Driftwood

Driftwood is a coloured concrete mix option available in South East Queensland from Holcim.

Let’s first show the difference in colour this mix has compared to plain concrete. The 2 photos below show Driftwood on the left, and plain concrete on the right. The Driftwood concrete is still green, so will likely fade more than shown here which means the colour will be lighter again. The plain concrete has cured for about 2 weeks in the photo below.

These photos are ‘off form’ finish, which means a smooth finish surface is made by using marine ply as the formwork. No manual or powered tool finishing is done to achieve this look. Some air bubbles are present in the face of the structure as in this instance this portion of the work is either unseen, or will be covered in some amount, so trying to ensure no air bubbles were present wasn’t high priority when this was poured.

Next, let’s look at Driftwood coloured mix when it is finished using an acid etch.

Acid Etch

Acid etch finish can be used when you want a very light wear on the top of the concrete. This amount of wear off the top is even less than if you were to do a very light water wash.

Acid etch is going to eat the top of the surface slightly, and allow the really fine sand and concrete dust to come off the top.

How strong the acid used should be depends on a few factors. How long since the concrete was poured, how deep of an etch is wanted, and even if the concrete has been in the shade or not can affect what’s needed.

Let’s take a look at some photos of Driftwood after acid etching has been applied.

The left photo shows Driftwood after 1 pass with acid etch. Mix ratio was 1:4 acid to water, and scrubbing with a stiff broom was applied. The surface is wet in these photos to maximise colour and surface texture contrast. The darker parts are where the dark blue stone fines are being revealed. The lighter, smoother looking areas are where the acid has not eaten through the surface concrete because of inconsistency in curing – some patches are harder than others – and that’s what creates this mish mash of colour vs grit.

The right photo shows the surface after 2 passes od acid etch. Mix ratios were 1:4 and 1:2, so the second pass the acid was twice as strong. Spot acid was also applied to more stubborn areas as required to try to get as consistent overall look.

Next, let’s compare wet vs dry appearance of Driftwood coloured mix.

Wet vs Dry Look

In these 2 photos, we have both 1 pass with the acid etch at 1:4. Left is wet with water and right is after the water has dried out. This is also the day immediately after the pour, so the richness of the concrete colour is still at its maximum in these photos.

The left photo also shows a comparison of Driftwood against plain broomed finish concrete which was done a few weeks earlier, and you can see a difference of wet to dry on the plain concrete as well.

Summary

The final look of these slabs, after the 2 passes of acid etch and dried out, gave a very sandy look which fit with the area the job was in.

If any more exposure of the stone in the mix was desired, the finish probably would have had to change to be a light wash exposure because acid wouldn’t get much more off of the surface (1:2 is rather strong and creates strong fumes when doing it).

The only other option to get more exposure without doing a conventional exposure washing would be to have a mechanical scrubbing tool to scrub the surface with, or maybe a very high powered water pressure washer power head.

What do you think?

What do you think of the Driftwood colour, or the acid etch finish? Where would you use this type of finish? Do you prefer 1 pass or 2 passes with the acid? Tell us what you think using the comments below.