Blogs

Sealing Concrete

Introduction

I did mention on my micro JoJo page that algal growth was a problem with water collected in a clear container. Also, if you look at some of the other pictures on that page, you will notice algae growing on the concrete around the JoJo. With the heavy rains during the 2024/25 rainy season, this growth became really unsightly. I could not use an algaecide, as the runoff from this concrete was directly into the garden.

My thoughts turned to getting rid of the algae and then sealing the concrete as this might prevent the algae from making a comeback.

The experiment

Before trying to seal the concrete, I had to clean the algae off the concrete. In my first experiment, I scrubbed a small area with Handy Andy, then sprayed that same area with diluted brown vinegar, as this seemed to be a relatively environmentally safe way to kill the algae and any residual spores.

In order to seal the concrete, to try and stop the algae from regrowing, I used a sealer called Proseal which had been on a shelf in my garage for more than 30 years.

I was pleasantly surprised that after three months, the old sealer did prevent the algae from regrowing on my test patch.

In fact, the sealer worked so well, that after six months, the algae had not returned. Unfortunately, the company which had made the sealer was no longer in existence, so I had to look for an alternative as there was less than 2L of the Proseal left.

Experiment 2

As the area to be cleaned was pretty large for scrubbing, and it was rather awkward to get behind the tank, I decided to buy a pressure washer. On the pressure washer's page I have mentioned the problems I encountered in trying to clean this piece of concrete. However, I did get it done. After cleaning the concrete slab, I sprayed a 50% brown vinegar and water solution on the slab, again to kill any residual algal spores. The slab was allowed to dry for 48 hours as it was rather still rather cool in early spring.

As a sealer, I decided to try Warrior Paints' Paving Sealer on the recommendation of the owner of the local Warrior Paints store. What I did was to paint one half of the slab with the remaining Proseal, and the other half with the Warrior Paving Sealer.

The following picture was taken about two months after the sealers had been applied, and after more than 150mm of rain had fallen.

The left side of the slab was treated with Proseal, and the right with Warrior Paving Sealer. The left side looks a bit better than the right side, but as yet there is no algal growth.

I will update this page again in the new year.

(17 November 2025)