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I'm cleaning the mortar off a new clinker brick wall. Walls actually. I hate this job. The builder told me to wash down the wall with weak HCl, leave it for a minute or two, and then spray it off with a pressure hose (eg Kärcher or Gerni). There are lots of problems with this. The main one is that the HCl gets painted on with a coarse bristled brush and splashes everywhere you don't want it to be. The protective clothing is a huge impediment to being able to do the actual job. The safety eye protection fogs up and you can't see how well you've cleaned. Once the bricks are wet, the mortar residue becomes transparent, so it looks clean, only to dry out and turn white again. Then there's the problem with blasting weak acid all over the place. I really hate this job.

So I was thinking that in order get some control over the application of the acid, it would be great if it was the consistency of paint. Then I could apply to only those areas that it needs to be. Question is, how do I make my dilute HCl the consistency of paint? Please feel free to correct me if viscosity is not the right word.

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If the solution is not too concentrated and you dont need it to be stable for a prolonged period, many viscosity modifiers can be used. I would start trying something simple, like CMC based wallpaper paste.

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  • $\begingroup$ So, for the uninitiated, CMC is carboxymethyl cellulose. Will adding the acid to a CMC solution cause a reaction that will neutralise the effectiveness of either or both constituents? $\endgroup$
    – DatumPoint
    Commented Feb 6, 2019 at 14:11
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    $\begingroup$ I wouldn´t expect any chemical reactions right away. Over time the cellulose polymer will probably hydrolyse in an acid solution but it will be a slow process. The effect of polymers like CMC on viscosity is however significantly influenced by pH, so if the solution is too acid, you will lose some effect. Give it a try, manipulating the viscosity of liquids is an art you have to learn by experience :-) $\endgroup$
    – FrankS
    Commented Feb 6, 2019 at 17:39

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