quercus1, usually when these types of sealants are allowed to cure properly, as per the manufacturers instructions, they are quite safe to use as you plan to use them.
I have used many types of sealants and adhesives, over the years in and around the ponds, without any adverse effects.
Be sure to let it cure completely and wash it off thoroughly afterwards and you should not have any problems.
"Horton"

Thanks, I wasn't sure about the PL brand polyurethane. The label says not recommended for under water. Yet it is supposed to be water proof. I suspect they don't want people using the product where there is a problem with water pressure. I picked up a tube of both the black roof type and the gray self leveling concrete type for horizontal surfaces. The self leveling doesn't say anything about not using it under water. I will post back on how they worked out.

Quercus1

The black or yellow sealants for use in the water are great and flexible although their expansion can cause a nuisance in small spaces. I use them and am happy. Other sealants it is wise to read the fine print as waterproof and underwater can be very different characteristics.

following what turned out to be sound advice from the forum, I have used a fair amount of hydraulic cement to good end. Inexpensive, comes in small enough container, centuries of use in underwater situations. Easy to mix but only in small batches as it sets up quickly. Totally pliable and great for the small openings you describe.

Some will disagree with me, but I don't think that just one product can resolve the different sealing problems in the system; best to find a range of helpful products and keep them handy. Good luck.

Mike

I had considered HC, but from what I have read, I need at least 24 hours without it freezing. Anyone care to address this issue? Currently here in the high desert it is freezing every night. At best I would get around 16-18 hours of above 32 degree temps. If I did all the patches with HC and let it set for most of a day, then turned on the water fall on, would that work? If the fall still leaked, how hard is it to patch again with the HC?
Thanks Quercus1

quercus1, I agree with Mike completely, having experimented with many sealers and cements over the years.
Some work in contact with water, some do not.
I have used hydraulic cement many times in the past and it has done well.
I have applied it around waterfalls in the early spring time, when there was still the chance of freezing temperatures at night.
I covered the area that I had used the hydraulic cement on with a tarpaulin, under which I installed a 100 watt light-bulb.
The tarpaulin,plus the heat from the bulb, kept the area frost free over night until the cement had a chance to cure.
The good thing about hydraulic cement is that you can apply it almost anytime, to a crack or space in between the rocks, as long as the surface is clean, because it will set up underwater.
"Horton"

Well it is cement I will try first.
Can you guys give me some pointers on use? I have a couple of options available. I believe Lowe's has Quikrete and Home Depot has Rapid Set. The Rapid Set brand has 2 products wunderfixx and mortar mix. Both are made with hydraulic cement. I am not sure if HD has the wunderfixx, could the mortar mix work or should I go with the quickrete Hydraulic Water-Stop Cement (no. 1126)? Are their any other products that are easily available?

Any pointers on application?

Thanks Quercus1

quercus - I have used QuikCrete with success but have no knowledge of others. It sets up in about 5 minutes, so you have to be smart about how much to mix and what you can do in a brief time. I checked my tub and could find no reference to curing time. The only caution is in a hot and dry setting it needs to be protected from evaporation.

The Quikcrete site reports that when setting a post it will be fully set in 20-40 minutes and use warmer water to mix the colder the temperatures are.

Also checked my black waterfall foam--sets in 12-24 hours but can be hastened by applying water. Recommended usage is at 65F and above. Great Stuff is about the same.

No definitive answers to your problem.

You might consider a trial run. The HC is cheap in 3 pound tub. Seal a crack, join two stones, whatever, and see how it goes. Give it some time and turn on the water, see what happens. Cracks can be repaired with a couple of products. If it or the foam or other products don't work waiting for more favorable temperatures may be your best option.

If you try it, let us know what happens.

Mike

Just as an adjunct to Mike,s post.
If you have a lot of rocks to fill between then I would suggest you use the mortar mix that contains hydraulic cement. It would be more economical than using straight H.C. Water Stop I believe.
If in the future, a crack does appear after you have cemented the rocks together. You can mix up a slurry of Hydraulic Cement [Water Stop] and paint it over the crack[s] using a paint brush. Or paint a sealing coat over the mortar mix joints after they set.
It makes a great sealer used this way.
Hydraulic cement contains more lime than ordinary cement, to make it set up quicker. That is why it gets hot when you mix it with water.
It is advisable to wear rubber gloves, if you intend pressing HC into the spaces between the rocks with your fingers, as the wet lime can remove a layer or two of skin from your hands.
"Horton"

Thanks Guys
I am off this morning to Lowes and HD to see what I can find.
Quercus1

That's great information Horton--gone in my Clippings file for springtime reference and use

Mike

Mike, you will be able to produce a 'best seller' from all the information stored that "clippings file". LOL
"Horton"

Shucks Horton, I'm just the humble editor who collected those essays from knowledgeable ponders. Credit where credit is due.

Then again, if there's big bucks, book tours, limos, Oprah, it might be different.

I keep learning here and store it away in clippings so as not to forget. Now, if I could remember I have a clippings file!

Mike

The HC worked great. I have a 100 watt light on it tonight. Boy does that stuff get hard quick. After 30 min, I could hardly scratch it with an ice pick. Got a few things still to foam, then I will check for leaks.
Thanks again for the great advice!

Quercus1

"Boy does that stuff get hard quick."

Quercus,It must be the Cialis in it!??
If there is a problem with it still setting after four hours, contact your [pond] doctor!!!!LOL
"Horton"

Quercus - good job. Did you fill just cracks or cement stones together as well? Turned on water yet?

Well Horton, if ever there were a Clipping I better collect, you have provided it lol

Happy New Year all

Mike

No water yet. I used foam on most of the rocks. Used HC on the cracks. Today I am going to try to finish up the rest of my foam work. If all goes well, the water test will go tomorrow. I was trying to save all the foam work in groups so as not to waste any foam. I have the one main water fall and then a side trickle to bleed off extra water from the filter. I still have to finish up the rock work on the side water feature. The HC works well, if one could just get it to cure a little slower it would be even better. Has anyone tried adding some fire clay to the HC? I was thinking it would allow you to roll the HC out into a small string that could be easily placed in small cracks. I may mix some up as an experiment and see.

Got to get busy, daylight is burning!

Happy New Years
Quercus1

there is someone on the forum who really advocates HC and once described rolling strings as you desire. Can't remember who. I think I recall that the key is timing and speed--do it at just the right moment before it sets up. You also might consider mixing it in a different proportion, thicker I suppose. I did a quick search with no luck--maybe you will do better. I have no idea what additives might do to the setting up or water fastness.

Mike