Why Are Plasterboard Joints Cracking Even When They’ve Been Scrimmed?

1. The Plasterboard Is Moving

This is one of the first things to look at.

If the boards aren’t properly supported or fixed, small amounts of movement can put stress directly through the joint. Scrim helps reinforce that joint, but it can’t make a moving board stand still.

Check the boards around the crack for movement and make sure the edges are properly supported and securely fixed.

If the problem is underneath, another skim over the top isn’t going to make it disappear for long.

2. The Scrim Hasn’t Bonded Properly

Self-adhesive scrim needs a decent surface to stick to.

Dust, moisture and other contamination on the plasterboard can all affect how well the tape bonds. If the scrim starts lifting or moving while the joint is being finished, you’re not getting the reinforcement you expected.

A clean, dry surface and a scrim with good adhesion will make life considerably easier.

Because nobody wants to spend half the job repeatedly sticking the same bit of scrim back down.

3. You’re Using the Wrong Scrim for the Job

Scrim isn’t necessarily a one roll fits all product.

Standard plasterboard work is one thing, but moisture resistant boards, wet areas and other specialist applications can have different requirements.

It’s worth checking that the scrim you’re using is actually suitable for the board and environment you’re working with.

Walther Strong has different scrims designed for different applications, including traditional plasterboard work, moisture resistant applications and options with increased adhesion and tensile strength.

Not sure which one you need? Read our Complete Guide to Scrim Tape Types.

4. There’s Too Much Movement at the Joint

Buildings move. Timber moves. Materials expand and contract. That’s normal.

Problems start when there’s more movement than the finished joint can handle.

Temperature and moisture changes, movement in timber framing or general settlement can all put additional stress through plasterboard joints.

If you’re repairing the same crack again and again, it’s worth looking beyond the surface to work out what’s actually moving.

Otherwise, you’re essentially giving the crack a fresh coat of paint before its next appearance.

5. The Joint Hasn’t Been Finished Properly

Even a well scrimmed joint can cause problems if the finishing process isn’t right.

The scrim needs to sit properly across the joint and be fully covered as part of the chosen plastering or jointing system.

Rushing drying times, poor preparation or problems with the finishing material can all affect the final result.

Scrim is part of the system, not a substitute for the rest of it.

6. The Crack Has Been Repaired, But the Cause Hasn’t

This is a big one with recurring cracks.

If a crack appears, gets filled, disappears and then comes back in exactly the same place, repeatedly filling the surface probably isn’t going to solve it.

Before repairing the finish again, check:

• Is there movement in either board?
• Are the board edges properly supported?
• Are the fixings secure?
• Has the scrim lifted or failed to bond?
• Is moisture affecting the area?
• Is the crack appearing where different materials meet?

Find the reason it’s cracking first. Then fix the finish.

It saves doing the same job twice.

Plasterboard Joints Cracking: Has the Scrim Failed?

Not necessarily.

It’s easy to blame the bit you can see, but cracking along a plasterboard joint doesn’t automatically mean there’s something wrong with the scrim.

Scrim reinforces the joint. It can’t compensate for excessive movement, loose boards or problems elsewhere in the installation.

If you’re seeing recurring cracks, look at the whole joint rather than immediately reaching for another roll of tape.

Does the Type of Scrim Matter?

For everyday plasterboard work, a good quality self-adhesive scrim may be all you need.

But not every job is everyday plasterboard.

Different boards and environments can call for different properties, whether that’s greater adhesion, moisture resistance or increased tensile strength.

That’s exactly why the Walther Strong scrim range isn’t just the same tape in four different colours.

From traditional White Scrim to HD Orange Scrim, moisture resistant Blueline Scrim and waterproof HD Blue Scrim, there’s an option for different applications and requirements.

Explore the Walther Strong Scrim Tape range.

Before You Blame the Scrim…

If a plasterboard joint is cracking even though it’s been scrimmed, don’t automatically assume the scrim is the problem.

Check what’s happening underneath.

Movement, support, fixings, surface preparation, the type of scrim and the finishing process can all play a part.

Scrim can reinforce a properly prepared joint. What it can’t do is perform miracles on a board that’s moving around behind it.

Find the cause, fix the problem and then worry about making it look pretty again.