Thread: Brick / Decorative Facing Block Cleaner recommendations

Originally Posted by RS2OOO

Is someone able to recommend a good product for cleaning my pond's decorative blockwork?

It has suddenly got really bad now and looks a right state.

If only harsh chemicals are available I could get away with doing the sides while the covers are still on, but the coping stones are even worse and they'll need doing too but obviously have high risk of the cleaner getting into the pond.

If it means using 2 products, one for the sides and a less dangerous one for the coping then so be it.

Standard jet wash not do the job mate . Done plenty drives and walls ect

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Brick acid and a stiff paint brush or better a car detailing brush on the sides, to work the stuff in to the contours before a jet wash.

Copings could be tricky, but a slower gentler application of the brick acid before wiping off might do it

You could try white vinegar Steve,works on mold on fence panels but you need to leave it on for a while to do its job, then jet wash off.

Both white vinegar and brick acid would have the same affect if they got in the pond. Depending on quantity they would start to lower the pH.
Brick acid is muriatic acid, and I've seen people on forums recommend adding it to a pond to lower the PH. I doubt that is sensible, but possibly a bit reassuring for you to use it?

Google says vinegar has a pH of 2.5 and brick acid anything from 0-2ph. But you dilute the brick acid, so it's probably safer. Anything from 1:5 to 1:16. So you could start off heavily diluted and see if it works.

This one is ph neutral but it's £80!
BuildKleen mortar and brick cleaner.

https://acute.uk.com/product/mortar-...aner-20-litre/

.... Actually it's £24 for 5 Litres. £80 is for 20 litres

https://acute.uk.com/product/mortar-...eaner-5-litre/

I had a bad case of black lichen growth on the patio slabs and tried pressure washing, white vinegar, patio cleaner etc. None of the them worked.
The product that did the trick was and industrial strength bleach, Sodium Hypochlorite.

It is a bleach but very strong. Wear very old clothes and shoes when you are using it.

Some facts about sodium hypochlorite that may be useful. If not just ignore them.

"Pure" sodium hypochlorite is usually manufactured at 35% strength and is sold at that strength for swimming pool sanitation but is commonly diluted down depending on the purpose for which it's sold.

The Amazon Patio Cleaner is 14 - 15%. Household bleach averages around 7 - 10% strength.

All strengths evaporate chlorine to the air when opened (hence the smell) and the higher the strength, the faster it evaporates its chlorine content.

Household bleach lasts longer in the small bottles it's sold in because the small volume of air in a bottle that is filled to its top when sold doesn't allow much room for chlorine to evaporate.

The reason that products like the patio cleaner is sold a 14 - 15% strength is that it will have been made at 15% strength but will begin to evaporate chlorine straight away even before it has been sold and may already be down to 14% at the time of sale.

So, the moral of this is to use the Patio Cleaner or any of higher strength form quickly and don't store then for "next time" because the strength will be noticeably weaker.

An afterthought about sodium hypochlorite:

When using sodium hypochlorite, you don't necessarily need to use eye protection - you only need to protect the eyes you want to keep!

Originally Posted by RS2OOO

The sodium hypochlorite arrived today, 3 days late having received a message from courier that it was damaged in transit.

It had been re-packaged by Fedex and arrived with the box soaking wet and the huge amount of plastic packaging wrap pooling with bleach.

One of the bottles has been opened as the sealing ring is broken, but it doesn't look like much is missing.

I wonder how much this might have affected the strength in view of Syd's comment about evaporation.

Had to leave the 5 litre bottles in the garden otherwise it would stink the house out.

As soon as the chlorine in sodium hypochlorite has air space above it, it will begin to evaporate which is why 15% strength is usually sold as 14-15% strength so as not to fall foul of Trades Description regulations if some chlorine has already evaporated prior to sale. The very small air space above it in a bottle or tub won't have allowed much to evaporate but having been given the chance to evaporate with a loose lid, evaporation will have started so I would use it as soon as possible because it may already (snatching educated guess out of the air) be down to about 13-14% already. Otherwise it will be OK.

Sodium Hypochlorite did the job with ease.

Masked up all the composite decking and brushed it on as 50/50 with water using a thick soft bristled fence painting brush, left for 10 minutes and jet washed off.

Still have the back half of pond to do and only did the coping stones up to where the covers sit so now they are half black and half clean. My plan for this to avoid contamination into the pond will be to put t-towels in the solution and lay them on the coping before drying off with a towel, then jetwashing the dried residue the next day.

Before (Had already tried the right half with vinegar and household bleach):




After:





Before:





After, and it looks a completely different colour: