April 02, 2004

In This Issue of The Acid Staining Newsletter

Is it Concrete? Only Your Builder Knows For Sure

I frequently get calls from people who have just bought a home or condo, removed the carpeting, and found something underneath which they believe is concrete. They see my website and think that a nice acid stain job will be the perfect solution to their ugly floor problem. It certainly can be, IF the floor they are looking at is a genuine concrete slab. Sometimes, other products have been put down which look like concrete and are not.

The most common is a white leveling compound made with gypsum and called Gypcrete. Builders often use this on upper floors to level out areas of sub flooring and provide a good base for tile or wood. Unfortunately, staining Gypcrete is out, since it does not take the stain well and is too soft and easily abraded to use as a final flooring material.

We were recently called in to consult on a repossessed home that the owners had been trying to transform in their best do-it-yourself fashion. The house was not built on a slab, but upon short piers with plywood floors. They then poured a cementitious topping layer throughout the house and troweled it coarsely in spots and smoothly in others. The material had a pink-beige cast and, once they scored 2-foot squares into it with a grinder, it did have a look reminiscent of porous limestone laid down in slabs.

The problem was that the topping was only 3/8" thick and when the sub flooring flexed under it, long cracks began to appear, telegraphing the joints between pieces of plywood. We did some stain samples and found that our stain was extremely reactive with this material. Our palest colors became a dark brown. We could have stained by greatly diluting our stain with water, but we decided not to take the job.

Once you work on a floor the owner tends to hold you responsible for future problems, even though you had nothing to do with that aspect of construction. It looked to us as though many more problems might appear on this floor, so we recommended carpet or wood be put on top of it.

Many good cementitious topping materials are now being manufactured to accept stain well and conceal old, gnarly concrete slabs. Before you put a lot of labor into these, be sure that you know the toppings have been properly applied, because future delamination can be a problem with thin toppings. The original slab should be cleaned and roughed up by shot blasting or grinding, then polymer glue applied, and THEN the cementitious topping. Perhaps the safest thing is to apply the topping materials yourself, since it is likely that the client will hold you responsible in any case.

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