Will colouring mortar weaken it?

Question

My neighbour has recently had some work done to her roof. The old mortar was red and the new mortar is grey (uncoloured). So it looks a little silly with both colours present.

She's not very happy about this and when she complained they told her that colouring the mortar would make it weaker and more likely to crumble.

Whilst that sounds feasible it also sounds like an excuse. Surely the strength of the mortar is down to the ratio & quality of the mix, isn't it?

(The mortar at the front of the house is red, the replaced mortar at the side is not)

Answer 1

What is mortar doing on the roof???? you mean brick siding up to the roof or on the chimney?

Regardless, adding mortar dye will not weaken the mortar if used properly. I would bet a paycheck that the contractor forgot to add it and is covering his butt. A good contractor would have discussed any concerns with the customer before doing the work. To use a different colored mortar on a repair where visible, sounds pretty incompetent to me.

Answer 2

I agree with shirlock homes. It will not weaken it if used properly. As for what to do now. You can dye it. There are acid stains and water-based dyes.

It seems like acid stain would work better, but it is much harder to make it go where you want it. It is so thin that it just spreads everywhere. Painters tape just soaks it up.

The water based stain is thicker so you can put it where you need it.

Answer 3

Coloring mortar and concrete is a widespread practice. Maybe it causes slight weakening, but not something to make a big deal of.

For example, I often see colored paving tile (made of concrete) in my region and I can't say it's worn out more than uncolored one. Also paving tile is an example of material which is exposed to extreme wear and so its manufacturers wouldn't go for it if it had negative consequeneces.

Of course, you need to use special pigment and do it right.