A Guide for Concrete Painting of The Slab Soffit (Ceiling)

Concrete painting is one of the essential engineering breakthrough mankind has discovered. This tremendously promotes better aesthetic to any structure at the most economical advantages. Being the final scope of the project completion, architects and engineers have to be knowledgeable about the proper application and surface preparation of the concrete surface for painting works.

Depending on the specifications of the painting used as stated on its brochures, most of the manufacturer and suppliers would want their painting products to be partnered with their own concrete sealers and primers. This is a prerogative of the architects to explore these painting materials for budget purposes. Thus, an architect or interior designer with several experiences on painting works is a good investment for most clients.

To proceed with the step-by step-guide on painting concrete slab soffit, please read further.

1. See to it that plastered wall has completely dried up

Due to time constraints, some quality engineers, civil engineers, and architects missed that plastered wall has to be completely dried up before the actual concrete painting operation for the slab soffit. Know that concrete members like beams and columns have to attain its designed strength in 28 days. Not attaining these structural designed loads would mean rectification, retro-fitting or worse, demolition if necessary. Engineers and architects should see to it that the specified load capacity of the structural member is already attained before proceeding with the actual painting works.

In addition, not only key structural member has to be dried up, but also plastered walls before commencing painting on concrete ceiling works. Normally, most painting supplier suggests these plastered walls be dried up for 14 days before the surface preparation. This two-week time should completely dry up the inner part of the plastered wall.

Proceeding with the painting works with undried inner portion of the plastering works would later cause problems like bulging of the skimmed coated wall. This is because of the water moisture trapped inside the plastered wall cannot exit thus forming bulged painted wall. Although these can be rectified by chiseling this out, primed and repainted, it is really best to let the plastered wall complete dry up before proceeding with painting works.

2. Patch surface holes and uneven surface

There are several products on the market that is available for this purpose, patching the holes caused by concrete nails, cut pipes, cartoons, tie wires and formwork.  Those unnecessary materials are left over during the preparation of the slab and were not able to remove before pouring concrete on the slab. You may check the best product for your use.

3. Surface preparation

Thoroughly clean the surface and at least make it dust-free, grease-free and oil-free. Some builders use power washing technique, a combination of pressure washer and blower to clean the concrete surface. Any foreign materials added to the primer would cause the painting produce unpleasant results. Grinding is also required to smoothen the plywood marks on the slab soffit, use hand-held power tools for grinding.

For surfaces with existing painting, completely peel off the painting with the designated tools.

Concrete in nature is not watertight, thus, sealing the concrete surface is relevant before the painting. This is necessary to prevent moisture seepage inside the ceiling soffit, deteriorating the reinforcing bars and promoting the growth of molds that causes unpleasantly damp feeling inside the closed room.

Quality Engineer tips
• It is advisable to properly grind the slab soffit especially the formwork marks. Scrape the cement splashes, if any, this is to ensure that the concrete ceiling or soffit is ready to receive the first paint application.  
• You as a quality engineer must conduct an internal checking before raising an inspection request for joint inspection with the consultant or engineer.
• Proceed for the painting of ceiling only if the wall is plastered. 

4. Use proper tools

After seeing to it that every hole is filled, the surface is thoroughly cleaned and straight, proceed with the coarse coat and medium coat the followed with first and second fine coat application. Do not forget to use proper tools and accessories to give you the output you desire.

See to it that before proceeding with the actual painting work, the length of the rollers, the painting pads, spray machine and stairs or lift needed, and enough gallons of paintings needed are all ready to be used right away on site.  This is to ensure the homogeneity of the surface output. It is advisable that a single plane of the wall be painted on the same setting for best results. Do not forget to prepare personal protective equipment (PPE) prior to painting works.

5. Paint the surface of the concrete

After ensuring that the 3 coats such as coarse, first fine and second fine coat have completely dried up, proceed with the final painting of the surface. Normally, suppliers advise up to three coatings for best result. But for economical purposes, others would just allow up to second coat only. See to it that architects, engineers, and the supplier agree on the number of coatings for warranty purposes. Basically, suppliers would warrant their product to last up 5 to 10 years before fading.

Some suppliers would want to give a demo of the product before the actual application to provide knowledge on the manpower on site. Construction management may always ask the suppliers for a demo.

This guide should give the architect or engineer on site an idea of the workflow sequence of painting concrete works. As a requisite, it is advisable to protect other architectural scopes from painting blotting especially the tiled floor, the doors and windows, and other already installed equipment and accessories like the fire alarm of air ventilation and other related MEP installations before proceeding with the painting works. Rectifying these blotted or inked architectural scope need tremendous works. It is always best to be cautious rather than rectify.

What is the paint system you follow for the painting of concrete ceiling?  Do you follow the same procedure above?