UK.D-I-Y FAQ PART 2: MISCELLANEOUS: **UPDATED**
Matthew Marks
Last Updated: 18th May 1999
Changes this time:
Section 14 and 15 added
0 CONTENTS
==========
1. USING SILICONE SEALER
2. PAINTING TILES
3. REMOVING ARTEX
4. DROPPING WIRES THROUGH CAVITIES
5. REMOVING SCRATCHES FROM PLASTIC
6. DRILLING SMOOTH HOLES
7. WASP BYKES (AKA NESTS OR BIKES)
8. FLOOR CLEANING
9. SEALING GAPS BETWEEN FLOORBOARDS
10. WOODWORM TREATMENT
11. REMOVING LEAD PAINT
12. FIXING BLOWN PLASTER
13. REMOVING PAINTED WALLPAPER
14. INSULATION AND CONDENSATION
15. REPAIRING LATH AND PLASTER CEILINGS
1 USING SILICONE SEALER
=======================
(John Laird: jo...@yrsk.demon.co.uk; edited by Matthew Marks; additional
material from Rick Hughes: rick_...@qmail.newbridge.com)
You should be able to remove old sealant with a sharp razor blade and
some care. Run the blade down the wall and along the bath to release the
edges, and with a bit of luck the strip should come out in one go - good
stuff has more of an affinity for itself than the surrounding material.
If it has squeezed down into a crack, it may be easier to cut through the
strip and leave the rest behind - if it's well stuck, I'd figure you may
as well leave it. Then make sure there's no residual dust and that the
surfaces are completely dry. Meths has been suggested as an aid to remove
old sealant, and certainly cleans the surfaces.
As for mould resistance, I've never had any problem with the more expensive,
high-silicone varieties. Whatever you do, don't buy cheap stuff ! You should
be able to tell the difference from the pack - if "silicone" doesn't appear,
or if it doesn't tell you that a vinegar smell is released during curing,
leave well alone. Wickes charge about 4-5 pounds for a 310ml tube. Get a
sealant "gun" as well. Cheaper sealants are acrylic-based and much less
durable.
1. Cut the nozzle to the right size. Easily said, of course, but in fact
too small an aperture is just as difficult to deal with as too large.
2. Try to squeeze the stuff out *all in one go*. Don't squeeze the gun
too hard, and you should be able to go round a whole bath in just a
few minutes. This leaves you free to get on with the smoothing without
worrying about the gun oozing all round - release the trigger pressure
when you've done and lay it down somewhere you won't stand on it.
3. Find a smoothing implement with the right curvature. Whatever you do,
don't try to use a wet finger. Attempt no 1 at our bath went wrong this
way, or rather it failed the "spouse test" despite being serviceable!
(Nos 2 and 3 were cheap sealants, no 4 was back to silicone.)
I eventually found an old, rounded kitchen knife had just the right shape.
4. Keep the knife (or whatever) wet at all times, and clean it frequently
with copious quantities of kitchen towel, re-wetting it before moving on.
(this stuff is *sticky*).
5. With care, it is possible to go over the strip a couple of times, the
first pass getting rid of excess sealant (as well as squeezing it into
the gap), with the second pass putting a smooth finish on. Try to "cut"
through the excess sealant on both surfaces with the edge of your knife.
Then leave it all alone for a couple of days.
6. Finally, remove the excess strip outside your "cut" edge, with a sharp
blade. If there's only a small amount, you may even find you can rub it
off with a dry finger. This is easier than trying to produce a perfect
finish when the sealant is still wet - invariably you poke something
into the beautifully curved corner and wreck it. Alternatively, you can
lay down two strips of masking tape either side of the join. Once a skin
begins to form, pull off the tape at an angle.
Et voila ! Easy really, after 3 or 4 goes :-)
2 PAINTING TILES
================
(Steve Barnes: sba...@msmail.bfsec.bt.co.uk 23/4/96)
1. Clean the tiles with a weak detergent, and remove any blemishes.
2. Clean with cellulose thinners to make sure there is no grease on the
tiles. Be sure not to touch the tiles after you do this!
3. Paint with a plaster primer and allow to dry for 24-48 hours.
4. Apply your finishing coat (liquid gloss recommended).
MM: Tile paint is also now available!
3 REMOVING ARTEX
================
(Matthew Marks 23/4/96)
As this crops up so often in the newsgroup, there must be an awful lot of
people who hate the stuff :-). Anyway, the consensus seems to be NOT to
sand it - not only does this produce a horrendous amount of dust but early
Artex contained asbestos fibres - but to remove with a steam wallpaper
stripper. Failing that, you can always plaster over it.
4 DROPPING WIRES THROUGH CAVITIES
=================================
(Can't remember: please identify yourself to claim credit! 7/5/96)
It can be very difficult to drop a cable down a cavity wall and retrieve it
through a small hole into the cavity. Make the hole large enough to feed a
loop of old steel measuring tape through it. As you push the tape into the
hole, it will expand into a loop along the sides of the cavity. When you
dangle the cable approximately above the hole, it will go through the
loop, and pulling the tape out will then retrieve the cable.
(Jim Mortimer: jim.mo...@bbc.co.uk 16/5/97)
I find that curtain wire, of the type used to hang net curtains on is
ideal for this kind of job, as well as a drawstring for running cables
or hoses through any complicated route as it's so bendy.
(Richard Gethin: Ric...@rgethin.demon.co.uk 19/11/98)
The lid from 16mm mini trunking is very good for pushing along
voids/hooking cables in voids.
(Mungo Henning: mun...@itacs.strath.ac.uk 16/5/97)
Buy a small length of ferrous chain (like the stuff which would be used
in the dog-lead of a small mutt) of about three or four inches long (or long
enough to be 'sufficiently' weighty: depends on the quality of the links) and
tie it to a bobbin of twine. Drop this down the cavity, having inserted a
magnet at the place where you wish to retrieve the cable. With a strong enough
magnet, the chain will stick and you will be able to pull the twine through.
I now have an old 35mm-film container which contains the chain connected to
the twine, and a separate magnet attached to an old telescopic aerial (neat
for the tool-case). Works a treat so long as you don't drop the chain onto
Live and Earth!
Another idea is to connect a lilliput bulb via bulb holder
onto some co-ax cable (of the same diameter). Connect the other end to a
suitable battery. This helps when you need to see into a cavity hole. The
light has been worth its weight in gold over the last few years.
5 REMOVING SCRATCHES FROM PLASTIC
=================================
(Donald Gray: D.G...@AutoComm.cityscape.co.uk 10/5/96)
You can do a great job repolishing plastics, especially harder
plastics like Perspex. It depends on the depth of scratch on which technique
to use.
Deepish scratches:-
1. Start off with "Wet & Dry" paper (say grade 600) using a soapy
water as a lubricant. (The water is vital to keep the paper grains
free.) Gently "grind" away at the area until you cannot see the original
scratches. (The area will go like frosted glass, but don't worry at
this just yet!);
2. Change grade of Wet & Dry to 800 and do the same;
3. Change to grade 1200 wet & dry. do same grinding...
(The basic principle behind this is to substitute deep scratches with
shallower and shallower ones.);
4. Once you have got through the 1200 grade process, thoroughly clean &
dry the area;
5. Use "Duraglit" or "Brasso" BRASS polish to remove the "frosted"
effect;
6. Once this looks nice and shiny, use a SILVER polish to give a
final finish.
For fine scratches, start at 4) above.
SECRET: Take time; don't rush it. Even when you think the scratches have
gone, give the process a bit longer. There are NO short cuts to polishing,
but it can be done in less time that one thinks....
Most DIY or car maintenance stores now stock the finer grades of
"Wet & Dry" papers. (Tip: I keep a penknife razor sharp using 600 &
800 grade!) Don't forget: Soapy water is ESSENTIAL.
6 DRILLING SMOOTH HOLES
=======================
(Ken Clark: k...@g4mpq.avel.co.uk 20/6/96)
For those who like me, have limited facilities and have difficulty
drilling largish holes in sheet metal, there is a simple way of
ensuring that you end up with a smooth hole without burrs. Position
and secure the work as usual. Drill a small pilot hole as a matter of
good practice. Take a piece of thin cloth about 3 x 3 inches and fold
it twice to make a small pad. Place the pad over the small hole and
bring the large drill down so that it takes the spinning cloth through
the hole as the large drill makes it's way through the metal. If you
practice on a couple of pieces first you'll rapidly see what is
expected - it's easy, safe and it does make a beautifully smooth,
round hole instead of the octagonal horrors I always used to make. Oh,
and it doesn't matter too much about the colour of the cloth!
7. WASP BYKES (AKA NESTS OR BIKES)
==================================
(Barrie Walker: bwa...@csl.co.uk 29/7/97)
Disclaimer
----------
This is all derived from the postings to this group, or possibly discussions
with friends, who would have been posting had they access. I myself have no
extraneous knowledge of the subject.
Background
----------
Wasps seem to come to life in the spring and die off in late autumn. Unlike
bees, they build new bykes each year. They never use an old byke and the
presence of an old one doesn't, of itself, encourage them to use that place
again, but what encouraged them to build there in the first place (e.g.
proximity of fruit trees) may well still be present. You may have to address
this for a complete solution.
The size of the bykes can vary wildly from that of a golf-ball to that of a
football. The larger ones can house tens of thousands of wasps.
During the winter, the byke will be empty - the queen away hibernating
somewhere warm and the workers all dead - so dealing with that [old] byke
achieves nothing - indeed, some say that they make very good insulation.
On the other hand, sealing the hole they were getting in by will give that
place one less tick in the `Which Byke?' guide. Note that, if the hole is
needed for ventilation, some suitably-sized mesh could be used.
In Defence of Wasps
-------------------
You should think twice before getting rid of a byke unnecessarily as the wasps
are hard working gardener's assistants, eating insects, caterpillars and other
nasties. You may be well to actually encourage at least one byke about the
garden (though not in the house) as they do a fine job of culling greenfly and
the like.
Dealing with Them
-----------------
There follows various ways of dealing with bykes once found. In the DIY
section, inclusion does not suggest suitability.
Non-DIY
-------
1. Professional Exterminators
Typically they will come and remove the byke and spray powder insecticide
around. This may cost up to UKP 50 +.
2. The Local Council
Phone the council pest control people and they'll send someone to deal with
it. Cost varies from place to place, with some places even doing it free
of charge (which sounds like a very good deal to me if it's on offer) but
this is getting rarer.
3. Your local Angling Club
Contact the secretary of your local club. They use wasps as bait and will
often come and remove the byke for you free of charge.
DIY
---
4. Laisser Faire
If it's late enough in the season and you can stand it, just leave them
be. Once the season is over (no more wasps), block the entrance hole (see
above) and hope for the best - it worked for me. However, some people are
allergic to wasp stings, so this may not be a valid option.
For the other methods you need to be able to see the byke, and you need to be
active when the wasps aren't, i.e. when it's cold and/or after dark. Some claim
to have done this often without once getting stung! But be careful, protect
all areas of skin especially the face. Multiple stings can be potentially
life-threatening. Whatever you do, don't be a hero!
5. Obtain (the only product mentioned by name in the postings) a powder by Bio
called Wasp Nest Destroyer costing (then) UKP 2.65. Bearing in mind the
precautions above, puff the powder on the entry to the bykes. One
application should suffice. An ant-killer powder may be just about as
effective.
6. You should be able to get an aerosol spray or non-aerosol liquid jet (c.
UKP 5) from your local garden centre. Bearing in mind the precautions above,
spray the concoction on the byke itself. With the liquid jet you may not
have to get any closer that 15ft depending on your ability to aim.
7. Obtain a 200ml tin of lighter-fluid (contact poison for wasps) and a 350ml
spray can of clear acrylic spray (e.g. a Holts touch-up can!). After dusk,
when they're drowsy, coat anything that flies in the acrylic. Once
everything's quiet, drench the byke in lighter fluid. Later, when there's
no more buzzing, remove the byke and, preferably, burn it. Note that
lighter fluid is basically petrol and is highly volatile and inflammable.
8. You can also get an aerosol that emits a freezing blast and literally
freezes and stops them in mid flight. You can direct the same product into
the byke too. You've still got to kill them but it may give you a
breathing space and allow you to do the deed during daylight.
Pedalling the `Byke' Word
-------------------------
Andy Dingley enlightened (some of) us, "Etymology is unknown, and although it
originally applied to wild bees (not a hive or skep of cultivated bees), it
also has a long pedigree of application to nests or swarms of wasps, hornets
and even flies."
8. FLOOR CLEANING
=================
(Charles (Joe) Stahelin: j...@stahelin.demon.co.uk 23/9/97)
8.1 Introduction
----------------
The following notes were written in 1990 on the basis
of hands -on experience before my retirement in 1987. In the seventies
and early eighties there had been a great deal of development covering,
effectively, three generations of floor dressings - a term used to
describe the modern liquid floor polishes: this resulted in the once
established habit of stripping off all polish at regular intervals being
abandoned and replaced by more effective systems of floor maintenance.
Money was getting tight and it could be clearly seen that it would get
tighter yet. The producers of floor cleaning products had to compete
for sales on the basis of price both in the tin and on the floor, as
well as appearance. It was a period of rapid and important development
but I have to admit to not being fully conversant with developments that
have arrived on the scene since 1987. I recommend investigation, and
where possible practical testing, before anyone commits themself,
finally, to the use of a particular process or product. If access to
schools or similar institutions is possible, a look around the floors in
the middle of term, looking into the edges and corners and doing the
Finger Test (described in section 6), is worthwhile: if all is well try to
get into friendly conversation with the caretaker who, as (s)he is not in a
position to sell, may be regarded as an independent adviser.
8.2 General
-----------
There is no real difference in the processes for hard
floors whatever equipment is selected for use. At the outset it is
essential that all trace of any cleaning agent or dressing that may have
been applied previously has been removed, and that there is no residual
alkalinity (some detergents and all polish stripping solutions being
alkaline). It is also essential that the floor is dust-free: this can
be achieved by the use of a vacuum or by damp mopping. To sum up, the
floor should be as nearly as possible as new.
8.3 Porous Floors
-----------------
If the floor is porous (unglazed tiles, some compositions - but see
paragraph 10 below for wood, cork and similar). It is advisable to start
off by applying a Water-Based Floor Seal which will fill the pores and make
a good base for the floor dressing. Seals are similar to the top
dressing but contain a high proportion of solids. If a floor seal is
not used on a porous floor it may be necessary to apply substantially
more coats of dressing to achieve a surface than would otherwise be the
case. Floor seal is usually less costly than the dressing and its use
when indicated will save time and effort.
8.4 Non-Porous Floors
---------------------
If the floor is non-porous (or after sealing as in paragraph 3): apply
thin and even coats of polish allowing each coat to dry before applying
the next. The first coat is applied over the whole floor, right up
to the walls: the second coat stops between three and six inches away
from skirting boards, and all subsequent coats stop about nine inches,
but not less than six inches away from skirtings. On a `new' floor
three thin coats are advised as a minimum. In any case, continue
applying coats until a 'surface' is achieved: the situation can best be
judged by looking at the floor obliquely against a light source, natural
or artificial. When a surface has been achieved it is beneficial to
apply further thin coats to heavy wear areas such as doorways (roughly
in a fan shape narrowing towards the door), on the treads of staircases,
in areas where walkers change direction, and below work areas where feet
are likely to be shuffled about..
Note: If the means is available, the buffing of the floor
between coats, between alternative coats, or whenever time permits, is
recommended as it hardens the finish and is understood to improve its
wearing properties.
8.5 Maintenance
---------------
On a day-to-day basis, unless the floor is subjected to
heavy wear, it should be necessary only to remove surface dirt by
brushing, by vacuuming, or by damp/wet mopping, or by a combination of
these - different methods being used on different parts of the floor
according to need. A final vacuum over the whole of the floor is always
worthwhile. Periodically, in order to restore the floor to as new, or
daily in heavy wear areas, the floor will need to be buffed with a
cleaning/polishing pad under some sort of appliance. It is, however,
important that sticky messes are first spot-cleaned by mopping or
washing. Provided that the floor has an adequate covering of polish
the buffing process will both convert normal dirt to loose dust and work
the polish on the floor, making good fair wear and tear, including shallow
scratches, without the application of new polish. This buffing process
is improved with the application of a very fine spray of water
containing a small quantity of neutral detergent: this can be dispensed
conveniently from a trigger bottle. The detergent acts as a wetting
agent, reducing the surface tension of the water in the spray, and does
not act as a specific cleaning agent in this application. The water
spray should be almost invisible: if too much is applied the floor and
the buffing pad gets wet, the polish on the floor re-emulsifies, and
everything becomes difficult, time consuming, and therefore expensive.
It should be noted that, in the processes so far described, there has
been no application of polish apart from that applied in setting-up the
floor from 'new'. The use of a dilute polish solution when Spray
Cleaning (the recognised term for the process described in the previous
paragraph) is recommended by most people in the business on the basis
that as well as making it easier to restore the surface it also deposits
a sufficient quantity of floor dressing to extend the period of use
between re-applications of polish. Personally I do not support this on
the grounds that the emulsifier and plasticisers in the sprayed polish
soften that already on the floor, resulting in polish from the floor's
high spots being swaged over dirt particles lying in low spots (e.g. the
bottom of scratches) and thus enclosing them within a layer of polish.
This needs further investigation - I tend to wonder whether this idea
arose from the need of the manufacturers to increase throughput when the
general practice of stripping polish from floors as a matter of routine
was abandoned.
Further applications of polish must be made at intervals in order to
maintain a useful layer of polish all over the floor surface, edges
excepted. It is probably better to undertake this as and when
convenient opportunities occur rather than to wait until the failure of
ordinary maintenance processes indicates the need for it to be done.
Small areas of the floor can be treated in isolation provided that they
are properly prepared and provided that polish is not applied to areas
that have not been prepared: this implies including in the prepared
area a buffer zone of about six inches which extends beyond the worn
area onto floor that still bears a useful polish film.
Proper preparation before applying polish is vital. Essentially, it
is the same as for preparing a new floor except that the floor does not
have to be bottomed: to do so is to waste a good foundation of
expensive polish. The existing polish surface must be cleaned
thoroughly, all embedded grit, etc, being removed. This is best done
by using the appropriate pad under a machine or bumper. Failing a
suitable appliance hands and knees work with a scouring pad seems
indicated but it would be worthwhile trying out some ad hoc arrangement
with an old broom and a suitable scourer - fairly fine steel wool (Grade
0) is very suitable. Scouring finished, remove all dust by vacuum,
damp mop or similar, then apply polish as for a new floor.
9. SEALING GAPS BETWEEN FLOORBOARDS
===================================
(Matthew Marks)
People often ask how to prevent icy draughts coming up through gaps between
shrunken floorboards. The boards can, of course, be removed and re-layed
properly butted (and tools are available to ensure this), but this is a major
job. Also, floor coverings will stop the air movement. Besides that, people
have come up with various suggestions:-
-papier mache, sanded afterwards
-narrow strips/wedges of wood
-silicone sealant, if it will stay put while it sets (NB you can't paint/
varnish this)
-if tongue and groove, varnish will seal many gaps
-if access to the underside of the floor is possible, polystyrene tiles wedged
between the joists, or polythene sheet stapled to them (Note: do not allow
electrical cables to come into contact with expanded polystyrene, as it leaches
the plasticiser out of the cables. Protect with polythene sheet, etc.)
-wax, but only if re-applied regularly
10 WOODWORM TREATMENT
=====================
(Matthew Marks 1/4/98)
People often wonder if holes in items of furniture etc are a new or an old
attack. If they are new, the holes will be clean (new-looking wood visible
inside), and there will be little piles of woody dust below them, if the
item hasn't been moved. If old, the holes will be dirty.
It is recommended to treat with dedicated woodworm fluid, rather than general
purpose timber treatment. Follow instructions on the can.
11 REMOVING LEAD PAINT
======================
(Chris French Chris...@spennithorne.demon.co.uk 15/4/98)
Buildings built in the 1960's or earlier are likely to contain lead. While
sound paint surfaces present no risk, particles or flakes of lead paint
present a risk to health, especially to children if ingested.
Lead paint can be removed safely as long as some simple precautions are
taken. The main aim is to avoid producing any dust containing lead or
lead fumes which can be released if the paint is burnt.
Removal
-------
Don't burn off with a blowtorch, as this produces lead fumes.
Don't rub down dry, especially with a power sander, as this produces lead
rich dust, which will spread around the house.
Use a hot air gun (but don't burn paint), chemical paintstripper, or
rub down wet, using "wet or dry" paper.
Disposal
--------
Dispose of all paint debris in a sealed plastic bag in dustbin. Don't use
a normal domestic vacuum to clean up, as the filters are not normally fine
enough to trap the lead dust: hire an high efficiency industrial one instead.
After Work
----------
Wash hands etc. thoroughly before eating and after finishing work
This information was taken from a leaflet published by the
Paintmakers' Association,
James House
Bridge Street
Leatherhead
Surrey
KT22 7EP
Tel. 01372 360660
Fax. 01372 376069
12 FIXING BLOWN PLASTER
=======================
(Stuart Grant: s...@cwcom.net 21/9/98; edited by Matthew Marks)
Sometimes plastered solid walls become "blown", i.e. the basecoat becomes
separated from the wall behind. This can be detected by tapping the plaster:
it will sound hollow where it is blown. It could stay like that for many
years without trouble or it could crumble away and fall at the next shock
wave from a heavy lorry passing. If it falls off in 3 years you'll have no
comeback on today's plasterer.
A simple fix is to glue the loose areas back to the masonry with
PVA bonding. Drill a 1/4inch hole sloping 45deg down near the top of the
loose area and work a six inch length of 1/4" neoprene tubing into the
hole. Seal around with blu-tack. Attach the other end of the tube to a
washing up liquid bottle with the bottom cut off to form a funnel and
securely tape it to the wall above. Fill the funnel with PVA watered
down to the consistency of full milk and leave it to flow slowly into
the hollow behind the loose plaster. Pressing the loose area gently in
and out will help the flow and spread the bonding. A second hole at the
bottom of the area will tell you when the bonding has got there. Don't
try and hurry things with a squeezey bottle or you could push the
plaster off and break it. It should be fixed and dry in 24 hours.
PVA can also be used to fix sagging lath and plaster ceilings: prop the
sagging plaster back into place, and apply watered-down PVA from above.
13 REMOVING PAINTED WALLPAPER
=============================
(Mike Dean: mad...@garak.idiscover.co.uk 15/9/98)
Painted or vinyl wallpaper can be hard to remove, as the paint/plastic stops
the water you apply getting to the dried paste behind. You therefore have to
score it with a special tool, or some nails hammered through a piece of wood.
After this, apply the same technique as for ordinary wallpaper: use the hottest
water you can stand, and put some washing-up liquid in it to encourage it to
adhere to the paper. Most importantly: give it time to work.
14 INSULATION AND CONDENSATION
==============================
(Matthew Marks 17/5/99)
14.1 The Problem
----------------
In our eagerness to slap up insulation everywhere, the potential problem
of condensation is sometimes overlooked. Air can hold a certain amount of
water vapour, and the higher its temperature, the more vapour it can
contain. Air in houses in winter often contains more moisture (from
breathing, washing, cooking, etc) than the cold air outside can hold.
Thus, if you insulate a surface but do nothing to stop vapour penetration
(and things like plaster, wood, brick, concrete, mineral wool, and even
expanded polystyrene allow vapour to penetrate easily), you may get a
problem. This is what happens:
INSIDE | INSULATION | BRICK WALL | OUTSIDE
| | |
temp.+++ | |
| + | |
| + | |
| + | |
hum. ******* + | |
| *****+ | |
| **X** | |
| +***** |
| ++++*+*+*++ |
| | **+*+++++++++ |
| | ***** ++++++++++++++
| | ***** |
| | ***** |
| | *******
| | |
The above attempt at ASCII art (if it *really* doesn't make sense then it
serves you right for viewing in a proportional font) shows a cross
section through an insulated wall, with temperature and absolute humidity
graphs superimposed. The temperature and humidity each side of the wall
are those of the atmosphere on each side. Although the temperature
inside is higher than outside, the humidity line is below the temperature
line at each point, representing less than 100% _relative_ humidity -
i.e. humidity relative to the maximum amount of water vapour the air can
hold at a particular temperateure.
The insulation retards heat transfer better than the wall behind, so the
temperature drops much more quickly within the insulation than within the
wall. However, the insulation and the wall are equally vapour permeable,
so the absolute humidity drops linearly. At point X, the two lines cross
- at this point in the insulation the air gets too cold to support the
amount of moisture it is carrying. In other words, dew point (100%
relative humidity) has been reached, and condensation will occur. At
this position it is known as interstitial condensation, and will saturate
the insulation, rendering it less effective. More seriously, it may
cause rot in any supporting timbers. It is particularly bad in this
location because there is no ventilation to remove it quickly when
conditions are more favourable (less absolute humidity and/or higher
outside temperature.)
14.2 The Solution
-----------------
The solution is to put in a vapour barrier, like polythene sheet or a foil
backing to plasterboard, to alter the profile of the vapour concentration
through the wall. You will then get something like this:
INSIDE #| INSULATION | BRICK WALL | OUTSIDE
#| | |
temp.++++ | |
#| + | |
#| + | |
#| + | |
hum. ***| + | |
*| + | |
*| + | |
*| + | |
*| +++++++++++ |
*| | +++++++++++ |
*| | ++++++++++++++
********************* |
#| | ******************** |
#| | ************
#| | |
The step change in humidity caused by the vapour barrier (symbol #) has
made sure that the relative humidity is well below 100% thoughout the
wall. The vapour barrier is not assumed to be perfect (it will have
joins, nail holes, etc), so the absolute humidity just behind the vapour
barrier is still a little higher than outside, but an imperfect vapour
barrier is usually good enough in most circumstances.
Note that the position of the vapour barrier is very important: it has to
be on the _warm_ side of the major insulating element. If it is on the cold
side, it will make matters worse by maintaining higher humidity
through the insulation.
As has been mentioned, the problem of condensation is worse if there isn't
good ventilation to blow away the vapour when conditions allow it to
evaporate, such as in insulated walls, where a vapour barrier is
essential. However, you can usually get away with insulating the floor of
the loft if there is good eaves ventilation and the insulation is baked
regularly when the sun shines. But if the loft is boarded, any
condensation will take much longer to evaporate. It is thus a good idea
to place a vapour barrier underneath loft insulation in these
circumstances, especially over humid areas such as bathrooms. Foil backed
plasterboard is ideal, but strips of polythene between the rafters will do
some good. Don't loop it over the rafters or it will be on the cold side
of the insulation at some points. If the loft becomes a heated habitable
room, the problem is transferred to the insulation above, because that is
where the temperature gradient occurs. For the same reason, condensation
between floors isn't usually a problem, and it is rare to have air bricks
to allow ventilation. (Air bricks below ground floor level are to allow
damp rising from the ground, as well as humidity from above, to be
dispersed.)
15. REPAIRING LATH AND PLASTER CEILINGS
=======================================
(Matthew Marks 18/5/99, with input from Stuart Grant s...@cwcom.net)
Ceilings and stud partition (i.e. not solid) walls were made out of lath
and plaster before plasterboard was invented. Laths are thin strips of
wood which are nailed between supporting timbers, separated by small gaps.
When the laths are plastered, the plaster is squeezed between the laths
and the resulting "nibs" hold the plaster in position.
Over the years, these nibs can break off (due to movement of the ceiling
or disturbance from above), and the ceiling can start to sag. It is also
possible that the laths become detached from the supporting timbers
(usually due to the nails rusting if the structure has been damp).
If a ceiling is bulging due to nibs breaking off, it can be repaired, if
you have access from above. Hoover out any debris from between the laths
and the sagging plaster (which may be easier if you cut out a lath), then
carefully prop the plaster back into position with a large board, so that
the load is evenly spread, and find some way of maintaining the board in
position. Apply PVA glue liberally from above, diluted one part glue to
three parts water, and remove the props 24 hours later.
It is also possible to glue laths back to joints using liberal amounts of
undiluted PVA glue between laths and joists before propping the ceiling
back into position. Nailing the laths is likely to damage the plaster
too much.
If the ceiling is particularly bad, you can either remove it and start
again, or plasterboard over it. Removing ceilings is a horribly messy job
and, if you remove the laths too, you will have to take away any loft
insulation first; but you will not lose any height when you install the
new ceiling, and it may be better if you have coving.
It is best to screw rather than nail the new plasterboard in place.
Nailing is less reliable, causes more disturbance (to the house as well as
its occupants!), and is not much easier if you have access to an electric
screwdriver. Special plasterboard screws are designed to hold the board
firmly, if you take care to tighten them flush but not to break through
the paper surface. They are available long enough to pass through an
existing ceiling. It goes without saying that the fixings should be into
the joists, not the laths!
Plasterboard is available in taper-edged form, where a small area along
the long edges is thinner. If the fixings are in this thinner section,
then the joints can be taped (with plasterboard tape, which prevents
cracking of the skim coat) and the area filled with a skim (top) coat of
plaster to give a good finish. The short edges are parallel with the
joists, and the board is cut to co-incide with them, preventing any
movement here, although making finishing to a high standard tricky.
Alternatively, standard plasterboard can be used, the joints taped, and
the whole ceiling skimmed. It is a good idea to use foil backed
plasterboard in upstairs bathrooms, to reduce the possibility of
condensation in the roof space. Ordinary plasterboard should be mounted
with the "bad" side (where the joins between front and back paper are)
downwards if it is intended to skim the whole surface, because plaster
sticks to this side better.
Most DIYers are of the opinion that plastering large areas is best left to
the professional.
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Matthew @rd.bbc.co.uk My opinions, not Auntie's
For the uk.d-i-y FAQ, goto http://www.axp.mdx.ac.uk/~john49/faq0.htm