Granite Sluiceway Waterproofing

[thunberg]

Not sure if this is the right forum to post this in, but I appreciate any help or direction anyone may be able to offer.

I own a 19th century Greek Revival former woolen mill located in Southern RI, and have been in the process of restoring it over the past few years. There's a dam, gatehouse, and associated sluiceway on the property, and one of the nagging issues is that before I purchased the property, a section of the sluiceway was rebuilt with granite masonry walls that leak quite badly.

The property is here -- Google Map -- Street View

Note that I'm currently diverting water upstream and the sluiceway is currently 2-3' below normal level, as can be seen by the algae line.

When the water level is normal, there's enough water getting through, or under, that the parking lot has a steady stream in it, which can be seen here via Google Maps:

Photos:














I've talked to quite a few people about this and would like some additional input on the following options as I'm most likely missing something:

1. Rebuild the wall using hydraulic mortar, as apparently this wasn't used in the original construction.

2. Chip out the interior mortar, and repoint with hydraulic mortar.

3. Spray the interior of the wall with a dark gunite.

4. Varying forms of granite / masonry sealer.

I'm not entirely concerned with cost, more doing it right in the most watertight and permanent way possible so that this isn't an ongoing maintenance issue. Thoughts?

[PoolDoc]

I went ahead and enabled your post, even though it's not really the sort of question we handle here, because I think a lot of people will find it interesting. However, there are only a handful of folks here who could help, and they may not have time. As I believe you you recognize, you are working on a project where there is not a standard correct solution -- anything you do will be somewhat experimental.

Two suggestions for other places to look:

1. Search Google for forums frequented by contractors doing "watershaping" (decorative water installations). Those guys are more likely to have dealt with problems like this, than pool guys.

2. Try poolspaforum.com, which has a much higher % of pool contractors, then we do here. (I tend to run them off here, because they can't keep themselves from recommending 'pool-store' style chemical advice.)

I'll make one suggestion about the work itself, and then back out.

In my opinion, if you want "the most watertight and permanent" solution AND want to maintain appearance AND cost is not a huge issue, THEN I think you may want to consider stripping inside and top of the wall, and added a solid poured reinforced concrete wall, to which you could then re-apply the stone. Depending on what sort of gunite contractor you can find, a reinforced gunite wall could substitute for a poured wall. Poured concrete is a much more common skill, of course. Either way, you can do the bottom of the channel in whichever material (gunite or poured concrete) you use for the wall.

Two cautions:

First: Expansion joint design and installation will be critical, and few contractors (or engineers) seem to be very good at it. I don't have a solution for you, except to note that you need to look for, and find one. And once you find one, YOU will need to be on site at the critical points, to verify that this solution is installed as designed. It's picky work, and shortcuts that will last a year or two abound.

Second, both concrete and gunite contractors like wet concrete because it's easier to handle. However, in an exposed wall, over-watered concrete = porous concrete = concrete subject to freeze/thaw damage. Your weather (Providence, RI) is not as cold as I would have guessed (I looked) but it's cold enough to cause significant winter damage to wet porous concrete exposed to freezing air. One advantage of using a formed concrete wall: you can use very dry concrete, with only the water needed for hydration, vibrated into forms. Done properly, this results in a dense concrete not easily penetrated by water, and thus, resistant to freeze thaw damage. Some ongoing maintenance to the rock work is probably unavoidable.

[thunberg]

Good feedback, thanks. I'll look into watershaping and check out the other forum. As to the poured concrete interior, that's an interesting solution and seems at first blush like a good compromise between maintaining the aesthetics and coming up with a water barrier.

[Marin]

I'm going to have to think on this one, but here are my initial thoughts;
1 - Can you circle in the photo what was rebuilt vs what is original?
2 - Can you show exactly where the water is leaking? If it's just the dark area right of the steps, it seems minor.
3 - Is water actually weeping through the mortar? Or coming underneath the wall?
3a - Are you certain there is no crack towards the bottom of the wall allowing water to pass? This seems to be a more likely scenario to me, especially if you are just getting water from the area by the steps. If that's the case, you can chase out the bad area and patch with hydraulic cement.

A couple points I need to make;
A - Gunite itself is not waterproof. That's why plaster is added as a finish.
B - If it is a weepage (don't know if that's a word, but it works for me) issue, it's going to be the mortar, not the stone. I say that because a water sealant product is going to be surface specific. No point in buying expensive stone sealant when mortar sealant is what you need.