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Staining occurs when plasterboards are left undecorated and the surface begins to darken.
Plasterboard liner paper is made to the same basic formulation throughout the world. When subjected to light and heat the liners can undergo a complex reaction which results in the formation of a highly soluble, deep coloured layer on the paper surface. The application of texture coating to such a surface results in the deep coloured material becoming dissolved and migrating through to the surface of the coating where it dries out to form a stain. A common comparison can be seen almost every day in the yellowing of newspaper left in the sun.
The problem is often found when houses have been boarded and left untreated at that stage over an extended period of time, usually in the summertime. The manifestation can vary significantly even within a house depending on the aspect of the particular rooms i.e. whether north or south facing and the relative coolness over a period. As an example – if a board liner is exposed to indirect sunlight at a temperature of 18 C (65F) it will take 8 weeks to achieve a moderate discolouration whereas at 27C (80F) the same level of discolouration can take place in 10 days. The action is present over winter months as well but at a much slower rate because of the reduced daylight time and lower temperatures.
The staining material produced on the surface of the plasterboard also possesses detergent properties. This can result in rapid absorption of water into the plasterboard and under these circumstances can result in staining.
Generally problems can be prevented by the application of a single coat of sealer immediately after taping and pre-caulking is completed. It should be noted that in a few cases where the plasterboard has been exposed to hot conditions for long periods the discolouration of the surface can be so severe that the only practical solution is to re-board.
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