A few months ago I coated my 1940's CMU basement walls with Thoroseal. The coating began began flaking off one of the walls, so I removed the Thoroseal to reapply. I originally cleaned the walls with TSP and wanted to try something different this time around. Any thoughts on biodegradable etchers? Or something like Behr's Concrete and Masonry Cleaner and Etcher? I am shying away form more harsh etchers given that these are indoor walls. Thanks!

 

TSP is a great detergent but it most be rinsed well! If residue is left on the substrate it will prevent paint from getting a good bond with the substrate. I've never used thoroseal but assume the same would apply. I've used TSP a good bit on the exterior where I could rinse with a pressure washer [or even a garden hose] but have never used it on the inside because of how difficult it is to rinse off the residue.

Are you sure the wall will need to be re washed? Most any cleaner will need to be rinsed but most aren't as hard to rinse off as TSP.

 

It sounds like you have a moisture problem and need to address that on the outside with gutters, downspout extensions and grading first. Just about nothing on a wall can stand up long term to moisture coming through from the outside.

 

I'm planning to rewash the walls before trying the Thoroseal again. The only wall that is pealing is the last wall that was washed/coated, so I may not have washed or rinsed thoroghly. Just wondering if a biodegradable etcher would do a better job of preparing the block.

 

Define your repeated "biodegradable" request. I would use muriatic acid to etch the cement block. Muriatic acid is hydrochloric acid which is a "natural" compound containing hydrogen and chlorine. Both are common, naturally occurring elements and it's the acid inside your stomach. Diluting it with water and contact with bases like cement neutralizes the ph. It's not biologically degradable in the common sense but it is a simple, natural chemical that is easily neutralized so I think that fits your desire.

If you do decide to use muriatic acid make sure you read up how to properly and safely handle it. It is the strongest acid the average person can easily buy and can be hazardous if not used properly. That aside, it is very good at etching and preparing concrete to receive treatments. And since it's nothing but acid it rinses away cleanly and does not leave behind a residue like many other products.

 

IMO muratic acid isn't needed on block, it's more for smooth concrete like floors or poured walls .... not counting cleaning up messy mortar work I would think that the failed coating would have pulled off most of the TSP residue and unless there are other concerns - rinsing should be enough.

 

stickshift's on the right track,,, i think you're using the wrong material if there's lots of water vapor laterally permeating the block,,, btw, IF you want to neutralize acid, use ammonia,,, we use 1 HCl: 6wtrs,,, ammonia is 1 : 6

 

If you re-apply Thoroseal, make sure the wall is misted lightly just before applying it. It also helps to use the some Acryl 60 in the Thoroseal mix and mix strictly according to the directions, including the time of the period to allow it to "fatten up".

Dick