A nil-exposure finish is the most difficult result for any polished concrete contractor to achieve, so it is important we set your expectations from the beginning to get the best possible outcome. The single most important factor is your slab. You will need a great concreter and the right concrete, we recommend a 40 MPa mix, finished to a Class A standard with little-to-no undulations in the floor.
We have a very important nil-stone-exposure concrete pour guide that is essential for your concreter and builder to follow, just ask our friendly office staff for a copy to pass on to your builder, architect and concreter. If your slab is poured correctly and to this guide, our tradesmen have the best chance of achieving a consistent no-stone-exposure look with minimal imperfections. If the concrete is not poured to specification, is very soft, or has other issues, we may not be able to achieve the look you are after.
Please note, we are not responsible for the standard of your slab and cannot guarantee the finish. All of the outcomes below are possible and are not considered a defect of the polished concrete floor, because they are caused by the concrete itself, the curing or the placement, all out of OzGrind's control.
Where surface undulations create high spots, these areas are likely to achieve some slight stone exposure.
Low spots may not be reached by the machine when grinding and polishing, leaving the concrete crust in place. These areas will look and feel different to the rest of the floor.
Imperfections from the troweling and burnishing process will still be visible, as we only grind 1-2 mm off the surface. Grinding further to remove them means additional cost and more stone exposure. Expect screed marks, helicopter marks, boot prints and light patches.
If the floor is undulated and uneven, some undulations will likely remain in the surface after completion. The higher your gloss level, the more visible the undulations become.
Recycled water used in the slab mix can cause browning discolouration that may be visible in the finish. Staining left by builders or other trades before we arrive may not be removed by grinding 1-2 mm and can remain visible after polishing.
Because more cementitious surface is visible in this process, swirls, strikes or scratches around low spots and gouged or chipped areas can be more noticeable, especially on a lower-MPa slab.
Holes and blow-outs may not be able to be filled or polished. With little-to-no grinding, repair compound applied to shallow holes often will not stay in and plucks out when the machine passes over it. No filling or repair of holes or blow-outs is allowed for in nil-exposure quotes, so additional charges may apply if required, and there is no guarantee they will all be filled.
With so much cementitious surface visible, crazing and shrinkage cracks can appear more prominent. These occur due to factors including incorrect curing, incorrect mixing or placement, or environmental conditions such as sun, temperature, wind or rain. They are aesthetic only, do not affect the structural integrity of the slab, and are not considered a defect.
If you have any questions in relation to this document, please do not hesitate to contact our friendly office staff on 07 3177 3367 or enquiries@ozgrind.com.au.
By signing below I confirm that I understand OzGrind is not responsible for the standard of my slab and cannot guarantee the nil-exposure finish. I accept that the outcomes described above are possible and are not considered a defect of the polished concrete floor. I confirm I have received, read and understood all content in this document and the important terms & conditions in my quote.
Tell us about your space and whether your slab is new or existing. We will come back within 48 hours with honest advice and a no-obligation quote.
