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Drying time before redecoration of damp wall

Discussion in 'Plastering and Rendering' started by George Hartshorn, 5 Jan 2021.

  1. George Hartshorn

    George Hartshorn

    3 Jan 2021
    Thanks Received:
    United Kingdom
    • commercial links removed
    I am purchasing a lower ground floor flat and we have identified that there is a fairly bad damp problem.

    We have had a damp specialist in and they have recommended the treatment outlined at the end of this post.

    They have mentioned we should give the plaster 1 month per 25mm of wall thickness to dry out before redecoration (225mm = 9months), and even then only a basic coat of non-vinyl matt emulsion. Full redecoration shouldn't be done for a year.

    We'll be moving into the flat approximately 2-3 months after doing the work, and we're not particularly keen on having unpainted walls for the first 6 months were living there

    Many other places reccomend 12 weeks before applying decoration.

    - Would we be making a massive mistake by putting on a basic coat of paint when we move in?
    - Would this add to the total drying time before we can do a full redecoration?
    - Any recommendations from anyone who has done similar work in the past?

    Thanks in advance for you help

    Recommended treatment

    Remove wall plaster to the heights indicated on the enclosed sketch plan and remove resulting debris from site

    o Rake out joints in so prepared masonry and remove loose laitance.

    o Apply salt Neutraliser to so prepared wall surface

    o mix 1 part **** with 24parts water. All water should be fresh, clean and free from oil or other organic contaminants.

    o First Coat: Prepare 3 parts sand and 1 part cement using the dilute **** solution prepared above. The sand should be specified as washed, sharp sand, loam free which satisfies British Standard BS882:1992 “M” Grading.

    o Use the minimum **** gauging solution to ensure a dense coat. As a guide, no more than 8 litres should be used for every 50kg of dry mix.

    o Compact resulting mix well into the raked out joints, and render to give an overall thickness of 12mm. Do not over trowel. When cement achieves first set, scratch to form a key.

    o Second Coat: The mix is as for the first coat except that water is used instead of **** solution. This is applied as a further 12mm coat, giving a total thickness of 24mm for both coats. This coat should be applied before the first coat has finally set in order to obtain a satisfactory adhesion between the two coats. Scratch the surface to form a key. Do not over trowel.

    Finishing Coat: this should consist of a 3mm layer of gypsum skim finish or similar finish. Do not polish.

    o Ensure that backing plaster is not in direct contact with the solid floor and that a gap of 25mm is left between the wall and the floor, to be covered by reinstated skirting boards.

    o Re-instate skirting’s and fittings


    o It should be kept in mind that whilst the insertion of a chemical damp proof course will inhibit further moisture from rising up the wall, the moisture present will take time to dry out, a guideline is one month per 25mm of wall thickness. Any decoration following treatment should not be carried out until the new plaster has fully dried out and should then be regarded as temporary; I recommend a single coat of non-vinyl, water-based, matt emulsion or plaster primer. Final decoration should not be carried out for at least 12 months following treatment
    Last edited by a moderator: 5 Jan 2021
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  4. Rageyboy91


    14 Dec 2020
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    United Kingdom
    I'm no expert and take what I say with a grain of salt but make sure you find the source of damp before you do anything, as adding cement render over the top of the problem will just make it come back again as it will trap in the moisture. Check the ground levels outside, look for leaks etc not sure if you had an invasive damp survey where they took samples for salts etc but they should really be indentifying the source of the sample. Sorry I couldnt answer your question. Check below and look at peter wards stuff. Best of luck:)


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