Blotchy Hull Advice

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Johnny_Boy
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Joined: Sat Oct 10, 2009 10:53 am

Blotchy Hull Advice

Post by Johnny_Boy »

canoe.jpg
I was hoping to get some advice on my canoe build. I bought Canoecraft a few years ago and have been slowly but surely building a Bob's Special. I couldn't get clean cedar locally so I used redwood. Last night after sanding the hull with 80 grit using the random orbital sander I got the hull wet to raise the grain. The book mentions that we do this to decompress the fibers so we can sand them off and this helps with dark spots because now they won't soak up the epoxy at different rates. I was pretty surprised however in that my hull looked really blotchy. I don't think this is what Ted had in mind. My question is if there is something I can do besides painting the boat to reduce this blotchy effect. I would also like your opinion on what might have caused this. I didn't think redwood was a blotchy wood so I was thinking the ROS caused this effect. Should I stain it or will this just look like a blotchy stain job too? I need some kind of wood conditioner but don't know what works with epoxy. Please help.
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Rod Tait

Re: Blotchy Hull Advice

Post by Rod Tait »

It is hard to tell from your photo whether it is the wood or the sanding. It is wood after all and has variations in grain, colour and whether the grain is open to soak up more liquid or not.

If you have sanded the boat several times, wetted down and then sanded again, I think that it is what it is. Different colours in the wood. It is what gives your boat character.

I will usually sand 80 grit followed by 120. Then wet down, sand again with either 80 if needed and 120 again, wet down and look for obvious scratches or marks. Sand 120, wet down again. Once I am happy that there are no marks with water, I finish up with 120 and then glass.
BearLeeAlive
Posts: 196
Joined: Tue Aug 18, 2009 7:00 pm

Re: Blotchy Hull Advice

Post by BearLeeAlive »

I really don't think it is the sanding at all, as it is limited to segments of the individual strips, and does not encompass any adjoining strips. If the hull was wet when this photo was taken, I would chalk it up to the porosity of softwoods, or more accurately that these woods typically do not absorb evenly. Staining softwoods. especially with a water based stain, will produce a very similar appearance, one that is often corrected by using a pre-stain.

Does the wood maintain this appearance once it has dried out, and the raised grain removed? If so, I doubt that using a clear epoxy finish would bring out the same degree of blotchiness. Even if it did show some, I would look at is as character, as Rod suggested.
-JIM-
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HighPlainsDrifter
Posts: 77
Joined: Tue Mar 22, 2011 9:30 pm
Location: Brookings, SD USA

Re: Blotchy Hull Advice

Post by HighPlainsDrifter »

I see a pattern that looks like waves and to me it looks like a sanding problem.

Enlarge the picture, lean back from the computer screen (best for my eyes) and look at the first 6 dark planks, left side, and just under the light colored planks.

The wave looks like it crosses the grain of the planks and generally goes fore and aft.

Now the question. Could you have run the RO rapidly up and down those planks while moving fore and aft?
Johnny_Boy
Posts: 2
Joined: Sat Oct 10, 2009 10:53 am

Re: Blotchy Hull Advice

Post by Johnny_Boy »

Thanks for your responses. HighPlainsDrifter - I was using the RO sander up and down while moving fore and aft and I could see some of that pattern, before and after wetting the hull, so I think I have some of that effect going on. BearLeeAlive - I also think I have some of the individual strips soaking up the water differently so I probably have two effects going on. Yesterday when it was dry I sanded horizontally with no vertical first with 100 grit and then 150, a fair amount a material was removed. The attached photo is after sanding and you can kind of see a little of the same pattern so I think it is there to stay. Rod Tait - I did sand it down good then wet and sanded again last night so I think I got a little character going on. I did notice in Canoecraft last night after the fiber glassing section that the last item on the troubleshooting list was blotchy spots and Ted's recommendation was more sanding. So if I get a wild hair tonight I could wet it again and put the sand paper to it tomorrow to see if it improves, however, i think I just got some of that good old fashion character going on. Hopefully the horizontal sanding last night removed any tiger striping effect. Thanks everyone for the input.
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Denis
Posts: 313
Joined: Tue May 11, 2004 8:11 am
Location: Lakefield, Ontario

Re: Blotchy Hull Advice

Post by Denis »

If you still have time and access to a 1/2 sheet or 1/3 sheet flat sander perhaps dampen hull again and sand with 180. I find the final sanding with 180 gives a cleaner look after it is glassed. It seems to my eye anyway finishing with 120 (which is where i usually stop ) leaves it a bit muddy looking to my eye.

Anyways good luck with it and I would suggest living with it for awhile with varnish before deciding to paint it. No one but you will notice any flaws

:laughing

Denis
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