12-10-2012, 01:13 PM
Hi Andy,
The little I know:
- The amount of water you add to cement has a bearing on the final strength of the mix. Too much water=too weak.
- When cement sets, it's a chemical reaction, not a reaction to water as such.
- Making and pouring a mix, and then having it rained on, shouldn't make a difference because the water will sit on top and mixing/dilution will be minimal.
- Allowing rain to fall onto a dry-mix seems to be very imprecise and I wouldn't expect it to work well.
- Fence posts is an exception to the rule because, done properly, the concrete is little more than packing, and the strength or otherwise of the mix is not an issue. I know people that don't use concrete at all - they argue that by leaving out the cement, the aggregates allow moisture to flow away from the base of the post. I can see their point. Last time I did it, I used a type of post fix where you pack it in dry and pour water in.
That is the limit of my knowledge, and that's been picked up over the years by reading around - I'm not a qualified builder!
I guess that we should be asking questions about the size of the trench and the required strength, as well as soil type. It's all a bit "finger in air" at the best of times, and concrete just seems to work well most of the time in my experience.
Good luck,
Mark
The little I know:
- The amount of water you add to cement has a bearing on the final strength of the mix. Too much water=too weak.
- When cement sets, it's a chemical reaction, not a reaction to water as such.
- Making and pouring a mix, and then having it rained on, shouldn't make a difference because the water will sit on top and mixing/dilution will be minimal.
- Allowing rain to fall onto a dry-mix seems to be very imprecise and I wouldn't expect it to work well.
- Fence posts is an exception to the rule because, done properly, the concrete is little more than packing, and the strength or otherwise of the mix is not an issue. I know people that don't use concrete at all - they argue that by leaving out the cement, the aggregates allow moisture to flow away from the base of the post. I can see their point. Last time I did it, I used a type of post fix where you pack it in dry and pour water in.
That is the limit of my knowledge, and that's been picked up over the years by reading around - I'm not a qualified builder!
I guess that we should be asking questions about the size of the trench and the required strength, as well as soil type. It's all a bit "finger in air" at the best of times, and concrete just seems to work well most of the time in my experience.
Good luck,
Mark
