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How to get rid of brown discoloration on your concrete surface?

08/28/2015
Particularly in the hot season phenolic resin coating suffers from intensive solar radiation, likely to leave brown color remains on the concrete surface. However, this undesirable impact on your concrete surface can be minimized or even prevented. phenolic_blog
Have you seen them? Those brown – sometimes curved – discolorations emerging on the concrete surface after stripping the formwork? Bad news is: When using phenolic resin plywood, no matter the supplier it comes from, discoloration is very likely because the plywood’s characteristics have a non-UV-resistant nature. The good news: You can reduce the impairment of your concrete result or even prevent it if you take some simple measures.

Situation 1 | You use phenolic resin plywood and want to reduce discoloration

#1 Minimize exposure of phenolic resin coating to UV-radiation Protect the plywood from intensive solar radiation e.g. by storing them vertically with the concrete touching surfaces facing each other or by covering the panels.

#2 Watch out for contamination Keep the formwork clean before pouring concrete. Remove dirt, rust, finger prints etc. on the plywood’s surface before usage.

#3 Adjust your construction cycle Loosen the tie rods in each panel and remove immediately from the concrete before starting with the next one. If not, you risk that formwork panels detach from the concrete surface at certain areas while still touching the concrete surface at other areas. This may result in a gap between hardened concrete and formwork, where condensed water arises and transports dirt, residues of concrete or release agent and/or dissolved phenolic resin to the concrete surface.

Situation 2 | You used phenolic resin plywood and want to remove discoloration

In some cases the discoloration of concrete surfaces could be removed successfully with a weak acid such as low-concentrated formic acid. An alternative are professional cleaning agents that can be used on site (consulting from a concrete or stone cleaning company beforehand is recommended). Also mechanical instruments for removal are an option such as treating the concrete surface through grinding and patching. However, any removal activities should be executed first on a test area as efforts may result in a different visual appearance of the concrete surface and could emphasize the flaws.

Situation 3 You want to prevent discoloration in general

The best way to prevent discoloration caused by phenolic resin obviously is to work with alternative thermoplastic plywood. Why not work with Doka’s Xlife plywood?  
Daniela Ehrenreich, Manager of the Concrete Laboratory at Doka, is an industry expert as has been responsible for concrete testing and research within Research & Development Department for more than 7 years. Holding a Master’s degree in Civil Engineering, she started her professional career with Doka in 2006 as a Structural Engineer. Today, she plans, executes and evaluates tests on the relationship of concrete mixes with e.g. formwork panel coatings or release agents and shares her knowledge as a trainer for architectural concrete challenges.