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!