masonry paint

[Daniel3103]

Hello,

I have some blockwork that is apparent underneath a couple of rendered walls. The photo below shows one of these places. I would like to paint the blockwork, and I am looking to use a light-coloured paint to make it look similar to the rendering above.

I have two questions:

1. White streak marks sometimes appear on the blockwork. These marks are vertical. Any idea what they are, and do I need to do something about them?

2. If I use masonry paint, will it make the surface look homogeneous over the blocks, hiding the individual blocks and the mortar between them? Or do I need to spread a layer of cement over the blocks first?

[Nickfromwales]

Some folk will use a slurry and brush that on, then paint. 
 

@nod ?

[nod]

20 minutes ago, Nickfromwales said:

Some folk will use a slurry and brush that on, then paint. 
 

@nod ?

Slurry will be perfect 

K Rend do a paint that will match your render (enhancer) 

 

[Tony L]

The white streaks could be efflorescence.  This normally appears as patches, rather than streaks.  Efflorescence is caused by salts dissolved in water rising up through porous brick/block work; the water dries, leaving the salts behind.

 

Perhaps somebody with more knowledge than me will be along to tell you what you can do about it.  You should be able to wash/scrub it off, but unless you treat the wall in some way it will return.  If a wall is built with a DPC entirely above ground level, efflorescence should only appear below the DPC.

[Daniel3103]

Thanks for all the advice.

 

RE slurry - is this available from local DIY shops?

 

RE efflorescence - I’ll look into it. This would make sense, since the wall was built without a damp proof course, so water could rise through it and leave salts behind. Or maybe wates is dripping from the render above, then onto the blockwork below and leaving salts behind. That latter possibility could explain the fact that the white marks appear as streaks rather than patches.

 

I will research efflorescence and see what treatment I may need before painting the wall - but maybe someone on this forum can advise further about this?

[Bramco]

We have the same problem at the edge of our patio. Similar blocks that we need to treat to stop the efflorescence.

 

Internally, we've used zinser peal stop but not sure if this would work externally.