Concrete bench sighted......

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BiggerHammer:
The table looks spectacular. Very well done. As to the painting there are several two part epoxies used mainly for garage/warehouse floors. Very durable and oil resistant/proof. I have used one type in a warehouse environment, lots of forklift/pallet use and hydraulic fluids and oil had no effect on it. Not sure how well it would hold up to longer term oil exposure.

http://www.sherwin-williams.com/pro/products/hc_shieldcrete_epoxy_concrete_floor_coating/?referringCategory=interior_paint_coatings/masonry_concrete_products/

something like the shieldcrete epoxy was what we used. Though ours was an Industrial product. Probably the same thing. Been years can't remember the name of the original product. Hope this helps with your decision.

PekkaNF:

--- Quote from: John Hill on August 11, 2011, 05:21:54 PM ---Pekka, I will need to pay careful attention to the advice they give me about sealers and painting, but I think I need to let the bench 'sit' for some weeks before doing anything to it.

--- End quote ---

Very true, If you let it cure in peace, it won't "sweat" under paint. I have seen regulary on the mill sites that sealer or such are soread on the floor pretty early, then they assemble all electric cabinets and swithch gear, but primer and twopacks are done very much later, least month or so. I'm pretty sure they would finnish the floor as early as techically possible.

Self cast concrete would need surface ground, I don't know this english name for the weak porous layer that appears over agitated concrete surface, and it has to go off. When I have been on the mill site, some concrete has been chisseld out before groutting under machine feets/plates. Your table looks different, it probably needs very little other preparatio than vacuum cleaning before sealer/primer.

Pekka

Pete.:
You can consider the concrete 'set' after 2 days where it can bear a load, and 'cured' after 28 days which is the usual timescale for a cube test (where they take a sample of the concrete at the time of pouring, ram it into a measured cube form and then later measure the amount of force needed to crush that cube, giving the concrete strength). some people cube test at 7 days. I think that 7 would be plenty for your purposes after that you're not going to get any dimensional changes.

Keeping it damp and covered will give you the best cure as if the water held inside is all used up before the reaction is complete then curing strength will be reduced. In reality, just making sure it doesn't have the sun beating down on it will be good enough. You might get small cracks in it during the curing but don't worry, just seal them up when you do the surface.

John Hill:
Pekka, Pete, the bench would have been poured earlier this week and will be delivered on Monday morning, so it has about 5 days standing in the yard before they bring it to me. This is the middle of winter but the temperature barely freezes and right now we have quite damp conditions which I think is ideal for giving this concrete a good start in life!

They mentioned putting on a sealer before they bring it to me but I dont really know anything about that.

I do have a complication in that my shop is limited in size and I have no means of lifting the lathe onto the bench. What I can do is move the lathe on rollers until it is under a 'strong point' over my garage door. So I can lift the lathe off the existing metal cabinets then slide the bench under it and lower the lathe on, the bench will be on load skates so I can push the bench (with the lathe on it) into the final position when I will put wooden blocks under the bench feet and take the load skates back to the hire shop.

The lathe will be in the approximate position but on wooden blocks until I can get the mounting bolts installed. That is the way it must stay until it is time to put the surface finish on and hopefully the bench will be in its stable state and I can level the lathe on it.

I am going to have to be really, really careful to avoid oil spots getting on the surface during the three weeks or so that it is sitting in the shop with the lathe on it (on wooden blocks). Will sheets of plastic over the top interfere with the cureing process?

Pekka, I have seen reference, when reading the various paint cans, that concrete may have to be etched prior to painting. I really dont want to do that as it would have to be done in my shop and it apparently requires a lot of water for washing afterwards. However, as far as I know, the top of the bench is not the top of the casting as it was cast inverted and this surface was against a steel plate so perhaps that weak porous layer is not there.

Pete.:
You're quite right if it was cast inverted the face will be stronger and less likely to lose dust because the fatty surface is created by the finishing process and fines floating up when the concrete is wet. Covering the bench would not harm the curing but at all since it's a chemical reaction.

Personally, if it were mine, I would dress the edges and seal or paint it now then fit the lathe. Concrete is very tolerant of variable conditions when curing. The 'shrinking' you see talked about is minute (better than tenths of an inch for that size) and most of it is done now anyway. I painted my workshop floor about a week after it was laid with no problems and that was just left to air cure.

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