What drummy render means
Drummy render is render that has come away from the concrete shell behind it. The surface still looks intact, but there’s an air gap underneath, so when you tap it, it sounds hollow, like a drum. That hollow sound is where the name comes from, and it’s the clearest sign that the bond has failed.
It’s one of the most common problems we find in older pools, and it’s easy to miss because it often looks perfectly fine until it lets go. If you want the short explainer, our guide what is drummy render covers the basics.
Why render goes drummy
- Age. The bond between render and shell weakens over the years.
- Water getting behind it. Through hairline cracks, failed tiles or poor edge detail, water works behind the render and breaks the bond.
- Poor original prep. If the shell wasn’t prepared properly when the render went on, it never fully bonded.
- Ground and shell movement. Small movements can separate the render from the concrete.
- Freshly failed finish. A failing surface lets moisture in, and the render underneath starts to let go.
It’s rarely about how well you’ve looked after the pool. It’s usually about what happened behind the surface, where you couldn’t see.
Why painting over it fails
A coat of paint or a new thin finish sits on top of the render. If the render is hollow, the new surface is only as strong as a layer that’s already lost its grip. When the render lets go, whatever is on top goes with it, usually as a bubble, a blister or a patch that falls away. You’ve paid for the job and you’ll pay again.
This is the clearest example of why we say a fresh coat of paint isn’t a resurface. If you want to see when paint is the honest answer, read our pool painting page. Drummy render is not one of those cases.
How we sound it out
Finding drummy render is a hands-on job. The pool is drained safely, after we check ground conditions and the hydrostatic valve, and then the whole shell is sounded out.
- We tap the surface across the whole pool with a hammer or similar tool, listening for the hollow note.
- Hollow areas are marked out, because the sound change is the best guide to where the bond has failed.
- We note the size and spread of each area, since a few small patches and a pool full of them are different jobs.
- We check what’s causing it, such as failed tiles or cracks letting water in, so the cause is fixed too.
The marked-out map is what your written quote is built from, so the price reflects the real extent of the problem.
Cut out and re-render
Cut out
The hollow render is cut out back to where it’s sound and well bonded. We cut past the edge of the hollow area, not just up to it, so the repair sits on solid material.
Prepare the shell
The exposed concrete is cleaned and prepared so the new render has something to grip. Any exposed reinforcing steel is checked and treated.
Re-render
New render is applied, built up in layers where needed and finished flush with the surrounding surface. It needs to cure properly before the next stage.
Make good
Once it’s cured, the area is ready for the new finish. This is why drummy render repair is almost always done as part of a full resurface: the old surface is coming off, the repairs are done on a bare shell, and the new finish goes on a sound base.
Straight advice: a few small drummy patches in an otherwise sound pool can be repaired on their own. If it’s widespread, repairing everything and resurfacing is usually better than patching one section at a time.
What if I ignore it
Drummy render doesn’t fix itself, and it tends to spread. Water gets behind it, the bond weakens further and the hollow areas grow. Eventually the render lets go, which can mean sharp edges, rough patches and exposed shell. It’s also a sign that water may already be getting into places it shouldn’t. Cracks are a common way in, and our pool crack repair page explains how those get dealt with.
What the repair involves for you
For you, the job is mostly waiting and deciding. The pool has to be empty and dry for the render work, and the new render needs to cure before the finish goes on. We explain the sequence at the quote stage, so you know what happens when, and we plan the work around the date you want to be swimming. If tiles or coping are loose as well, it’s cheapest to deal with them at the same visit.
Booking a render inspection
We inspect first, sound out the render and quote the repair in writing, so you know what you’re paying for. Pool season opens in November and render repairs are best done before it, so booking early gives you the widest choice of dates, whether you want to swim by November, Christmas or later in summer. We work across all of Greater Sydney, and the full range of repairs is on our pool repairs page.
