Waterproofing Water Tanks

It's an application that is one of the most testing in any waterproofing application, and one that Gripset has been around and involved with for decades now.

So first with the typical type of construction that you're going to have with water tanks, normally they are concrete, concrete poured, concrete block, rendered masonry, and now the other one that we see very, very commonly is the Dincel walls and like a PVC formwork type mode, which they use for water tanks because of the ease of construction.

The type of construction will impact your surface preparation. Really important to remember that  and the recommended system that you're going to use. So, for example, if it's brickwork or blockwork, it needs to be bagged off or lightly rendered. And don't just do that with some sort of cheap sand cement system where it's mixed four or five to one sand cement. Make sure it's got a decent ratio of cement, our preference is a three to one mix, and an additive like the Gripset 11Y in that to ensure that the additive and that bagging system penetrates, bonds really well, and starts to seal the surface. Really important. Things like Dincel and PVC, we love that because it needs special primers like our Gripset OP, and we use that all the time. So you need to ensure that those surfaces are prepared correctly.

Is the tank below or above ground? There is potential water ingress between the wall-floor joints and that can be different if it's a below ground tank, like a cellar basement system, than above ground.

And the use of the water ... is it for potable water? For drinking? Human consumption? Then you're going to need to select a different membrane system than if it's for water storage, like for fire tanks where you're just holding water for sprinkler systems. These are the important factors to take into consideration with your waterproofing selection. Get that piece right. Ask us questions, understand that, then plan.

So surface preparation, like everything in our mantra and our bible, the Gripset bible, very, very critical for membrane success. Get that right.

The mortar joints, there should be no perp joints, mortar joints that are exposed. With brickwork and blockwork - filled, rendered, or bagged over, completely concealed so it's a seamless wall finish.

Things like curing agents and surface residues, particularly with poured concrete, need to be removed first. Either degreased or pressure-cleaned off to make sure that they do not impact the adhesion of the membrane system that's going over the top of them. And as we said before, Dincel needs to be primed with Gripset OP to key the membrane system that we'd put on top.

Square tanks are easy because we use our normal detailing system, but circular tanks can be more challenging on how you detail the wall-floor junction, which is still challenging. So things like a coved joint or a curved coved fillet at that wall-floor junction is critical, so it goes around and you don't have those tight joints at that area and allows the membrane finish to be applied quite easily in that situation. So these are things you take aware of before you start applying the membrane for new structures.

So, many times we have existing water tanks, existing structures we've got to either repair or do work on, and so often the internal worn floor surface can become weak and defective for a variety of reasons and that can get to the point where you can actually see exposed aggregate in the concrete, and that may need a concrete repair material to be used or a new baying rendering system as well. And as I said earlier, the Gripset 11Y additive is ideal. It can handle immersed conditions and we always recommend it for those sorts of repairs.

Cracks ... Quite often they are found in older, existing concrete structures. They need to be chased out and filled and treated in the right way. And find out if they are a live or static crack, because the way you treat them could be different. If it's a crack or joint that's going to move, particularly under the weight of the water when it's filled, things like our Elastoproof Joint Band may need to be incorporated in just part of that crack repair method. But take note of what that crack is, how deep it is, if it's superficial, and how you're going to treat that prior to getting the membrane system on board.

Spalling concrete cancer. There's a range of concrete repair materials out there on how you treat those, get that right first, treat that rusted steel. Don't just think you can membrane over that or just put a bit of patching mortar over it and hope for the best, because that is like cancer. It will just continue to be disruptive to the structure later.

And things like rising moisture or weeping can be common with a lot of underground tanks. So, it there's an active leak, you need to plug that first, things like our Gripset C-Plug, you use a water plug to stop the active leak. If it's not active and it's just damp, it may just need some sort of special priming system, like our Gripset E60, our epoxy primer to block that out first. But really important that existing structures, all the things that could go wrong, you take note of cause you've inherited an older problem and it's a lot different than the way you treat a new tank.

Membrane systems now. So it's important that they are durable and robust. Obviously they need to handle constant immersion conditions. Nine times out of ten, your water tank is not exposed to UV lights, so that's not a critical piece, but if it is, you need to make sure you've got a UV resistant membrane system. That is very uncommon with these types of structures that we're talking about, but if you ever come across that, take that into account.

For the fact that most of them will have a roof on them, you need to make sure that the membrane that's being used is safe to be used in a confined area. That is always an issue because health conditions inside these areas, we don't have air circulation and air flow, is going to be challenging on your health. And others that could be on-site or around you. So make sure that you've got a membrane system that can handle that.

If it is for drinking water, it needs to be compliant to AS4020, for potable water consumption. Really important. The membrane should be certified. You can check that out on the Australian Water Quality Centre, with the certificate there. They would have a register of approved products, but make sure that is approved with what you're using for drink water conditions.

A degree of flexibility, it can't be a rigid system. It needs to be able to handle some sort of crack bridging because there may be anticipated movement, either from the substrate itself or the pressure on the walls and the floor once water is filled into it. And can the membrane handle both negative and positive hydrostatic conditions.
So your membrane options ... Cementitious membranes are very, very popular for these applications. There are sheet systems out there you can use, but I'm going to keep it to today's discussion around the liquid or cementitious systems. You need to pick systems that A, have a history of successful applications for immersed areas. Anyone that says, "Oh we've got a test report" and haven't done water tanks before is a no no because this is not an application where you want to come back 12 months later, 2 years later. Make sure the membrane is suitable and can be backed up by testimonials and a history of applications.

Like I said before, durable and robust. It needs to be fast curing because it's obviously in areas that you don't get a lot of air flow, because as I said before with the confined space. And if it's a repair system, you're more often than not going in a damp substrate. So it needs to be able to cure where you're not always going to get the same air circulation you would have for another waterproofing application, outside for example.

Things like being robust enough that it won't blister, it won't re-emulsify. Critical things that can handle early water contact. We mentioned about the potable water certification, the non-toxic element is very important. And the hydrostatic resistance.

As far as Gripset goes, we love water tanks. We've got a number of systems. We've been doing this for a long time, but one that is the most popular in our range now is our Gripset C-1P, for the fact that it's single component, flexible cementitious, takes both positive and negative hydrostatic pressure, easily to be used on damp substrates, and it's potable water approved.

Gripset 2P, it's a more flexible version of the C-1P. It's our two part cementitious. Same thing. It's a bit more flexible than the C-1P, but is potable water approved, can go on damp substrates, and suitable for above ground tanks. It doesn't have the same negative hydrostatic pressure as our C-1P system.

The other one is our Gripset E60. Very high on negative hydrostatic resistances, our water-based epoxy. Highly durable, handles positive and negative pressure. Very low water dirt retention, which is a benefit sometimes if you need that in a water tank application where it's easy to clean and easy to see what's on the base of the tank. Suitable for solid structures more so, so air is not going to have so much movement. Potable water approved as well.

If you have any questions, call the Gripset team on 1-800-650-435.