ON THE BALL: PINHOLE PREVENTION Stephen Boulton, Technical Service Manager at F. Ball and Co Ltd., explains the
methods to prevent pinholing in levelling compounds and the science behind why it happens in the first place.
An all too pervasive occurrence, pinholing in a levelling compound can spoil the aesthetics of a finished floor and, in more serious cases, lead to floor failure.
Pinholing occurs when trapped air (either from absorbent subfloors, such as concrete or sand/cement screeds, or as a result of the levelling compound mixing process) rises through the levelling compound to the surface as small bubbles, where they ‘pop’. At the latter stages of curing, the compound is too viscous to fill up the spaces where the air bubbles had been, leaving unsightly holes in the cured levelling compound that have the appearance of small craters or pinholes.
With floorcoverings such as vinyl, these pinholes can leave very unsightly outlines from beneath the surface of the floor, which spoils the finished aesthetic.
There are two main ways to avoid this problem on a flooring job: using a primer and using a spiked roller.
THE IMPORTANCE OF PRIMING
The problem of pinholing will be exacerbated if the levelling compound is applied to an absorbent subfloor that has not been primed. Without a primer, the subfloor will absorb water from the levelling compound mix, leading to unacceptably rapid drying where the air can’t make its way to the surface in time for the compound to still be liquid enough to fill in the holes.
Primers are designed to prevent this unacceptably rapid drying of levelling compounds and adhesives, improving bond performance to ensure a long lasting, durable floor finish. When a primer is applied, a film is created across the surface of the floor, which prevents air from escaping and reduces the incidence of pinholing.
There are general-purpose primers on the market that can be used over absorbent surfaces. Specialist primers for use over non-absorbent and calcium sulphate screeds are also available. Application is usually recommended by roller or brush to ensure even coverage of the primer, which is often coloured to make this easier to gauge.
18 | TIP OF THE MONTH PRIMER PRODUCT FOCUS
F. Ball’s Stopgap P131 general purpose primer is designed to promote the adhesion of Stopgap levelling compounds and to prevent unacceptably rapid drying of adhesives and levelling compounds to smooth absorbent subfloors.
Acrylic primers, such as F. Ball’s Stopgap P121, are specially formulated to penetrate calcium sulphate based screeds prior to the application of Stopgap 1100 Gypsum smoothing underlayment, thereby reducing rapid drying and subsequent pinholing.
Stopgap P141 is a fast-drying acrylic primer that has been specially formulated to promote adhesion between Stopgap levelling compounds and non-absorbent subfloors. It dries to create a textured surface for enhanced bond performance and it offers a superior ability to better withstand the increased stress that thicker levelling compounds experience when drying.
SPIKED ROLLERS
Using a spiked roller can also help to reduce the occurrence of pinholing, as the spikes allow air to escape and the levelling compound to set with a smooth, blemish-free appearance. The roller should be used gently over the applied levelling compound, while still wet, covering the whole floor area.
The spiked roller also smooths out flow lines to achieve an optimum, uniform appearance, and enables different batches of levelling compounds to blend together, assisting flow properties to create a smooth, even floor finish.
Despite being a common occurrence, pinholing can be avoided with the right preparation by priming the subfloor and using a spiked roller before and after the application of a levelling compound. For further advice on obtaining the perfect finish, contact the F. Ball technical department.
www.f-ball.com
www.tomorrowscontractfloors.com
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