Repainting concrete where paint has fallen off

[khunPer]

I'm in line with other posters.

 

The white crystals (crystallized salts) is probably cause by not well enough mixed mortar, and/or not well enough cured and dried plaster before painting.

 

My pro painter adviser told me to leave the plastered walls for three month before adding primer.

 

When old paint etc. has been cleaned off, let the wall(s) dry out for some time.

 

Use a primer suitable for topping on old paint, for example TOA Quick Primer or like, could also be TOA ExtraWet Primer or like. I mention TOA only, because I have used that brand with excellent results; however other brands might be equal good or better, but don't buy the cheapest products.

 

I always use two layers of primer. New walls are softly sandpapered before adding primer.

 

Make sure that both primer, and later paint coats, covers fully, and don't thin more than necessary to work with the paint, and let the paint work – not you – i.e. use enough paint on roller and brush; great advises from my pro mentor.

 

Use high quality semi-gloss acrylic paint on top. I used TOA SuperShield. Semi-gloss makes the paint better weather resistant, and what might seem to be too much gloss will actually disappear in short time. I used three layers of overcoat, and I make sure each layer is well dried, before adding the next, preferably I do one layer a day.

 

I only had one smaller area with a similar problem as described by OP – crystallized salts – on my now almost 9-year old house, and the above mentioned repair method worked well; same method was also used when originally painting the house.

????

Edited April 11, 2019 by khunPer

[transam]

The ploblem here is.....House is built up with no air space...After the concrete stuff is done they fill in the floor level with sand/soil, chuck a load of water on it to compress it, thin layer of screed then tile....Water can up and down at will in the soil....If the soil/floor level is higher than outside then emulsion will be attacked.....Just sorting a little of that at my place...

 

IF one wants to be clever then one must "seal" the internal concrete before the floor infill, but you would have to do that yourself as the locals will....????

[myshem]

hello, how could I do to have a concrete color look house ? what should I put on the cement to protect the house wall exterior walls ? Thanks.

[transam]

1 minute ago, myshem said:

hello, how could I do to have a concrete color look house ? what should I put on the cement to protect the house wall exterior walls ? Thanks.

Nufink.....????

[The Theory]

The wall getting moisture from somewhere. There could be an invisible hair crack along the wall that water runs in that all the way. You need to find it 1st before painting again. 

[khunPer]

12 hours ago, myshem said:

hello, how could I do to have a concrete color look house ? what should I put on the cement to protect the house wall exterior walls ? Thanks.

Clear colorless primer or clear cement lacquer.

[ross163103]

My house also has this problem, the most I've gotten out of it is around 3-4 years. I've tried pressure washing, wire brushing, letting it dry for a few weeks, primers, water sealers, etc, all to no avail. I agree with what some of the posters are saying; the lime/alkaline leaches into the wall and makes the paint flake off from the inside. Water sealers only serve to keep water out, they don't help when it's coming from within. Anyway, sorry no solutions from me, but I do feel your pain. Seems most buildings in Thailand have this issue.

[RocketDog]

On 4/5/2019 at 5:37 PM, seajae said:

when you have a rendered wall to paint normally you let it dry completely then block it to remove all the loose surface then apply the correct coats of paint, this simply doesnt happen here  as they want everything done straight away. The peeling paint is at the bottom of the wall which is the natural place for moisture to travel in the cement render taking all the lime with it which in turn caused the paint to bubble then peel. Moisture guard is designed for exterior walls to stop water penetrating the walls not coming out of the wall, you need to allow the rendered walls to dry fully then clean them off to stop the lime problem

 

I finally decoded 'render' to be concrete! 55555. Now your advice makes good sense.

[The Deerhunter]

On 4/16/2019 at 9:02 AM, RocketDog said:

I finally decoded 'render' to be concrete! 55555. Now your advice makes good sense.

We also sometimes translate render or rendering ( which are actually the correct trade terms in English) as "plaster" or "plastering", which is understandable but actually plastering is another process using different materials.

I also understand that water trickles down (as many people have pointed out), but DAMP ALSO RISES, (as in "rising damp", refer to Leonard Rossiter in BBC comedy of the same name); in the absence or failure of the essential dampcourse membane.   Which membrane is NOT installed in most Thai buildings I have examined.  I am an old guy of 72 but in my younger days back home, concrete or concrete  block, or solid brick walls were usually (always????) fitted with a bituminous membrane called Malthoid, as a dampcourse membrane between the foundation and the wall, where I come from.  Ventilated brick veneer on a raised base is a different subject altogether, but regardless, here in LOS, I always leave a full month before painting.

So, dampness trying to escape and damage paint here in LOS is NOT always "falling damp."  I have 25 year old walls on this property that the paint fails on STILL!  For which I tend to blame continuing rising damp.

Edited April 17, 2019 by The Deerhunter

[RocketDog]

On 4/17/2019 at 7:32 PM, The Deerhunter said:

We also sometimes translate render or rendering ( which are actually the correct trade terms in English) as "plaster" or "plastering", which is understandable but actually plastering is another process using different materials.

I also understand that water trickles down (as many people have pointed out), but DAMP ALSO RISES, (as in "rising damp", refer to Leonard Rossiter in BBC comedy of the same name); in the absence or failure of the essential dampcourse membane.   Which membrane is NOT installed in most Thai buildings I have examined.  I am an old guy of 72 but in my younger days back home, concrete or concrete  block, or solid brick walls were usually (always????) fitted with a bituminous membrane called Malthoid, as a dampcourse membrane between the foundation and the wall, where I come from.  Ventilated brick veneer on a raised base is a different subject altogether, but regardless, here in LOS, I always leave a full month before painting.

So, dampness trying to escape and damage paint here in LOS is NOT always "falling damp."  I have 25 year old walls on this property that the paint fails on STILL!  For which I tend to blame continuing rising damp.

It's pretty easy to believe you're correct. I made a mental note to add a barrier if I ever have a wall built here. For a while I fantasized about selling my property in my Homeland and building a house here.

 

But after reading horror stories on TVF and watching Thai 'artisans' at work I think it's a bridge too far for me.

 

Thanks for the education.