Advice needed on making my own flags - Additive to prevent wear

[Baldy]

I am experimenting trying to make my own flags which have the appearance of stone. I have done a few small prototypes but have noticed that the sand and cement part of the concrete tends to wear away leaving the aggregate exposed. Is there anything I can add to the concrete which will give it a hard wearing surface. I would also like to know what would be the ideal mix for concrete flags and the ideal size of chippings. I am a complete novice so any advice would be appreciated.

[Tony McC]

This has come up on numerous previous occasions - please use the Search tool to track down the other threads on this subject.

[Baldy]

Thanks Tony,
I have had a good look on the forum and visited your web site on a number of occasions, but I have found very little info on making your own flags. I have used the search tool with many different terms, to try and find out if there is an additive which can be added to the concrete to give it a hard wearing surface. The only thing I have found mentioned is rapid set frostproofer. Would this additive help to give a hard wearing surface and prevent the sand and cement from dusting away leaving the aggregate exposed. I know you are very busy with the forum so your advice is very much appreciated.

[mouldmaker]

If your concrete is any good you won't need additives. If the surface is wearing away it could be a number of things either individually or in combination, ie weak concrete mix, concrete too wet when pouring, concrete hanging around too long between mixing and pouring, excess mould oil.

A plasiciser can make your concrete a little harder because it enables you to reduce your water content, but you should be able to get it right without.

[Baldy]

I have tried different mixes 4:2:1 and 3:2:1 that's 4 parts aggrigate to 2 parts sharp sand to 1 part cement. I do not know the ideal proportions for strength and durability, and I was hopeing someone could tell me. Also what volume of water to add as a proportion of the mix. I suppose from the name mouldmaker that this sort of thing is your main area of expertise, so I am greatful for any guidance.

[Baldy]

One more thing, is there an ideal type of aggrigate for this purpose, for example 6mm lime stone chippings. For my experiments I have been using pea gravel, I was wondering if this could be to blame for the sand and cement crumbling near the face of the flag. As pea gravel has quite a smooth surface compared to lime stone and therefore the sand and cement element of the concrete may not bond as well.

[mouldmaker]

An angular 6mm limestone will be ideal.

[Baldy]

Thanks mouldmaker but did you read my previous post on ideal proportions.

[Tony McC]

There are two key reasons why I don't cover DIY manufacturing on the website: 1 - it hardly ever produces a decent flag, and 2 - there is so-o-o-o much variation in coarse and fine aggregates throughout these islands that a concrete mix that works well in Northampton might be a complete failure in Southampton.

Manufacturers rely on a thorough understanding of their local aggregates, tweaking their mix recipes this way and that way in a continual effort to produce the highest possible quality of concrete. If I was to publish the mix used by a manufacturer in Wigan, you can be sure that a manufacturer from somewhere else will claim their mix is better, or that I'm using too much sand, or the wrong type of aggregate. There is no single "right" mix - just dozens of "good" mixes, depending on where you are.

[mouldmaker]

As Tony says, there's no magic formula, just hard work.

[Baldy]

Thanks for the advice, it looks like I will have to learn the hard way by trial and error. If I produce anything thats nearly as good as the commercially available flags that mimic stone, I will let you know.

I would like to congratulate you for creating such an informative web site. I will be referring back to it many times as I progress through my various projects. Keep up the good work.

[mouldmaker]

Out of interest, where are you sourcing your moulds? And where in the UK are you?

[Baldy]

I have made various prototype moulds my self, they are made of resin rather than rubber. I first made a mould which could break apart, but this in itself causes problems. So my latest attempt is a one piece mould with angled sides so that I can hopefully drop the slab out once cured. None of my equipment is professional purpose made as I didn't want to go to any great expense at this stage.

[Baldy]

I am in the Oldham area near to Manchester.