Motar lines discolouring after painting brick wall


4 Aug 2003
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United Kingdom
We recently had the roof of our conservatory replaced and the utility block (posh name for the old outhouse) wall which it was attached to obviously got very wet. It's now back as an internal wall and we have been painting it and having some issues (though not with the other brick walls which were similarly exposed).

It's not plastered or rendered and it's (London I think) brick which was previously painted. Now when painting it the mortar lines "bleed" through in a yellowish colour. We were only freshening it up so used B&Q own brand smooth masonary paint.

Any ideas how to get around this?
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To be honest it does sound like a problem with moisture, you should crank up the heating to allow the wall to dry out.

When this is done brush the wall down useing a stiff bristle brush, this will ensure any loose or flaking paintwork is removed. This can often occur after a paint system has been subject to this type of damage yet may not in the first instance be visable to the naked eye.

Then give the wall one coat of an Alkali Resisting Primer, you should then be ok to carry on with any paint system you choose.

There's no flaking paint and before painting it was a consistent colour - just needed freshening.

The bricks are still damp as I drilleed a couple of holes to hang some shelves on one side of the wall and the drill had that feeling and dust of damp/wet brick. Gonna take some time to dry I guess as its a full brink length non cavity wall.

Got a dehumidifier running 24/7 to try and help
Just a thought (quite an expensive one, but might allow me to finish the visible side of the wall quickly and let the other side cope with the dryin out) could I use Zinsser Bulls Eye 1-2-3 - Primer Sealer and Stain Killer.

The wall area affected is not too big - less than 2 sq metres - so only a small tin required. Then I could finish the good side and leave the back side unfinished to allow it to breath.

Stupid idea or not?
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Sorry, I really can't offer you a quick fix here. That wall really should be dry before you paint it.

Couls be the alkali in the cement render attacking the pigment in the paint..its called 'alkaline burn'..although it normally leaves a white mark on coloured paints..

I would do as the Dec says and go over it with alkali resisting warned is strong stuff!

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