Failed Ceiling Tile Test

Nothing disastrous, not a structural issue… but it didn’t go as planned and it is ugly as sin.

We have been doing a lot of test pours to figure out how to pour concrete for the lower ceilings in the tiny cottage. The above mold made of 1/2″ pink foam that has a plastic sheet coating is the basic form we use for this test. That part works.

This test was 1/4″ of white concrete which was allowed to cure for a week. Then we poured 1.75″ of grey concrete on top of that. What we should have gotten was a tile that was white on one side and grey on the other. The idea is to use less of the expensive white concrete and then use the grey for the structural element.

Unfortunately the dark color, the iron oxide in the grey concrete, bled down through the white. The resulting tile was quite ugly. Back to the drawing board. Perhaps with a thicker layer of white cement this would have worked.

I may end up just pouring white concrete for the entire thickness of the ceilings. It will be more expensive but fortunately the tiny cottage is small. This is just for the loft, attic and utility room which are the ceilings of the front room, bedroom and bathroom respectively. The miser in me does not want to waste so much good white cement but I really don’t want a ceiling that looks like that.

I’m also toying with various impression techniques such as hay, leaves and various edge moldings.

Outdoors: 76°F/44°F Mostly Sunny
Farm House: 76°F/61°F
Tiny Cottage: 62°F/68°F East Insulation, Pillar Caps

About Walter Jeffries

Tinker, Tailor...
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7 Responses to Failed Ceiling Tile Test

  1. karl says:

    i’d have thought that’d work. more curing time on the white layer? i guess layer bonding might be a problem?

  2. Mia says:

    This may be a silly question, but here goes…. Could’nt you use the unattractive grey cement and then paint it?

  3. Mia, then I would have to repaint it eventually and there are chemicals in virtually all paints that I don’t want to have in the house, or at least minimize. By making the white concrete be the ceiling it means it is pressure washable.

    Another way I looked at was using plaster for the lower layer. I did many tests and got quite good at doing the plaster pour – the results are excellent. Unfortunately the plaster is not durable enough. One of my goals is that the entire building is rugged so every year or few we can move all our stuff out and do a real spring cleaning. There are floor drains for this in the slab.

  4. Anonymous says:

    Walter – I know you’re trying to avoid chemicals, but how about an acrylic concrete sealer/bonder? It might prevent the bleed-through and enhance the bond between the two pours.


  5. Good thought, Kevin. I will do some tests with that idea. Thanks!

  6. natschultz says:

    Hi, I just found your site while researching barrel vaults. I think it is totally awesome that you are building your own house! I love that you’re in Vermont, since I’m in the Northeast too, and so much alternative building info is based on Southwestern climates.
    I have some advice on your ceiling tiles (sorry if you’ve already finished them): If they are not structural (mortared into the other concrete parts) you can use lime instead of Portland cement. It is naturally white, however it takes a lot longer to cure (weeks). I also saw your page on parging and using lime on the concrete walls – I have been doing a lot of research on lime vs. Portland cement, and sadly, they DO NOT mix! The best info on this comes out of England, where there are tons of old buildings and lots of research has been done over the last century. Apparently, after WWII, they fixed a lot of the old buildings using Portland cement, but over the years the patching actually fell apart – separated from the natural lime mortar, and the buildings were worse than after the bombing. So, that is why they repair all old buildings with lime mortar and horsehair plaster now. Basically, Portland cement is made with limestone – but it is fired to a few thousand degrees, whereas natural lime is created at only 900 degrees, so the higher temp changes the chemical makeup, and it no longer bonds with natural lime. This is also why P.C. does not breathe and traps moisture in, whereas natural lime breathes and moisture naturally flows in and out.
    As for fly ash (pozzolan), I can’t seem to find any either, except for industry. However, you can get natural pozzolans through ceramic supply companies – it is volcanic ash. You can add pozzolans to both Portland and natural lime – the Romans used broken pottery shards and volcanic ash in their lime cement – that it why it is so strong and has lasted so long.
    I didn’t know about lime corroding steel, so that was good to learn; natural reinforcement is used in lime – reeds, straw, horsehair. BTW: aluminum corrodes in cement, especially if it touches any steel – bad chemical reaction (I don’t know what would happen in pure lime though).
    Hope this helps. Good luck with your house!

  7. Hi Nat, thanks for the info. We ended up not going with lime at all because it is not as washable. One of our goals is to be able to empty the cottage and wash it out time to time. For the ceiling we did a molded poured white concrete with white sand and inlayed stones. You can see that here and here, here. It came out great. As it ages it is getting white and whiter.

    We did find a source of fly ash from ST Griswold in Burlington, VT but I have not yet gotten to finish experimenting with it so it hasn’t gone into any real work yet.

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