Hydraulic lime?

[PeteH]

Hi all,
firstly I’d like to thank FB for their plans and everyone on this site who have shared their wealth of knowledge and experiences
I am getting close to the actual oven build now, finishing off my hearth insulation stage and am now debating on using hydraulic lime in the oven mortar mix instead of hydrated lime, cement and fireclay
I understand that the home brew mix is a tried and tested mortar(and if it ain’t broke don’t fix it!) but I remember using hydraulic lime mix years ago on a brick laying / rendering workshop and was great to work with, had good adhesive properties and didn’t dry out so quickly like cement. I do realise however they’ll be trade offs with drying time and speed of build but I’m not in a rush
I was thinking upon a 2.5 or 3 to 1 mix ratio sand:lime?
Has anyone used to it in their builds, and if so was it a fail or success?

Regards Pete
Ps will by starting my own thread soon

[Wickolad]

Hi Pete, cannot really comment on use of hydrolic lime as no experience with it. However, I can vouch for the homebrew mix 3:1:1:1
3x sand, 1x lime, 1x portland cement & 1x powdered fire clay.
As you previously said, if its not broke why fix it. I agree, it worked great for me.
Good luck with the build.
Regards,
Lance.

[PeteH]

Hi Lance thanks

I got a bag of hydraulic lime for another project (rendering) it haven’t used it and thought it might me a good substitute for using both cement and hydrated lime together
Working well so far with fireclay and a little Portland in mix
have been using a 9:3:2:1 ratio
sand : hydraulic lime : fireclay : cement
Sand is dried sieved plastering sand and fireclay is dust collected by hoover when dry cutting firebricks
Have done first 2 courses/chains and it set quickly if anything a little to quickly for my skill/speed level even with the prewet bricks
Am going to omit the cement part completely in the next course and up the fireclay amount so will be a 3:1:1 sand:hydraulic lime:clay mix
My understanding on previous threads is that the hydrated lime is air set and hydraulic lime sets with water and (as contains clay) so no need for the Portland cement?
Will let you all know it fares as I progress through the build and gradient increases but can always revert to using a little Portland if need be
Regards

Pete

[Wickolad]

Hi Peter,
well done on getting your first couple courses down. I too was very tempted to use the refratory dust collected in the Henry hoover connected to the saw in a bid to reduce dust clouds (even though pre-soaked bricks), thinking on the lines of same alumina content in the mortar as the refractory brick. However, I just wasn't brave enough to experiment.

Regarding the homebrew going off quickly, that appears to be the norm for the stuff. Little and often seems to be the key. But having looked up the difference between hydrolic and hydrated lime, it seems hydrolic lime sets faster, so it could be you're up against setting time more so than usual if I interpreted correctly.

Good luck with the rest of your build and hope you enjoy the project as much as I did. Frustrating at times but well worth it.

Best wishes,
Lance.

[PeteH]

Hi Lance thanks
Just looked through your build again, very impressed and love the “crazy tiling” of the outer dome
I’m guessing you’ve some experience in building, I’ve done a good few patios and stuff on the horizontal plane but get vertigo building vertical
Taking this build slow, and good think about using hydraulic lime is you can add a little water when it becomes drier although will have to leave Portland out if I do this
Forgot to wet course I was laying upon and it sucked the mortar dry instantly
Pete