Weathershield bubbling and discolouration

modelreject

Hi all,

I did a bit of research before sanding down a concrete window sill and repainting but yet I have some issues. Luckily it was only the one sill so hopefully I will be able to redo it and perfect it for other sills.

If you look closely you will see yellow discolouration to the left.
https://skitch.com/clintonbeattie/e88h3/preview

Here you will see small bubbling.
https://skitch.com/clintonbeattie/e887r/p1010792.jpg

I sanded the sill down to bare concrete although some places had thin areas of very old paint. I wire brushed it also.
I painted on a dry day, thinned down first coat with water and left 4 hours before second coat, as stated on tin.

I am wondering where the yellow discolouration is coming from and why it is bubbling. Today it is wet and humid but I am sure this is not meant to happen.

Should I have put on a primer?

Many thanks,
C

nickj_2

the only think i can think of is that the surface had dampness in it , this would cause the discolouration and bubbling .
if you burst the spots , you may find there is dampness behind it , this would stain the paint brown and cause it to bubble ..
to solve this , you will need to strip as much f it off and allow it to dry - this could take several days .it may need then treating with a stain block and then painting

modelreject

Thanks for that. Can you recommend a stain block?

nickj_2

polycell do one , or you could try a bit of solvent based white undercoat first if you have some .... surface must be dry before painting and also look out for anywhere moisture can be seeping under the paint from the sides of sill

modelreject

When the weather picks up, who knows when that will be, I will do all that you have suggested. Thanks!

zeldagoblin

This could be my husband posting, I had to double check! He just spent days getting our front sill back to bare concrete, and spent nearly £30 on some Dulux Weathershield. We were actually going to prime, but the tin recommended watering down the paint as primer, so we went with that option, and we got the exact same results as you! The photo looks like our sill, except our bubbling is a little more severe.

After some research it looks like a primer would have been the best choice, so he is pretty annoyed that the tin recommended thinned down paint. More work rubbing down now.

He is going to email them with some feedback.