Surface Preparation Guide for Concrete FloorsFebruary 17, 2014
Concrete floors are the ideal option for many industrial and commercial environments, particularly where heavy machinery is involved. Some domestic premises can also benefit from the surface, such as in utility rooms, driveways and garages.
Having a concrete floor laid is a job for professionals. However, once completed, treating and painting the surface can be carried out by anyone in possession of a decent DIY grounding, the correct equipment and a few useful tips…
NB: It’s important to note that the advice below is based on concrete floors that do not need repairs to cracks or other damage. The tips are based on preparing your floor for cosmetic finishing, not for structural repairs.
Before you start, it is imperative that the concrete or screed should be clean and dry. This is basic common sense – you wouldn’t apply paint to a damp wall or varnish a wet fence. Use high pressure water jetting or, if indoors, a wire brush to clean the area and remove any loose stones or debris, and leave to dry. Some areas where oil or grease has been spilt will require a more heavy duty cleaning process, and the addition of chemical cleaning products may be needed.
It may be advisable to vacuum the surface once again after drying to ensure that no debris remains.
Providing the floor you are applying surface materials to is indoors and protected from the elements, it will need a minimum of 28 days between the concrete being laid and any further work being carried out on it. This is known as the ‘curing’ period, and means that the concrete can fully harden before use. If the floor is outside, this period will be extended – particularly if it has been exposed to rainfall.
There are specialised water-based epoxy paints that can be applied during curing, as they allow the drying process to continue underneath. However, to be certain of the best results, it is best to wait for the full 28 days.
Checking for Cement Laitance
One of the common issues faced when painting a concrete floor occurs when the surface has had too much of a finishing product applied to it. This can cause what’s known as a ‘cement laitance’, and can lead to a brittle top layer on the flooring. Over time, this can become scratched and can break up easily, meaning that any paint bonded to it will do the same. Attempt to carefully scratch the surface; if it scratches very easily to a depth of 1-2mm, this could indicate cement laitance, and the layer will have to be removed (usually by high power vacuum blast cleaning) before continuing.
Once all the processes above have been carried out, you are ready for painting. Start by applying a sealant to ensure effective water resistance, as well as to protect against scratches and abrasions. Follow this with a primer coat so that the top coat has something to bond strongly to, checking the manufacturer’s instructions in regard to application and drying time.
Finally, apply your paint. It is vital that you select paint that is appropriate for the job you’re carrying out, and be wary that it may require 2 or 3 coats, giving at least 24 hours between the application of the final coat and moving furniture or equipment onto the surface.
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