Zinnser cover stain for caulk

[ptarmigan]

Need to prime some caulk at wall/ceiling join to stop cracking when the emulsion goes on,have read that oil based undercoat does the job but can only find water based in small tins so can i use Zinsser cover stain that i have?

 

[opps]

I think it will work. I have not used Coverstain but I often use Zinsser BIN.

For the record, I seldom get cracking when I use Everbuild 125 caulk and apply the emulsion directly.

 

[ptarmigan]

Thank's oops i will give it a try,out of curiosity do you know why it sometimes cracks like is it a chemical thing or expansion.

 

[opps]

I am not totally sure. I suspect that the caulk is still still releasing solvents/VOCs.

If you were to leave it for a few months, the paint when applied might not craze.

If you think that caulk is bad- try painting oil based undercoat over MS polymer sealants such as CT1. Weeks after the sealant has been applied, if you undercoat it with oil based UC the UC remains tacky for days. I have to apply acrylic UC first and then can apply the oil based UC.

 

[ptarmigan]

opps,
Found out we have some paint boffins at work and asked them why emulsion cracks unless sealed and they said it's the solvents in the emulsion leaching out or being drawn into the caulk,he said a ****y coat of pva on the caulk would stop it.

 

[opps]

Thanks for the update.