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

Hey, Steve56! It is actually some of your posts about sealing a Snow White, and it then doing well -- whereas one of your acquaintances went through several (4, I think?) hones which all had cracking problems -- which got me on this kick.

Originally Posted by Steve56

[...] 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. [...]

Could you expound on what about it failed miserably? I am rather curious, for obvious reasons.

Originally Posted by Steve56

[...] 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. [...]

Yes, the durability of the coating when immersed in water is an open question. Really though, I am using the soakers as more of a test to see how well the urethane will hold up before slathering it onto the Snow White which should be a much easier proposition for the sealant to handle, long term.
But, I am also curious to see if maybe I can turn the King into a kind of "perma-wet" stone; that seems like it would be interesting also -- in the somewhat unlikely scenario that the urethane coating proves both watertight and resistant to perpetual contact with water... And as for the 220 pink brick -- that thing is, in my admittedly limited experience with waterstones, the first time I am getting frustrated with how thirsty a stone is; no soaking for any length of time gets it to hold any significant amount of water on top; I can work up a mud which then holds a little water, but doing so wears the stone faster than I need to, and also limits me to grinding on said mud, which is slower than light pressure on the stone with no mud, and therefore not necessarily how I would prefer to use the stone in all cases. Hence, I'd get more use out of Pinky if I could finagle some way for it to hold more water near its surface and not just pass it straight through like nickel beer.

Hey Occamstrop!

The Suehiro coat failed because it absorbed just as much water as before and took just as long to dry.

The Snow White failed too, just not with me. It never cracked on me with or without the coating, but after coating and using it for a while, I sent it to a friend in Lake City, FL who had been through 4. Sure enough, after a while he notices fine spiderweb cracks on the surface which is how all 4 of his began failing.

I don't know what the difference/cause is. My first thought was water, but we both use distilled water to hone with. Humidity maybe?

The idea to coat the Snow White came from the Shapton Kuromaku/Pros that also once had a cracking problem in the Westen US. Allegedly they reformulated the stones, but the Pros also appear to be coated on the sides (they're 2-sided now) and the Kuromakus on the sides and graphics side. So I decided to try coating the sides and back of the SW then send it to my pal as an 'acid test'. Oh well, sometimes you eat the bear and sometimes the bear eats you...

Cheers, Steve

I've sealed my 1k & 3k Choseras and my 5k Chosera, that I purchased used, came to me sealed. I live in dry Colorado. I don't think the sealing had any effect on the checking. My 3k was checked when I got it and seems to have healed itself. The 5k checked after I got it, but I think that is just the nature of the stone.