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How to waterproof outdoor structures

Leaking balconies, tiled areas and other outdoor structures are problems I deal with every day. I want to share some of the outdoor structure waterproofing issues I’ve dealt with and give you my top fixes.

Of course, this post is just an overview and every situation is different, so I recommend seeking professional advice before you attempt any DIY fixes.

What causes leaking balconies?

Roughly 90 per cent of the structure failures I see are caused by poor workmanship, detailing and design rather than the membrane itself.

Lack of falls, no overflow, and insufficient drainage outlets.

Lack of falls, no overflow, and insufficient drainage outlets.

Are all contractors created equal?

If you own a building, you need to make sure any contractor you use for remedial repairs is experienced in that specific type of work.

I’m often approached to fix building defects after a lot of money has already been spent – often because the contractor doesn’t have the knowledge or skills needed for the job.

Large amounts of money are often wasted on unnecessary repairs.

For example, at a recent job, a $12,000 ventilation system was installed in a sub-floor space that held 50-75 mm of surface water after heavy rain. We simply installed drainage to draw off the water in the first place, which was far more efficient and cost effective.

 

There is not continuation of the membrane over the low walls. Water bubbles appear behind the paint. There are leaks into the unit below.

There is not continuation of the membrane over the low walls. Water bubbles appear behind the paint. There are leaks into the unit below.

Expert engineer?

In another case, a so-called ‘expert engineer’ wrote a report listing a massive amount of rising damp in a property when in reality only one small area was affected. We installed ventilation at 40 per cent of the cost of new dampcourses, which had been recommended. The installation of dampcourses would have done nothing to fix the problem.

The PVC membrane (white) finishes just below the tile level rather than higher up. The pipe should pass through a sleeve that the membrane is sealed to.

The PVC membrane (white) finishes just below the tile level rather than higher up. The pipe should pass through a sleeve that the membrane is sealed to.

Money well spent

If an experienced contractor suggests paid investigation work, this can be money well spent. Alternatively a consultant can prepare a report and scope of the work needed.

Keep in mind however, that while investigation work can be worthwhile, inviting multiple contractors to provide quotes could also be a waste of money.

Waterproofing warranties

I’ve had one project where around $150,000 was wasted on ‘repairs’ – all of which failed.

I use all types of membranes and have had to repair or replace most types – liquid, sheet and loose laid PVC – that have been incorrectly applied. All have their advantages and disadvantages.

The planter soil finishes above the top of the PVC membrane. The top of the membrane does not have a pressure seal. No protection board against the membrane. The membrane system does not continue up and over the side walls.

The planter soil finishes above the top of the PVC membrane. The top of the membrane does not have a pressure seal. No protection board against the membrane. The membrane system does not continue up and over the side walls.

My advice is to ask for a manufacturer’s warranty, normally for a period of 10 years. The technical rep from the supplier will visit the site and inspect the work as part of this process.

In a current contract I’m working on, the membrane has had many failures due to poor workmanship and design, despite being of high quality. The clients paid a premium for this system, but failed to get the manufacturer’s back up. The contractor who installed it is no longer in business and multiple areas on the building need to be redone at considerable expense.

What to be aware of

Owners should also be careful when using companies who advertise that they can ‘fix leaking balconies or showers without removing tiles’. There are cases where this can be a successful, cost-effective solution. In general, however, I suggest being cautious and reading the fine print of the warranty because these warranties often have a lot of ‘outs’.

Trees too large / cracked brickwork and membrane failure.

Trees too large / cracked brickwork and membrane failure.

Rooftop terrace / Planter. Obvious lack of maintenance.

Rooftop terrace / Planter. Obvious lack of maintenance.

Why getting an expert remedial contractor is so important, the original membrane installed by the builder failed, the repair job by another contractor paid by the client also failed. I often fix things for the third and in one case the fourth time.

Why I don’t like loose laid membranes. When there is a leak the water just tracks under it all over the place. At least with a liquid membrane system and in most cases a stuck on sheet membrane any leak occurs at the failure point. This also demonstrates why the edge details are so important for membranes and absolutely critical for loose laid ones.

Waterproofing checklist

If you’re waterproofing an exposed, above-ground outdoor structure, use this simple checklist to make your life easier:

  1. Use a solid, well-built base under the membrane: The base must be constructed using moisture-resistant material with all holes or gaps filled.
  2. Do not apply the membrane to a level surface: The membrane must be applied to a surface with the required falls to the drainage outlet. Do not use the tile screed to form the required falls.
  3. Use a continuous membrane system: This must run from the outside edge, across the base and under the sills to the inside of the doors.
  4. Ensure the membrane turns up at the edge: Keep a suitable distance above the finished surface.
  5. Make waterproofing continuous: On low walls and on brick walls, the membrane should run under the wall then over it once it’s built.
  6. Build a well-designed drainage system: It needs to cope with heavy rain to catch water and discharge it into the storm water system without backing up.
  7. Ensure sufficient overflows: This prevents water entering the building.
  8. Create a raised hob: A must-have for under items including columns, air conditioning outlets, plumbing and vents.
  9. Avoid fixing balustrade posts through the membrane: In general, the membrane must finish above the finished tile level.
  10. Allow for movement: This includes wall and base junctions, structural expansion joints and sheet joints.
  11. Make sure tiles aren’t glued to membranes: This should only be done if there is no other option.
  12. Get a ten-year manufacturer’s warranty
  13. Use compatible materials from the same supplier: This includes the membrane, sealants and adhesives. Get advice from the technical department if in doubt. I use Ardex Australia.
  14. Isolate the membrane during building works: Wait until the tiler has laid the screed over it before any other works are done in the area.
  15. Make sure the membrane is UV stable: They can break down quickly otherwise.
  16. Keep maintenance up to date: This includes keeping drains clear of debris, salt deposits and ensuring expansion joints are in good condition.

Additional information

If you’d like to learn more about waterproofing your outdoor structures, check out these links and resources:

Over to you

Have you had an issue with leaking balconies or other outdoor structures? What was the cause and how did you fix it? We’d love to hear, so please comment below.

Got a question?

If you would like us to take a look at a leaking structure on your property, give Peter a call on 0412 355 887, or contact us for an obligation-free quote.


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