checking prevention

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CaseyS
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checking prevention

Post by CaseyS »

I think I've read it here 4 oz cloth will keep any ply from checking. Am I correct?



ks8
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Re: checking prevention

Post by ks8 »

Worked for me. Also used 6 oz in some places. None of the 4 oz areas have broken open in around five years. If there are checks already, squeege in some wood flour blend to stabilize it before the cloth goes on. I've learned to do this wet on wet and save a couple steps. Best solution, of course, is wood that doesn't check, but I built the first one this way to learn the worst case and gain the best tips for others from experience. Compared to the work cost... good wood is cheaper. :lol: But I hope to enjoy this boat until one of us leaves here. Hope you enjoy the build and launch as well. :)

Careful when sanding the 4 oz. It's too easy to break through. Until my laminating skills improved, I had some slight pooling under the glass, and bumps at the pooling, where the glass was then cut through when sanding those high mounds. Mostly dime size, some quarter, but not even a dozen total on the seat tops. Still, no checking. The remaining glass is holding it all stable. All the same, careful sanding it. :)

cottontop
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Re: checking prevention

Post by cottontop »

Casey is correct. I used either 4 or 6 ounce. It is still holding up well after 5 years. John

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PAR
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Re: checking prevention

Post by PAR »

A light sheath on anything other then Douglas fir will prevent checking. I've seen checking under 6 oz. cloth with Douglas fir, so you should consider 8 oz. as the minimum, to insure surface veneer stabilization on this species.

ks8
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Re: checking prevention

Post by ks8 »

PAR wrote:A light sheath on anything other then Douglas fir will prevent checking. I've seen checking under 6 oz. cloth with Douglas fir, so you should consider 8 oz. as the minimum, to insure surface veneer stabilization on this species.
Did the checking happen after the glassing with 6 oz, breaking the glass, delaminating, or, did you *see* checking under the glass (meaning someone may have glassed over the checking without properly filling the checks). I had some checking of my Doug fir before I glassed, but then gooed up the cracks and glassed over it and had no worries for a few years (while it was still unpainted). Glass is intact after painting several more years as well, 4 oz and 6oz sections. If you saw checking crack 4 or 6oz glass, I will update my recommendations. There is that nagging question of whether it glassed well (fill the checks properly), and was it dimensional DF or plywood? I appreciate your vast experience PAR. :)

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PAR
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Re: checking prevention

Post by PAR »

Yes, checking under the sheathing after cure. I've seen it on both painted surfaces and brightly finished. I suspect Douglas fir could also check under 8 ounce if the veneer is thick enough, but in most small boats, using reasonable quality plywood, the veneers should be thin enough to lock down with 8 ounce. The hybrids now being called Douglas fir are mostly plantation grown stock. These sub species (how they get away calling it Douglas fir, I don't know) hybrids are very fast growing and as a result set up huge internal stresses within each log. When eventually harvested, these stresses are partly released when cut into dimensional stock, but some remain, which cause warps, twists, splits and checks. As rotary peeled stock for plywood the tremendous difference between winter and summer growth wood in each veneer tends to cause them to check badly. Much more so then old growth or even some of the older replacement second growth. It's this very difference between winter and summer growth density that also causes Douglas fit to "washboard" when you try to sand it.

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Re: checking prevention

Post by Spokaloo »

Keep an eye on who made your Doug Fir, as there are places that make good quality stuff from naturally grown wood, and others that are doing the plantation thing or forcing DF to grow in places it doesn't naturally occur.

Look for these stamps on fir ply:

Hood Lumber

Roseburg

Boise Cascade

I wouldn't trust anything from LP (louisiana pacific) as they try to cheat here and there with the fir species as described above.

E

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Re: checking prevention

Post by ks8 »

I've got Roseburg and so far its good under the glass. All the same, good info for the future. Thank you PAR and E. :)

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