This hints and tips will explain the various uses and techniques for laying a chipboard sub-floor. There are three main uses for chipboard; as the subfloor on timber floor joists, as a floating floor on insulation and concrete and for boarding lofts. The first use, on timber joists, is commonly the technique used on new builds and renovations. If you find yourself with a house with old rotten floorboards then a chipboard sub floor is a quick cheap and solid replacement.

The Product

There are three main types of chipboard on the market.

 The classis 8”x4” sheet. Available at DIY sheds and builders merchants in thicknesses from 12mm to 25mm. This is the cheapest way to buy chipboard (expect to pay from £10 a sheet for 18mm) but it is the hardest to transport, requires the most cutting and has no tongue and grooved edges. I would steer clear of this board for flooring.

I would just like to digress at this point onto the topic of imperial v metric. I am not being old school by using imperial measurements, it is our archaic system that is to blame. Timber sheet materials are sold as 8x4 and they measure 2440mm x 1220mm. Confusingly, plasterboard sold as 8x4 sheets is supplied in the metric equivalent so it measures 2400mm x 1200mm. So two sheet materials nominally the same size are actually quite different so bear it in mind when setting out noggins and studwork. I don’t make the rules (well not yet anyway!)… it is just the way it is.

Loft Boards. Most commonly available in the DIY stores, these normally come as packs of three, each measuring 1220 x 320 x 18mm. They cost less than a fiver for a pack and come with T&G edges to create a strong interlocking floor. These boards are specifically designed for boarding lofts by a DIYer who has to take them up through a loft hatch. As such they are perfect for the job and are much better for the job than buying 8x4 sheets and chopping them up. Any savings in materials will be lost in time spent cutting, and the T&G edges make for a much more professional job.

P5 V313 chipboard. The professionals choice. Available in a standard size of 2400 x 600mm in a choice of two thicknesses, 18 or 22mm. For some time there were two types of board, P4 and P5. Only the latter was moisture resistant so it was dyed green. Now the manufactures have done away with P4 meaning all chipboard is P5 so there is no need for the green colouration. This simplifies matters a little and seems to have given the manufacturers a dubious claim to environmental responsibility by no longer using dye.

These boards have the advantage of T&G on all four sides, and come in large sheet sizes making them very economical to use, retailing at about £6 a sheet for 18mm.

Boarding a Loft

If you can get the V313 into you loft then use it. If not then go with the smaller loft boards. The principle of laying any wooden floor is the same. The key elements are as follows:

• Fix boards at right angles to the ceiling joist
• Join the short edges on the centre of joists
• Stagger the short end joints across the floor in a brick pattern.
• Screw boards down when working in a loft as nailing could disturb plasterwork on the underside of the ceiling. Use screws 2.5 times the depth of the board. I would recommend a 50mm No.4 screw.
• Given the infrequency of use, there is no need to glue the boards in a loft. 

Special considerations for lofts.

At TBE we have always tried to exercise a bit of laissez-faire and give our readers respect as capable workers but the following should be considered as common sense precautions.

•  Are the ceiling joists able to take the weight of the boards and the mountain of junk you are going to put on top of them? If in doubt seek advice or reconsider the aims of the project.
• If your loft has modern levels of insulation you will probably find the insulation is much deeper than the ceiling joists. Do not squeeze the insulation down. Instead counter-batten across the joists with the relevant depth of timber and place the top layer of insulation within the counter battens. Then fix the chipboard at right angles to the counter battens.
• Do not block ventilation at the eaves, trap cables, or even more shocking, screw through any cables.
• Halogen lights. If you have halogen lights these can be problematic as they need ventilation around them to keep them cool. Ensure there is no insulation on top or near them and an adequate air flow around the lights. It would be best to avoid covering the lights at all if possible, perhaps leaving a square of floor out around them.
•  Loft conversions. Boarding the loft is not the first stage in a DIY conversion to get that extra bedroom. To officially (i.e. when the property is sold) add an extra room via the loft it must comply with a host of regulations regarding loft conversions. If you want to go down that route, speak to an architect and don’t even bother to start by putting a floor down.

A Floating floor

This is a great alternative to screeding a floor, and an excellent way of getting insulation into a previously cold floor. You will only use this method in a drastic renovation or extension as it is very disruptive to rip up an existing screed. But if you want to consider it, here is the way to go.

The concrete sub-floor needs to be smooth and level otherwise any bumps will translate through to the chipboard. NHBC guidelines require no more than 5mm deviation under a 3m straight edge. If you have a troublesome concrete floor then apply a self-levelling compound first.  

If the concrete slab does not already have a DPM then one should be incorporated at this stage and lap up the walls above finished floor level. Alternatively, consider a two coat liquid DPM. 

Lay insulation, either Jablite(polystyrene) or Celotex (PU rigid board) type depending on the required U-value. A minimum 25mm is recommended for floating floors but most jobs will specify more than that. The insulation should be staggered and laid carefully to ensure it sits flat without bouncing on off-cuts of insulation or other debris.

Install a vapour and moisture control barrier above the insulation to keep the chipboard dry with any joints in the barrier overlapped and taped.

On top of this the chipboard can be laid out in a brick pattern, making sure the joints in the insulation do not coincide with joints in the chipboard. On all floors an expansion gap must be allowed. Minimum 12mm all the way round will suffice, but increasing if a single run of floor exceeds 6m. Allow for expansion at doorways by using thresholds.

Also consider access for pipes and cables. Glued floors cannot be taken apart once dry so ensure all work below the floor is complete and satisfactory.

Floating chipboard floors should be glued on all the edges using a generous amount of PVA glue. Apply a bead into the groove and on the top edge of the tongue. Once the glue is dry you have a well insulated, perfectly flat floor ready for the final floor covering.

On Timber joists

Fitting chipboard to timber joists is again a relatively simple task. As above, the boards need to have the short ends staggered and joined on the centre of joists. Where this is not possible fix noggins between the joists. V313 can be nailed or screwed. As a personal preference I prefer to use screws but nailing is probably a little quicker. Glue must also be used in the same way as a floating floor but to go the extra mile, put a bead of glue onto the joist. This will help eliminate squeaking.

 When screwing into joists it is always a good idea to mark the centre line so you don’t miss with your screws or nails. It only takes a few extra minutes but is worth it. Marking is absolutely critical where pipes or cables cross joists. In an ideal world, they will pass through holes drilled in the centre of the joists so as long as your screws are not too long you should have no trouble. But often there will have been some notching of the top of the joist. In this instance be extra sure that you have marked the area where the pipes or cables are so you know not to put any fixings in. If you have underfloor heating in trays suspended between the joists then go its time to get really scared! Tempting though it is to walk away, if you think about it logically, if the joists are properly marked up and the ‘no-fixing zones’ are clearly marked you will be fine. Preparation and patience are the key in this instance.

 And finally, written on each board are the words “Lay this side up”. Just a tip….

Chipboard floors are the industry standard and offer a very economical, quick and simple method of creating a perfect subfloor. The floating floor technique offers an excellent alternative to screeding and should be considered in renovations as an opportunity to get insulation into previously cold floors. The world has moved on from floorboards. Many are reluctant to embrace a floor that cannot be taken up again without serious upheaval, but why should a floor need to come up again? If there are further electrics or plumbing to do then the job is not ready for the floor to be fixed. If the services are all in then either leave access panels or accept that they are all present and correct.

There is a building product out there which has some truly remarkable characteristics, so I thought it only fair that I should tell you about it, and offer some hints on how to use it successfully. When used in renders it can self heal tiny cracks that may form. It allows the building to breath so avoiding damp. It is also a ‘sacrificial’ layer. After it has degraded (as all exterior coatings do eventually) it can be removed and replaced without damage to the underlying structure. When used in brick laying it is flexible enough to move with the building thus avoiding cracks in the mortar. It is also porous so moisture can escape through it rather than the brick, and so preserve the face of the brick. Truly an incredible product.

“What is it? When did it arrive on the market? Can I get it at B&Q?” I hear you cry. ‘It’ is of course lime putty. Alas, with all our eggs firmly in the basket of modernism we have neglected the lessons from the past. This cutting edge product is in fact thousands of years old, but today fewer people know how to use it than ever before. You will struggle to find it in the builders merchants, and the boys and girls at the DIY sheds will probably point you in the direction of the Toys ‘r’ Us if you ask them for it. Ever the fan of the underdog, The Building Experience is championing this venerable muck and we would encourage builders and DIYers, especially those with old properties, to show some pluck and try something new… even if it is very old. Confused? Read on…

What is it?

If you want a chemistry lesson you are in the wrong place, but the basics are as follows. Burn some Quicklime, chuck a load of water on top of it (a process called slaking), let it stew for a few months and then sell it as matured slaked lime putty. As the end user we skip the burning and slaking and buy it in 25kg tubs ready for mixing. When you take the lid off you have a pure white lump with the consistency of cheese.

I have not come across another area of the building trade so hazy and ill-defined as the use of lime putty. After extensive research on the web, in books and with companies specializing in restoration products there is still no discernible consensus on the best way to use lime putty. The notes that follow are a synthesis of advice given and our own experiences of what worked for us. It is by no means beyond reproach but it was learnt the hard way.

Mixing

• Lime putty is NOT the same as cement, do not treat it as such.
• Lime putty sets by carbonation. It chemically reacts with carbon dioxide in the air and slowly changes form to calcium carbonate. Consequently if there is no air, there is no carbonation and so the mix will not set. It will last indefinitely in the tubs (the layer of water is there to stop the lime contacting with the air) and any sand/putty mix will also last some time if kept covered.
•  A mix of 3/3.5:1 (Sharp Sand:Lime) is suitable for most applications. The putty is not easy to shovel so it is best to mix with two identical containers, one for sand and one for the putty to give correct ratios.
• The putty is very stiff to start but once you turn it over with the sands a few times it begins to loosen up. If you wish use a plasterers whisk and drill to knock the putty up first. This saves a lot of shovelling. The wetness of the sand also affects the ease of the mix and the final consistency.
• Once you have knocked up the amount you need either heap it in a pile and cover it with plastic sheets or put it back in empty tubs with a layer of water on top. Go home, and when you come back the next day be prepared for something magical. Yesterdays stiff lumpy mess will have softened into a perfect creamy mix. At this point you can mix cement, plaster or a pozoloid depending on your requirements. This will dry the mix so you will need to add a small amount of water to compensate. Once you have knocked the mix up again you are ready for action.

Application

• Techniques for plastering have been covered in other hints and tips but there are a few points to bear in mind.
• Lime putty was, and is, mainly for old buildings with a rustic look. Do not expect, or attempt a perfect finish. A coarser, uneven finish actually gives a greater surface area for moisture to escape from the walls of the building. More importantly the putty is unsuited to being overworked so keep trowelling to a minimum.
• The mix is best applied with a hurling or gauging trowel rather than a float. It can be thrown onto the wall in a ‘wristy’ action, smoothed once and left alone to set. Then the wall can be levelled with a wooden float as the mix hardens but this should be minimal and executed with a light touch.
• Direct sunlight will dry the mix too quickly, and rain will not allow it to set at all. The answer is Hessian sacking laid in front of the render to protect it from the elements and allow the slow carbonation process to take place in its own time. It may sound like an effort but it is well worth it.

Wear decent gloves when working with lime putty. Dry hands are an occupational hazard when working with cement but lime is even worse so cover those pinkies or prepare yourself for a world of pain. The rest is a question of your individual skill on the trowel. Allow plenty of time, apply two or even three coats on subsequent days and enjoy working with a fantastic building product.

• Most important is the background upon which you are going to apply your tiles, the smoother and flatter this is, the better your chances of success. With a flat surface and the correct trowel you will soon get used to applying just the right amount of adhesive ensuring a clean and tidy job.

• Choose the right tiles. If you wish to drive yourself mad with frustration, please purchase glass mosaics. Impossible to cut neatly and supplied on cardboard backing sheets, these are not ideal starter tiles. Alternatively, large (10”x8” perhaps), good quality, white ceramic tiles are relatively cheap, easy to cut, easy to lay and always look good.

• Choose the right adhesive. This is a question of experimentation, but they do differ from one brand to the next. Firstly, if installing in a wet area make sure your adhesive is waterproof. Secondly, ensure the adhesive is suitable for your background. All this information is on the packaging. Thirdly, avoid quick drying trade adhesives until you are more experienced, as the last thing you need is to be rushed. Lastly, use a ready mixed wall adhesive rather than a powder. This eliminates the challenge of getting the mix right.

• Avoid all in one grout and adhesive at all costs. Buy good adhesive, buy good grout. Separately.

• Do you really need that border tile? It is very tempting to add dados, borders or upstands but remember YOU will have to put them on the wall. Profiles that protrude beyond the wall tiles are gathering places for water, muck and mould. They create issues round windows and other openings that wouldn’t have occurred otherwise and they often detract from what would have been a clean and simple look. Consider carefully, and try and dissuade your other half from getting carried away in the tile showroom.

So now you have followed my advice and bought your plain white tiles and accessories, its time to tile!

Marking out is important. You need a level horizontal line all the way round the room to follow. Hopefully this will be the floor, worktop, shower tray or skirting. If you do not have a level to start from, start one tile up from the bottom and fix a batten all the way round the room and tile from that. Afterwards, remove the batten and cut the bottom row of tiles in.

Often overlooked by novice tilers but very important, is the vertical spacing of the tiles. Rarely do tiles fit perfectly along the wall. A couple of minutes with the tape measure will save much cutting later on. It is most important to avoid very thin pieces in one corner. Find the middle of the room and measure out to the corners to see how the tiles will work out. It is best to get the tiles in the corners the same size. It only takes a few minutes and will make a big difference to the finish.

In a moment of flippancy, one could say it is a simple job of sticking the ceramic to the wall so it looks nice, and why complicate matters? Consistently throughout this series of hints and tips, the emphasis has been on the individual finding their own technique. Don’t expect to hold the trowel right first time but persevere and it will get easier with each tile. The essentials are as follows. Get the adhesive on the wall; spread it with a notched trowel and the press the tile onto the adhesive with even but firm pressure. Use tile spacers to maintain consistent gaps. Don’t put them in to the joints where four tiles meet, just insert one nib in between two tiles so they can be removed later. Assuming the wall is flat, make sure the edges of adjoining tiles are level with each other and keep an eye on horizontal and vertical joints to make sure they are consistent.

The general rule with tiling is if it looks good, it is good. With decent adhesive and a sound background, there is nothing else to worry about. The essentials of tiling are the same as most other building jobs. Good planning, good preparation, good measuring and good cutting.

Cleaning! The bold type is justified for this most important paragraph. Do not let the adhesive dry on the tiles and rake the joints out otherwise the adhesive will show through the grout and look horrendous. Keep a bucket full of water nearby (adding some hot water makes it more comfortable!) and clean with a sponge constantly to keep adhesive off the surface. Less speed more haste is the motto of the day when tiling. If you neglect the cleaning it will take you longer overall because you will spend hours cleaning off hardened adhesive. Excuse my over-emphasis, but this is the voice of painful experience!

Grouting

After the tiles have been on the walls for 24 hrs you can grout. Drying times depend on the type of grout but leave plenty of time to finish the job properly. Mix the grout into a paste and spread across the whole wall working into the joints with a rubber-edged grouting tool. Clean the surface of the tiles repeatedly as the grout hardens, frequently rinsing your sponge and changing the water in your bucket. Patience is a virtue as you can only work as fast as the grout will set. Clean repeatedly switching to a dry cloth to get the remnants of the grout of the face of the tiles. There are loads of grout finishing tools on the market but with thin joints, nothing beats a finger. When the tiles are clean and the gaps are filled equally, its job done.