Hydraulic cement is popular for its ability to effectively stop leaks in concrete and masonry. Many brands are touted as drying and stopping leaks, even when you have an active leak with flowing water.
So, what do you do when your hydraulic cement doesn’t look like it’s drying? And, what can you do to fix it?
Often, hydraulic cement only stays wet because it was mixed too wet. However, you could be having issues because of contamination, old cement, or a number of other issues. Troubleshooting those issues will be the key to figuring out if you can fix your hydraulic cement.
6 Reasons Why Hydraulic Cement Still Looks Wet
If your cement is failing to dry or it still looks wet after several days, there’s a good chance that something has gone wrong.
However, you should always double-check how long your brand of hydraulic cement takes to dry. Some brands take as long as 28 days.
1. Mixed Too Wet
Hydraulic cement takes anywhere from 3-5 minutes to dry for the “top” brands and up to 15 for brands not sold as leak stoppers. For most people, 3 minutes is not a lot of time to go from mixing cement to applying it into a hole.
A common result is that you might add more water, hoping to slow the curing time. Unfortunately, this doesn’t work. That’s because hydraulic cement doesn’t have oxychloride in it as regular cement does.
So, when anhydrous cement mixes with water, it forms hydrates within a few minutes. Those hydrates do not soften when exposed to water.
That makes hydraulic cement an ideal solution for stopping leaks. However, it also means that once it’s mixed, it can’t be remixed, and it won’t absorb more water.
Instead, you’ll have to rely on the surrounding mortar to absorb water from the cement. That can mean waiting for a very significant period of time for the cement to fully dry.
Here, your hydraulic cement will probably never dry to the strength you want it. Instead, you should likely remove the cement and re-apply it.
The new mix should be stiff and about the texture of peanut butter. If you can’t roll it into a ball, you’re mixing it too wet.
2. Cement Is Contaminated
If your cement is contaminated with oil or another substance, it might never be set.
Hydraulic cements are made up of very specific blends of Belite, Alite, Tricalcium Aluminate, and Brownmillerite. Those silicates allow the cement to set by forming bonds with water. Oil or grease can prevent those bonds from forming.
For example, if you haven’t properly cleaned the hole you’re trying to patch. If there’s oil or grease on the mortar, your hydraulic cement might not be set. The same could occur if you’ve oiled or greased the tools you’re using to mix it.
If this happens, the only fix will be to remove the cement and replace it.
3. Hydraulic Cement Was Re-Mixed
Hydraulic cement sets in 3-5 minutes for brands intended to stop leaks. If you overshoot that and try to remix it or try to mix more water in as it’s setting, you’ll just be adding more water.
Because the silicates will already have bonded with the water, the cement won’t absorb more water. Instead, your cement will just stay wet.
It may dry over time. That’s especially true if you’re putting it directly on dry cement or brick. However, drying will take a very long time.
In addition, your cement will never regain the hardness it did before. Therefore, the best fix is to remove the old cement and apply new.
4. Cement Is Too Old
Most hydraulic cement has a shelf life of about one year. After this, the package should be thrown away.
That’s because the longer the cement is stored, the more prone it is to being exposed to dampness.
For example, even if you have premixed hydraulic cement, it can still condensate. Over time, that will mean tiny portions of the cement harden and therefore won’t bond when mixed with water.
If you’ve used old cement, the only fix will be to remove it and re-do the patch.
5. Cement Is Not Applied Properly
Applying hydraulic cement means mixing about a pound at a time, rolling it into a ball, and pushing it as deeply into cracks and holes as possible.
In most cases, you should spend the full 3 minutes after mixing the cement working the putty into the crack you want to fill.
If you try to mix hydraulic cement to use to coat a floor, it won’t ever dry properly.
Also, if you apply it in patches that are too small, it might not properly seal the hole. This could cause leakage around the hole, meaning you’ll always see water on the cement.
In addition, most hydraulic cements require being applied to a wet surface.
For example, the U.S. Spec Hydraulic Cement “Rapid-Setting Hydraulic Patch” requires that you soak the area for 24 hours before applying the cement. That’s easy enough if you have an active leak but significantly harder if you don’t.
Many types of cement also allow you to simply spray the area down with water. However, the area should normally be wet to ensure the surrounding material does not absorb too much water from the hydraulic cement.
6. Cement Is Very Cold
Hydraulic cement does not set properly under 40 degrees Fahrenheit. In addition, it should not be applied in temperatures above 90 degrees Fahrenheit.
The colder your cement, the longer it will take to set and cure. Here, the optimum temperature is about 70 degrees. The warmer it is, the longer it will take to set.
What can you do if your repair site is too cold? Try using caulk as a temporary solution and then put the patch in when the weather warms up or you find a space heater.
How Long Does Hydraulic Cement Take To Dry?
Hydraulic cement is advertised as setting in 3-5 minutes.
While many people take that to mean how long it takes to dry, that couldn’t be further from the truth. Instead, it means that hydraulic cement stops being workable in 3-5 minutes. Other brands take 10-15 minutes to set.
However, setting isn’t “drying”. It’s just when the molecules start to stiffen.
Instead, hydraulic cement can take anywhere from 5-28 days to fully cure. The more water is around the cement, the slower it will dry.
So, if you’re plugging a leak or stopping one, you can expect the cement to remain somewhat soft for a very long time.
You can also speed up or slow down setting times by using warmer or colder water.
If you want to achieve a 5-minute setting time, you could try using cool water – at about 50-60 degrees Fahrenheit. On the other hand, if you want to increase the setting time, use water at about 80 degrees Fahrenheit.
If your concrete is set and is staying in place, don’t worry too much. That’s especially true if you’ve followed the instructions and not mixed it too wet.
As long as your plug isn’t leaking, you shouldn’t be too concerned. However, if your cement is still wet after about 28 days, you will have to take it out and re-do the patch.
Hydraulic Cement Application Tips
If you’re trying to stop a leak or plug a hole with hydraulic cement, it’s relatively easy to do. In most cases, hydraulic cement is beginner friendly.
However, you should always make sure you wear protective gloves and glasses. That’s important because hydraulic cement contains lime. When mixed with water, it will spill into your hands and cause burns.
In addition, if you have any sulfate mix of hydraulic cement, it’s important to wear acid-resistant protective clothing.
- Undercut the Area – Hydraulic cement will always bond better when given a large surface to bond to. For this reason, most brands recommend that you undercut around the hole to form a flat, wide space for the cement to bond to. Taking a chisel to your wall will do the trick.
- Clean the Area – Take time to clean your patch area. Here, you should use air, a brush, or water to flush out any loose particles and chips. In addition, if the site has been contaminated with grease or oil. E.g., in a garage or kitchen, it’s important to thoroughly clean that off first.
- Wet the Area – Old cement and mortar absorb water from the hydraulic cement. This can cause the cement to dry too fast, meaning that it doesn’t bond properly with the existing cement. For this reason, you should spray or soak the patch area. Some brands ask you to wet the area for over 24 hours before applying the patch. This makes hydraulic cement ideal in a damp basement or to stop an active leak. However, if you want to use it to patch a dry foundation, you’ll have to actively wet the area yourself over a day before patching the area.
- Mix in Small Batches – Hydraulic cement starts to set immediately when you add water. After about 3 minutes, it becomes nearly unworkable. And, if you add extra water at any point, you’ll simply reduce the ability of the cement to dry. Therefore, it’s recommended to mix hydraulic cement in very small batches. Don’t mix more than you can use in about 3 minutes.
- Get the Consistency Right – Hydraulic cement is intended to be mixed stiff, like a putty. Most brands should be about the consistency of thick peanut butter when done. You should be able to roll it into a ball and then press that into the hole you’re trying to patch.
- Pay Attention to the Temperature – Don’t apply your hydraulic cement if the area is too cold. In addition, the area has to stay above 40C for the first 24 hours after applying the patch. If the weather isn’t good enough, it’s always a good idea to wait with your patch.
- Apply from the Top Down – Hydraulic putty should always be applied from the top down. This gives the cement plenty of time to work into the cement without hardening and without creating uneven gaps at the bottom.
Eventually, if you get the temperature and consistency right, your hydraulic cement should be very easy to apply. However, it’s always important to read the instructions for your specific mix.
If you have a different mix or a hydraulic cement intended for a specific purpose, it might have slightly different instructions.
If your hydraulic cement still looks wet after you expect it to be dry, it might just need more drying time. Hydraulic cement can take up to 28 days to fully cure. However, you can also consider if you mixed it to the right consistency. Hydraulic cement should always be a thick putty. In addition, if the cement is old, was contaminated, or was applied on a cold surface, it might not dry properly.
In each of these cases, the only real fix is to remove the old hydraulic cement and replace it, following the instructions on your package.