Painted a concrete floor

Discussion in 'Painting and Decorating' started by Tonyblade, Nov 29, 2018.

  1. Tonyblade

    Tonyblade

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    Hello,
    I'm after a bit of advice please.

    I painted my garage floor and I have found that I'm getting a film of condensation on the top, specially this time of year.
    I got asked if I prepared the concrete floor before painting and I didn't.

    I was looking to try and remove all the paint with some sort of paint stripper and I was wondering which one is the best.


    Or is there any thing else I could use to put on top of the existing paint to stop the condensation.

    Thanks Tony
     
    Last edited: Nov 29, 2018
    Tonyblade, Nov 29, 2018
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  2. Tonyblade

    Doghouse Riley

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    If the air temperature in the garage is warmer than that of the concrete under the paint on the floor you'll get condensation.
    Best solution is to get some ventilation in the garage.
     
    Doghouse Riley, Nov 29, 2018
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  3. Tonyblade

    Tonyblade

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    Hello the only problem is it is a prefab garage so I can't do anything really.
    The garage door has air gaps .
     
    Tonyblade, Nov 30, 2018
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  4. Tonyblade

    piglet11

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    The conditions for condensation have always been there - humid air, cold surfaces.
    You didn't notice it before because the concrete is porous and absorbed the moisture - you've innocently given it a cold impervious surface and nowhere else to go. I have a garage with a painted floor but it's heated and insulated so no condensation. To be fair I had a lot of expensive tools and materials stored there, so it wasn't an option. What you haven't said is what you use it for. If you are adding to the problem by putting a wet vehicle in there, it just makes matters worse. The only practical thing you can do is to overlay it with ply or something. Before I painted mine, I overlaid it with oil tempered hardboard for dust control and that never got condesation. If your garage is prefabricated concrete, moisture will get through the walls as well. If it were mine and it was important enough, I would line the lot with rigid insulation and ply face it (keeping some air gaps)
     
    piglet11, Dec 7, 2018 at 10:11 AM
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  5. Tonyblade

    Tonyblade

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    I'm using it for my motorbike and tools And my bike never goes out in the rain. I was thinking of getting some paint remover and getting rid of the paint.
    But I have work benches so don't really want to use water to wash it away afterwards.
    I did start to use a heat gun and a scraper but was gonna take to long.
    Is there anything else you could suggest for getting rid of the paint

    Thanks Tony
     
    Tonyblade, Dec 7, 2018 at 6:40 PM
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  6. Tonyblade

    Tonyblade

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    What about if I used these garage floor panels and put them on top of the painted floor
     

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    Tonyblade, Dec 7, 2018 at 7:34 PM
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  7. Tonyblade

    piglet11

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    If the paint is a paint designed for concrete, it might be polyurethane which is hard to get off with solvents or strippers. I've used carbide bladed scrapers successfully in the past, just hard graft. Don't use heat as PU can give off cyanide vapours. I would leave it and cover it.
    Another solution I've used before putting anything on cold concrete is one of the polyester roofing felts (Tyvek e.g.) It's cheap and breathes. Don't use damp proof membrane like polythene. Your final surface needs to have some porosity if the air is moist and the surface cold. Timber-frame building panels are covered with building paper that acts like a roof felt. That might rule out the plastic tiles. I would still give ply a go. A 1200 x 2400-mm sheet of Far Eastern ply is cheap (FE is waterproof so doesn't fall apart). Thickness starts at about 4-mm and goes up. Get a small sheet of any ply (600 x 1200) from B&Q etc. and try it.
    What you haven't said is what the rest of the garage is made of and that will have a bearing.
     
    piglet11, Dec 8, 2018 at 10:41 AM
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  8. Tonyblade

    CarlH

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    I hate to sound discouraging, but it is generally considered (and my experiences bear this out!) that you cannot expect paint to stay in place on concrete unless the concrete is 100% dry.

    This does not address your question about the surface of the paint becoming wet, but other contributors have explained the probable cause of this problem.

    Ordinary concrete (as opposed to paving mix, or commercially made/delivered air-entrained concrete, is porous. So ground water is drawn up through it by capillary action.

    What I go on to say assumes that you used a general-purpose concrete mix for your floor slab and did not lay it, including the sides of the slab, on a damp-proof membrane.

    In practice, even inside a building such as a garage, rising damp may not be a nuisance provided the surface of the concrete is exposed to air currents, which allow the water rising to the surface to evaporate as fast as it appears. But if the surface is covered with an impermeable material (vinyl floor covering, concrete floor paint etc) the water cannot evaporate, and the capillary pressure either causes mould to grow under the floor covering (which may lift slightly in places) or simply lifts a lighter covering such as paint right off the surface. It tends to lift in patches, which then relieve the capillary pressure, so, depending on how much capillary action there is, this may leave substantial painted areas unaffected..

    I imagine that this also applies to the lacquer commonly used to beautify and "seal" the surface of pattern-imprinted-concrete driveways, as well as to garage floor paint. It would not be realistic to expect a concrete driveway to be cast in expensive air-entrained concrete (I don't know about the concrete used for pattern-imprinting, but my neighbour's drive of this type sheds its lacquer continuously and needs re-treating at least every three years). Nor could a driveway slab be laid on a DPM without making the job much more complex/expensive.

    12 years ago we cast a floor slab for a sizeable wooden outbuilding. This stands on the edges of the slab, and is strapped down to avoid any risk of gales etc dislodging it. We laid DPC strips for it to stand on, but this may have been unnecessary because the strong concrete mix that we used has proved to resist rising damp. The building is not specially ventilated, yet the floor is always very dry. Unpainted steel tools and equipment have not shown any surface rusting. The concrete was laid on a sub-base as outlined below. The ground below the sub-base is clay and we are at only 75 metres above sea level, so the clay is rarely dry and the ground water level is usually high. The building itself is of a much better and sturdier construction than an ordinary garden shed, and very draught-proof. The boarding is t&g so, apart from around the door, there are no draught gaps.

    If you have already laid your floor, and not used air-entrained concrete mix, or a DPM, there is no point in pressing this advice on you. A damp-proof membrane (DPM) needs to form a seamless "bag" for the concrete slab, so must be laid on a sub-base of rubble or compacted crushed limestone ("MOT") whose surface must be blinded (made smooth) with sharp sand or hoggin. In a brick/block garage with a normal DPC (damp-proof course) the DPM can extend above the floor surface and then be covered with a brick or tiled skirting so that no damp brickwork is exposed. Your garage does not have a DPC, but the concrete from which the posts and panels were cast may be a strong enough mix to make it more or less waterproof.

    As things stand with your job it sounds as if contributors who consider that the wetting of the surface of the painted finish is due to condensation are right. However, unless you used a mix for your concrete which should make it very resistant to capillary action I fear that the paint will sooner or later start lifting - unless you are on a very well-drained sandy soil, say.

    AIR ENTRAINED CONCRETE

    i owe what knowledge I have on this matter to the long-out-of print "Which? Book of Do It Yourself". This gives the "recipe" for paving mix concrete as an alternative, for a small job, to proper air-entrained concrete from a ready-mixed concrete supplier. You may still find copies of this DIY "bible" for sale on Ebay. My edition is from 1992. There was at least one further edition. After this, the Consumers' Organisation (Which?) unaccountably ceased publication of this, and all the rest of an equally invaluable range of DIY manuals.
     
    CarlH, Dec 8, 2018 at 12:06 PM
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