Haymes Ultracover fans know—nothing ruins Insta-worthy walls like skipping this one simple step

May 13, 2025

No Undercoat, No Peace: Why Skipping This Step Wrecks Your Wall

Achieve a pro-grade finish on plasterboard with this one game-changing prep move

You’d be surprised how many beautifully planned DIY rooms get let down by one quiet mistake: skipping the undercoat. It's like baking a cake but missing the baking powder—everything looks fine coming together… until it’s not.

New plasterboard might look ready to paint, but it’s thirsty, porous, and full of little quirks you can’t always see. That bare surface can wreak havoc on your top coat — leading to patchy colour, uneven texture, or a finish that just won’t stick. That’s why — no matter if you’re creating a moody bedroom nook or refreshing a rental living room — getting friendly with an undercoat is your secret weapon.

So, what exactly does undercoat do?

Let’s break down three core reasons why painting an undercoat on plasterboard isn’t just optional — it’s non-negotiable if you care about the end result.

1. It seals the surface (and saves your top coat from overworking)

Plasterboard is like a desert after a week-long heatwave — totally parched. If you paint straight onto it, most of the paint’s moisture gets soaked up instantly, causing blotchy patches and colour that dries darker than expected.

By using a quality undercoat like Haymes Ultracover — which works as a primer, sealer and undercoat all in one — you’re applying a smart, even shield before the final colour. Think of it as skincare for your wall: cleanse first, then moisturise.

Pro tip: A sealed surface not only helps your paint glide on more smoothly — it also cuts down how much top coat you need. That’s time saved, and fewer tins opened.

2. It creates a smooth, even canvas for your colour

Ever painted a wall and spotted weird lines, minor dents or joins that look way more obvious once the colour hits? Yep — bare plasterboard exaggerates every tiny flaw. An undercoat acts like the smoothing filter you didn’t know you needed.

Products like Haymes Ultracover are specifically designed for this kind of prep. It fills small imperfections, offers excellent sanding properties and still manages to dry quick enough to keep your weekend project on schedule. The end result: your walls will feel refreshingly flat and your paint job will look far more expensive than it actually was.

3. It boosts the lifespan of your finished paint — seriously

Nothing’s more frustrating than doing the job, stepping back… and then seeing it start to fail months later. Peeling. Cracking. Discolouring. Most of the time, it’s not poor paint — it’s poor prep.

An undercoat improves something called adhesion — the grip your top layer has to the wall underneath. Skip it, and even premium paints might start to break off over time, especially in high-traffic or high-humidity rooms. The right prep lets your colour cling tightly to a stable surface beneath. So it stays newer, longer — even in bathroom nooks or behind busy hallway furniture.

How to undercoat plasterboard the right way

If prepping sounds tedious — here's the upside. It’s a pretty fast process with the right gear.

Start with sugar soap to give things a proper clean.
Roll on a coat of Haymes Ultracover, using a mid-pile roller for even spread.
Let it dry (about 2 hours)

In-store gear to make it breezy

We’ve put together handy bundles that usually include sugar soap, sanding pads, and undercoat-friendly rollers that glide without shedding fluff. Ask us to point you to what works — or grab a Roller Kit off the shelf and tick it off in one swoop.

So, is undercoat really that important?

It’s not just important — it’s the difference between a paint job that looks fine and one that stops people mid-scroll.

Prep doesn’t get the glory. It’s the opening act most people forget... but it sets up the whole experience. When you undercoat right, your top coat performs at its best — evenly, true to colour, and ready to last. It’s short effort now, for long satisfaction later.

Happy painting,
Candeece