Some professional painting contractors apply primer coating in a building wall. After that they apply top coating even after delaying 4 to 5 months of primer coating. If it is delayed such a long time will the top coat adhere properly on primer coating surface? In such process will the longevity of top coating not be affected?
It is very difficult to give a simple answer to this questions since the impact of the time between application of primer and topcoat is highly dependent on both properties of primer and topcoat as well as the conditions of exposure. There are several possible mechanisms that can reduce the adhesion between primer and topcoat which is often referred to as intercoat adhesion. Most important ones are:
1. Contamination of the primer with dirt or material migrating from the building wall. Low molecular weight materials present at the surface can create weak boundary layer which can reduce adhesion between primer and topcoat. Therefore cleaning of the primer prior to application of the topcoat is recommended if time between application is in the range of months.
2. Degradation of the primer by UV light or moisture (hydrolysis), the extent to which this can happen depends on one hand on the environmental conditions during exposure and on the other hand on the chemical stability of the primer.
3. Film formation processes. If the nature of the waterborne primer is such that dispersion particles will make the primer more dense by ongoing coalesence it might have a negative impact on the adhesion of the topcoat if no surface treament like sanding is performed. Similar effects might be seen in alkydresins based coating due to ongoing oxidative crosslinking or in reactive two pack systems.
To summarize: there is a reasonable change that extending the time between application of primer and topcoat has a negative impact on the intercoat adhesion and hence the longivity of the topcoat.
The maximum allowable time between application and of primer and topcoat can only be determined experimentally.
I hope this has answered you question
Kind regards
Mari de Meijer
Thank you Dr Mari de Meijer for explaining all possible points which may affect the adhesion of top finishing coat after primer coating on building walls. Will you please provide me a reference if you have where I can get minimum and maximum time duration of applying a top coat after primer coating on a building wall? Best regards
Thanks for your question, Parashuram Sahu. This is not exactly my parish, but I will answer.
It all depends on the influencing factors and the quality of the product:
1. The type of wall and its physical qualities - cement (we know), wet or dry wall, how porous is the material from which it is built;
2. Humidity and temperature outside or in the apartment;
3. What is the primer made of.
4. What are the physical parameters of the environment where the wall is located: dust, smog, rain, snow, sandstorms, etc.
This requires laboratory tests.
If there are manufacturers of both finish coating and primer, you should carefully read the instructions for using these products. Usually, manufacturers write all the characteristics and methods of use on the packaging. Or contact them officially and their answer will be a guarantee of the work performed.
It is important that, in order to properly putty all surfaces, you need to wait the period of time indicated by the manufacturer on the package after the primer.
Kind attention to Dr Mari de Meijer. Thank you for responding to my question and briefed all possible points regarding time gap between primer coating and top coating on building walls. For a specific project I want to know how much maximum time gap is permitted between primer coating and top coat finishing on building walls. If you have any answer to my specific question will you please provide me ? Best regards
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