Thread: Sealing synthetic waterstones

TLDR: I'm thinking about coating various waterstones in spar urethane. In some cases to protect the stones long-term, and in other cases in an attempt to diminish their water consumption in use. Thoughts are welcome.

After acquiring a few low- and mid-range (400, 1000, 3000) Naniwa Chosera stones -- which have indeed been very nice so far -- I have been holding off on the higher grits because of accounts of cracking, crazing and crumbling I've seen around. That is, I had been holding off on the higher grits... until I found a sweet deal on an 8k Snow White which I couldn't resist. Which leads me to the question of sealing synthetic waterstones to protect them from long-term damage.

I have seen both cashew lacquer and epoxy recommended here and there for sealing; but both of those would be more -- expense and trouble -- than I really want to spend on this endeavor. So, at least for the time being, I plan on using some spar urethane which I have and am experimenting with already -- mainly because it was available and quite cheap. And I'll use it up for outdoor wood projects either way...

To start with, I am sealing 5 sides of a Naniwa dressing stone (the kind included with the Choseras) to see how it behaves, and how it holds up to prolonged exposure to water. If that works out well after curing, I am thinking about sealing up a King Deluxe 1000 which I think could benefit from being less thirsty, despite the fact that I already permasoak it. Same goes for a 220 grit "Pink Brick" I recently acquired and is a thirsty beast. I figure that whatever exposure to water the splash-&-go Choseras get would be light-duty compared to the soakers, so the King and company should be a decent test to see how the urethane holds up.

Beyond wondering about how the sealant will perform with water, I am also concerned about how the oil-based spar urethane might react with the magnesia-based Naniwas. I believe both the Naniwa dressing stone and the King Deluxe are clay binders which should be quite resilient to being exposed to sundry substances -- not sure about Pinky, though. On the other hand, the magnesia-bound Naniwas seem to demand kid gloves for small things like soaking and drying; so coating them in oil-based sealant is of some concern.

Any thoughts about this last point would be most welcome, although input of any sort could prove helpful.

I see no benefit to sealing synthetics and it might cause damage due to differing rates of expansion and contraction during wetting and drying. This is strictly speculation on my part as I've never tried it.

One of the main selling points of spar urethane is it's ability of expand and contract with temperature changes when used in its intended role as an outside wood finish. I am hence hopeful that this aspect shouldn't pose issue.

Setting aside the non magnesia-binder stones I mentioned in my post, the main objective of this endeavor is to have the Snow White only absorb water from the work surface on top. It has been my observation that when sharpening on my 1k Chosera, water gets everywhere, top, sides and around the base on the stand; and then when I slowly dry it, it dries somewhat unevenly. I dry it and the 3000 upside down to avoid having water linger around the base and soak the stone longer than necessary, and the water that soaks in during the sharpening slowly percolates out through the top.

I feel that this could be improved upon if I can seal all the non-working sides of the stones: then water will only absorb into the surface which I am most often going to lap off in due course regardless, and, seing as how it will only enter the stone through the top, when I turn it over for drying presumably the water will drip out from the unsealed top and drying will happen evenly across that face while being prevented from happening quickly from the sides by the sealant.

I am finding that I would have a harder time still justifying my HAD if these somewhat expensive high-grit stones -- which should last me at least a decade, if not more -- start cracking and crazing in a year or two...

I would worry about sealing 5 sides, because water that penetrates into the bottom of the stone would have no easy way out. Then again, maybe that would cause a slower and more even drying process... It will also be interesting to see what it's like honing on top of a pool of water... It will be an interesting experiment.

That was exactly my concern. If water only can enter on the top it will soak into the hone more there than in other areas. Some hones do swell slightly. Having only one point of entry and egress for the water might cause internal stress.

Occam please let us know how it goes if you give it a try.

Originally Posted by holli4pirating

[...] that penetrates into the bottom [...]

heh heh heh.

Originally Posted by Utopian

[...] If water only can enter on the top it will soak into the hone more there than in other areas. Some hones do swell slightly. Having only one point of entry and egress for the water might cause internal stress. [...]

This is a something I've wondered about, yes. That said, I'm already using Choseras which come attached to bases; so by necessity there's always some parts which get wetter than others (heh).

When using them, I just spray the top with a little water, let that soak in for a minute or two to improve the feeling of the hone and then add a little more water as needed. In fact, doing it this way, I notice that the edges of the hone need more water sooner than the middle. These Naniwas aren't very thirsty at all, so I assume that water doesn't soak in very deep, but it does seem to get drawn into the edges more readily.

Which is to say that: (a) I'm already wetting various sections of the stone differently -- particularly if one also considers the deeper parts of the stone which I guess never get any water, assuming no prolonged soaking -- so that differential expansion/contraction is presumably already happening now, and that won't change much if I seal the underside and the sides, I don't think; and (b) given that the edges of the top already dry out a little faster than the middle, I actually imagine that sealing the sides could make the entire top face act more uniformly with regards to water absorption.

But these are just some of my observations based on limited usage, what I hypothesize could explain them, and what I imagine might happen if I apply some sealant to the hones. I'll be sure to post back with results if I go ahead with the more expensive magnesia waterstones.

As far the King stone is concerned, it won't be subjected to repeated wet/dry cycles if all goes to plan, given that it usually just resides in water all the time. I imagine that if I seal it on 5 sides when it's dry, then water will just soak in from the open side, puddle inside it when in use, and just kind of stay there when it goes back in the bucket -- Assuming the urethane holds up to underwater use, which isn't obvious to me at this point.

However, this talk of expansion and contraction of hones in relation to their water content has got me wondering, and I think that I will take a couple of measurements of Kings in both their dry and soaked states, just for fun. It would be more interesting to perform a similar test on a magnesia Naniwa, but I don't want to soak one for any prolonged period of time.

In the meantime, I have a needlessly glossy dressing stone in need of further curing before I try dunking it in water...

I've only ever sealed one synth, though Max at JNS recommends sealing all stones natural or synth. The Shapton Pros appear to be sealed on the sides (and on the back for the old ones and Kuromaku) with something like tile sealer or what the Japanese called 'Hone Coat'.

Once I tried sealing a large Suehiro 1k - basically a King 1k - with lacquer to do what you mentioned, reduce water absorption. It failed miserably. However, it dried out in about the same time, many days lol, so I don't think there's any risk of water staying in a hone that you'd perma-soak anyway.

I definitely wouldn't seal a stone that I perma-soaked, I'd doubt that the coating would stay on over time and I don't understand what you'd accomplish by coating a perma-soaked stone.

Cheers, Steve

Originally Posted by holli4pirating

I would worry about sealing 5 sides, because water that penetrates into the bottom of the stone would have no easy way out. Then again, maybe that would cause a slower and more even drying process... It will also be interesting to see what it's like honing on top of a pool of water... It will be an interesting experiment.

So, a few months later and a few pounds heavier...

I finally felt the need to hone a razor on the permasoaked King Deluxe 1k I sealed in spar urethane last year -- I've used it a few times on knives and sundry things since then, but no razors until today; and I figured I might as well report back with some thoughts:

I'm finding the properties of the sealed King pretty great, actually: It doesn't dry out at all, that means no needing to add more water which sometimes spills over the sides if I add too much, whilst also diluting the slurry even if I'd rather keep it as is.

In fact, slurry is why I felt like grabbing the King today -- I wanted something which would muddy more than the Chosera 800 I was working with, even with the very light pressure I'm using on a supple full hollow grind. The King fit the bill nicely and this way the slurry doesn't dry into thick mud too quickly, or at all in fact, which is how I like it for a razor.

Not drying out on account of the stone being waterlogged and the sealant preventing water egress from the 5 sealed sides also means that for once there isn't a puddle forming under the King. Another nice win.

On the other hand, if someone is in the habit of using the stone's drying out to their advantage, perhaps because they've intergrated the progressively dryer mud into the way they use the stone, they could be frustrated by how wet the surface stays virtually indefinitely -- although I don't find working the mud on a 1k King in this fashion to be useful for razors. Regardless, the slurry's remaining completely wet and not drying to a thicker mud does hamper the stone's tendency to impart a dark hazy finish, based on the few knives and chisels I've experimented with.

Those are the more pertinent observations I can think of with regards to the actual usage of the sealed permasoaked King. That said, there are a few other little nuggets of dubious usefulness I've collected:

The thinner coats of urethane I used on the King 1k worked well compared to the Naniwa dressing stone; that and allowing for roughly double the curing time between coats resolved having parts of the sealant remain soft, absorb water and discolor when submerged for long periods.

Once submerged for a while, the surface texture of the urethane went from smooth to bumpy -- I think it must be tiny bubbles trapped by brushing, which expand with water. I left the stone to dry out once -- it does take much longer to dry out completely now -- and the surface regained it's smoothness. So -- and not that it matters -- but if I did seal Choseras in a similar fashion I do not think their coating would feel rough like the soaked King's, on account of much shorter exposure to water.

All told, the sealant has been underwater since shortly after my last post here, and it's held up fine. I am however careful not to let the coated surfaces rub or knock against other stones because I doubt that it would take much to lose the watertightness.

Also, the sealant layer has a tendency to stick around even as the stone is worn down beneath it from usage. Hence I have to take care to cut/grind the extra sealant at the edge where the top meets the sides as part of maintaining/flattening the stone, otherwise pieces of sealant flake off. Because of this, I've slightly tweaked my usual way of chamfering the edges with a diamond plate to be more deliberate way than usual: making an effort to cut the layer without pealing it from the stone.

I must say that a more strongly bonded layer, epoxy for instance, presumably wouldn't have either of these last two issues. Cost notwithstanding...

Finally, looking back on this thread I remembered that mould had been brought up as a concern -- although I believe that it must have been in reference to my plan of eventually sealing Choseras rather than the the intermediary step of the permasoaked King stone; because Choseras must be dried between uses, almost by definition; at which time mould could become an issue, I'm assuming -- In any case, Sealing the King hasn't changed anything with regards to mould: a cap full of bleach every few weeks, when I change the water in its happy little bucket aquarium, has worked very nicely so far.

One of these days, I'll finally get around to sealing my Snow White like I've been meaning to.