Painting concrete block walls

[hdv]

Sorry to sort of hijack this thread, but all this is very interesting to me at the moment, as I am confronted with a related problem.

The souterrain in my new house in Sweden has been coated with all sorts of non-permeable coating (paint, woven vinyl wallpaper, and linoleum on parts of the walls and floor). I am planning to strip all this from the walls and possibly the floors too, as there already is some mould in the souterrain and I really want to get rid of it (bad lungs). You can smell it is damp in there. However, I am wondering if this will improve the ability of the walls to breathe. The reason is that I suspect that all pores will be closed with glue and/or paint. I fear it would be almost impossible to remove that to open the pores again. How would you approach such a case?

 

[six-point socket II]

The Festool answer to that is the Renofix. (RG 130 ECI- )

Everything that can be scraped, stripped i.e. off first, then grind.

Choose abrasive according to what the wall is made of.

Dust extractor with self-clean, separator and air cleaner/purifier/scrubber highly recommended, there’s going to be a massive amount of dust you will need to control. (PPE and if necessary setting up dust walls and dust doors I consider being a given in this situ.)

After that, permeable materials/coatings only, no wallpaper paste.

Kind regards,
Oliver

 

[six-point socket II]

One more thing, I forgot yesterday: If there is any gypsum based plaster on the walls currently, that has to go completely. Saves you the grinding, as that will come of with a small rotary hammer + broad chisel fast and easy. The need for grinding would then only depend on how you want to proceed with those walls/ ultimately which finish you want.

Kind regards,
Oliver

 

[mino]

One more thing, I forgot yesterday: If there is any gypsum based plaster on the walls currently, that has to go completely. Saves you the grinding, as that will come of with a small rotary hammer + broad chisel fast and easy. ...

We have concrete walls in our 1960s flat and the only thing which is pretty much impossible to get off them "easily" is gypsum. That is, without having something like a RENOFIX on hand. Maybe the US has different gypsum compositions, but the one over here is extremely sticky and also relatively soft - meaning it does not "chip off" the wall, as in, at all. Though is no mold there either, so maybe moldy gypsum would be easier to get off even if "our" kind.

I can imagine that with less "stiff" walls, or with old brick walls, plaster can go off easily - being the "hard" material that chips off.

 

[Packard]

In the 1950s to the 1960s USA, Sheetrock (gypsum board) would sometimes be fortified with asbestos, so take all necessary precautions.

My house was built in 1953 and the walls and ceiling are metal lath and plaster (about 1-1/4” thick) prefab panels. My neighbor’s house, built at the same time used Sheetrock. Other neighbors had conventional plaster walls. All by the same contractor. So your house had an early version of gypsum board. Have it tested if you are doing a lot of work on it.

 

[six-point socket II]

If there is mold, there is most likely moisture. If gypsum based plaster is exposed to moisture for prolonged times it is destroyed and looses any and all adhesion. When tapped with either knuckle or screwdriver handle it will sound hollow, and come right off with little to no effort in fairly large chunks with the right chisel.

Grinding to remove at scale, is the worst idea possible in that very instance.

Been there, done that, got the T-Shirt to prove it.

—

Plasterboard is a whole different story but most likely not applicable here.

Kind regards,
Oliver

 

[hdv]

Thanks for thinking with me.

I am afraid it will come to polishing after I have removed all stuff that should not be there. I am quite sure I won't be able to do that without damaging the surface. Thus I (or better said my wallet does) fear a Renofix might indeed be in my future to make the walls presentable again.

Gypsum is about the only thing tat isn't on these walls. So that is one problem I don't have to consider. On the other hand, I found that the glue used to stick the linoleum to the floor and walls is a real pain in the backside to remove.

 

[hdv]

@six-point socket II : I will definitely use my Sundström full-face mask when doing this job. The CTL26AC will have to earn its keep when I am doing this as well. There's just one door leading up to the house, so I will be taping that to keep the dust from getting upstairs. The door to the outside will be opened all the while for sure. Let's hope that will prove to be sufficient to keep my lungs and the house clean.

 

[Packard]

@six-point socket II : I will definitely use my Sundström full-face mask when doing this job. The CTL26AC will have to earn its keep when I am doing this as well. There's just one door leading up to the house, so I will be taping that to keep the dust from getting upstairs. The door to the outside will be opened all the while for sure. Let's hope that will prove to be sufficient to keep my lungs and the house clean.

A couple of 20” box fans used as exhaust will help also. Best to set the exhaust near where you are working so as not to draft the dust across the room.

 

[six-point socket II]

@six-point socket II : I will definitely use my Sundström full-face mask when doing this job. The CTL26AC will have to earn its keep when I am doing this as well. There's just one door leading up to the house, so I will be taping that to keep the dust from getting upstairs. The door to the outside will be opened all the while for sure. Let's hope that will prove to be sufficient to keep my lungs and the house clean.

Place either a dust door, or simply masking foil, in front of that upstairs door. Seal well.

Without knowing about the surroundings, if you can vent outside without disturbing neighbors/ by-passers you can obviously do that with box fan(s) as suggested. I would sill advise to get (rent from reputable source) an air scrubber that will filter.

For the glue issue, if that is still present: Festool offers a special “thermo” wheel for that. It is for heat sensitive materials, that will melt and clog regular diamond abrasives: https://www.festool.com/accessory/s...anding-discs/768023---dia-thermo-d130-premium

It’s available in both 130 and 150mm.

Might be worth looking into as well, depending on how much is left to do - when you’re getting the Renofix anyway.

Kind regards,
Oliver

 

[hdv]

I didn't think about using one or more box fans yet. Good idea. If I am not mistaken, I might even have a self-made one somewhere in the attic.

I will seal the door to the house in any case, so that won't be a problem (I hope, dust seems to have a way to always get in places where you don't want it).

Venting to the outside won't be an issue. The closest house is more than 100 meters away. And during this time of the year most houses are not occupied anyway.

I will definitely use an air scrubber in addition to a mask. I always do with jobs that generate dust. After this, I will probably need new filters...

The Renofix is new to me, so thanks for the link to "thermo" wheel. I didn't know that existed. Looks like something I might need.

To be honest, this is not a job I am looking forward to. But it has to be done, so no use bickering about it. The are some things that take precedence right now, but later this winter I will have to make time to do this.

Thanks for all your insights!

 

[Packard]

For block walls, I’ve had the best luck using a masonry primer first, then a quality acrylic topcoat so the wall can still breathe. It sticks well and doesn’t peel like old oil paints sometimes do. I did something similar after getting , since the cleaner air made me want to freshen up the whole space. A 3/4‑inch roller cover helps push paint into all the pores.

Thanks for that information. I have been having back issues and I have been avoiding this project. It should be done, but I don’t want to pay an outside contractor for the work. The doctors are working on the issue and I remain (slightly) hopeful.

 

[Michael Kellough]

An airless paint sprayer does a good job of getting paint into the texture masonry walls too.

 

[Sparktrician]

An airless paint sprayer does a good job of getting paint into the texture masonry walls too.

I might be careful with that thinking, especially if you want the block wall to be able to breathe.

 

[Michael Kellough]

I might be careful with that thinking, especially if you want the block wall to be able to breathe.

Good advice. I only used it on above ground walls. Hopefully that’s okay.

 

[Packard]

When I was in high school, all the walls in the school were cinderblock, and painted glossy. Starting around 5 foot high to the ceiling (about 10 - 12 feet high) the walls were white. Below that to the terrazzo floor, medium to dark green.

The lower half got repainted frequently, the upper half got washed down during summer recess. I don’t recall the upper half ever being repainted.

In any case, low maintenance. And that is what I was looking for. Back in the early 1960s, that probably meant oil based paint, brushed on.

I’d like to replicate that look with a water based paint, but the whole wall one color.

 

[Cheese]

This may or may not be of any interest to you Packard as it all depends upon what look you want to achieve.
The foundation wall on the outside of our house has over the years (the house was built in 1952) become "dirty" looking and the surface uneven in appearance. I've seen folks paint the concrete blocks on the outside with regular paint but after some time, it always cracks and starts to peel off.
Consequently, I decided to paint the concrete blocks with a very thin slurry of Portland cement. No sand, just the bare Portland cement powder watered down so that the liquid was the color of Portland cement with the consistency of "thick water" or milk. After 20+ years the concrete blocks are still Portland color and the foundation still looks nice & clean after being exposed continuously to weather. The Portland + water slurry is thin so it soaks in to the concrete block and allows it to breathe but enough color remains to tint the blocks.
Before I settled on the Portland color I sampled several other cement powders that are slightly different in color depending upon their contents.
The down side of this process is you're restricted to only a few color hues from gray to white and beige. I did the same thing to a sidewalk and that too lasted about 8 years despite the foot traffic.

 

[Packard]

This may or may not be of any interest to you Packard as it all depends upon what look you want to achieve.
The foundation wall on the outside of our house has over the years (the house was built in 1952) become "dirty" looking and the surface uneven in appearance. I've seen folks paint the concrete blocks on the outside with regular paint but after some time, it always cracks and starts to peel off.
Consequently, I decided to paint the concrete blocks with a very thin slurry of Portland cement. No sand, just the bare Portland cement powder watered down so that the liquid was the color of Portland cement with the consistency of "thick water" or milk. After 20+ years the concrete blocks are still Portland color and the foundation still looks nice & clean after being exposed continuously to weather. The Portland + water slurry is thin so it soaks in to the concrete block and allows it to breathe but enough color remains to tint the blocks.
Before I settled on the Portland color I sampled several other cement powders that are slightly different in color depending upon their contents.
The down side of this process is you're restricted to only a few color hues from gray to white and beige. I did the same thing to a sidewalk and that too lasted about 8 years despite the foot traffic.

Interesting.

You would think that with the porous nature of the cement blocks and mortar, that adhesion would not be an issue (first coat only). Subsequent coats would be the same as any other substrate. But apparently that is not the case.

I know that adhesion is good when topcoating over matte finish paint. (Though I always lay down a thin coat of SealCoat between the paint and the clear top coat).

In any case, the adhesion over concrete (and brick) runs contrary to my intuition.

 

[Michael Kellough]

Interesting.

You would think that with the porous nature of the cement blocks and mortar, that adhesion would not be an issue (first coat only). Subsequent coats would be the same as any other substrate. But apparently that is not the case.

I know that adhesion is good when topcoating over matte finish paint. (Though I always lay down a thin coat of SealCoat between the paint and the clear top coat).

In any case, the adhesion over concrete (and brick) runs contrary to my intuition.

Think in the cases Cheese mentioned moisture gets under the paint so adhesion fails.

 

[mino]

As MK stated.

Keep in mind there is a difference between the indoor side of a wall and the outdoor one. Outdoors you absolutely need water vapour permeable paint, stucco or whatever other covering that will allow the wall to breathe.

Inside, you still want it as such a wall works to naturally compensate indoors air humidity swings during the year. This is unlike with a stick-frame wall that is incapable of breathing - is is one of reasons stick-frame houses are frowned upon in Europe - a stick-frame structure cannot naturally manage indoors humidity like a brick-walled one can be made to.

That said, indoors side of the same wall can be "closed" and prevented breathing in cases where there is sufficient external insulation such that water vapor condensation on the wall surface during winter is not a concern and there is no capillary action issue either from the foundations. It is still a bad idea as it kills one of the main benefits of a brick wall, but, technically, it can be done and work well. That scenario is probably what you observed in the public buildings as well.


EDIT:
Precising MK comment:

Think in the cases Cheese mentioned moisture [I][B]accumulate[/B][/I][B][I][B]s[/B] [/I][/B][S]gets[/S] under the paint so adhesion fails.

What happens is the blocks "pull" humidity from the air or during rain and this cannot escape during the cold night when it would want to ... it instead accumulates below the paint where it condensates and even freezes during cold nights. The freezing is what makes the paint peel off eventually, no matter how sticky the surface is.