Evan, Dan and everyone, started to sand/grind the drips. Actually mostly grind the drips because neither sander nor hand sanding removes them. Tiring job but i see that surface becomes smoother. I have a question;

As you see i remove the Primer and the initial epoxy coat from months ago mostly during sand/grinding and reach the raw okume often. So when i finish first sanding should i apply epoxy resin once more to the hull before the primer? By the way primer i use is also epoxy based.

Or i can directly apply primer (1-2 coats) and fairing compund next. Then use the long boards to locate highs/lows?

Preparing sanding boards on the other hand.

Another question. You know i build the boat outdoor but in a simple shelter. I had not epoxy coated the internal surfaces of hull parts. No rain directly over the boat but i guess humidity changes even within day. Is it a major problem in terms of moistire absorbtion?

Thank you all in advance.

Duysal
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fallguy1000
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Re: HMD 21 starting - help

Post by fallguy1000 »

Really, it is up to you. Epoxy neat coats are thicker than primer.

If you want to get the boat a little more fair, you can neat coat it. I read somewhere that epoxy coats are about 4 times thicker than typical paints, so you can use neat coating if you think it can help. I looked for a source to cite, but came up with nothing. We did three build coats on my brother's Windward 15 and they really made the deck look perfect, but that was for bright finishing.

There is a downside risk that your neatcoats run on your steep verticals, so you'll need to make them very smooth and with great care if you choose to do so. Another downside is raw epoxy is a bit of a bear to sand, which is why we use compounds.

Another thing for you is the boat is really dofficult to see at this point whether it is fair or not. This will not be helped by neat coating.

I personally would prime it, see how it looks. Run your hands up and down the sides with your eyes closed and feel for waviness. Personally, I would not neat coat. Hope I laid out my rationale.

The only way I would consider neat coating is if the hull were only plywood and not sheathed in glass.
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duysall83
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Re: HMD 21 starting - help

Post by duysall83 »

fallguy1000 wrote: Fri Mar 05, 2021 8:41 am Really, it is up to you. Epoxy neat coats are thicker than primer.

If you want to get the boat a little more fair, you can neat coat it. I read somewhere that epoxy coats are about 4 times thicker than typical paints, so you can use neat coating if you think it can help. I looked for a source to cite, but came up with nothing. We did three build coats on my brother's Windward 15 and they really made the deck look perfect, but that was for bright finishing.

There is a downside risk that your neatcoats run on your steep verticals, so you'll need to make them very smooth and with great care if you choose to do so. Another downside is raw epoxy is a bit of a bear to sand, which is why we use compounds.

Another thing for you is the boat is really dofficult to see at this point whether it is fair or not. This will not be helped by neat coating.

I personally would prime it, see how it looks. Run your hands up and down the sides with your eyes closed and feel for waviness. Personally, I would not neat coat. Hope I laid out my rationale.

The only way I would consider neat coating is if the hull were only plywood and not sheathed in glass.
Hello Dan,

If its up to me i dont coat epoxy :) hull is glassed till 20 cm above chine as on the plans. So my concern is all after the end of glass to side upper edge. Would the primer replace what neat epoxy would do for encapsulation of wood?

fallguy1000
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Re: HMD 21 starting - help

Post by fallguy1000 »

Ahh, I see...

Personally, there has been a lot of people posting with paint and finish problems on any wood that is not sheathed in glass. A lot depends on paint color plan.

A dark paint, I would sheath it with at least four ounce, but even down to 1.5 oz cloth would work.

A lighter paint, I think you can get away without sheathing. Some of this depends on where use is planned. If you are in a hot place, I would sheath it all paints.

There is some risk of me making the designer mad here, but I personally would sheath it with a light woven; a couple follow on layers of no sand neat coats over the glass plus a foot up, 8" up, 4" up until the weave vanishes; then sand the neat coats and fair the joint with a fairing board.

I would not be too worried about your plywood getting too damp. A lot depends on climate. It can happen, but you would need to be running ambient rh around 90- 100% all the time. As long as your wood is below 15% moisture; which is really quite high; you'll be okay. I would guess you are at 12, but not fully sure other than your are somewhere in Turkey.
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duysall83
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Re: HMD 21 starting - help

Post by duysall83 »

I'm close to İstanbul. Not crazy humidity here, at least compare to how i feel in Jakarta :) i learned not to complain about humidity after been there many times.

Dan i dont plan to glass above chine. Actually i worry if any structural problem occur if i dont renew the neat epoxy before primer.

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Re: HMD 21 starting - help

Post by Cowbro »

I might be one of the ones Dan was referring to about fighting paint/plywood issues for non-glassed plywood. And yeah, if i was at your stage in the build with the boat still upside down, i would put some 4-6oz glass on the sides for protection/longevity.

You mention that you sanded through to the plywood in some locations, I would definitely re-coat those in epoxy before continuing. I don't know if you need to spot repair or coat the entire hull, but i would not put primer over the bare wood.

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Re: HMD 21 starting - help

Post by fallguy1000 »

duysall83 wrote: Fri Mar 05, 2021 10:16 am I'm close to İstanbul. Not crazy humidity here, at least compare to how i feel in Jakarta :) i learned not to complain about humidity after been there many times.

Dan i dont plan to glass above chine. Actually i worry if any structural problem occur if i dont renew the neat epoxy before primer.
Well, you asked me. I gave my opinion.

Both Matt Gent and Cowbro are having issues with unsheathed ply. It is basically a week's work for insurance against paint issues later.

Any epoxy coating is NOT considered structural. If you sanded through glass below waterlines; those must be repaired with glass and epoxy.

Good luck. The boat looks like it is coming along nicely.

Fairing is a pain.

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duysall83
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Re: HMD 21 starting - help

Post by duysall83 »

Thank you both,

Either glass or epoxy coat then. Good that i asked before continuing with primer as it is straight forward :)

Name is Duysal.

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