Why did mildew grow on this particular block?

[jalmberg]

I built this block this spring. It's my first one and I learnt a valuable lesson in basic joinery: don't glue end grain. As you can see, the end grain glue joint failed, although the strop kept the block together so it didn't explode under tension.

My real question is, why did mildew grow on this block? The wood is maple, and I gave it the linseed oil bath treatment frequently mentioned on this forum.

I had it shackled to the deck of my boat as a sheet block. It was exposed to the elements all summer long, but didn't sit in a puddle of water, or anything like that.

It looked fine for most of the summer, but in August we had the usual hot weather with no wind, I was working long hours, and the boat didn't get any use for a few weeks.

By the end of August, I had a nice crop of mildew.

The odd thing is, I built three other blocks out of white oak, with the grain in the right direction for gluing. Not only did these blocks not suffer glue joint failure (no surprise there), but they did not get mildewed. They had the same linseed oil treatment.

Is maple particularly susceptible to mildew?
http://photos.identry.com/blog/mk3block1.png

[jalmberg]

Here's a picture of one of the oak blocks that did not get mildewed. In fact, it looks pretty much the same as before I installed it on the boat this summer.

http://photos.identry.com/blog/oak_block_med.jpg

Same rope for strop.

I have another oak block that is still shackled to the deck. It has no mildew at all. Really strange...

Would varnish be a better finish?

[David G]

Not strange at all. Maple is an inappropriate species for this task. Way too much food within to feed the growth of critters - as you foto clearly illustrates. Lots of species available that won't have that problem: teak; mahogany; black locust; cherry; walnut; white oak; sapele; khaya; etc.

[jalmberg]

That was my guess, but I was hoping someone with more experience could confirm.

Yet another lesson learned... there are so darned many of them. |:)

Thanks!

[jalmberg]

I just blogged about this lesson and gave you credit for the answer, David. Thanks a lot.

http://www.unlikelyboatbuilder.com/2012/01/mark-iii-block-update.html

[Jefe]

Not strange at all. Maple is an inappropriate species for this task. Way too much food within to feed the growth of critters - as you foto clearly illustrates. Lots of species available that won't have that problem: teak; mahogany; black locust; cherry; walnut; white oak; sapele; khaya; etc.


So why is Maple so good for cutting boards?
(sorry for thread drift)

[David G]

Maple is good for cutting boards because it's closed-grain. Doesn't absorb food juices & odors. It also tends to retard bacterial growth. At the same time, it's not good to live outdoors, because its high sugar content tends to feed fungal growth - as illustrated by this block.

[James McMullen]

In general, it seems like the paler species of wood like maple or spruce or ash or pine tend to be less durable and more rot prone than the darker colored species like oak or mahogany or fir. The only real exceptions I can think of are white cedar and Port Orford cedar. Extra tannins or absorbed minerals or something in the darker stuff? Don't know exactly why, but it seems like a good rule of thumb.

[Ron Williamson]

Not such a great rule,really.
Hickory and ash(green and black),ironwood and soft maple(not very soft,BTW) have dark heartwood, and yellow poplar is all over the place from very light to black.
Eastern white cedar heartwood isn't much different from the lightest red cedar heartwood.
IIRC the piece of Sitka that's in The GarageMahal is darker than white cedar.

I totally forgot about elm,birch and red oak having dark heart and being crap.
R

[James McMullen]

Ron, I think you're somewhat missing my point. Besides, only ash out of that top list is a boat timber, and that only for lightweight boats like canoes stored out of the weather. "Ironwood"? Not ironbark, surely. What species is called the popular name "ironwood" there in Ontario? I have not heard of it. You also couldn't be wronger about elm unless you're talking about some other subspecies I haven't worked with. Elm steambends quite well and is tougher and more split resistant than white oak. It can be an excellent choice for boat frames, stringers, keel shoes, gunwales. . . I have several hardwood cleats carved from elm that have worn as well and lasted as long as locust ones.

[Canoeyawl]

Is the maple food not covered and protected with linseed oil? Or does the mildew go right through it?

[jalmberg]

Is there any up to date reference book that goes into detail about the various properties of wood, particularly wood used for boats?

I stress up to date, because it doesn't help to read how lignum vitae, for example, is the best thing for blocks if it's all but impossible to buy/afford.

[Canoeyawl]

It is probably not mildew at all, but Stachybotrys chartarum (http://forum.woodenboat.com/wiki/Stachybotrys_chartarum) - The black mold (often called mildew) which lives on sails, shower walls, and other places where moisture levels are high.


wiki (http://en.wikipedia.org/wiki/Mildew)

[richbeck]

Ironwood = Ipe. maybe not technically, but if you call a lumber yard and order Ironwood chances are they will send you Ipe.

[David G]

Is the maple food not covered and protected with linseed oil? Or does the mildew go right through it?

Not... it's not protected by the oil treatment. Way too permeable. OP does not specify raw or boiled linseed oil. If the former... it's also great fungus food.

[jalmberg]

Not... it's not protected by the oil treatment. Way too permeable. OP does not specify raw or boiled linseed oil. If the former... it's also great fungus food.

Boiled.

[jalmberg]

Is there any up to date reference book that goes into detail about the various properties of wood, particularly wood used for boats?

I stress up to date, because it doesn't help to read how lignum vitae, for example, is the best thing for blocks if it's all but impossible to buy/afford.

My own question got me thinking and I started searching for resources and 'discovered' that Wooden Boat mag has a regular column written by Richard Jagels, professor of forest biology at the University of ME.

I've been reading WB of years, and I must confess I never noticed this column. Must go back and read them all.

[Canoeyawl]

Not... it's not protected by the oil treatment. Way too permeable. OP does not specify raw or boiled linseed oil. If the former... it's also great fungus food.

Hmmm... What's the point of using it at all I wonder?

[Peerie Maa]

I'm not going to start an argument about species names again, but. In the UK ash and elm are the traditional materials for block making, elm being the most favoured due to its interlocking grain. Oak is durable but inclined to split. If you were looking at the yachtie end of the market teak would be used, but not manogamy as it is less durable.

[Peerie Maa]

Hmmm... What's the point of using it at all I wonder?
Its good for wood, improves the colour, but it must be varnished or it will blacken in time.

[Ron Williamson]

James
I've obviously missed your point,but in my own defense,maple,where we started, ain't boat wood neither,but there it is.
According to my reading and experience,elm may be a great and tough wood,like ash and hickory,but it isn't durable,ie rot resistant.
What we call ironwood is eastern Hophornbeam,(Carpineaus Virginiana or something).
Bluenose II is built from birch and red oak,IIRC.Bad choice.

In a few years,a noobie or two will find this in a search and figure that since he has something dark coloured in his firewood pile, he can build an heirloom boat out of it.
I'm just trying to provide some counter-balance for future generations.Social responsibility and all that.:D

[Peerie Maa]

According to my reading and experience,elm may be a great and tough wood,like ash and hickory,but it isn't durable,ie rot resistant.

How rot resistant do you need for a block? I have blocks and dead eyes in my shed that are 100 yo and still as good as new. Elm is durable if it is kept wet (keels and bottom planking) or dry (blocks and row boats kept ashore). It will rot if it cycles between wet and dry, or where a component spans both wet and dry locations, like a stern post.

[oakman]

Just a note about linseed oils, they are not all created equal. If you purchased you linseed form the local hardware store, raw or boiled, over time it will go black with mold.

For boat purposes you need to purchase cleaned linseed oil, one that has had the proteins removed. I source mine here: www.solventfreepaint.com

I finished the exterior woodwork of a restaurant in NYC that was fabricated out of antique pine with this oil about 6 years ago. The only problems showing are at the bottom of the wood work since the installers did not heed my advice and seal the back of the molding and install with bedding. No blackening at all.

Check out the photo: 5morandi.jpg (http://images.nymag.com/listings/restaurant/5morandi.jpg)

O

[James McMullen]

Ron, I see your point now and concur that my own point was perhaps too vague. I have had decent enough luck with elm myself though. My sources list elm heartwood as "moderately durable" which puts it in the same category as mahogany or D. Fir. Perhaps it depends on whether the elm lumber you use was killed by Dutch Elm Disease or harvested live whether or not it is more decay resistant.

Cheers! :)

[Canoeyawl]

There are Elm trees standing in Maine that were dead twenty years ago. They still have twigs on them and look like they will have leaves in the spring. Of course we know better, and I truly miss the lovely elms that turned every street in New England into a sort of cathedral.
There is an Elm stump next to our house that was cut in 1958 and it was a "bump" in the greensward for about fourty years. In fact it didn't disappear until the town put in a sewer system and had to go through it. In my experience Elm is very rot resistant and a "moderately durable" rating seems conservative.
Now for a Durable rating, there are Chestnut logs down at the shore that were cribbing and ways for ships built over a century ago. The tide has come in and out over them for a hundred years and they still look pretty good.
I should be clear that I am talking about American Elm, which is basically extinct.