Stain and Sealers for an Outdoor Slate Patio

I think you have it backwards, actually. The stains will continue to develop as atmospheric and exposure effects take their toll.

Sealing the new blue cleaved will actually work against their desire. The rust and yellow stains is a result of oxidation form the elements and atmosphere. Sealing it will keep it from oxidizing reacting.

If you want to get the blue stuff stained try a piece that is not installed and wipe with a weak solution of muriatic (hydrochloric) acid. Let set for a few minutes, then rinse and neutralize with lime or soda. After a couple of tries with different times, and dilutions you'll be as good as a counterfeiter at Mardi Gras passing that slate...

milo

I think the stains were created underground in faults in the slate. The guys at the quarry broke them on the loose cleave lines where water had got in and done its chemical and physical deposition. I just found the tighter ones. Some are iron stains and some are just clay. Unfortunately they are coming off fairly easily. Actually I have seen a change in slate for facing houses in recent years too. The old stuff had lots of browns and reds but as they got deeper in the quarry, the newer stuff is all blue and people are not so keen on it. I have already used muriatic acid on the first pateo to clean off cement stains on the final result. It does not change the blue, even pure. It takes away some of the yellow and red. So something else is required. It is not the end of the world if I do not find a stainer. They find the work good enough. But it would be neat to know and useful on this job or in the future. Brian

Interesting!

milo

I would say they are fighting a loosing battle. I have not seen any clear sealer yet that the UV will eventually damage one way or another.

The sealer will never be a 100% effective, it will end up being worn away where they walk which will give more dramatic color changes and probably spoil the effect they were looking for, then they will want to strip the sealer which will change the colors again etc.

Would have thought the best is to leave well enough alone.

I agree, but I promised that I would look into it. Brian

Aqua Mix 562-946-6877 www.aquamix.com/

HMK Stone Care 800-424-2465 www.hmkstonecare.com

*products advertised as producing a "wet look" are superior at penetration and will bring out the natural colors.

I told them of the danger of a wet and slippy look. I have seen sealed concrete that is slippier than ice when it gets wet and cold. And i mentioned the yellowing over the years problem.

I have advised them against the sealer but it is probably 50 50 if they listen or not. Any word on staining slate? I have never done it myself.

Brian

Yellowing over years is not characteristic of these type sealers. The wet look type penetrates better and lessens the effect of powdering and paths developing.

Few things will stain slate but some are hard-water, chicken fat but I assume it is of Vermont and absorption is minimal. You could sprinkle cast iron shavings and keep the patio wet for a week or two and see what amount of staining you get, try it on a sample first.

I think they're stuck with the blue, they got what they paid for.

Hi,

the stains will intensify with time and new ones will show up.

Most slate contains more or less pyrite (FeS₂) and this is weathering to FeOOH (rust) and the sulphur finally ends up after intermediate reactions/oxidations as gypsum if some Calcium is existing, else the sulfuric acid (from oxidised H₂S) will find some other playgrounds.

The problem with going yellowy is some weathering of the slate itself - depending on silica content and integrity within days to centuries - and reacting to clay minerals that contain some iron - so not white but yellowish.

To prevent this you can melt on a slightly heated surface some paraffin or rub in liquid paraffin. Anything else will cost more except crude oil - but bad smell. Any very fluid colorless paint will work too.

Maybe a good idea to try with "water-glass" (the potassium-silicate version, the cheaper sodium-silicate will give rise to white cloudy surfaces).

RHABE

The wax will create a yellowing and patchy peeling after years, don't do that.

The acrylic sealers do penetrate and actually perform the function.

I don't agree.

If you really use paraffin then it may stain by absorption of soluble organics (asphalt) from the slate.

But peel-off is not happening if you really melted the paraffin on the hot slate. The paraffin will be sucked into the tiny pores and anchored there.

Same as in the pores of anodised aluminum to protect the pores and underneath bare metal.

Same as in paper to get good HF-properties.

RHABE